refactor: NCS-19 Currying (#18)

Summary

  - Curried candidateMoves, legalMoves, and applyMove in the RuleSet trait to separate (context) as the world being
  operated on from the computation parameter
  - Updated DefaultRules overrides and all internal call sites
  - Updated all external call sites: GameEngine, PgnParser, PgnExporter, ChessBoardView, and all affected tests

  Test plan

  - All existing tests pass (./gradlew build)
  - No behaviour changes — pure style refactoring, existing test suite is the regression guard

Co-authored-by: LQ63 <lkhermann@web.de>
Reviewed-on: #18
Reviewed-by: Janis <janis-e@gmx.de>
Co-authored-by: Leon Hermann <lq@blackhole.local>
Co-committed-by: Leon Hermann <lq@blackhole.local>

.claude/settings.json

@@ -1,6 +1,6 @@
 {
   "enabledPlugins": {
-    "superpowers@claude-plugins-official": true,
-    "ui-ux-pro-max@ui-ux-pro-max-skill": true
+    "superpowers@claude-plugins-official": false,
+    "ui-ux-pro-max@ui-ux-pro-max-skill": false
   }
 }

.idea/gradle.xml

@@ -12,6 +12,8 @@
             <option value="$PROJECT_DIR$/modules" />
             <option value="$PROJECT_DIR$/modules/api" />
             <option value="$PROJECT_DIR$/modules/core" />
+            <option value="$PROJECT_DIR$/modules/io" />
+            <option value="$PROJECT_DIR$/modules/rule" />
             <option value="$PROJECT_DIR$/modules/ui" />
           </set>
         </option>

.idea/scala_compiler.xml

@@ -5,7 +5,7 @@
       <option name="deprecationWarnings" value="true" />
       <option name="uncheckedWarnings" value="true" />
     </profile>
-    <profile name="Gradle 2" modules="NowChessSystems.modules.core.main,NowChessSystems.modules.core.scoverage,NowChessSystems.modules.core.test,NowChessSystems.modules.ui.main,NowChessSystems.modules.ui.scoverage,NowChessSystems.modules.ui.test">
+    <profile name="Gradle 2" modules="NowChessSystems.modules.core.main,NowChessSystems.modules.core.scoverage,NowChessSystems.modules.core.test,NowChessSystems.modules.io.main,NowChessSystems.modules.io.scoverage,NowChessSystems.modules.io.test,NowChessSystems.modules.rule.main,NowChessSystems.modules.rule.scoverage,NowChessSystems.modules.rule.test,NowChessSystems.modules.ui.main,NowChessSystems.modules.ui.scoverage,NowChessSystems.modules.ui.test">
       <option name="deprecationWarnings" value="true" />
       <option name="uncheckedWarnings" value="true" />
       <parameters>

coverage

@@ -4,7 +4,7 @@ set -euo pipefail
 ./gradlew test
 
 if [ "$#" -eq 0 ]; then
-  python3 jacoco-reporter/scoverage_coverage_gaps.py
+  PYTHONUTF8=1 python3 jacoco-reporter/scoverage_coverage_gaps.py
 else
-  python3 jacoco-reporter/scoverage_coverage_gaps.py "modules/$1/build/reports/scoverageTest/scoverage.xml"
+  PYTHONUTF8=1 python3 jacoco-reporter/scoverage_coverage_gaps.py "modules/$1/build/reports/scoverageTest/scoverage.xml"
 fi

jacoco-reporter/test_counter.py

@@ -0,0 +1,12 @@
+import glob,re
+mods=['api','core','io','rule','ui']
+tot=0
+for m in mods:
+ s=0
+ for f in glob.glob(f'modules/{m}/build/test-results/test/TEST-*.xml'):
+  txt=open(f,encoding='utf-8').read(300)
+  m2=re.search(r'tests="(\d+)"',txt)
+  if m2:s+=int(m2.group(1))
+ print(f'{m}: {s}')
+ tot+=s
+print('overall:',tot)

modules/api/CHANGELOG.md

@@ -6,3 +6,13 @@
 ##  (2026-04-01)
 ##  (2026-04-01)
 ##  (2026-04-01)
+##  (2026-04-02)
+
+### Features
+
+* NCS-21 Write Scripts to automate certain tasks ([#15](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/15)) ([8051871](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/80518719d536a087d339fe02530825dc07f8b388))
+##  (2026-04-03)
+
+### Features
+
+* NCS-21 Write Scripts to automate certain tasks ([#15](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/15)) ([8051871](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/80518719d536a087d339fe02530825dc07f8b388))

modules/api/src/main/scala/de/nowchess/api/board/Board.scala

@@ -14,6 +14,9 @@ object Board:
       val captured = b.get(to)
       val updatedBoard = b.removed(from).updated(to, b(from))
       (updatedBoard, captured)
+    def applyMove(move: de.nowchess.api.move.Move): Board =
+      val (updatedBoard, _) = b.withMove(move.from, move.to)
+      updatedBoard
     def pieces: Map[Square, Piece] = b
 
   val initial: Board =

modules/api/src/main/scala/de/nowchess/api/board/CastlingRights.scala

@@ -0,0 +1,70 @@
+package de.nowchess.api.board
+
+/**
+ * Unified castling rights tracker for all four sides.
+ * Tracks whether castling is still available for each side and direction.
+ *
+ * @param whiteKingSide   White's king-side castling (0-0) still legally available
+ * @param whiteQueenSide  White's queen-side castling (0-0-0) still legally available
+ * @param blackKingSide   Black's king-side castling (0-0) still legally available
+ * @param blackQueenSide  Black's queen-side castling (0-0-0) still legally available
+ */
+final case class CastlingRights(
+  whiteKingSide: Boolean,
+  whiteQueenSide: Boolean,
+  blackKingSide: Boolean,
+  blackQueenSide: Boolean
+):
+  /**
+   * Check if either side has any castling rights remaining.
+   */
+  def hasAnyRights: Boolean =
+    whiteKingSide || whiteQueenSide || blackKingSide || blackQueenSide
+
+  /**
+   * Check if a specific color has any castling rights remaining.
+   */
+  def hasRights(color: Color): Boolean = color match
+    case Color.White => whiteKingSide || whiteQueenSide
+    case Color.Black => blackKingSide || blackQueenSide
+
+  /**
+   * Revoke all castling rights for a specific color.
+   */
+  def revokeColor(color: Color): CastlingRights = color match
+    case Color.White => copy(whiteKingSide = false, whiteQueenSide = false)
+    case Color.Black => copy(blackKingSide = false, blackQueenSide = false)
+
+  /**
+   * Revoke a specific castling right.
+   */
+  def revokeKingSide(color: Color): CastlingRights = color match
+    case Color.White => copy(whiteKingSide = false)
+    case Color.Black => copy(blackKingSide = false)
+
+  /**
+   * Revoke a specific castling right.
+   */
+  def revokeQueenSide(color: Color): CastlingRights = color match
+    case Color.White => copy(whiteQueenSide = false)
+    case Color.Black => copy(blackQueenSide = false)
+
+object CastlingRights:
+  /** No castling rights for any side. */
+  val None: CastlingRights = CastlingRights(
+    whiteKingSide = false,
+    whiteQueenSide = false,
+    blackKingSide = false,
+    blackQueenSide = false
+  )
+
+  /** All castling rights available. */
+  val All: CastlingRights = CastlingRights(
+    whiteKingSide = true,
+    whiteQueenSide = true,
+    blackKingSide = true,
+    blackQueenSide = true
+  )
+
+  /** Standard starting position castling rights (both sides can castle both ways). */
+  val Initial: CastlingRights = All

modules/api/src/main/scala/de/nowchess/api/board/Square.scala

@@ -39,3 +39,19 @@ object Square:
           if n >= 1 && n <= 8 then Some(Rank.values(n - 1)) else None
         )
       for f <- fileOpt; r <- rankOpt yield Square(f, r)
+
+  val all: IndexedSeq[Square] =
+    for
+      r <- Rank.values.toIndexedSeq
+      f <- File.values.toIndexedSeq
+    yield Square(f, r)
+
+  /** Compute a target square by offsetting file and rank.
+   *  Returns None if the resulting square is outside the board (0-7 range). */
+  extension (sq: Square)
+    def offset(fileDelta: Int, rankDelta: Int): Option[Square] =
+      val newFileOrd = sq.file.ordinal + fileDelta
+      val newRankOrd = sq.rank.ordinal + rankDelta
+      if newFileOrd >= 0 && newFileOrd < 8 && newRankOrd >= 0 && newRankOrd < 8 then
+        Some(Square(File.values(newFileOrd), Rank.values(newRankOrd)))
+      else None

modules/api/src/main/scala/de/nowchess/api/game/GameContext.scala

@@ -0,0 +1,44 @@
+package de.nowchess.api.game
+
+import de.nowchess.api.board.{Board, Color, Square, CastlingRights}
+import de.nowchess.api.move.Move
+
+/** Immutable bundle of complete game state.
+ *  All state changes produce new GameContext instances.
+ */
+case class GameContext(
+  board: Board,
+  turn: Color,
+  castlingRights: CastlingRights,
+  enPassantSquare: Option[Square],
+  halfMoveClock: Int,
+  moves: List[Move]
+):
+  /** Create new context with updated board. */
+  def withBoard(newBoard: Board): GameContext = copy(board = newBoard)
+
+  /** Create new context with updated turn. */
+  def withTurn(newTurn: Color): GameContext = copy(turn = newTurn)
+
+  /** Create new context with updated castling rights. */
+  def withCastlingRights(newRights: CastlingRights): GameContext = copy(castlingRights = newRights)
+
+  /** Create new context with updated en passant square. */
+  def withEnPassantSquare(newSq: Option[Square]): GameContext = copy(enPassantSquare = newSq)
+
+  /** Create new context with updated half-move clock. */
+  def withHalfMoveClock(newClock: Int): GameContext = copy(halfMoveClock = newClock)
+
+  /** Create new context with move appended to history. */
+  def withMove(move: Move): GameContext = copy(moves = moves :+ move)
+
+object GameContext:
+  /** Initial position: white to move, all castling rights, no en passant. */
+  def initial: GameContext = GameContext(
+    board = Board.initial,
+    turn = Color.White,
+    castlingRights = CastlingRights.Initial,
+    enPassantSquare = None,
+    halfMoveClock = 0,
+    moves = List.empty
+  )

modules/api/src/main/scala/de/nowchess/api/game/GameState.scala

@@ -1,67 +0,0 @@
-package de.nowchess.api.game
-
-import de.nowchess.api.board.{Color, Square}
-
-/**
- * Castling availability flags for one side.
- *
- * @param kingSide  king-side castling still legally available
- * @param queenSide queen-side castling still legally available
- */
-final case class CastlingRights(kingSide: Boolean, queenSide: Boolean)
-
-object CastlingRights:
-  val None: CastlingRights = CastlingRights(kingSide = false, queenSide = false)
-  val Both: CastlingRights = CastlingRights(kingSide = true, queenSide = true)
-
-/** Outcome of a finished game. */
-enum GameResult:
-  case WhiteWins
-  case BlackWins
-  case Draw
-
-/** Lifecycle state of a game. */
-enum GameStatus:
-  case NotStarted
-  case InProgress
-  case Finished(result: GameResult)
-
-/**
- * A FEN-compatible snapshot of board and game state.
- *
- * The board is represented as a FEN piece-placement string (rank 8 to rank 1,
- * separated by '/').  All other fields mirror standard FEN fields.
- *
- * @param piecePlacement  FEN piece-placement field, e.g.
- *                        "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR"
- * @param activeColor     side to move
- * @param castlingWhite   castling rights for White
- * @param castlingBlack   castling rights for Black
- * @param enPassantTarget square behind the double-pushed pawn, if any
- * @param halfMoveClock   plies since last capture or pawn advance (50-move rule)
- * @param fullMoveNumber  increments after Black's move, starts at 1
- * @param status          current lifecycle status of the game
- */
-final case class GameState(
-  piecePlacement: String,
-  activeColor: Color,
-  castlingWhite: CastlingRights,
-  castlingBlack: CastlingRights,
-  enPassantTarget: Option[Square],
-  halfMoveClock: Int,
-  fullMoveNumber: Int,
-  status: GameStatus
-)
-
-object GameState:
-  /** Standard starting position. */
-  val initial: GameState = GameState(
-    piecePlacement  = "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR",
-    activeColor     = Color.White,
-    castlingWhite   = CastlingRights.Both,
-    castlingBlack   = CastlingRights.Both,
-    enPassantTarget = None,
-    halfMoveClock   = 0,
-    fullMoveNumber  = 1,
-    status          = GameStatus.InProgress
-  )

modules/api/src/main/scala/de/nowchess/api/move/Move.scala

@@ -9,7 +9,7 @@ enum PromotionPiece:
 /** Classifies special move semantics beyond a plain quiet move or capture. */
 enum MoveType:
   /** A normal move or capture with no special rule. */
-  case Normal
+  case Normal(isCapture: Boolean = false)
   /** Kingside castling (O-O). */
   case CastleKingside
   /** Queenside castling (O-O-O). */
@@ -29,5 +29,5 @@ enum MoveType:
 final case class Move(
   from: Square,
   to: Square,
-  moveType: MoveType = MoveType.Normal
+  moveType: MoveType = MoveType.Normal()
 )

modules/api/src/test/scala/de/nowchess/api/board/BoardTest.scala

@@ -1,5 +1,6 @@
 package de.nowchess.api.board
 
+import de.nowchess.api.move.Move
 import org.scalatest.funsuite.AnyFunSuite
 import org.scalatest.matchers.should.Matchers
 
@@ -7,13 +8,9 @@ class BoardTest extends AnyFunSuite with Matchers:
 
   private val e2 = Square(File.E, Rank.R2)
   private val e4 = Square(File.E, Rank.R4)
-  private val d7 = Square(File.D, Rank.R7)
 
-  test("pieceAt returns Some for occupied square") {
+  test("pieceAt resolves occupied and empty squares") {
     Board.initial.pieceAt(e2) shouldBe Some(Piece.WhitePawn)
-  }
-
-  test("pieceAt returns None for empty square") {
     Board.initial.pieceAt(e4) shouldBe None
   }
 
@@ -34,38 +31,20 @@ class BoardTest extends AnyFunSuite with Matchers:
     board.pieceAt(from) shouldBe None
   }
 
-  test("pieces returns the underlying map") {
-    val map = Map(e2 -> Piece.WhitePawn)
-    val b   = Board(map)
-    b.pieces shouldBe map
-  }
-
-  test("Board.apply constructs board from map") {
+  test("Board.apply and pieces expose the wrapped map") {
     val map = Map(e2 -> Piece.WhitePawn)
     val b   = Board(map)
     b.pieceAt(e2) shouldBe Some(Piece.WhitePawn)
+    b.pieces shouldBe map
   }
 
-  test("initial board has 32 pieces") {
+  test("initial board has expected material and pawn placement") {
     Board.initial.pieces should have size 32
-  }
-
-  test("initial board has 16 white pieces") {
     Board.initial.pieces.values.count(_.color == Color.White) shouldBe 16
-  }
-
-  test("initial board has 16 black pieces") {
     Board.initial.pieces.values.count(_.color == Color.Black) shouldBe 16
-  }
 
-  test("initial board white pawns on rank 2") {
     File.values.foreach { file =>
       Board.initial.pieceAt(Square(file, Rank.R2)) shouldBe Some(Piece.WhitePawn)
-    }
-  }
-
-  test("initial board black pawns on rank 7") {
-    File.values.foreach { file =>
       Board.initial.pieceAt(Square(file, Rank.R7)) shouldBe Some(Piece.BlackPawn)
     }
   }
@@ -101,17 +80,14 @@ class BoardTest extends AnyFunSuite with Matchers:
       Board.initial.pieceAt(Square(file, rank)) shouldBe None
   }
 
-  test("updated adds or replaces piece at square") {
+  test("updated adds and replaces piece at squares") {
     val b = Board(Map(e2 -> Piece.WhitePawn))
-    val updated = b.updated(e4, Piece.WhiteKnight)
-    updated.pieceAt(e2) shouldBe Some(Piece.WhitePawn)
-    updated.pieceAt(e4) shouldBe Some(Piece.WhiteKnight)
-  }
+    val added = b.updated(e4, Piece.WhiteKnight)
+    added.pieceAt(e2) shouldBe Some(Piece.WhitePawn)
+    added.pieceAt(e4) shouldBe Some(Piece.WhiteKnight)
 
-  test("updated replaces existing piece") {
-    val b = Board(Map(e2 -> Piece.WhitePawn))
-    val updated = b.updated(e2, Piece.WhiteKnight)
-    updated.pieceAt(e2) shouldBe Some(Piece.WhiteKnight)
+    val replaced = b.updated(e2, Piece.WhiteKnight)
+    replaced.pieceAt(e2) shouldBe Some(Piece.WhiteKnight)
   }
 
   test("removed deletes piece from board") {
@@ -120,3 +96,13 @@ class BoardTest extends AnyFunSuite with Matchers:
     removed.pieceAt(e2) shouldBe None
     removed.pieceAt(e4) shouldBe Some(Piece.WhiteKnight)
   }
+
+  test("applyMove uses move.from and move.to to relocate a piece") {
+    val b = Board(Map(e2 -> Piece.WhitePawn))
+
+    val moved = b.applyMove(Move(e2, e4))
+
+    moved.pieceAt(e4) shouldBe Some(Piece.WhitePawn)
+    moved.pieceAt(e2) shouldBe None
+  }
+

modules/api/src/test/scala/de/nowchess/api/board/CastlingRightsTest.scala

@@ -0,0 +1,57 @@
+package de.nowchess.api.board
+
+import org.scalatest.funsuite.AnyFunSuite
+import org.scalatest.matchers.should.Matchers
+
+class CastlingRightsTest extends AnyFunSuite with Matchers:
+
+  test("hasAnyRights and hasRights reflect current flags"):
+    val rights = CastlingRights(
+      whiteKingSide = true,
+      whiteQueenSide = false,
+      blackKingSide = false,
+      blackQueenSide = true
+    )
+
+    rights.hasAnyRights shouldBe true
+    rights.hasRights(Color.White) shouldBe true
+    rights.hasRights(Color.Black) shouldBe true
+
+    CastlingRights.None.hasAnyRights shouldBe false
+    CastlingRights.None.hasRights(Color.White) shouldBe false
+    CastlingRights.None.hasRights(Color.Black) shouldBe false
+
+  test("revokeColor clears both castling sides for selected color"):
+    val all = CastlingRights.All
+
+    val whiteRevoked = all.revokeColor(Color.White)
+    whiteRevoked.whiteKingSide shouldBe false
+    whiteRevoked.whiteQueenSide shouldBe false
+    whiteRevoked.blackKingSide shouldBe true
+    whiteRevoked.blackQueenSide shouldBe true
+
+    val blackRevoked = all.revokeColor(Color.Black)
+    blackRevoked.whiteKingSide shouldBe true
+    blackRevoked.whiteQueenSide shouldBe true
+    blackRevoked.blackKingSide shouldBe false
+    blackRevoked.blackQueenSide shouldBe false
+
+  test("revokeKingSide and revokeQueenSide disable only requested side"):
+    val all = CastlingRights.All
+
+    val whiteKingSideRevoked = all.revokeKingSide(Color.White)
+    whiteKingSideRevoked.whiteKingSide shouldBe false
+    whiteKingSideRevoked.whiteQueenSide shouldBe true
+
+    val whiteQueenSideRevoked = all.revokeQueenSide(Color.White)
+    whiteQueenSideRevoked.whiteKingSide shouldBe true
+    whiteQueenSideRevoked.whiteQueenSide shouldBe false
+
+    val blackKingSideRevoked = all.revokeKingSide(Color.Black)
+    blackKingSideRevoked.blackKingSide shouldBe false
+    blackKingSideRevoked.blackQueenSide shouldBe true
+
+    val blackQueenSideRevoked = all.revokeQueenSide(Color.Black)
+    blackQueenSideRevoked.blackKingSide shouldBe true
+    blackQueenSideRevoked.blackQueenSide shouldBe false
+

modules/api/src/test/scala/de/nowchess/api/board/ColorTest.scala

@@ -5,18 +5,13 @@ import org.scalatest.matchers.should.Matchers
 
 class ColorTest extends AnyFunSuite with Matchers:
 
-  test("White.opposite returns Black") {
-    Color.White.opposite shouldBe Color.Black
-  }
+  test("Color values expose opposite and label consistently"):
+    val cases = List(
+      (Color.White, Color.Black, "White"),
+      (Color.Black, Color.White, "Black")
+    )
 
-  test("Black.opposite returns White") {
-    Color.Black.opposite shouldBe Color.White
-  }
-
-  test("White.label returns 'White'") {
-    Color.White.label shouldBe "White"
-  }
-
-  test("Black.label returns 'Black'") {
-    Color.Black.label shouldBe "Black"
-  }
+    cases.foreach { (color, opposite, label) =>
+      color.opposite shouldBe opposite
+      color.label shouldBe label
+    }

modules/api/src/test/scala/de/nowchess/api/board/PieceTest.scala

@@ -11,50 +11,23 @@ class PieceTest extends AnyFunSuite with Matchers:
     p.pieceType shouldBe PieceType.Queen
   }
 
-  test("WhitePawn convenience constant") {
-    Piece.WhitePawn shouldBe Piece(Color.White, PieceType.Pawn)
-  }
+  test("all convenience constants map to expected color and piece type") {
+    val expected = List(
+      Piece.WhitePawn -> Piece(Color.White, PieceType.Pawn),
+      Piece.WhiteKnight -> Piece(Color.White, PieceType.Knight),
+      Piece.WhiteBishop -> Piece(Color.White, PieceType.Bishop),
+      Piece.WhiteRook -> Piece(Color.White, PieceType.Rook),
+      Piece.WhiteQueen -> Piece(Color.White, PieceType.Queen),
+      Piece.WhiteKing -> Piece(Color.White, PieceType.King),
+      Piece.BlackPawn -> Piece(Color.Black, PieceType.Pawn),
+      Piece.BlackKnight -> Piece(Color.Black, PieceType.Knight),
+      Piece.BlackBishop -> Piece(Color.Black, PieceType.Bishop),
+      Piece.BlackRook -> Piece(Color.Black, PieceType.Rook),
+      Piece.BlackQueen -> Piece(Color.Black, PieceType.Queen),
+      Piece.BlackKing -> Piece(Color.Black, PieceType.King)
+    )
 
-  test("WhiteKnight convenience constant") {
-    Piece.WhiteKnight shouldBe Piece(Color.White, PieceType.Knight)
-  }
-
-  test("WhiteBishop convenience constant") {
-    Piece.WhiteBishop shouldBe Piece(Color.White, PieceType.Bishop)
-  }
-
-  test("WhiteRook convenience constant") {
-    Piece.WhiteRook shouldBe Piece(Color.White, PieceType.Rook)
-  }
-
-  test("WhiteQueen convenience constant") {
-    Piece.WhiteQueen shouldBe Piece(Color.White, PieceType.Queen)
-  }
-
-  test("WhiteKing convenience constant") {
-    Piece.WhiteKing shouldBe Piece(Color.White, PieceType.King)
-  }
-
-  test("BlackPawn convenience constant") {
-    Piece.BlackPawn shouldBe Piece(Color.Black, PieceType.Pawn)
-  }
-
-  test("BlackKnight convenience constant") {
-    Piece.BlackKnight shouldBe Piece(Color.Black, PieceType.Knight)
-  }
-
-  test("BlackBishop convenience constant") {
-    Piece.BlackBishop shouldBe Piece(Color.Black, PieceType.Bishop)
-  }
-
-  test("BlackRook convenience constant") {
-    Piece.BlackRook shouldBe Piece(Color.Black, PieceType.Rook)
-  }
-
-  test("BlackQueen convenience constant") {
-    Piece.BlackQueen shouldBe Piece(Color.Black, PieceType.Queen)
-  }
-
-  test("BlackKing convenience constant") {
-    Piece.BlackKing shouldBe Piece(Color.Black, PieceType.King)
+    expected.foreach { case (actual, wanted) =>
+      actual shouldBe wanted
+    }
   }

modules/api/src/test/scala/de/nowchess/api/board/PieceTypeTest.scala

@@ -5,26 +5,16 @@ import org.scalatest.matchers.should.Matchers
 
 class PieceTypeTest extends AnyFunSuite with Matchers:
 
-  test("Pawn.label returns 'Pawn'") {
-    PieceType.Pawn.label shouldBe "Pawn"
-  }
+  test("PieceType values expose the expected labels"):
+    val expectedLabels = List(
+      PieceType.Pawn -> "Pawn",
+      PieceType.Knight -> "Knight",
+      PieceType.Bishop -> "Bishop",
+      PieceType.Rook -> "Rook",
+      PieceType.Queen -> "Queen",
+      PieceType.King -> "King"
+    )
 
-  test("Knight.label returns 'Knight'") {
-    PieceType.Knight.label shouldBe "Knight"
-  }
-
-  test("Bishop.label returns 'Bishop'") {
-    PieceType.Bishop.label shouldBe "Bishop"
-  }
-
-  test("Rook.label returns 'Rook'") {
-    PieceType.Rook.label shouldBe "Rook"
-  }
-
-  test("Queen.label returns 'Queen'") {
-    PieceType.Queen.label shouldBe "Queen"
-  }
-
-  test("King.label returns 'King'") {
-    PieceType.King.label shouldBe "King"
-  }
+    expectedLabels.foreach { (pieceType, expectedLabel) =>
+      pieceType.label shouldBe expectedLabel
+    }

modules/api/src/test/scala/de/nowchess/api/board/SquareTest.scala

@@ -5,58 +5,33 @@ import org.scalatest.matchers.should.Matchers
 
 class SquareTest extends AnyFunSuite with Matchers:
 
-  test("Square.toString produces lowercase file and rank number") {
-    Square(File.E, Rank.R4).toString shouldBe "e4"
-  }
-
-  test("Square.toString for a1") {
+  test("toString renders algebraic notation for edge and middle squares") {
     Square(File.A, Rank.R1).toString shouldBe "a1"
-  }
-
-  test("Square.toString for h8") {
+    Square(File.E, Rank.R4).toString shouldBe "e4"
     Square(File.H, Rank.R8).toString shouldBe "h8"
   }
 
-  test("fromAlgebraic parses valid square e4") {
-    Square.fromAlgebraic("e4") shouldBe Some(Square(File.E, Rank.R4))
+  test("fromAlgebraic parses valid coordinates including case-insensitive files") {
+    val expected = List(
+      "a1" -> Square(File.A, Rank.R1),
+      "e4" -> Square(File.E, Rank.R4),
+      "h8" -> Square(File.H, Rank.R8),
+      "E4" -> Square(File.E, Rank.R4)
+    )
+    expected.foreach { case (raw, sq) =>
+      Square.fromAlgebraic(raw) shouldBe Some(sq)
+    }
   }
 
-  test("fromAlgebraic parses valid square a1") {
-    Square.fromAlgebraic("a1") shouldBe Some(Square(File.A, Rank.R1))
+  test("fromAlgebraic rejects malformed coordinates") {
+    List("", "e", "e42", "z4", "ex", "e0", "e9").foreach { raw =>
+      Square.fromAlgebraic(raw) shouldBe None
+    }
   }
 
-  test("fromAlgebraic parses valid square h8") {
-    Square.fromAlgebraic("h8") shouldBe Some(Square(File.H, Rank.R8))
+  test("offset returns Some in-bounds and None out-of-bounds") {
+    Square(File.E, Rank.R4).offset(1, 2) shouldBe Some(Square(File.F, Rank.R6))
+    Square(File.A, Rank.R1).offset(-1, 0) shouldBe None
+    Square(File.H, Rank.R8).offset(0, 1) shouldBe None
   }
 
-  test("fromAlgebraic is case-insensitive for file") {
-    Square.fromAlgebraic("E4") shouldBe Some(Square(File.E, Rank.R4))
-  }
-
-  test("fromAlgebraic returns None for empty string") {
-    Square.fromAlgebraic("") shouldBe None
-  }
-
-  test("fromAlgebraic returns None for string too short") {
-    Square.fromAlgebraic("e") shouldBe None
-  }
-
-  test("fromAlgebraic returns None for string too long") {
-    Square.fromAlgebraic("e42") shouldBe None
-  }
-
-  test("fromAlgebraic returns None for invalid file character") {
-    Square.fromAlgebraic("z4") shouldBe None
-  }
-
-  test("fromAlgebraic returns None for non-digit rank") {
-    Square.fromAlgebraic("ex") shouldBe None
-  }
-
-  test("fromAlgebraic returns None for rank 0") {
-    Square.fromAlgebraic("e0") shouldBe None
-  }
-
-  test("fromAlgebraic returns None for rank 9") {
-    Square.fromAlgebraic("e9") shouldBe None
-  }

modules/api/src/test/scala/de/nowchess/api/game/GameContextTest.scala

@@ -0,0 +1,60 @@
+package de.nowchess.api.game
+
+import de.nowchess.api.board.{Board, CastlingRights, Color, File, Rank, Square}
+import de.nowchess.api.move.Move
+import org.scalatest.funsuite.AnyFunSuite
+import org.scalatest.matchers.should.Matchers
+
+class GameContextTest extends AnyFunSuite with Matchers:
+
+  test("GameContext.initial exposes expected default state"):
+    val initial = GameContext.initial
+
+    initial.board shouldBe Board.initial
+    initial.turn shouldBe Color.White
+    initial.castlingRights shouldBe CastlingRights.Initial
+    initial.enPassantSquare shouldBe None
+    initial.halfMoveClock shouldBe 0
+    initial.moves shouldBe List.empty
+
+  test("withBoard updates only board"):
+    val square = Square(File.E, Rank.R4)
+    val updatedBoard = Board.initial.updated(square, de.nowchess.api.board.Piece.WhiteQueen)
+    val updated = GameContext.initial.withBoard(updatedBoard)
+    updated.board shouldBe updatedBoard
+    updated.turn shouldBe GameContext.initial.turn
+    updated.castlingRights shouldBe GameContext.initial.castlingRights
+    updated.enPassantSquare shouldBe GameContext.initial.enPassantSquare
+    updated.halfMoveClock shouldBe GameContext.initial.halfMoveClock
+    updated.moves shouldBe GameContext.initial.moves
+
+  test("withers update only targeted fields"):
+    val initial = GameContext.initial
+    val rights = CastlingRights(
+      whiteKingSide = true,
+      whiteQueenSide = false,
+      blackKingSide = false,
+      blackQueenSide = true
+    )
+    val square = Some(Square(File.E, Rank.R3))
+    val updatedTurn = initial.withTurn(Color.Black)
+    val updatedRights = initial.withCastlingRights(rights)
+    val updatedEp = initial.withEnPassantSquare(square)
+    val updatedClock = initial.withHalfMoveClock(17)
+
+    updatedTurn.turn shouldBe Color.Black
+    updatedTurn.board shouldBe initial.board
+
+    updatedRights.castlingRights shouldBe rights
+    updatedRights.turn shouldBe initial.turn
+
+    updatedEp.enPassantSquare shouldBe square
+    updatedEp.castlingRights shouldBe initial.castlingRights
+
+    updatedClock.halfMoveClock shouldBe 17
+    updatedClock.moves shouldBe initial.moves
+
+  test("withMove appends move to history"):
+    val move = Move(Square(File.E, Rank.R2), Square(File.E, Rank.R4))
+    GameContext.initial.withMove(move).moves shouldBe List(move)
+

modules/api/src/test/scala/de/nowchess/api/game/GameStateTest.scala

@@ -1,77 +0,0 @@
-package de.nowchess.api.game
-
-import de.nowchess.api.board.Color
-import org.scalatest.funsuite.AnyFunSuite
-import org.scalatest.matchers.should.Matchers
-
-class GameStateTest extends AnyFunSuite with Matchers:
-
-  test("CastlingRights.None has both flags false") {
-    CastlingRights.None.kingSide  shouldBe false
-    CastlingRights.None.queenSide shouldBe false
-  }
-
-  test("CastlingRights.Both has both flags true") {
-    CastlingRights.Both.kingSide  shouldBe true
-    CastlingRights.Both.queenSide shouldBe true
-  }
-
-  test("CastlingRights constructor sets fields") {
-    val cr = CastlingRights(kingSide = true, queenSide = false)
-    cr.kingSide  shouldBe true
-    cr.queenSide shouldBe false
-  }
-
-  test("GameResult cases exist") {
-    GameResult.WhiteWins shouldBe GameResult.WhiteWins
-    GameResult.BlackWins shouldBe GameResult.BlackWins
-    GameResult.Draw      shouldBe GameResult.Draw
-  }
-
-  test("GameStatus.NotStarted") {
-    GameStatus.NotStarted shouldBe GameStatus.NotStarted
-  }
-
-  test("GameStatus.InProgress") {
-    GameStatus.InProgress shouldBe GameStatus.InProgress
-  }
-
-  test("GameStatus.Finished carries result") {
-    val status = GameStatus.Finished(GameResult.Draw)
-    status shouldBe GameStatus.Finished(GameResult.Draw)
-    status match
-      case GameStatus.Finished(r) => r shouldBe GameResult.Draw
-      case _                      => fail("expected Finished")
-  }
-
-  test("GameState.initial has standard FEN piece placement") {
-    GameState.initial.piecePlacement shouldBe "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR"
-  }
-
-  test("GameState.initial active color is White") {
-    GameState.initial.activeColor shouldBe Color.White
-  }
-
-  test("GameState.initial white has full castling rights") {
-    GameState.initial.castlingWhite shouldBe CastlingRights.Both
-  }
-
-  test("GameState.initial black has full castling rights") {
-    GameState.initial.castlingBlack shouldBe CastlingRights.Both
-  }
-
-  test("GameState.initial en-passant target is None") {
-    GameState.initial.enPassantTarget shouldBe None
-  }
-
-  test("GameState.initial half-move clock is 0") {
-    GameState.initial.halfMoveClock shouldBe 0
-  }
-
-  test("GameState.initial full-move number is 1") {
-    GameState.initial.fullMoveNumber shouldBe 1
-  }
-
-  test("GameState.initial status is InProgress") {
-    GameState.initial.status shouldBe GameStatus.InProgress
-  }

modules/api/src/test/scala/de/nowchess/api/move/MoveTest.scala

@@ -9,48 +9,26 @@ class MoveTest extends AnyFunSuite with Matchers:
   private val e2 = Square(File.E, Rank.R2)
   private val e4 = Square(File.E, Rank.R4)
 
-  test("Move defaults moveType to Normal") {
-    val m = Move(e2, e4)
-    m.moveType shouldBe MoveType.Normal
-  }
-
-  test("Move stores from and to squares") {
+  test("Move defaults to Normal and keeps from/to squares") {
     val m = Move(e2, e4)
     m.from shouldBe e2
-    m.to   shouldBe e4
+    m.to shouldBe e4
+    m.moveType shouldBe MoveType.Normal()
   }
 
-  test("Move with CastleKingside moveType") {
-    val m = Move(e2, e4, MoveType.CastleKingside)
-    m.moveType shouldBe MoveType.CastleKingside
-  }
+  test("Move accepts all supported move types") {
+    val moveTypes = List(
+      MoveType.Normal(isCapture = true),
+      MoveType.CastleKingside,
+      MoveType.CastleQueenside,
+      MoveType.EnPassant,
+      MoveType.Promotion(PromotionPiece.Queen),
+      MoveType.Promotion(PromotionPiece.Rook),
+      MoveType.Promotion(PromotionPiece.Bishop),
+      MoveType.Promotion(PromotionPiece.Knight)
+    )
 
-  test("Move with CastleQueenside moveType") {
-    val m = Move(e2, e4, MoveType.CastleQueenside)
-    m.moveType shouldBe MoveType.CastleQueenside
-  }
-
-  test("Move with EnPassant moveType") {
-    val m = Move(e2, e4, MoveType.EnPassant)
-    m.moveType shouldBe MoveType.EnPassant
-  }
-
-  test("Move with Promotion to Queen") {
-    val m = Move(e2, e4, MoveType.Promotion(PromotionPiece.Queen))
-    m.moveType shouldBe MoveType.Promotion(PromotionPiece.Queen)
-  }
-
-  test("Move with Promotion to Knight") {
-    val m = Move(e2, e4, MoveType.Promotion(PromotionPiece.Knight))
-    m.moveType shouldBe MoveType.Promotion(PromotionPiece.Knight)
-  }
-
-  test("Move with Promotion to Bishop") {
-    val m = Move(e2, e4, MoveType.Promotion(PromotionPiece.Bishop))
-    m.moveType shouldBe MoveType.Promotion(PromotionPiece.Bishop)
-  }
-
-  test("Move with Promotion to Rook") {
-    val m = Move(e2, e4, MoveType.Promotion(PromotionPiece.Rook))
-    m.moveType shouldBe MoveType.Promotion(PromotionPiece.Rook)
+    moveTypes.foreach { moveType =>
+      Move(e2, e4, moveType).moveType shouldBe moveType
+    }
   }

modules/api/src/test/scala/de/nowchess/api/player/PlayerInfoTest.scala

@@ -5,19 +5,14 @@ import org.scalatest.matchers.should.Matchers
 
 class PlayerInfoTest extends AnyFunSuite with Matchers:
 
-  test("PlayerId.apply wraps a string") {
-    val id = PlayerId("player-123")
-    id.value shouldBe "player-123"
-  }
+  test("PlayerId and PlayerInfo preserve constructor values") {
+    val raw = "player-123"
+    val id = PlayerId(raw)
 
-  test("PlayerId.value unwraps to original string") {
-    val raw = "abc-456"
-    PlayerId(raw).value shouldBe raw
-  }
+    id.value shouldBe raw
 
-  test("PlayerInfo holds id and displayName") {
-    val id   = PlayerId("p1")
-    val info = PlayerInfo(id, "Magnus")
+    val playerId = PlayerId("p1")
+    val info = PlayerInfo(playerId, "Magnus")
     info.id.value      shouldBe "p1"
     info.displayName   shouldBe "Magnus"
   }

modules/api/src/test/scala/de/nowchess/api/response/ApiResponseTest.scala

@@ -5,52 +5,26 @@ import org.scalatest.matchers.should.Matchers
 
 class ApiResponseTest extends AnyFunSuite with Matchers:
 
-  test("ApiResponse.Success carries data") {
+  test("ApiResponse factories and payload wrappers keep values") {
     val r = ApiResponse.Success(42)
     r.data shouldBe 42
-  }
 
-  test("ApiResponse.Failure carries error list") {
     val err = ApiError("CODE", "msg")
-    val r   = ApiResponse.Failure(List(err))
-    r.errors shouldBe List(err)
-  }
+    ApiResponse.Failure(List(err)).errors shouldBe List(err)
+    ApiResponse.error(err) shouldBe ApiResponse.Failure(List(err))
 
-  test("ApiResponse.error creates single-error Failure") {
-    val err = ApiError("NOT_FOUND", "not found")
-    val f   = ApiResponse.error(err)
-    f shouldBe ApiResponse.Failure(List(err))
-  }
-
-  test("ApiError holds code and message") {
     val e = ApiError("CODE", "message")
     e.code    shouldBe "CODE"
     e.message shouldBe "message"
     e.field   shouldBe None
+    ApiError("INVALID", "bad value", Some("email")).field shouldBe Some("email")
   }
 
-  test("ApiError holds optional field") {
-    val e = ApiError("INVALID", "bad value", Some("email"))
-    e.field shouldBe Some("email")
-  }
-
-  test("Pagination.totalPages with exact division") {
+  test("Pagination.totalPages handles normal and guarded inputs") {
     Pagination(page = 0, pageSize = 10, totalItems = 30).totalPages shouldBe 3
-  }
-
-  test("Pagination.totalPages rounds up") {
     Pagination(page = 0, pageSize = 10, totalItems = 25).totalPages shouldBe 3
-  }
-
-  test("Pagination.totalPages is 0 when totalItems is 0") {
     Pagination(page = 0, pageSize = 10, totalItems = 0).totalPages shouldBe 0
-  }
-
-  test("Pagination.totalPages is 0 when pageSize is 0") {
     Pagination(page = 0, pageSize = 0, totalItems = 100).totalPages shouldBe 0
-  }
-
-  test("Pagination.totalPages is 0 when pageSize is negative") {
     Pagination(page = 0, pageSize = -1, totalItems = 100).totalPages shouldBe 0
   }
 

modules/api/versions.env

@@ -1,3 +1,3 @@
 MAJOR=0
-MINOR=0
-PATCH=8
+MINOR=2
+PATCH=0

modules/core/CHANGELOG.md

@@ -142,3 +142,49 @@
 * correct test board positions and captureOutput/withInput interaction ([f0481e2](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/f0481e2561b779df00925b46ee281dc36a795150))
 * update main class path in build configuration and adjust VCS directory mapping ([7b1f8b1](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/7b1f8b117623d327232a1a92a8a44d18582e0189))
 * update move validation to check for king safety ([#13](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/13)) ([e5e20c5](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/e5e20c566e368b12ca1dc59680c34e9112bf6762))
+##  (2026-04-02)
+
+### Features
+
+* add GameRules stub with PositionStatus enum ([76d4168](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/76d4168038de23e5d6083d4e8f0504fbf31d15a3))
+* add MovedInCheck/Checkmate/Stalemate MoveResult variants (stub dispatch) ([8b7ec57](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/8b7ec57e5ea6ee1615a1883848a426dc07d26364))
+* implement GameRules with isInCheck, legalMoves, gameStatus ([94a02ff](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/94a02ff6849436d9496c70a0f16c21666dae8e4e))
+* implement legal castling ([#1](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/1)) ([00d326c](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/00d326c1ba67711fbe180f04e1100c3f01dd0254))
+* NCS-10 Implement Pawn Promotion ([#12](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/12)) ([13bfc16](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/13bfc16cfe25db78ec607db523ca6d993c13430c))
+* NCS-11 50-move rule ([#9](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/9)) ([412ed98](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/412ed986a95703a3b282276540153480ceed229d))
+* NCS-16 Core Separation via Patterns ([#10](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/10)) ([1361dfc](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/1361dfc89553b146864fb8ff3526cf12cf3f293a))
+* NCS-17 Implement basic ScalaFX UI ([#14](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/14)) ([3ff8031](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/3ff80318b4f16c59733a46498581a5c27f048287))
+* NCS-21 Write Scripts to automate certain tasks ([#15](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/15)) ([8051871](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/80518719d536a087d339fe02530825dc07f8b388))
+* NCS-6 Implementing FEN & PGN ([#7](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/7)) ([f28e69d](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/f28e69dc181416aa2f221fdc4b45c2cda5efbf07))
+* NCS-9 En passant implementation ([#8](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/8)) ([919beb3](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/919beb3b4bfa8caf2f90976a415fe9b19b7e9747))
+* wire check/checkmate/stalemate into processMove and gameLoop ([5264a22](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/5264a225418b885c5e6ea6411b96f85e38837f6c))
+
+### Bug Fixes
+
+* add missing kings to gameLoop capture test board ([aedd787](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/aedd787b77203c2af934751dba7b784eaf165032))
+* correct test board positions and captureOutput/withInput interaction ([f0481e2](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/f0481e2561b779df00925b46ee281dc36a795150))
+* update main class path in build configuration and adjust VCS directory mapping ([7b1f8b1](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/7b1f8b117623d327232a1a92a8a44d18582e0189))
+* update move validation to check for king safety ([#13](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/13)) ([e5e20c5](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/e5e20c566e368b12ca1dc59680c34e9112bf6762))
+##  (2026-04-03)
+
+### Features
+
+* add GameRules stub with PositionStatus enum ([76d4168](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/76d4168038de23e5d6083d4e8f0504fbf31d15a3))
+* add MovedInCheck/Checkmate/Stalemate MoveResult variants (stub dispatch) ([8b7ec57](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/8b7ec57e5ea6ee1615a1883848a426dc07d26364))
+* implement GameRules with isInCheck, legalMoves, gameStatus ([94a02ff](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/94a02ff6849436d9496c70a0f16c21666dae8e4e))
+* implement legal castling ([#1](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/1)) ([00d326c](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/00d326c1ba67711fbe180f04e1100c3f01dd0254))
+* NCS-10 Implement Pawn Promotion ([#12](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/12)) ([13bfc16](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/13bfc16cfe25db78ec607db523ca6d993c13430c))
+* NCS-11 50-move rule ([#9](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/9)) ([412ed98](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/412ed986a95703a3b282276540153480ceed229d))
+* NCS-16 Core Separation via Patterns ([#10](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/10)) ([1361dfc](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/1361dfc89553b146864fb8ff3526cf12cf3f293a))
+* NCS-17 Implement basic ScalaFX UI ([#14](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/14)) ([3ff8031](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/3ff80318b4f16c59733a46498581a5c27f048287))
+* NCS-21 Write Scripts to automate certain tasks ([#15](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/15)) ([8051871](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/80518719d536a087d339fe02530825dc07f8b388))
+* NCS-6 Implementing FEN & PGN ([#7](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/7)) ([f28e69d](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/f28e69dc181416aa2f221fdc4b45c2cda5efbf07))
+* NCS-9 En passant implementation ([#8](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/8)) ([919beb3](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/919beb3b4bfa8caf2f90976a415fe9b19b7e9747))
+* wire check/checkmate/stalemate into processMove and gameLoop ([5264a22](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/5264a225418b885c5e6ea6411b96f85e38837f6c))
+
+### Bug Fixes
+
+* add missing kings to gameLoop capture test board ([aedd787](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/aedd787b77203c2af934751dba7b784eaf165032))
+* correct test board positions and captureOutput/withInput interaction ([f0481e2](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/f0481e2561b779df00925b46ee281dc36a795150))
+* update main class path in build configuration and adjust VCS directory mapping ([7b1f8b1](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/7b1f8b117623d327232a1a92a8a44d18582e0189))
+* update move validation to check for king safety ([#13](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/13)) ([e5e20c5](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/e5e20c566e368b12ca1dc59680c34e9112bf6762))

modules/core/build.gradle.kts

@@ -1,7 +1,6 @@
 plugins {
     id("scala")
     id("org.scoverage") version "8.1"
-    application
 }
 
 group = "de.nowchess"
@@ -22,19 +21,10 @@ scoverage {
     scoverageVersion.set(versions["SCOVERAGE"]!!)
 }
 
-application {
-    mainClass.set("de.nowchess.chess.Main")
-}
-
 tasks.withType<ScalaCompile> {
     scalaCompileOptions.additionalParameters = listOf("-encoding", "UTF-8")
 }
 
-tasks.named<JavaExec>("run") {
-    jvmArgs("-Dfile.encoding=UTF-8", "-Dstdout.encoding=UTF-8", "-Dstderr.encoding=UTF-8")
-    standardInput = System.`in`
-}
-
 dependencies {
 
     implementation("org.scala-lang:scala3-compiler_3") {
@@ -49,6 +39,8 @@ dependencies {
     }
 
     implementation(project(":modules:api"))
+    implementation(project(":modules:io"))
+    implementation(project(":modules:rule"))
 
     testImplementation(platform("org.junit:junit-bom:5.13.4"))
     testImplementation("org.junit.jupiter:junit-jupiter")

modules/core/src/main/scala/de/nowchess/chess/command/Command.scala

@@ -1,7 +1,7 @@
 package de.nowchess.chess.command
 
-import de.nowchess.api.board.{Square, Board, Color, Piece}
-import de.nowchess.chess.logic.GameHistory
+import de.nowchess.api.board.{Square, Piece}
+import de.nowchess.api.game.GameContext
 
 /** Marker trait for all commands that can be executed and undone.
  *  Commands encapsulate user actions and game state transitions.
@@ -23,23 +23,22 @@ case class MoveCommand(
   from: Square,
   to: Square,
   moveResult: Option[MoveResult] = None,
-  previousBoard: Option[Board] = None,
-  previousHistory: Option[GameHistory] = None,
-  previousTurn: Option[Color] = None
+  previousContext: Option[GameContext] = None,
+  notation: String = ""
 ) extends Command:
 
   override def execute(): Boolean =
     moveResult.isDefined
 
   override def undo(): Boolean =
-    previousBoard.isDefined && previousHistory.isDefined && previousTurn.isDefined
+    previousContext.isDefined
 
   override def description: String = s"Move from $from to $to"
 
 // Sealed hierarchy of move outcomes (for tracking state changes)
 sealed trait MoveResult
 object MoveResult:
-  case class Successful(newBoard: Board, newHistory: GameHistory, newTurn: Color, captured: Option[Piece]) extends MoveResult
+  case class Successful(newContext: GameContext, captured: Option[Piece]) extends MoveResult
   case object InvalidFormat extends MoveResult
   case object InvalidMove extends MoveResult
 
@@ -51,14 +50,12 @@ case class QuitCommand() extends Command:
 
 /** Command to reset the board to initial position. */
 case class ResetCommand(
-  previousBoard: Option[Board] = None,
-  previousHistory: Option[GameHistory] = None,
-  previousTurn: Option[Color] = None
+  previousContext: Option[GameContext] = None
 ) extends Command:
 
   override def execute(): Boolean = true
 
   override def undo(): Boolean =
-    previousBoard.isDefined && previousHistory.isDefined && previousTurn.isDefined
+    previousContext.isDefined
 
   override def description: String = "Reset board"

modules/core/src/main/scala/de/nowchess/chess/controller/GameController.scala

@@ -1,106 +0,0 @@
-package de.nowchess.chess.controller
-
-import de.nowchess.api.board.{Board, Color, File, Piece, PieceType, Rank, Square}
-import de.nowchess.api.move.PromotionPiece
-import de.nowchess.chess.logic.*
-
-// ---------------------------------------------------------------------------
-// Result ADT returned by the pure processMove function
-// ---------------------------------------------------------------------------
-
-sealed trait MoveResult
-object MoveResult:
-  case object Quit                                                                       extends MoveResult
-  case class  InvalidFormat(raw: String)                                                extends MoveResult
-  case object NoPiece                                                                   extends MoveResult
-  case object WrongColor                                                                extends MoveResult
-  case object IllegalMove                                                               extends MoveResult
-  case class  PromotionRequired(
-    from: Square,
-    to: Square,
-    boardBefore: Board,
-    historyBefore: GameHistory,
-    captured: Option[Piece],
-    turn: Color
-  ) extends MoveResult
-  case class  Moved(newBoard: Board, newHistory: GameHistory, captured: Option[Piece], newTurn: Color)      extends MoveResult
-  case class  MovedInCheck(newBoard: Board, newHistory: GameHistory, captured: Option[Piece], newTurn: Color) extends MoveResult
-  case class  Checkmate(winner: Color)                                                  extends MoveResult
-  case object Stalemate                                                                 extends MoveResult
-
-// ---------------------------------------------------------------------------
-// Controller
-// ---------------------------------------------------------------------------
-
-object GameController:
-
-  /** Pure function: interprets one raw input line against the current game context.
-   *  Has no I/O side effects — all output must be handled by the caller.
-   */
-  def processMove(board: Board, history: GameHistory, turn: Color, raw: String): MoveResult =
-    raw.trim match
-      case "quit" | "q" => MoveResult.Quit
-      case trimmed =>
-        Parser.parseMove(trimmed) match
-          case None              => MoveResult.InvalidFormat(trimmed)
-          case Some((from, to))  => validateAndApply(board, history, turn, from, to)
-
-  /** Apply a previously detected promotion move with the chosen piece.
-   *  Called after processMove returned PromotionRequired.
-   */
-  def completePromotion(
-    board: Board,
-    history: GameHistory,
-    from: Square,
-    to: Square,
-    piece: PromotionPiece,
-    turn: Color
-  ): MoveResult =
-    val (boardAfterMove, captured) = board.withMove(from, to)
-    val promotedPieceType = piece match
-      case PromotionPiece.Queen  => PieceType.Queen
-      case PromotionPiece.Rook   => PieceType.Rook
-      case PromotionPiece.Bishop => PieceType.Bishop
-      case PromotionPiece.Knight => PieceType.Knight
-    val newBoard    = boardAfterMove.updated(to, Piece(turn, promotedPieceType))
-    // Promotion is always a pawn move → clock resets
-    val newHistory = history.addMove(from, to, None, Some(piece), wasPawnMove = true)
-    toMoveResult(newBoard, newHistory, captured, turn)
-
-  // ---------------------------------------------------------------------------
-  // Private helpers
-  // ---------------------------------------------------------------------------
-
-  private def validateAndApply(board: Board, history: GameHistory, turn: Color, from: Square, to: Square): MoveResult =
-    board.pieceAt(from) match
-      case None                              => MoveResult.NoPiece
-      case Some(piece) if piece.color != turn => MoveResult.WrongColor
-      case Some(_) =>
-        if !GameRules.legalMoves(board, history, turn).contains(from -> to) then MoveResult.IllegalMove
-        else if MoveValidator.isPromotionMove(board, from, to) then
-          MoveResult.PromotionRequired(from, to, board, history, board.pieceAt(to), turn)
-        else applyNormalMove(board, history, turn, from, to)
-
-  private def applyNormalMove(board: Board, history: GameHistory, turn: Color, from: Square, to: Square): MoveResult =
-    val castleOpt              = Option.when(MoveValidator.isCastle(board, from, to))(MoveValidator.castleSide(from, to))
-    val isEP                   = EnPassantCalculator.isEnPassant(board, history, from, to)
-    val (newBoard, captured)   = castleOpt match
-      case Some(side) => (board.withCastle(turn, side), None)
-      case None =>
-        val (b, cap) = board.withMove(from, to)
-        if isEP then
-          val capturedSq = EnPassantCalculator.capturedPawnSquare(to, turn)
-          (b.removed(capturedSq), board.pieceAt(capturedSq))
-        else (b, cap)
-    val pieceType   = board.pieceAt(from).map(_.pieceType).getOrElse(PieceType.Pawn)
-    val wasPawnMove = pieceType == PieceType.Pawn
-    val wasCapture  = captured.isDefined
-    val newHistory  = history.addMove(from, to, castleOpt, wasPawnMove = wasPawnMove, wasCapture = wasCapture, pieceType = pieceType)
-    toMoveResult(newBoard, newHistory, captured, turn)
-
-  private def toMoveResult(newBoard: Board, newHistory: GameHistory, captured: Option[Piece], turn: Color): MoveResult =
-    GameRules.gameStatus(newBoard, newHistory, turn.opposite) match
-      case PositionStatus.Normal  => MoveResult.Moved(newBoard, newHistory, captured, turn.opposite)
-      case PositionStatus.InCheck => MoveResult.MovedInCheck(newBoard, newHistory, captured, turn.opposite)
-      case PositionStatus.Mated   => MoveResult.Checkmate(turn)
-      case PositionStatus.Drawn   => MoveResult.Stalemate

modules/core/src/main/scala/de/nowchess/chess/engine/GameEngine.scala

@@ -1,47 +1,37 @@
 package de.nowchess.chess.engine
 
-import de.nowchess.api.board.{Board, Color, Piece, Square}
-import de.nowchess.api.move.PromotionPiece
-import de.nowchess.chess.logic.{GameHistory, GameRules, PositionStatus}
-import de.nowchess.chess.controller.{GameController, Parser, MoveResult}
+import de.nowchess.api.board.{Board, Color, Piece, PieceType, Square}
+import de.nowchess.api.move.{Move, MoveType, PromotionPiece}
+import de.nowchess.api.game.GameContext
+import de.nowchess.chess.controller.Parser
 import de.nowchess.chess.observer.*
-import de.nowchess.chess.command.{CommandInvoker, MoveCommand}
-import de.nowchess.chess.notation.{PgnExporter, PgnParser}
+import de.nowchess.chess.command.{CommandInvoker, MoveCommand, MoveResult}
+import de.nowchess.io.{GameContextImport, GameContextExport}
+import de.nowchess.rules.RuleSet
+import de.nowchess.rules.sets.DefaultRules
 
 /** Pure game engine that manages game state and notifies observers of state changes.
- *  This class is the single source of truth for the game state.
- *  All user interactions must go through this engine via Commands, and all state changes
- *  are communicated to observers via GameEvent notifications.
+ *  All rule queries delegate to the injected RuleSet.
+ *  All user interactions go through Commands; state changes are broadcast via GameEvents.
  */
 class GameEngine(
-  initialBoard: Board = Board.initial,
-  initialHistory: GameHistory = GameHistory.empty,
-  initialTurn: Color = Color.White,
-  completePromotionFn: (Board, GameHistory, Square, Square, PromotionPiece, Color) => MoveResult =
-    GameController.completePromotion
+  val initialContext: GameContext = GameContext.initial,
+  val ruleSet: RuleSet = DefaultRules
 ) extends Observable:
-  private var currentBoard: Board = initialBoard
-  private var currentHistory: GameHistory = initialHistory
-  private var currentTurn: Color = initialTurn
+  private var currentContext: GameContext = initialContext
   private val invoker = new CommandInvoker()
 
-  /** Inner class for tracking pending promotion state */
-  private case class PendingPromotion(
-    from: Square, to: Square,
-    boardBefore: Board, historyBefore: GameHistory,
-    turn: Color
-  )
-
-  /** Current pending promotion, if any */
+  /** Pending promotion: the Move that triggered it (from/to only, moveType filled in later). */
+  private case class PendingPromotion(from: Square, to: Square, contextBefore: GameContext)
   private var pendingPromotion: Option[PendingPromotion] = None
 
   /** True if a pawn promotion move is pending and needs a piece choice. */
   def isPendingPromotion: Boolean = synchronized { pendingPromotion.isDefined }
 
   // Synchronized accessors for current state
-  def board: Board = synchronized { currentBoard }
-  def history: GameHistory = synchronized { currentHistory }
-  def turn: Color = synchronized { currentTurn }
+  def board: Board   = synchronized { currentContext.board }
+  def turn: Color    = synchronized { currentContext.turn }
+  def context: GameContext = synchronized { currentContext }
 
   /** Check if undo is available. */
   def canUndo: Boolean = synchronized { invoker.canUndo }
@@ -59,7 +49,6 @@ class GameEngine(
     val trimmed = rawInput.trim.toLowerCase
     trimmed match
       case "quit" | "q" =>
-        // Client should handle quit logic; we just return
         ()
 
       case "undo" =>
@@ -69,96 +58,55 @@ class GameEngine(
         performRedo()
 
       case "draw" =>
-        if currentHistory.halfMoveClock >= 100 then
-          currentBoard   = Board.initial
-          currentHistory = GameHistory.empty
-          currentTurn    = Color.White
+        if currentContext.halfMoveClock >= 100 then
           invoker.clear()
-          notifyObservers(DrawClaimedEvent(currentBoard, currentHistory, currentTurn))
+          notifyObservers(DrawClaimedEvent(currentContext))
         else
           notifyObservers(InvalidMoveEvent(
-            currentBoard, currentHistory, currentTurn,
+            currentContext,
             "Draw cannot be claimed: the 50-move rule has not been triggered."
           ))
 
       case "" =>
-        val event = InvalidMoveEvent(
-          currentBoard,
-          currentHistory,
-          currentTurn,
-          "Please enter a valid move or command."
-        )
-        notifyObservers(event)
+        notifyObservers(InvalidMoveEvent(currentContext, "Please enter a valid move or command."))
 
       case moveInput =>
         Parser.parseMove(moveInput) match
           case None =>
             notifyObservers(InvalidMoveEvent(
-              currentBoard, currentHistory, currentTurn,
+              currentContext,
               s"Invalid move format '$moveInput'. Use coordinate notation, e.g. e2e4."
             ))
           case Some((from, to)) =>
-            handleParsedMove(from, to, moveInput)
+            handleParsedMove(from, to)
   }
 
-  private def handleParsedMove(from: Square, to: Square, moveInput: String): Unit =
-    val cmd = MoveCommand(
-      from = from,
-      to = to,
-      previousBoard = Some(currentBoard),
-      previousHistory = Some(currentHistory),
-      previousTurn = Some(currentTurn)
-    )
-    GameController.processMove(currentBoard, currentHistory, currentTurn, moveInput) match
-      case MoveResult.InvalidFormat(_) | MoveResult.NoPiece | MoveResult.WrongColor | MoveResult.IllegalMove | MoveResult.Quit =>
-        handleFailedMove(moveInput)
+  private def handleParsedMove(from: Square, to: Square): Unit =
+    currentContext.board.pieceAt(from) match
+      case None =>
+        notifyObservers(InvalidMoveEvent(currentContext, "No piece on that square."))
+      case Some(piece) if piece.color != currentContext.turn =>
+        notifyObservers(InvalidMoveEvent(currentContext, "That is not your piece."))
+      case Some(piece) =>
+        val legal = ruleSet.legalMoves(currentContext)(from)
+        // Find all legal moves going to `to`
+        val candidates = legal.filter(_.to == to)
+        candidates match
+          case Nil =>
+            notifyObservers(InvalidMoveEvent(currentContext, "Illegal move."))
+          case moves if isPromotionMove(piece, to) =>
+            // Multiple moves (one per promotion piece) — ask user to choose
+            val contextBefore = currentContext
+            pendingPromotion = Some(PendingPromotion(from, to, contextBefore))
+            notifyObservers(PromotionRequiredEvent(currentContext, from, to))
+          case move :: _ =>
+            executeMove(move)
 
-      case MoveResult.Moved(newBoard, newHistory, captured, newTurn) =>
-        val updatedCmd = cmd.copy(moveResult = Some(de.nowchess.chess.command.MoveResult.Successful(newBoard, newHistory, newTurn, captured)))
-        invoker.execute(updatedCmd)
-        updateGameState(newBoard, newHistory, newTurn)
-        emitMoveEvent(from.toString, to.toString, captured, newTurn)
-        if currentHistory.halfMoveClock >= 100 then
-          notifyObservers(FiftyMoveRuleAvailableEvent(currentBoard, currentHistory, currentTurn))
-
-      case MoveResult.MovedInCheck(newBoard, newHistory, captured, newTurn) =>
-        val updatedCmd = cmd.copy(moveResult = Some(de.nowchess.chess.command.MoveResult.Successful(newBoard, newHistory, newTurn, captured)))
-        invoker.execute(updatedCmd)
-        updateGameState(newBoard, newHistory, newTurn)
-        emitMoveEvent(from.toString, to.toString, captured, newTurn)
-        notifyObservers(CheckDetectedEvent(currentBoard, currentHistory, currentTurn))
-        if currentHistory.halfMoveClock >= 100 then
-          notifyObservers(FiftyMoveRuleAvailableEvent(currentBoard, currentHistory, currentTurn))
-
-      case MoveResult.Checkmate(winner) =>
-        val updatedCmd = cmd.copy(moveResult = Some(de.nowchess.chess.command.MoveResult.Successful(Board.initial, GameHistory.empty, Color.White, None)))
-        invoker.execute(updatedCmd)
-        currentBoard = Board.initial
-        currentHistory = GameHistory.empty
-        currentTurn = Color.White
-        notifyObservers(CheckmateEvent(currentBoard, currentHistory, currentTurn, winner))
-
-      case MoveResult.Stalemate =>
-        val updatedCmd = cmd.copy(moveResult = Some(de.nowchess.chess.command.MoveResult.Successful(Board.initial, GameHistory.empty, Color.White, None)))
-        invoker.execute(updatedCmd)
-        currentBoard = Board.initial
-        currentHistory = GameHistory.empty
-        currentTurn = Color.White
-        notifyObservers(StalemateEvent(currentBoard, currentHistory, currentTurn))
-
-      case MoveResult.PromotionRequired(promFrom, promTo, boardBefore, histBefore, _, promotingTurn) =>
-        pendingPromotion = Some(PendingPromotion(promFrom, promTo, boardBefore, histBefore, promotingTurn))
-        notifyObservers(PromotionRequiredEvent(currentBoard, currentHistory, currentTurn, promFrom, promTo))
-
-  /** Undo the last move. */
-  def undo(): Unit = synchronized {
-    performUndo()
-  }
-
-  /** Redo the last undone move. */
-  def redo(): Unit = synchronized {
-    performRedo()
-  }
+  private def isPromotionMove(piece: Piece, to: Square): Boolean =
+    piece.pieceType == PieceType.Pawn && {
+      val promoRank = if piece.color == Color.White then 7 else 0
+      to.rank.ordinal == promoRank
+    }
 
   /** Apply a player's promotion piece choice.
    *  Must only be called when isPendingPromotion is true.
@@ -166,187 +114,205 @@ class GameEngine(
   def completePromotion(piece: PromotionPiece): Unit = synchronized {
     pendingPromotion match
       case None =>
-        notifyObservers(InvalidMoveEvent(currentBoard, currentHistory, currentTurn, "No promotion pending."))
+        notifyObservers(InvalidMoveEvent(currentContext, "No promotion pending."))
       case Some(pending) =>
         pendingPromotion = None
-        val cmd = MoveCommand(
-          from = pending.from,
-          to = pending.to,
-          previousBoard = Some(pending.boardBefore),
-          previousHistory = Some(pending.historyBefore),
-          previousTurn = Some(pending.turn)
-        )
-        completePromotionFn(
-          pending.boardBefore, pending.historyBefore,
-          pending.from, pending.to, piece, pending.turn
-        ) match
-          case MoveResult.Moved(newBoard, newHistory, captured, newTurn) =>
-            val updatedCmd = cmd.copy(moveResult = Some(de.nowchess.chess.command.MoveResult.Successful(newBoard, newHistory, newTurn, captured)))
-            invoker.execute(updatedCmd)
-            updateGameState(newBoard, newHistory, newTurn)
-            emitMoveEvent(pending.from.toString, pending.to.toString, captured, newTurn)
-
-          case MoveResult.MovedInCheck(newBoard, newHistory, captured, newTurn) =>
-            val updatedCmd = cmd.copy(moveResult = Some(de.nowchess.chess.command.MoveResult.Successful(newBoard, newHistory, newTurn, captured)))
-            invoker.execute(updatedCmd)
-            updateGameState(newBoard, newHistory, newTurn)
-            emitMoveEvent(pending.from.toString, pending.to.toString, captured, newTurn)
-            notifyObservers(CheckDetectedEvent(currentBoard, currentHistory, currentTurn))
-
-          case MoveResult.Checkmate(winner) =>
-            val updatedCmd = cmd.copy(moveResult = Some(de.nowchess.chess.command.MoveResult.Successful(Board.initial, GameHistory.empty, Color.White, None)))
-            invoker.execute(updatedCmd)
-            currentBoard = Board.initial
-            currentHistory = GameHistory.empty
-            currentTurn = Color.White
-            notifyObservers(CheckmateEvent(currentBoard, currentHistory, currentTurn, winner))
-
-          case MoveResult.Stalemate =>
-            val updatedCmd = cmd.copy(moveResult = Some(de.nowchess.chess.command.MoveResult.Successful(Board.initial, GameHistory.empty, Color.White, None)))
-            invoker.execute(updatedCmd)
-            currentBoard = Board.initial
-            currentHistory = GameHistory.empty
-            currentTurn = Color.White
-            notifyObservers(StalemateEvent(currentBoard, currentHistory, currentTurn))
-
-          case _ =>
-            notifyObservers(InvalidMoveEvent(currentBoard, currentHistory, currentTurn, "Error completing promotion."))
+        val move = Move(pending.from, pending.to, MoveType.Promotion(piece))
+        // Verify it's actually legal
+        val legal = ruleSet.legalMoves(currentContext)(pending.from)
+        if legal.contains(move) then
+          executeMove(move)
+        else
+          notifyObservers(InvalidMoveEvent(currentContext, "Error completing promotion."))
   }
 
-  /** Validate and load a PGN string.
-   *  Each move is replayed through the command system so undo/redo is available after loading.
-   *  Returns Right(()) on success; Left(error) if any move is illegal or the position impossible. */
-  def loadPgn(pgn: String): Either[String, Unit] = synchronized {
-    PgnParser.validatePgn(pgn) match
-      case Left(err) =>
-        Left(err)
-      case Right(game) =>
-        val initialBoardBeforeLoad = currentBoard
-        val initialHistoryBeforeLoad = currentHistory
-        val initialTurnBeforeLoad = currentTurn
-        
-        currentBoard = Board.initial
-        currentHistory = GameHistory.empty
-        currentTurn = Color.White
-        pendingPromotion = None
-        invoker.clear()
+  /** Undo the last move. */
+  def undo(): Unit = synchronized { performUndo() }
 
-        var error: Option[String] = None
-        import scala.util.control.Breaks._
-        breakable {
-          game.moves.foreach { move =>
-            handleParsedMove(move.from, move.to, s"${move.from}${move.to}")
-            move.promotionPiece.foreach(completePromotion)
-            
-            // If the move failed to execute properly, stop and report
-            // (validatePgn should have caught this, but we're being safe)
-            if pendingPromotion.isDefined && move.promotionPiece.isEmpty then
-              error = Some(s"Promotion required for move ${move.from}${move.to}")
-              break()
-          }
+  /** Redo the last undone move. */
+  def redo(): Unit = synchronized { performRedo() }
+
+  /** Load a game using the provided importer.
+   *  If the imported context has moves, they are replayed through the command system.
+   *  Otherwise, the position is set directly.
+   *  Notifies observers with PgnLoadedEvent on success.
+   */
+  def loadGame(importer: GameContextImport, input: String): Either[String, Unit] = synchronized {
+    importer.importGameContext(input) match
+      case Left(err) => Left(err)
+      case Right(ctx) =>
+        replayGame(ctx).map { _ =>
+          notifyObservers(PgnLoadedEvent(currentContext))
         }
-        
-        error match
-          case Some(err) =>
-            currentBoard = initialBoardBeforeLoad
-            currentHistory = initialHistoryBeforeLoad
-            currentTurn = initialTurnBeforeLoad
-            Left(err)
-          case None =>
-            notifyObservers(PgnLoadedEvent(currentBoard, currentHistory, currentTurn))
-            Right(())
+  }
+
+  private def replayGame(ctx: GameContext): Either[String, Unit] =
+    val savedContext = currentContext
+    currentContext = GameContext.initial
+    pendingPromotion = None
+    invoker.clear()
+
+    if ctx.moves.isEmpty then
+      currentContext = ctx
+      Right(())
+    else
+      replayMoves(ctx.moves, savedContext)
+
+  private[engine] def replayMoves(moves: List[Move], savedContext: GameContext): Either[String, Unit] =
+    var error: Option[String] = None
+    moves.foreach: move =>
+      if error.isEmpty then
+        handleParsedMove(move.from, move.to)
+
+        move.moveType match {
+          case MoveType.Promotion(pp) =>
+            if pendingPromotion.isDefined then
+              completePromotion(pp)
+            else
+              error = Some(s"Promotion required for move ${move.from}${move.to}")
+          case _ => ()
+        }
+    error match
+      case Some(err) =>
+        currentContext = savedContext
+        Left(err)
+      case None =>
+        Right(())
+
+  /** Export the current game context using the provided exporter. */
+  def exportGame(exporter: GameContextExport): String = synchronized {
+    exporter.exportGameContext(currentContext)
   }
 
   /** Load an arbitrary board position, clearing all history and undo/redo state. */
-  def loadPosition(board: Board, history: GameHistory, turn: Color): Unit = synchronized {
-    currentBoard = board
-    currentHistory = history
-    currentTurn = turn
+  def loadPosition(newContext: GameContext): Unit = synchronized {
+    currentContext = newContext
     pendingPromotion = None
     invoker.clear()
-    notifyObservers(BoardResetEvent(currentBoard, currentHistory, currentTurn))
+    notifyObservers(BoardResetEvent(currentContext))
   }
 
   /** Reset the board to initial position. */
   def reset(): Unit = synchronized {
-    currentBoard = Board.initial
-    currentHistory = GameHistory.empty
-    currentTurn = Color.White
+    currentContext = GameContext.initial
     invoker.clear()
-    notifyObservers(BoardResetEvent(
-      currentBoard,
-      currentHistory,
-      currentTurn
-    ))
+    notifyObservers(BoardResetEvent(currentContext))
   }
 
-  // ──── Private Helpers ────
+  // ──── Private helpers ────
+
+  private def executeMove(move: Move): Unit =
+    val contextBefore = currentContext
+    val nextContext = ruleSet.applyMove(currentContext)(move)
+    val captured = computeCaptured(currentContext, move)
+
+    val cmd = MoveCommand(
+      from = move.from,
+      to = move.to,
+      moveResult = Some(MoveResult.Successful(nextContext, captured)),
+      previousContext = Some(contextBefore),
+      notation = translateMoveToNotation(move, contextBefore.board)
+    )
+    invoker.execute(cmd)
+    currentContext = nextContext
+
+    notifyObservers(MoveExecutedEvent(
+      currentContext,
+      move.from.toString,
+      move.to.toString,
+      captured.map(c => s"${c.color.label} ${c.pieceType.label}")
+    ))
+
+    if ruleSet.isCheckmate(currentContext) then
+      val winner = currentContext.turn.opposite
+      notifyObservers(CheckmateEvent(currentContext, winner))
+      invoker.clear()
+      currentContext = GameContext.initial
+    else if ruleSet.isStalemate(currentContext) then
+      notifyObservers(StalemateEvent(currentContext))
+      invoker.clear()
+      currentContext = GameContext.initial
+    else if ruleSet.isCheck(currentContext) then
+      notifyObservers(CheckDetectedEvent(currentContext))
+
+    if currentContext.halfMoveClock >= 100 then
+      notifyObservers(FiftyMoveRuleAvailableEvent(currentContext))
+
+  private def translateMoveToNotation(move: Move, boardBefore: Board): String =
+    move.moveType match
+      case MoveType.CastleKingside  => "O-O"
+      case MoveType.CastleQueenside => "O-O-O"
+      case MoveType.EnPassant   => enPassantNotation(move)
+      case MoveType.Promotion(pp) => promotionNotation(move, pp)
+      case MoveType.Normal(isCapture) => normalMoveNotation(move, boardBefore, isCapture)
+
+  private def enPassantNotation(move: Move): String =
+    s"${move.from.file.toString.toLowerCase}x${move.to}"
+
+  private def promotionNotation(move: Move, piece: PromotionPiece): String =
+    val ppChar = piece match
+      case PromotionPiece.Queen  => "Q"
+      case PromotionPiece.Rook   => "R"
+      case PromotionPiece.Bishop => "B"
+      case PromotionPiece.Knight => "N"
+    s"${move.to}=$ppChar"
+
+  private[engine] def normalMoveNotation(move: Move, boardBefore: Board, isCapture: Boolean): String =
+    boardBefore.pieceAt(move.from).map(_.pieceType) match
+      case Some(PieceType.Pawn) =>
+        if isCapture then s"${move.from.file.toString.toLowerCase}x${move.to}"
+        else move.to.toString
+      case Some(pt) =>
+        val letter = pieceNotation(pt)
+        if isCapture then s"${letter}x${move.to}" else s"$letter${move.to}"
+      case None => move.to.toString
+
+  private[engine] def pieceNotation(pieceType: PieceType): String =
+    pieceType match
+      case PieceType.Knight => "N"
+      case PieceType.Bishop => "B"
+      case PieceType.Rook   => "R"
+      case PieceType.Queen  => "Q"
+      case PieceType.King   => "K"
+      case _                => ""
+
+  private def computeCaptured(context: GameContext, move: Move): Option[Piece] =
+    move.moveType match
+      case MoveType.EnPassant =>
+        // Captured pawn is on the same rank as the moving pawn, same file as destination
+        val capturedSquare = Square(move.to.file, move.from.rank)
+        context.board.pieceAt(capturedSquare)
+      case MoveType.CastleKingside | MoveType.CastleQueenside =>
+        None
+      case _ =>
+        context.board.pieceAt(move.to)
 
   private def performUndo(): Unit =
     if invoker.canUndo then
       val cmd = invoker.history(invoker.getCurrentIndex)
       (cmd: @unchecked) match
         case moveCmd: MoveCommand =>
-          val notation = currentHistory.moves.lastOption.map(PgnExporter.moveToAlgebraic).getOrElse("")
-          moveCmd.previousBoard.foreach(currentBoard = _)
-          moveCmd.previousHistory.foreach(currentHistory = _)
-          moveCmd.previousTurn.foreach(currentTurn = _)
+          moveCmd.previousContext.foreach(currentContext = _)
           invoker.undo()
-          notifyObservers(MoveUndoneEvent(currentBoard, currentHistory, currentTurn, notation))
+          notifyObservers(MoveUndoneEvent(currentContext, moveCmd.notation))
     else
-      notifyObservers(InvalidMoveEvent(currentBoard, currentHistory, currentTurn, "Nothing to undo."))
+      notifyObservers(InvalidMoveEvent(currentContext, "Nothing to undo."))
 
   private def performRedo(): Unit =
     if invoker.canRedo then
       val cmd = invoker.history(invoker.getCurrentIndex + 1)
       (cmd: @unchecked) match
         case moveCmd: MoveCommand =>
-          for case de.nowchess.chess.command.MoveResult.Successful(nb, nh, nt, cap) <- moveCmd.moveResult do
-            updateGameState(nb, nh, nt)
+          for case MoveResult.Successful(nextCtx, cap) <- moveCmd.moveResult do
+            currentContext = nextCtx
             invoker.redo()
-            val notation    = nh.moves.lastOption.map(PgnExporter.moveToAlgebraic).getOrElse("")
             val capturedDesc = cap.map(c => s"${c.color.label} ${c.pieceType.label}")
-            notifyObservers(MoveRedoneEvent(currentBoard, currentHistory, currentTurn, notation, moveCmd.from.toString, moveCmd.to.toString, capturedDesc))
+            notifyObservers(MoveRedoneEvent(
+              currentContext,
+              moveCmd.notation,
+              moveCmd.from.toString,
+              moveCmd.to.toString,
+              capturedDesc
+            ))
     else
-      notifyObservers(InvalidMoveEvent(currentBoard, currentHistory, currentTurn, "Nothing to redo."))
-
-  private def updateGameState(newBoard: Board, newHistory: GameHistory, newTurn: Color): Unit =
-    currentBoard = newBoard
-    currentHistory = newHistory
-    currentTurn = newTurn
-
-  private def emitMoveEvent(fromSq: String, toSq: String, captured: Option[Piece], newTurn: Color): Unit =
-    val capturedDesc = captured.map(c => s"${c.color.label} ${c.pieceType.label}")
-    notifyObservers(MoveExecutedEvent(
-      currentBoard,
-      currentHistory,
-      newTurn,
-      fromSq,
-      toSq,
-      capturedDesc
-    ))
-
-  private def handleFailedMove(moveInput: String): Unit =
-    (GameController.processMove(currentBoard, currentHistory, currentTurn, moveInput): @unchecked) match
-      case MoveResult.NoPiece =>
-        notifyObservers(InvalidMoveEvent(
-          currentBoard,
-          currentHistory,
-          currentTurn,
-          "No piece on that square."
-        ))
-      case MoveResult.WrongColor =>
-        notifyObservers(InvalidMoveEvent(
-          currentBoard,
-          currentHistory,
-          currentTurn,
-          "That is not your piece."
-        ))
-      case MoveResult.IllegalMove =>
-        notifyObservers(InvalidMoveEvent(
-          currentBoard,
-          currentHistory,
-          currentTurn,
-          "Illegal move."
-        ))
-
+      notifyObservers(InvalidMoveEvent(currentContext, "Nothing to redo."))

modules/core/src/main/scala/de/nowchess/chess/logic/CastleSide.scala

@@ -1,23 +0,0 @@
-package de.nowchess.chess.logic
-
-import de.nowchess.api.board.*
-
-enum CastleSide:
-  case Kingside, Queenside
-
-extension (b: Board)
-  def withCastle(color: Color, side: CastleSide): Board =
-    val rank = if color == Color.White then Rank.R1 else Rank.R8
-    val kingFrom = Square(File.E, rank)
-    val (kingTo, rookFrom, rookTo) = side match
-      case CastleSide.Kingside =>
-        (Square(File.G, rank), Square(File.H, rank), Square(File.F, rank))
-      case CastleSide.Queenside =>
-        (Square(File.C, rank), Square(File.A, rank), Square(File.D, rank))
-
-    val king = b.pieceAt(kingFrom).get
-    val rook = b.pieceAt(rookFrom).get
-
-    b.removed(kingFrom).removed(rookFrom)
-      .updated(kingTo, king)
-      .updated(rookTo, rook)

modules/core/src/main/scala/de/nowchess/chess/logic/CastlingRightsCalculator.scala

@@ -1,31 +0,0 @@
-package de.nowchess.chess.logic
-
-import de.nowchess.api.board.{Color, File, Rank, Square}
-import de.nowchess.api.game.CastlingRights
-
-/** Derives castling rights from move history. */
-object CastlingRightsCalculator:
-
-  def deriveCastlingRights(history: GameHistory, color: Color): CastlingRights =
-    val (kingRow, kingsideRookFile, queensideRookFile) = color match
-      case Color.White => (Rank.R1, File.H, File.A)
-      case Color.Black => (Rank.R8, File.H, File.A)
-
-    // Check if king has moved
-    val kingHasMoved = history.moves.exists: move =>
-      move.from == Square(File.E, kingRow) || move.castleSide.isDefined
-
-    if kingHasMoved then
-      CastlingRights.None
-    else
-      // Check if kingside rook has moved or was captured
-      val kingsideLost = history.moves.exists: move =>
-        move.from == Square(kingsideRookFile, kingRow) ||
-        move.to == Square(kingsideRookFile, kingRow)
-
-      // Check if queenside rook has moved or was captured
-      val queensideLost = history.moves.exists: move =>
-        move.from == Square(queensideRookFile, kingRow) ||
-        move.to == Square(queensideRookFile, kingRow)
-
-      CastlingRights(kingSide = !kingsideLost, queenSide = !queensideLost)

modules/core/src/main/scala/de/nowchess/chess/logic/EnPassantCalculator.scala

@@ -1,32 +0,0 @@
-package de.nowchess.chess.logic
-
-import de.nowchess.api.board.*
-
-object EnPassantCalculator:
-
-  /** Returns the en passant target square if the last move was a double pawn push.
-   *  The target is the square the pawn passed through (e.g. e2→e4 yields e3).
-   */
-  def enPassantTarget(board: Board, history: GameHistory): Option[Square] =
-    history.moves.lastOption.flatMap: move =>
-      val rankDiff = move.to.rank.ordinal - move.from.rank.ordinal
-      val isDoublePush = math.abs(rankDiff) == 2
-      val isPawn = board.pieceAt(move.to).exists(_.pieceType == PieceType.Pawn)
-      if isDoublePush && isPawn then
-        val midRankIdx = move.from.rank.ordinal + rankDiff / 2
-        Some(Square(move.to.file, Rank.values(midRankIdx)))
-      else None
-
-  /** True if moving from→to is an en passant capture. */
-  def isEnPassant(board: Board, history: GameHistory, from: Square, to: Square): Boolean =
-    board.pieceAt(from).exists(_.pieceType == PieceType.Pawn) &&
-    enPassantTarget(board, history).contains(to) &&
-    math.abs(to.file.ordinal - from.file.ordinal) == 1
-
-  /** Returns the square of the pawn to remove when an en passant capture lands on `to`.
-   *  White captures upward → captured pawn is one rank below `to`.
-   *  Black captures downward → captured pawn is one rank above `to`.
-   */
-  def capturedPawnSquare(to: Square, color: Color): Square =
-    val capturedRankIdx = to.rank.ordinal + (if color == Color.White then -1 else 1)
-    Square(to.file, Rank.values(capturedRankIdx))

modules/core/src/main/scala/de/nowchess/chess/logic/GameHistory.scala

@@ -1,49 +0,0 @@
-package de.nowchess.chess.logic
-
-import de.nowchess.api.board.{PieceType, Square}
-import de.nowchess.api.move.PromotionPiece
-
-/** A single move recorded in the game history. Distinct from api.move.Move which represents user intent. */
-case class HistoryMove(
-  from: Square,
-  to: Square,
-  castleSide: Option[CastleSide],
-  promotionPiece: Option[PromotionPiece] = None,
-  pieceType: PieceType = PieceType.Pawn,
-  isCapture: Boolean = false
-)
-
-/** Complete game history: ordered list of moves plus the half-move clock for the 50-move rule.
- *
- *  @param moves         moves played so far, oldest first
- *  @param halfMoveClock plies since the last pawn move or capture (FIDE 50-move rule counter)
- */
-case class GameHistory(moves: List[HistoryMove] = List.empty, halfMoveClock: Int = 0):
-
-  /** Add a raw HistoryMove record. Clock increments by 1.
-   *  Use the coordinate overload when you know whether the move is a pawn move or capture.
-   */
-  def addMove(move: HistoryMove): GameHistory =
-    GameHistory(moves :+ move, halfMoveClock + 1)
-
-  /** Add a move by coordinates.
-   *
-   *  @param wasPawnMove true when the moving piece is a pawn — resets the clock to 0
-   *  @param wasCapture  true when a piece was captured (including en passant) — resets the clock to 0
-   *
-   *  If neither flag is set the clock increments by 1.
-   */
-  def addMove(
-    from: Square,
-    to: Square,
-    castleSide: Option[CastleSide] = None,
-    promotionPiece: Option[PromotionPiece] = None,
-    wasPawnMove: Boolean = false,
-    wasCapture: Boolean = false,
-    pieceType: PieceType = PieceType.Pawn
-  ): GameHistory =
-    val newClock = if wasPawnMove || wasCapture then 0 else halfMoveClock + 1
-    GameHistory(moves :+ HistoryMove(from, to, castleSide, promotionPiece, pieceType, wasCapture), newClock)
-
-object GameHistory:
-  val empty: GameHistory = GameHistory()

modules/core/src/main/scala/de/nowchess/chess/logic/GameRules.scala

@@ -1,47 +0,0 @@
-package de.nowchess.chess.logic
-
-import de.nowchess.api.board.*
-import de.nowchess.chess.logic.GameHistory
-
-enum PositionStatus:
-  case Normal, InCheck, Mated, Drawn
-
-object GameRules:
-
-  /** True if `color`'s king is under attack on this board. */
-  def isInCheck(board: Board, color: Color): Boolean =
-    board.pieces
-      .collectFirst { case (sq, p) if p.color == color && p.pieceType == PieceType.King => sq }
-      .exists { kingSq =>
-        board.pieces.exists { case (sq, piece) =>
-          piece.color != color &&
-          MoveValidator.legalTargets(board, sq).contains(kingSq)
-        }
-      }
-
-  /** All (from, to) moves for `color` that do not leave their own king in check. */
-  def legalMoves(board: Board, history: GameHistory, color: Color): Set[(Square, Square)] =
-    board.pieces
-      .collect { case (from, piece) if piece.color == color => from }
-      .flatMap { from =>
-        MoveValidator.legalTargets(board, history, from)           // context-aware: includes castling
-          .filter { to =>
-            val newBoard =
-              if MoveValidator.isCastle(board, from, to) then
-                board.withCastle(color, MoveValidator.castleSide(from, to))
-              else
-                board.withMove(from, to)._1
-            !isInCheck(newBoard, color)
-          }
-          .map(to => from -> to)
-      }
-      .toSet
-
-  /** Position status for the side whose turn it is (`color`). */
-  def gameStatus(board: Board, history: GameHistory, color: Color): PositionStatus =
-    val moves   = legalMoves(board, history, color)
-    val inCheck = isInCheck(board, color)
-    if moves.isEmpty && inCheck then PositionStatus.Mated
-    else if moves.isEmpty       then PositionStatus.Drawn
-    else if inCheck             then PositionStatus.InCheck
-    else                             PositionStatus.Normal

modules/core/src/main/scala/de/nowchess/chess/logic/MoveValidator.scala

@@ -1,183 +0,0 @@
-package de.nowchess.chess.logic
-
-import de.nowchess.api.board.*
-import de.nowchess.chess.logic.{CastleSide, GameHistory}
-
-object MoveValidator:
-
-  /** Returns true if the move is geometrically legal for the piece on `from`,
-   *  ignoring check/pin but respecting:
-   *  - correct movement pattern for the piece type
-   *  - cannot capture own pieces
-   *  - sliding pieces (bishop, rook, queen) are blocked by intervening pieces
-   */
-  def isLegal(board: Board, from: Square, to: Square): Boolean =
-    legalTargets(board, from).contains(to)
-
-  /** All squares a piece on `from` can legally move to (same rules as isLegal). */
-  def legalTargets(board: Board, from: Square): Set[Square] =
-    board.pieceAt(from) match
-      case None        => Set.empty
-      case Some(piece) =>
-        piece.pieceType match
-          case PieceType.Pawn   => pawnTargets(board, from, piece.color)
-          case PieceType.Knight => knightTargets(board, from, piece.color)
-          case PieceType.Bishop => slide(board, from, piece.color, diagonalDeltas)
-          case PieceType.Rook   => slide(board, from, piece.color, orthogonalDeltas)
-          case PieceType.Queen  => slide(board, from, piece.color, diagonalDeltas ++ orthogonalDeltas)
-          case PieceType.King   => kingTargets(board, from, piece.color)
-
-  // ── helpers ────────────────────────────────────────────────────────────────
-
-  private val diagonalDeltas:    List[(Int, Int)] = List((1, 1), (1, -1), (-1, 1), (-1, -1))
-  private val orthogonalDeltas:  List[(Int, Int)] = List((1, 0), (-1, 0), (0, 1), (0, -1))
-  private val knightDeltas:      List[(Int, Int)] =
-    List((1, 2), (1, -2), (-1, 2), (-1, -2), (2, 1), (2, -1), (-2, 1), (-2, -1))
-
-  /** Try to construct a Square from integer file/rank indices (0-based). */
-  private def squareAt(fileIdx: Int, rankIdx: Int): Option[Square] =
-    Option.when(fileIdx >= 0 && fileIdx <= 7 && rankIdx >= 0 && rankIdx <= 7)(
-      Square(File.values(fileIdx), Rank.values(rankIdx))
-    )
-
-  /** True when `sq` is occupied by a piece of `color`. */
-  private def isOwnPiece(board: Board, sq: Square, color: Color): Boolean =
-    board.pieceAt(sq).exists(_.color == color)
-
-  /** True when `sq` is occupied by a piece of the opposite color. */
-  private def isEnemyPiece(board: Board, sq: Square, color: Color): Boolean =
-    board.pieceAt(sq).exists(_.color != color)
-
-  /** Sliding move generation along a list of direction deltas.
-   *  Each direction continues until the board edge, an own piece, or the first
-   *  enemy piece (which is included as a capture target).
-   */
-  private def slide(board: Board, from: Square, color: Color, deltas: List[(Int, Int)]): Set[Square] =
-    val fi = from.file.ordinal
-    val ri = from.rank.ordinal
-    deltas.flatMap: (df, dr) =>
-      Iterator
-        .iterate((fi + df, ri + dr)) { case (f, r) => (f + df, r + dr) }
-        .takeWhile { case (f, r) => f >= 0 && f <= 7 && r >= 0 && r <= 7 }
-        .map { case (f, r) => Square(File.values(f), Rank.values(r)) }
-        .foldLeft((List.empty[Square], false)):
-          case ((acc, stopped), sq) =>
-            if stopped then (acc, true)
-            else if isOwnPiece(board, sq, color) then (acc, true)          // blocked — stop, no capture
-            else if isEnemyPiece(board, sq, color) then (acc :+ sq, true)  // capture — stop after
-            else (acc :+ sq, false)                                        // empty — continue
-        ._1
-    .toSet
-
-  private def pawnTargets(board: Board, from: Square, color: Color): Set[Square] =
-    val fi       = from.file.ordinal
-    val ri       = from.rank.ordinal
-    val dir      = if color == Color.White then 1 else -1
-    val startRank = if color == Color.White then Rank.R2.ordinal else Rank.R7.ordinal
-
-    val oneStep = squareAt(fi, ri + dir)
-
-    // Forward one square (only if empty)
-    val forward1: Set[Square] = oneStep match
-      case Some(sq) if board.pieceAt(sq).isEmpty => Set(sq)
-      case _                                     => Set.empty
-
-    // Forward two squares from starting rank (only if both intermediate squares are empty)
-    val forward2: Set[Square] =
-      if ri == startRank && forward1.nonEmpty then
-        squareAt(fi, ri + 2 * dir) match
-          case Some(sq) if board.pieceAt(sq).isEmpty => Set(sq)
-          case _                                     => Set.empty
-      else Set.empty
-
-    // Diagonal captures (only if enemy piece present)
-    val captures: Set[Square] =
-      List(-1, 1).flatMap: df =>
-        squareAt(fi + df, ri + dir).filter(sq => isEnemyPiece(board, sq, color))
-      .toSet
-
-    forward1 ++ forward2 ++ captures
-
-  private def knightTargets(board: Board, from: Square, color: Color): Set[Square] =
-    val fi = from.file.ordinal
-    val ri = from.rank.ordinal
-    knightDeltas.flatMap: (df, dr) =>
-      squareAt(fi + df, ri + dr).filterNot(sq => isOwnPiece(board, sq, color))
-    .toSet
-
-  private def kingTargets(board: Board, from: Square, color: Color): Set[Square] =
-    val fi = from.file.ordinal
-    val ri = from.rank.ordinal
-    (diagonalDeltas ++ orthogonalDeltas).flatMap: (df, dr) =>
-      squareAt(fi + df, ri + dr).filterNot(sq => isOwnPiece(board, sq, color))
-    .toSet
-
-  // ── Castling helpers ────────────────────────────────────────────────────────
-
-  private def isAttackedBy(board: Board, sq: Square, attackerColor: Color): Boolean =
-    board.pieces.exists { case (from, piece) =>
-      piece.color == attackerColor && legalTargets(board, from).contains(sq)
-    }
-
-  def isCastle(board: Board, from: Square, to: Square): Boolean =
-    board.pieceAt(from).exists(_.pieceType == PieceType.King) &&
-    math.abs(to.file.ordinal - from.file.ordinal) == 2
-
-  def castleSide(from: Square, to: Square): CastleSide =
-    if to.file.ordinal > from.file.ordinal then CastleSide.Kingside else CastleSide.Queenside
-
-  def castlingTargets(board: Board, history: GameHistory, color: Color): Set[Square] =
-    val rights = CastlingRightsCalculator.deriveCastlingRights(history, color)
-    val rank   = if color == Color.White then Rank.R1 else Rank.R8
-    val kingSq = Square(File.E, rank)
-    val enemy  = color.opposite
-
-    if !board.pieceAt(kingSq).contains(Piece(color, PieceType.King)) ||
-       GameRules.isInCheck(board, color) then Set.empty
-    else
-      val kingsideSq = Option.when(
-        rights.kingSide &&
-        board.pieceAt(Square(File.H, rank)).contains(Piece(color, PieceType.Rook)) &&
-        List(Square(File.F, rank), Square(File.G, rank)).forall(s => board.pieceAt(s).isEmpty) &&
-        !List(Square(File.F, rank), Square(File.G, rank)).exists(s => isAttackedBy(board, s, enemy))
-      )(Square(File.G, rank))
-
-      val queensideSq = Option.when(
-        rights.queenSide &&
-        board.pieceAt(Square(File.A, rank)).contains(Piece(color, PieceType.Rook)) &&
-        List(Square(File.B, rank), Square(File.C, rank), Square(File.D, rank)).forall(s => board.pieceAt(s).isEmpty) &&
-        !List(Square(File.D, rank), Square(File.C, rank)).exists(s => isAttackedBy(board, s, enemy))
-      )(Square(File.C, rank))
-
-      kingsideSq.toSet ++ queensideSq.toSet
-
-  def legalTargets(board: Board, history: GameHistory, from: Square): Set[Square] =
-    board.pieceAt(from) match
-      case Some(piece) if piece.pieceType == PieceType.King =>
-        legalTargets(board, from) ++ castlingTargets(board, history, piece.color)
-      case Some(piece) if piece.pieceType == PieceType.Pawn =>
-        pawnTargets(board, history, from, piece.color)
-      case _ =>
-        legalTargets(board, from)
-
-  private def pawnTargets(board: Board, history: GameHistory, from: Square, color: Color): Set[Square] =
-    val existing = pawnTargets(board, from, color)
-    val fi  = from.file.ordinal
-    val ri  = from.rank.ordinal
-    val dir = if color == Color.White then 1 else -1
-    val epCapture: Set[Square] =
-      EnPassantCalculator.enPassantTarget(board, history).filter: target =>
-        squareAt(fi - 1, ri + dir).contains(target) || squareAt(fi + 1, ri + dir).contains(target)
-      .toSet
-    existing ++ epCapture
-
-  def isLegal(board: Board, history: GameHistory, from: Square, to: Square): Boolean =
-    legalTargets(board, history, from).contains(to)
-
-  /** Returns true if the piece on `from` is a pawn moving to its back rank (promotion). */
-  def isPromotionMove(board: Board, from: Square, to: Square): Boolean =
-    board.pieceAt(from) match
-      case Some(Piece(_, PieceType.Pawn)) =>
-        (from.rank == Rank.R7 && to.rank == Rank.R8) ||
-        (from.rank == Rank.R2 && to.rank == Rank.R1)
-      case _ => false

modules/core/src/main/scala/de/nowchess/chess/notation/PgnExporter.scala

@@ -1,54 +0,0 @@
-package de.nowchess.chess.notation
-
-import de.nowchess.api.board.{PieceType, *}
-import de.nowchess.api.move.PromotionPiece
-import de.nowchess.chess.logic.{CastleSide, GameHistory, HistoryMove}
-
-object PgnExporter:
-
-  /** Export a game with headers and history to PGN format. */
-  def exportGame(headers: Map[String, String], history: GameHistory): String =
-    val headerLines = headers.map { case (key, value) =>
-      s"""[$key "$value"]"""
-    }.mkString("\n")
-
-    val moveText = if history.moves.isEmpty then ""
-    else
-      val groupedMoves = history.moves.zipWithIndex.groupBy(_._2 / 2)
-      val moveLines = for (moveNumber, movePairs) <- groupedMoves.toList.sortBy(_._1) yield
-        val moveNum = moveNumber + 1
-        val whiteMoveStr = movePairs.find(_._2 % 2 == 0).map(p => moveToAlgebraic(p._1)).getOrElse("")
-        val blackMoveStr = movePairs.find(_._2 % 2 == 1).map(p => moveToAlgebraic(p._1)).getOrElse("")
-        if blackMoveStr.isEmpty then s"$moveNum. $whiteMoveStr"
-        else s"$moveNum. $whiteMoveStr $blackMoveStr"
-
-      val termination = headers.getOrElse("Result", "*")
-      moveLines.mkString(" ") + s" $termination"
-
-    if headerLines.isEmpty then moveText
-    else if moveText.isEmpty then headerLines
-    else s"$headerLines\n\n$moveText"
-
-  /** Convert a HistoryMove to Standard Algebraic Notation. */
-  def moveToAlgebraic(move: HistoryMove): String =
-    move.castleSide match
-      case Some(CastleSide.Kingside)  => "O-O"
-      case Some(CastleSide.Queenside) => "O-O-O"
-      case None =>
-        val dest       = move.to.toString
-        val capStr     = if move.isCapture then "x" else ""
-        val promSuffix = move.promotionPiece match
-          case Some(PromotionPiece.Queen)  => "=Q"
-          case Some(PromotionPiece.Rook)   => "=R"
-          case Some(PromotionPiece.Bishop) => "=B"
-          case Some(PromotionPiece.Knight) => "=N"
-          case None                        => ""
-        move.pieceType match
-          case PieceType.Pawn =>
-            if move.isCapture then s"${move.from.file.toString.toLowerCase}x$dest$promSuffix"
-            else s"$dest$promSuffix"
-          case PieceType.Knight => s"N$capStr$dest$promSuffix"
-          case PieceType.Bishop => s"B$capStr$dest$promSuffix"
-          case PieceType.Rook   => s"R$capStr$dest$promSuffix"
-          case PieceType.Queen  => s"Q$capStr$dest$promSuffix"
-          case PieceType.King   => s"K$capStr$dest$promSuffix"

modules/core/src/main/scala/de/nowchess/chess/notation/PgnParser.scala

@@ -1,267 +0,0 @@
-package de.nowchess.chess.notation
-
-import de.nowchess.api.board.*
-import de.nowchess.api.move.PromotionPiece
-import de.nowchess.chess.logic.{CastleSide, GameHistory, HistoryMove, GameRules, MoveValidator, withCastle}
-
-/** A parsed PGN game containing headers and the resolved move list. */
-case class PgnGame(
-  headers: Map[String, String],
-  moves: List[HistoryMove]
-)
-
-object PgnParser:
-
-  /** Strictly validate a PGN text.
-   *  Returns Right(PgnGame) if every move token is a legal move in the evolving position.
-   *  Returns Left(error message) on the first illegal or impossible move, or any unrecognised token. */
-  def validatePgn(pgn: String): Either[String, PgnGame] =
-    val lines = pgn.split("\n").map(_.trim)
-    val (headerLines, rest) = lines.span(_.startsWith("["))
-    val headers  = parseHeaders(headerLines)
-    val moveText = rest.mkString(" ")
-    validateMovesText(moveText).map(moves => PgnGame(headers, moves))
-
-  /** Parse a complete PGN text into a PgnGame with headers and moves.
-   *  Always succeeds (returns Some); malformed tokens are silently skipped. */
-  def parsePgn(pgn: String): Option[PgnGame] =
-    val lines = pgn.split("\n").map(_.trim)
-    val (headerLines, rest) = lines.span(_.startsWith("["))
-
-    val headers  = parseHeaders(headerLines)
-    val moveText = rest.mkString(" ")
-    val moves    = parseMovesText(moveText)
-
-    Some(PgnGame(headers, moves))
-
-  /** Parse PGN header lines of the form [Key "Value"]. */
-  private def parseHeaders(lines: Array[String]): Map[String, String] =
-    val pattern = """^\[(\w+)\s+"([^"]*)"\s*\]$""".r
-    lines.flatMap(line => pattern.findFirstMatchIn(line).map(m => m.group(1) -> m.group(2))).toMap
-
-  /** Parse the move-text section (e.g. "1. e4 e5 2. Nf3") into resolved HistoryMoves. */
-  private def parseMovesText(moveText: String): List[HistoryMove] =
-    val tokens = moveText.split("\\s+").filter(_.nonEmpty)
-
-    // Fold over tokens, threading (board, history, currentColor, accumulator)
-    val (_, _, _, moves) = tokens.foldLeft(
-      (Board.initial, GameHistory.empty, Color.White, List.empty[HistoryMove])
-    ):
-      case (state @ (board, history, color, acc), token) =>
-        // Skip move-number markers (e.g. "1.", "2.") and result tokens
-        if isMoveNumberOrResult(token) then state
-        else
-          parseAlgebraicMove(token, board, history, color) match
-            case None       => state  // unrecognised token — skip silently
-            case Some(move) =>
-              val newBoard   = applyMoveToBoard(board, move, color)
-              val newHistory = history.addMove(move)
-              (newBoard, newHistory, color.opposite, acc :+ move)
-
-    moves
-
-  /** Apply a single HistoryMove to a Board, handling castling and promotion. */
-  private def applyMoveToBoard(board: Board, move: HistoryMove, color: Color): Board =
-    move.castleSide match
-      case Some(side) => board.withCastle(color, side)
-      case None =>
-        val (boardAfterMove, _) = board.withMove(move.from, move.to)
-        move.promotionPiece match
-          case Some(pp) =>
-            val pieceType = pp match
-              case PromotionPiece.Queen  => PieceType.Queen
-              case PromotionPiece.Rook   => PieceType.Rook
-              case PromotionPiece.Bishop => PieceType.Bishop
-              case PromotionPiece.Knight => PieceType.Knight
-            boardAfterMove.updated(move.to, Piece(color, pieceType))
-          case None => boardAfterMove
-
-  /** True for move-number tokens ("1.", "12.") and PGN result tokens. */
-  private def isMoveNumberOrResult(token: String): Boolean =
-    token.matches("""\d+\.""") ||
-    token == "*"               ||
-    token == "1-0"             ||
-    token == "0-1"             ||
-    token == "1/2-1/2"
-
-  /** Parse a single algebraic notation token into a HistoryMove, given the current board state. */
-  def parseAlgebraicMove(notation: String, board: Board, history: GameHistory, color: Color): Option[HistoryMove] =
-    notation match
-      case "O-O" | "O-O+" | "O-O#" =>
-        val rank = if color == Color.White then Rank.R1 else Rank.R8
-        Some(HistoryMove(Square(File.E, rank), Square(File.G, rank), Some(CastleSide.Kingside), pieceType = PieceType.King))
-
-      case "O-O-O" | "O-O-O+" | "O-O-O#" =>
-        val rank = if color == Color.White then Rank.R1 else Rank.R8
-        Some(HistoryMove(Square(File.E, rank), Square(File.C, rank), Some(CastleSide.Queenside), pieceType = PieceType.King))
-
-      case _ =>
-        parseRegularMove(notation, board, history, color)
-
-  /** Parse regular algebraic notation (pawn moves, piece moves, captures, disambiguation). */
-  private def parseRegularMove(notation: String, board: Board, history: GameHistory, color: Color): Option[HistoryMove] =
-    // Strip check/mate/capture indicators and promotion suffix (e.g. =Q)
-    val clean = notation
-      .replace("+", "")
-      .replace("#", "")
-      .replace("x", "")
-      .replaceAll("=[NBRQ]$", "")
-
-    // The destination square is always the last two characters
-    if clean.length < 2 then None
-    else
-      val destStr = clean.takeRight(2)
-      Square.fromAlgebraic(destStr).flatMap: toSquare =>
-        val disambig = clean.dropRight(2) // "" | "N"|"B"|"R"|"Q"|"K" | file | rank | file+rank
-
-        // Determine required piece type: upper-case first char = piece letter; else pawn
-        val requiredPieceType: Option[PieceType] =
-          if disambig.nonEmpty && disambig.head.isUpper then charToPieceType(disambig.head)
-          else if clean.head.isUpper then charToPieceType(clean.head)
-          else Some(PieceType.Pawn)
-
-        // Collect the disambiguation hint that remains after stripping the piece letter
-        val hint =
-          if disambig.nonEmpty && disambig.head.isUpper then disambig.tail
-          else disambig  // hint is file/rank info or empty
-
-        // Candidate source squares: pieces of `color` that can geometrically reach `toSquare`.
-        // We prefer pieces that can actually reach the target; if none can (positionally illegal
-        // PGN input), fall back to any piece of the matching type belonging to `color`.
-        val reachable: Set[Square] =
-          board.pieces.collect {
-            case (from, piece) if piece.color == color &&
-              MoveValidator.legalTargets(board, from).contains(toSquare) => from
-          }.toSet
-
-        val candidates: Set[Square] =
-          if reachable.nonEmpty then reachable
-          else
-            // Fallback for positionally-illegal but syntactically valid PGN notation:
-            // find any piece of `color` with the correct piece type on the board.
-            board.pieces.collect {
-              case (from, piece) if piece.color == color => from
-            }.toSet
-
-        // Filter by required piece type
-        val byPiece = candidates.filter(from =>
-          requiredPieceType.forall(pt => board.pieceAt(from).exists(_.pieceType == pt))
-        )
-
-        // Apply disambiguation hint (file letter or rank digit)
-        val disambiguated =
-          if hint.isEmpty then byPiece
-          else byPiece.filter(from => matchesHint(from, hint))
-
-        val promotion     = extractPromotion(notation)
-        val movePieceType = requiredPieceType.getOrElse(PieceType.Pawn)
-        val moveIsCapture = notation.contains('x')
-        disambiguated.headOption.map(from => HistoryMove(from, toSquare, None, promotion, movePieceType, moveIsCapture))
-
-  /** True if `sq` matches a disambiguation hint (file letter, rank digit, or both). */
-  private def matchesHint(sq: Square, hint: String): Boolean =
-    hint.forall(c => if c >= 'a' && c <= 'h' then sq.file.toString.equalsIgnoreCase(c.toString)
-    else if c >= '1' && c <= '8' then sq.rank.ordinal == (c - '1')
-    else true)
-
-  /** Extract a promotion piece from a notation string containing =Q/=R/=B/=N. */
-  private[notation] def extractPromotion(notation: String): Option[PromotionPiece] =
-    val promotionPattern = """=([A-Z])""".r
-    promotionPattern.findFirstMatchIn(notation).flatMap { m =>
-      m.group(1) match
-        case "Q" => Some(PromotionPiece.Queen)
-        case "R" => Some(PromotionPiece.Rook)
-        case "B" => Some(PromotionPiece.Bishop)
-        case "N" => Some(PromotionPiece.Knight)
-        case _   => None
-    }
-
-  /** Convert a piece-letter character to a PieceType. */
-  private def charToPieceType(c: Char): Option[PieceType] =
-    c match
-      case 'N' => Some(PieceType.Knight)
-      case 'B' => Some(PieceType.Bishop)
-      case 'R' => Some(PieceType.Rook)
-      case 'Q' => Some(PieceType.Queen)
-      case 'K' => Some(PieceType.King)
-      case _   => None
-
-  // ── Strict validation helpers ─────────────────────────────────────────────
-
-  /** Walk all move tokens, failing immediately on any unresolvable or illegal move. */
-  private def validateMovesText(moveText: String): Either[String, List[HistoryMove]] =
-    val tokens = moveText.split("\\s+").filter(_.nonEmpty)
-    tokens.foldLeft(Right((Board.initial, GameHistory.empty, Color.White, List.empty[HistoryMove])): Either[String, (Board, GameHistory, Color, List[HistoryMove])]) {
-      case (acc, token) =>
-        acc.flatMap { case (board, history, color, moves) =>
-          if isMoveNumberOrResult(token) then Right((board, history, color, moves))
-          else
-            strictParseAlgebraicMove(token, board, history, color) match
-              case None       => Left(s"Illegal or impossible move: '$token'")
-              case Some(move) =>
-                val newBoard   = applyMoveToBoard(board, move, color)
-                val newHistory = history.addMove(move)
-                Right((newBoard, newHistory, color.opposite, moves :+ move))
-        }
-    }.map(_._4)
-
-  /** Strict algebraic move parse — no fallback to positionally-illegal moves. */
-  private def strictParseAlgebraicMove(notation: String, board: Board, history: GameHistory, color: Color): Option[HistoryMove] =
-    val rank = if color == Color.White then Rank.R1 else Rank.R8
-    notation match
-      case "O-O" | "O-O+" | "O-O#" =>
-        val dest = Square(File.G, rank)
-        Option.when(MoveValidator.castlingTargets(board, history, color).contains(dest))(
-          HistoryMove(Square(File.E, rank), dest, Some(CastleSide.Kingside), pieceType = PieceType.King)
-        )
-      case "O-O-O" | "O-O-O+" | "O-O-O#" =>
-        val dest = Square(File.C, rank)
-        Option.when(MoveValidator.castlingTargets(board, history, color).contains(dest))(
-          HistoryMove(Square(File.E, rank), dest, Some(CastleSide.Queenside), pieceType = PieceType.King)
-        )
-      case _ =>
-        strictParseRegularMove(notation, board, history, color)
-
-  /** Strict regular move parse — uses only legally reachable squares, no fallback. */
-  private def strictParseRegularMove(notation: String, board: Board, history: GameHistory, color: Color): Option[HistoryMove] =
-    val clean = notation
-      .replace("+", "")
-      .replace("#", "")
-      .replace("x", "")
-      .replaceAll("=[NBRQ]$", "")
-
-    if clean.length < 2 then None
-    else
-      val destStr = clean.takeRight(2)
-      Square.fromAlgebraic(destStr).flatMap { toSquare =>
-        val disambig = clean.dropRight(2)
-
-        val requiredPieceType: Option[PieceType] =
-          if disambig.nonEmpty && disambig.head.isUpper then charToPieceType(disambig.head)
-          else if clean.head.isUpper then charToPieceType(clean.head)
-          else Some(PieceType.Pawn)
-
-        val hint =
-          if disambig.nonEmpty && disambig.head.isUpper then disambig.tail
-          else disambig
-
-        // Strict: only squares from which a legal move (including en passant/castling awareness) exists.
-        val reachable: Set[Square] =
-          board.pieces.collect {
-            case (from, piece) if piece.color == color &&
-              MoveValidator.legalTargets(board, history, from).contains(toSquare) => from
-          }.toSet
-
-        val byPiece = reachable.filter(from =>
-          requiredPieceType.forall(pt => board.pieceAt(from).exists(_.pieceType == pt))
-        )
-
-        val disambiguated =
-          if hint.isEmpty then byPiece
-          else byPiece.filter(from => matchesHint(from, hint))
-
-        val promotion     = extractPromotion(notation)
-        val movePieceType = requiredPieceType.getOrElse(PieceType.Pawn)
-        val moveIsCapture = notation.contains('x')
-        disambiguated.headOption.map(from => HistoryMove(from, toSquare, None, promotion, movePieceType, moveIsCapture))
-      }

modules/core/src/main/scala/de/nowchess/chess/observer/Observer.scala

@@ -1,21 +1,17 @@
 package de.nowchess.chess.observer
 
-import de.nowchess.api.board.{Board, Color, Square}
-import de.nowchess.chess.logic.GameHistory
+import de.nowchess.api.board.{Color, Square}
+import de.nowchess.api.game.GameContext
 
 /** Base trait for all game state events.
  *  Events are immutable snapshots of game state changes.
  */
 sealed trait GameEvent:
-  def board: Board
-  def history: GameHistory
-  def turn: Color
+  def context: GameContext
 
 /** Fired when a move is successfully executed. */
 case class MoveExecutedEvent(
-  board: Board,
-  history: GameHistory,
-  turn: Color,
+  context: GameContext,
   fromSquare: String,
   toSquare: String,
   capturedPiece: Option[String]
@@ -23,77 +19,57 @@ case class MoveExecutedEvent(
 
 /** Fired when the current player is in check. */
 case class CheckDetectedEvent(
-  board: Board,
-  history: GameHistory,
-  turn: Color
+  context: GameContext
 ) extends GameEvent
 
 /** Fired when the game reaches checkmate. */
 case class CheckmateEvent(
-  board: Board,
-  history: GameHistory,
-  turn: Color,
+  context: GameContext,
   winner: Color
 ) extends GameEvent
 
 /** Fired when the game reaches stalemate. */
 case class StalemateEvent(
-  board: Board,
-  history: GameHistory,
-  turn: Color
+  context: GameContext
 ) extends GameEvent
 
 /** Fired when a move is invalid. */
 case class InvalidMoveEvent(
-  board: Board,
-  history: GameHistory,
-  turn: Color,
+  context: GameContext,
   reason: String
 ) extends GameEvent
 
 /** Fired when a pawn reaches the back rank and the player must choose a promotion piece. */
 case class PromotionRequiredEvent(
-  board: Board,
-  history: GameHistory,
-  turn: Color,
+  context: GameContext,
   from: Square,
   to: Square
 ) extends GameEvent
 
 /** Fired when the board is reset. */
 case class BoardResetEvent(
-  board: Board,
-  history: GameHistory,
-  turn: Color
+  context: GameContext
 ) extends GameEvent
 
 /** Fired after any move where the half-move clock reaches 100 — the 50-move rule is now claimable. */
 case class FiftyMoveRuleAvailableEvent(
-  board: Board,
-  history: GameHistory,
-  turn: Color
+  context: GameContext
 ) extends GameEvent
 
 /** Fired when a player successfully claims a draw under the 50-move rule. */
 case class DrawClaimedEvent(
-  board: Board,
-  history: GameHistory,
-  turn: Color
+  context: GameContext
 ) extends GameEvent
 
 /** Fired when a move is undone, carrying PGN notation of the reversed move. */
 case class MoveUndoneEvent(
-  board: Board,
-  history: GameHistory,
-  turn: Color,
+  context: GameContext,
   pgnNotation: String
 ) extends GameEvent
 
 /** Fired when a previously undone move is redone, carrying PGN notation of the replayed move. */
 case class MoveRedoneEvent(
-  board: Board,
-  history: GameHistory,
-  turn: Color,
+  context: GameContext,
   pgnNotation: String,
   fromSquare: String,
   toSquare: String,
@@ -102,9 +78,7 @@ case class MoveRedoneEvent(
 
 /** Fired after a PGN string is successfully loaded and all moves are replayed into history. */
 case class PgnLoadedEvent(
-  board: Board,
-  history: GameHistory,
-  turn: Color
+  context: GameContext
 ) extends GameEvent
 
 /** Observer trait: implement to receive game state updates. */

modules/core/src/test/scala/de/nowchess/chess/command/CommandInvokerBranchTest.scala

@@ -1,216 +1,148 @@
 package de.nowchess.chess.command
 
-import de.nowchess.api.board.{Square, File, Rank, Board, Color}
-import de.nowchess.chess.logic.GameHistory
+import de.nowchess.api.board.{Square, File, Rank}
+import de.nowchess.api.game.GameContext
 import org.scalatest.funsuite.AnyFunSuite
 import org.scalatest.matchers.should.Matchers
 
 class CommandInvokerBranchTest extends AnyFunSuite with Matchers:
-  
+
   private def sq(f: File, r: Rank): Square = Square(f, r)
 
-  // ──── Helper: Command that always fails ────
   private case class FailingCommand() extends Command:
     override def execute(): Boolean = false
     override def undo(): Boolean = false
     override def description: String = "Failing command"
 
-  // ──── Helper: Command that conditionally fails on undo or execute ────
   private case class ConditionalFailCommand(var shouldFailOnUndo: Boolean = false, var shouldFailOnExecute: Boolean = false) extends Command:
     override def execute(): Boolean = !shouldFailOnExecute
     override def undo(): Boolean = !shouldFailOnUndo
     override def description: String = "Conditional fail"
 
   private def createMoveCommand(from: Square, to: Square, executeSucceeds: Boolean = true): MoveCommand =
-    val cmd = MoveCommand(
+    MoveCommand(
       from = from,
       to = to,
-      moveResult = if executeSucceeds then Some(MoveResult.Successful(Board.initial, GameHistory.empty, Color.White, None)) else None,
-      previousBoard = Some(Board.initial),
-      previousHistory = Some(GameHistory.empty),
-      previousTurn = Some(Color.White)
+      moveResult = if executeSucceeds then Some(MoveResult.Successful(GameContext.initial, None)) else None,
+      previousContext = Some(GameContext.initial)
     )
-    cmd
 
-  // ──── BRANCH: execute() returns false ────
-  test("CommandInvoker.execute() with failing command returns false"):
+  test("execute rejects failing commands and keeps history unchanged"):
     val invoker = new CommandInvoker()
     val cmd = FailingCommand()
     invoker.execute(cmd) shouldBe false
     invoker.history.size shouldBe 0
     invoker.getCurrentIndex shouldBe -1
 
-  test("CommandInvoker.execute() does not add failed command to history"):
-    val invoker = new CommandInvoker()
     val failingCmd = FailingCommand()
     val successCmd = createMoveCommand(sq(File.E, Rank.R2), sq(File.E, Rank.R4))
-    
     invoker.execute(failingCmd) shouldBe false
     invoker.history.size shouldBe 0
-    
     invoker.execute(successCmd) shouldBe true
     invoker.history.size shouldBe 1
-    invoker.history(0) shouldBe successCmd
+    invoker.history.head shouldBe successCmd
 
-  // ──── BRANCH: undo() with invalid index (currentIndex < 0) ────
-  test("CommandInvoker.undo() returns false when currentIndex < 0"):
-    val invoker = new CommandInvoker()
-    // currentIndex starts at -1
-    invoker.undo() shouldBe false
+  test("undo redo and history trimming cover all command state transitions"):
+    {
+      val invoker = new CommandInvoker()
+      invoker.undo() shouldBe false
+      invoker.canUndo shouldBe false
+      invoker.undo() shouldBe false
+    }
 
-  test("CommandInvoker.undo() returns false when empty history"):
-    val invoker = new CommandInvoker()
-    invoker.canUndo shouldBe false
-    invoker.undo() shouldBe false
+    {
+      val invoker = new CommandInvoker()
+      val cmd1 = createMoveCommand(sq(File.E, Rank.R2), sq(File.E, Rank.R4))
+      val cmd2 = createMoveCommand(sq(File.E, Rank.R7), sq(File.E, Rank.R5))
+      invoker.execute(cmd1)
+      invoker.execute(cmd2)
+      invoker.undo()
+      invoker.undo()
+      invoker.undo() shouldBe false
+    }
 
-  // ──── BRANCH: undo() with invalid index (currentIndex >= size) ────
-  test("CommandInvoker.undo() returns false when currentIndex >= history size"):
-    val invoker = new CommandInvoker()
-    val cmd1 = createMoveCommand(sq(File.E, Rank.R2), sq(File.E, Rank.R4))
-    val cmd2 = createMoveCommand(sq(File.E, Rank.R7), sq(File.E, Rank.R5))
-    
-    invoker.execute(cmd1)
-    invoker.execute(cmd2)
-    // currentIndex now = 1, history.size = 2
-    
-    invoker.undo()  // currentIndex becomes 0
-    invoker.undo()  // currentIndex becomes -1
-    invoker.undo()  // currentIndex still -1, should fail
+    {
+      val invoker = new CommandInvoker()
+      val failingUndoCmd = ConditionalFailCommand(shouldFailOnUndo = true)
+      invoker.execute(failingUndoCmd) shouldBe true
+      invoker.canUndo shouldBe true
+      invoker.undo() shouldBe false
+      invoker.getCurrentIndex shouldBe 0
+    }
 
-  // ──── BRANCH: undo() command returns false ────
-  test("CommandInvoker.undo() returns false when command.undo() fails"):
-    val invoker = new CommandInvoker()
-    val failingCmd = ConditionalFailCommand(shouldFailOnUndo = true)
-    
-    invoker.execute(failingCmd) shouldBe true
-    invoker.canUndo shouldBe true
-    
-    invoker.undo() shouldBe false
-    // Index should not change when undo fails
-    invoker.getCurrentIndex shouldBe 0
+    {
+      val invoker = new CommandInvoker()
+      val successUndoCmd = ConditionalFailCommand()
+      invoker.execute(successUndoCmd) shouldBe true
+      invoker.undo() shouldBe true
+      invoker.getCurrentIndex shouldBe -1
+    }
 
-  test("CommandInvoker.undo() returns true when command.undo() succeeds"):
-    val invoker = new CommandInvoker()
-    val successCmd = ConditionalFailCommand(shouldFailOnUndo = false)
-    
-    invoker.execute(successCmd) shouldBe true
-    invoker.undo() shouldBe true
-    invoker.getCurrentIndex shouldBe -1
+    {
+      val invoker = new CommandInvoker()
+      invoker.redo() shouldBe false
+    }
 
-  // ──── BRANCH: redo() with invalid index (currentIndex + 1 >= size) ────
-  test("CommandInvoker.redo() returns false when nothing to redo"):
-    val invoker = new CommandInvoker()
-    invoker.redo() shouldBe false
+    {
+      val invoker = new CommandInvoker()
+      val cmd = createMoveCommand(sq(File.E, Rank.R2), sq(File.E, Rank.R4))
+      invoker.execute(cmd)
+      invoker.canRedo shouldBe false
+      invoker.redo() shouldBe false
+    }
 
-  test("CommandInvoker.redo() returns false when at end of history"):
-    val invoker = new CommandInvoker()
-    val cmd = createMoveCommand(sq(File.E, Rank.R2), sq(File.E, Rank.R4))
-    
-    invoker.execute(cmd)
-    // currentIndex = 0, history.size = 1
-    invoker.canRedo shouldBe false
-    invoker.redo() shouldBe false
+    {
+      val invoker = new CommandInvoker()
+      val cmd1 = createMoveCommand(sq(File.E, Rank.R2), sq(File.E, Rank.R4))
+      val redoFailCmd = ConditionalFailCommand()
+      invoker.execute(cmd1)
+      invoker.execute(redoFailCmd)
+      invoker.undo()
+      invoker.canRedo shouldBe true
+      redoFailCmd.shouldFailOnExecute = true
+      invoker.redo() shouldBe false
+      invoker.getCurrentIndex shouldBe 0
+    }
 
-  test("CommandInvoker.redo() returns false when currentIndex + 1 >= size"):
-    val invoker = new CommandInvoker()
-    val cmd1 = createMoveCommand(sq(File.E, Rank.R2), sq(File.E, Rank.R4))
-    val cmd2 = createMoveCommand(sq(File.E, Rank.R7), sq(File.E, Rank.R5))
-    
-    invoker.execute(cmd1)
-    invoker.execute(cmd2)
-    // currentIndex = 1, size = 2, currentIndex + 1 = 2, so 2 < 2 is false
-    invoker.canRedo shouldBe false
-    invoker.redo() shouldBe false
+    {
+      val invoker = new CommandInvoker()
+      val cmd = createMoveCommand(sq(File.E, Rank.R2), sq(File.E, Rank.R4))
+      invoker.execute(cmd) shouldBe true
+      invoker.undo() shouldBe true
+      invoker.redo() shouldBe true
+      invoker.getCurrentIndex shouldBe 0
+    }
 
-  // ──── BRANCH: redo() command returns false ────
-  test("CommandInvoker.redo() returns false when command.execute() fails"):
-    val invoker = new CommandInvoker()
-    val cmd1 = createMoveCommand(sq(File.E, Rank.R2), sq(File.E, Rank.R4))
-    val redoFailCmd = ConditionalFailCommand(shouldFailOnExecute = false)  // Succeeds on first execute
-    
-    invoker.execute(cmd1)
-    invoker.execute(redoFailCmd)  // Succeeds and added to history
-    
-    invoker.undo()
-    // currentIndex = 0, redoFailCmd is at index 1
-    invoker.canRedo shouldBe true
-    
-    // Now modify to fail on next execute (redo)
-    redoFailCmd.shouldFailOnExecute = true
-    invoker.redo() shouldBe false
-    // currentIndex should not change
-    invoker.getCurrentIndex shouldBe 0
-
-  test("CommandInvoker.redo() returns true when command.execute() succeeds"):
-    val invoker = new CommandInvoker()
-    val cmd = createMoveCommand(sq(File.E, Rank.R2), sq(File.E, Rank.R4))
-    
-    invoker.execute(cmd) shouldBe true
-    invoker.undo() shouldBe true
-    invoker.redo() shouldBe true
-    invoker.getCurrentIndex shouldBe 0
-
-  // ──── BRANCH: execute() with redo history discarding (while loop) ────
-  test("CommandInvoker.execute() discards redo history via while loop"):
-    val invoker = new CommandInvoker()
-    val cmd1 = createMoveCommand(sq(File.E, Rank.R2), sq(File.E, Rank.R4))
-    val cmd2 = createMoveCommand(sq(File.E, Rank.R7), sq(File.E, Rank.R5))
-    val cmd3 = createMoveCommand(sq(File.D, Rank.R2), sq(File.D, Rank.R4))
-    
-    invoker.execute(cmd1)
-    invoker.execute(cmd2)
-    // currentIndex = 1, size = 2
-    
-    invoker.undo()
-    // currentIndex = 0, size = 2
-    // Redo history exists: cmd2 is at index 1
-    invoker.canRedo shouldBe true
-    
-    invoker.execute(cmd3)
-    // while loop should discard cmd2
-    invoker.canRedo shouldBe false
-    invoker.history.size shouldBe 2
-    invoker.history(1) shouldBe cmd3
-
-  test("CommandInvoker.execute() discards multiple redo commands"):
-    val invoker = new CommandInvoker()
-    val cmd1 = createMoveCommand(sq(File.E, Rank.R2), sq(File.E, Rank.R4))
-    val cmd2 = createMoveCommand(sq(File.E, Rank.R7), sq(File.E, Rank.R5))
-    val cmd3 = createMoveCommand(sq(File.G, Rank.R1), sq(File.F, Rank.R3))
-    val cmd4 = createMoveCommand(sq(File.D, Rank.R2), sq(File.D, Rank.R4))
-    
-    invoker.execute(cmd1)
-    invoker.execute(cmd2)
-    invoker.execute(cmd3)
-    invoker.execute(cmd4)
-    // currentIndex = 3, size = 4
-    
-    invoker.undo()
-    invoker.undo()
-    // currentIndex = 1, size = 4
-    // Redo history: cmd3 (idx 2), cmd4 (idx 3)
-    invoker.canRedo shouldBe true
-    
-    val newCmd = createMoveCommand(sq(File.B, Rank.R2), sq(File.B, Rank.R4))
-    invoker.execute(newCmd)
-    // While loop should discard indices 2 and 3 (cmd3 and cmd4)
-    invoker.history.size shouldBe 3
-    invoker.canRedo shouldBe false
-
-  // ──── BRANCH: execute() with no redo history to discard ────
-  test("CommandInvoker.execute() with no redo history (while condition false)"):
-    val invoker = new CommandInvoker()
-    val cmd1 = createMoveCommand(sq(File.E, Rank.R2), sq(File.E, Rank.R4))
-    val cmd2 = createMoveCommand(sq(File.E, Rank.R7), sq(File.E, Rank.R5))
-    
-    invoker.execute(cmd1)
-    invoker.execute(cmd2)
-    // currentIndex = 1, size = 2
-    // currentIndex < size - 1 is 1 < 1 which is false, so while loop doesn't run
-    
-    invoker.canRedo shouldBe false
-    
-    val cmd3 = createMoveCommand(sq(File.D, Rank.R2), sq(File.D, Rank.R4))
-    invoker.execute(cmd3)  // While loop condition should be false, no iterations
-    invoker.history.size shouldBe 3
+    {
+      val invoker = new CommandInvoker()
+      val cmd1 = createMoveCommand(sq(File.E, Rank.R2), sq(File.E, Rank.R4))
+      val cmd2 = createMoveCommand(sq(File.E, Rank.R7), sq(File.E, Rank.R5))
+      val cmd3 = createMoveCommand(sq(File.D, Rank.R2), sq(File.D, Rank.R4))
+      invoker.execute(cmd1)
+      invoker.execute(cmd2)
+      invoker.undo()
+      invoker.canRedo shouldBe true
+      invoker.execute(cmd3)
+      invoker.canRedo shouldBe false
+      invoker.history.size shouldBe 2
+      invoker.history(1) shouldBe cmd3
+    }
 
+    {
+      val invoker = new CommandInvoker()
+      val cmd1 = createMoveCommand(sq(File.E, Rank.R2), sq(File.E, Rank.R4))
+      val cmd2 = createMoveCommand(sq(File.E, Rank.R7), sq(File.E, Rank.R5))
+      val cmd3 = createMoveCommand(sq(File.G, Rank.R1), sq(File.F, Rank.R3))
+      val cmd4 = createMoveCommand(sq(File.D, Rank.R2), sq(File.D, Rank.R4))
+      invoker.execute(cmd1)
+      invoker.execute(cmd2)
+      invoker.execute(cmd3)
+      invoker.execute(cmd4)
+      invoker.undo()
+      invoker.undo()
+      invoker.canRedo shouldBe true
+      val newCmd = createMoveCommand(sq(File.B, Rank.R2), sq(File.B, Rank.R4))
+      invoker.execute(newCmd)
+      invoker.history.size shouldBe 3
+      invoker.canRedo shouldBe false
+    }

modules/core/src/test/scala/de/nowchess/chess/command/CommandInvokerTest.scala

@@ -1,81 +1,47 @@
 package de.nowchess.chess.command
 
-import de.nowchess.api.board.{Square, File, Rank, Board, Color}
-import de.nowchess.chess.logic.GameHistory
+import de.nowchess.api.board.{Square, File, Rank}
+import de.nowchess.api.game.GameContext
 import org.scalatest.funsuite.AnyFunSuite
 import org.scalatest.matchers.should.Matchers
 
 class CommandInvokerTest extends AnyFunSuite with Matchers:
 
   private def sq(f: File, r: Rank): Square = Square(f, r)
-  
+
   private def createMoveCommand(from: Square, to: Square): MoveCommand =
     MoveCommand(
       from = from,
       to = to,
-      moveResult = Some(MoveResult.Successful(Board.initial, GameHistory.empty, Color.White, None)),
-      previousBoard = Some(Board.initial),
-      previousHistory = Some(GameHistory.empty),
-      previousTurn = Some(Color.White)
+      moveResult = Some(MoveResult.Successful(GameContext.initial, None)),
+      previousContext = Some(GameContext.initial)
     )
 
-  test("CommandInvoker executes a command and adds it to history"):
+  test("execute appends commands and updates index"):
     val invoker = new CommandInvoker()
     val cmd = createMoveCommand(sq(File.E, Rank.R2), sq(File.E, Rank.R4))
     invoker.execute(cmd) shouldBe true
     invoker.history.size shouldBe 1
     invoker.getCurrentIndex shouldBe 0
 
-  test("CommandInvoker executes multiple commands in sequence"):
-    val invoker = new CommandInvoker()
-    val cmd1 = createMoveCommand(sq(File.E, Rank.R2), sq(File.E, Rank.R4))
     val cmd2 = createMoveCommand(sq(File.E, Rank.R7), sq(File.E, Rank.R5))
-    invoker.execute(cmd1) shouldBe true
     invoker.execute(cmd2) shouldBe true
     invoker.history.size shouldBe 2
     invoker.getCurrentIndex shouldBe 1
 
-  test("CommandInvoker.canUndo returns false when empty"):
-    val invoker = new CommandInvoker()
-    invoker.canUndo shouldBe false
-
-  test("CommandInvoker.canUndo returns true after execution"):
+  test("undo and redo update index and availability flags"):
     val invoker = new CommandInvoker()
     val cmd = createMoveCommand(sq(File.E, Rank.R2), sq(File.E, Rank.R4))
+    invoker.canUndo shouldBe false
     invoker.execute(cmd)
     invoker.canUndo shouldBe true
-
-  test("CommandInvoker.undo decrements current index"):
-    val invoker = new CommandInvoker()
-    val cmd = createMoveCommand(sq(File.E, Rank.R2), sq(File.E, Rank.R4))
-    invoker.execute(cmd)
-    invoker.getCurrentIndex shouldBe 0
     invoker.undo() shouldBe true
     invoker.getCurrentIndex shouldBe -1
-
-  test("CommandInvoker.canRedo returns true after undo"):
-    val invoker = new CommandInvoker()
-    val cmd = createMoveCommand(sq(File.E, Rank.R2), sq(File.E, Rank.R4))
-    invoker.execute(cmd)
-    invoker.undo()
     invoker.canRedo shouldBe true
-
-  test("CommandInvoker.redo re-executes a command"):
-    val invoker = new CommandInvoker()
-    val cmd = createMoveCommand(sq(File.E, Rank.R2), sq(File.E, Rank.R4))
-    invoker.execute(cmd)
-    invoker.undo() shouldBe true
     invoker.redo() shouldBe true
     invoker.getCurrentIndex shouldBe 0
 
-  test("CommandInvoker.canUndo returns false when at beginning"):
-    val invoker = new CommandInvoker()
-    val cmd = createMoveCommand(sq(File.E, Rank.R2), sq(File.E, Rank.R4))
-    invoker.execute(cmd)
-    invoker.undo()
-    invoker.canUndo shouldBe false
-
-  test("CommandInvoker clear removes all history"):
+  test("clear removes full history and resets index"):
     val invoker = new CommandInvoker()
     val cmd = createMoveCommand(sq(File.E, Rank.R2), sq(File.E, Rank.R4))
     invoker.execute(cmd)
@@ -83,7 +49,7 @@ class CommandInvokerTest extends AnyFunSuite with Matchers:
     invoker.history.size shouldBe 0
     invoker.getCurrentIndex shouldBe -1
 
-  test("CommandInvoker discards all history when executing after undoing all"):
+  test("execute after undo discards redo history"):
     val invoker = new CommandInvoker()
     val cmd1 = createMoveCommand(sq(File.E, Rank.R2), sq(File.E, Rank.R4))
     val cmd2 = createMoveCommand(sq(File.E, Rank.R7), sq(File.E, Rank.R5))
@@ -91,33 +57,11 @@ class CommandInvokerTest extends AnyFunSuite with Matchers:
     invoker.execute(cmd1)
     invoker.execute(cmd2)
     invoker.undo()
-    invoker.undo()
-    // After undoing twice, we're at the beginning (before any commands)
-    invoker.getCurrentIndex shouldBe -1
-    invoker.canRedo shouldBe true
-    // Executing a new command from the beginning discards all redo history
-    invoker.execute(cmd3)
-    invoker.canRedo shouldBe false
-    invoker.history.size shouldBe 1
-    invoker.history(0) shouldBe cmd3
-    invoker.getCurrentIndex shouldBe 0
-
-  test("CommandInvoker discards redo history when executing mid-history"):
-    val invoker = new CommandInvoker()
-    val cmd1 = createMoveCommand(sq(File.E, Rank.R2), sq(File.E, Rank.R4))
-    val cmd2 = createMoveCommand(sq(File.E, Rank.R7), sq(File.E, Rank.R5))
-    val cmd3 = createMoveCommand(sq(File.D, Rank.R2), sq(File.D, Rank.R4))
-    invoker.execute(cmd1)
-    invoker.execute(cmd2)
-    invoker.undo()
-    // After one undo, we're at the end of cmd1
     invoker.getCurrentIndex shouldBe 0
     invoker.canRedo shouldBe true
-    // Executing a new command discards cmd2 (the redo history)
     invoker.execute(cmd3)
     invoker.canRedo shouldBe false
     invoker.history.size shouldBe 2
-    invoker.history(0) shouldBe cmd1
+    invoker.history.head shouldBe cmd1
     invoker.history(1) shouldBe cmd3
     invoker.getCurrentIndex shouldBe 1
-

modules/core/src/test/scala/de/nowchess/chess/command/CommandInvokerThreadSafetyTest.scala

@@ -1,131 +0,0 @@
-package de.nowchess.chess.command
-
-import de.nowchess.api.board.{Square, File, Rank, Board, Color}
-import de.nowchess.chess.logic.GameHistory
-import org.scalatest.funsuite.AnyFunSuite
-import org.scalatest.matchers.should.Matchers
-import scala.collection.mutable
-
-class CommandInvokerThreadSafetyTest extends AnyFunSuite with Matchers:
-
-  private def sq(f: File, r: Rank): Square = Square(f, r)
-
-  private def createMoveCommand(from: Square, to: Square): MoveCommand =
-    MoveCommand(
-      from = from,
-      to = to,
-      moveResult = Some(MoveResult.Successful(Board.initial, GameHistory.empty, Color.White, None)),
-      previousBoard = Some(Board.initial),
-      previousHistory = Some(GameHistory.empty),
-      previousTurn = Some(Color.White)
-    )
-
-  test("CommandInvoker is thread-safe for concurrent execute and history reads"):
-    val invoker = new CommandInvoker()
-    @volatile var raceDetected = false
-    val exceptions = mutable.ListBuffer[Exception]()
-
-    // Thread 1: executes commands
-    val executorThread = new Thread(new Runnable {
-      def run(): Unit = {
-        try {
-          for i <- 1 to 1000 do
-            val cmd = createMoveCommand(
-              sq(File.E, Rank.R2),
-              sq(File.E, Rank.R4)
-            )
-            invoker.execute(cmd)
-        } catch {
-          case e: Exception =>
-            exceptions += e
-            raceDetected = true
-        }
-      }
-    })
-
-    // Thread 2: reads history during execution
-    val readerThread = new Thread(new Runnable {
-      def run(): Unit = {
-        try {
-          for _ <- 1 to 1000 do
-            val _ = invoker.history
-            val _ = invoker.getCurrentIndex
-            Thread.sleep(0) // Yield to increase contention
-        } catch {
-          case e: Exception =>
-            exceptions += e
-            raceDetected = true
-        }
-      }
-    })
-
-    executorThread.start()
-    readerThread.start()
-    executorThread.join()
-    readerThread.join()
-
-    exceptions.isEmpty shouldBe true
-    raceDetected shouldBe false
-
-  test("CommandInvoker is thread-safe for concurrent execute, undo, and redo"):
-    val invoker = new CommandInvoker()
-    @volatile var raceDetected = false
-    val exceptions = mutable.ListBuffer[Exception]()
-
-    // Pre-populate with some commands
-    for _ <- 1 to 5 do
-      invoker.execute(createMoveCommand(sq(File.E, Rank.R2), sq(File.E, Rank.R4)))
-
-    // Thread 1: executes new commands
-    val executorThread = new Thread(new Runnable {
-      def run(): Unit = {
-        try {
-          for _ <- 1 to 500 do
-            invoker.execute(createMoveCommand(sq(File.D, Rank.R2), sq(File.D, Rank.R4)))
-        } catch {
-          case e: Exception =>
-            exceptions += e
-            raceDetected = true
-        }
-      }
-    })
-
-    // Thread 2: undoes commands
-    val undoThread = new Thread(new Runnable {
-      def run(): Unit = {
-        try {
-          for _ <- 1 to 500 do
-            if invoker.canUndo then
-              invoker.undo()
-        } catch {
-          case e: Exception =>
-            exceptions += e
-            raceDetected = true
-        }
-      }
-    })
-
-    // Thread 3: redoes commands
-    val redoThread = new Thread(new Runnable {
-      def run(): Unit = {
-        try {
-          for _ <- 1 to 500 do
-            if invoker.canRedo then
-              invoker.redo()
-        } catch {
-          case e: Exception =>
-            exceptions += e
-            raceDetected = true
-        }
-      }
-    })
-
-    executorThread.start()
-    undoThread.start()
-    redoThread.start()
-    executorThread.join()
-    undoThread.join()
-    redoThread.join()
-
-    exceptions.isEmpty shouldBe true
-    raceDetected shouldBe false

modules/core/src/test/scala/de/nowchess/chess/command/CommandTest.scala

@@ -1,52 +1,24 @@
 package de.nowchess.chess.command
 
-import de.nowchess.api.board.{Board, Color}
-import de.nowchess.chess.logic.GameHistory
+import de.nowchess.api.game.GameContext
 import org.scalatest.funsuite.AnyFunSuite
 import org.scalatest.matchers.should.Matchers
 
 class CommandTest extends AnyFunSuite with Matchers:
 
-  test("QuitCommand can be created"):
+  test("QuitCommand properties and behavior"):
     val cmd = QuitCommand()
     cmd shouldNot be(null)
-
-  test("QuitCommand execute returns true"):
-    val cmd = QuitCommand()
     cmd.execute() shouldBe true
-
-  test("QuitCommand undo returns false (cannot undo quit)"):
-    val cmd = QuitCommand()
     cmd.undo() shouldBe false
-
-  test("QuitCommand description"):
-    val cmd = QuitCommand()
     cmd.description shouldBe "Quit game"
 
-  test("ResetCommand with no prior state"):
-    val cmd = ResetCommand()
-    cmd.execute() shouldBe true
-    cmd.undo() shouldBe false
-
-  test("ResetCommand with prior state can undo"):
-    val cmd = ResetCommand(
-      previousBoard = Some(Board.initial),
-      previousHistory = Some(GameHistory.empty),
-      previousTurn = Some(Color.White)
-    )
-    cmd.execute() shouldBe true
-    cmd.undo() shouldBe true
-
-  test("ResetCommand with partial state cannot undo"):
-    val cmd = ResetCommand(
-      previousBoard = Some(Board.initial),
-      previousHistory = None,  // missing
-      previousTurn = Some(Color.White)
-    )
-    cmd.execute() shouldBe true
-    cmd.undo() shouldBe false
-
-  test("ResetCommand description"):
-    val cmd = ResetCommand()
-    cmd.description shouldBe "Reset board"
+  test("ResetCommand behavior depends on previousContext"):
+    val noState = ResetCommand()
+    noState.execute() shouldBe true
+    noState.undo() shouldBe false
+    noState.description shouldBe "Reset board"
 
+    val withState = ResetCommand(previousContext = Some(GameContext.initial))
+    withState.execute() shouldBe true
+    withState.undo() shouldBe true

modules/core/src/test/scala/de/nowchess/chess/command/MoveCommandImmutabilityTest.scala

@@ -1,65 +0,0 @@
-package de.nowchess.chess.command
-
-import de.nowchess.api.board.{Square, File, Rank, Board, Color}
-import de.nowchess.chess.logic.GameHistory
-import org.scalatest.funsuite.AnyFunSuite
-import org.scalatest.matchers.should.Matchers
-
-class MoveCommandImmutabilityTest extends AnyFunSuite with Matchers:
-
-  private def sq(f: File, r: Rank): Square = Square(f, r)
-
-  test("MoveCommand should be immutable - fields cannot be mutated after creation"):
-    val cmd1 = MoveCommand(
-      from = sq(File.E, Rank.R2),
-      to = sq(File.E, Rank.R4)
-    )
-
-    // Create second command with filled state
-    val result = MoveResult.Successful(Board.initial, GameHistory.empty, Color.Black, None)
-    val cmd2 = cmd1.copy(
-      moveResult = Some(result),
-      previousBoard = Some(Board.initial),
-      previousHistory = Some(GameHistory.empty),
-      previousTurn = Some(Color.White)
-    )
-
-    // Original should be unchanged
-    cmd1.moveResult shouldBe None
-    cmd1.previousBoard shouldBe None
-    cmd1.previousHistory shouldBe None
-    cmd1.previousTurn shouldBe None
-
-    // New should have values
-    cmd2.moveResult shouldBe Some(result)
-    cmd2.previousBoard shouldBe Some(Board.initial)
-    cmd2.previousHistory shouldBe Some(GameHistory.empty)
-    cmd2.previousTurn shouldBe Some(Color.White)
-
-  test("MoveCommand equals and hashCode respect immutability"):
-    val cmd1 = MoveCommand(
-      from = sq(File.E, Rank.R2),
-      to = sq(File.E, Rank.R4),
-      moveResult = None,
-      previousBoard = None,
-      previousHistory = None,
-      previousTurn = None
-    )
-
-    val cmd2 = MoveCommand(
-      from = sq(File.E, Rank.R2),
-      to = sq(File.E, Rank.R4),
-      moveResult = None,
-      previousBoard = None,
-      previousHistory = None,
-      previousTurn = None
-    )
-
-    // Same values should be equal
-    cmd1 shouldBe cmd2
-    cmd1.hashCode shouldBe cmd2.hashCode
-
-    // Hash should be consistent (required for use as map keys)
-    val hash1 = cmd1.hashCode
-    val hash2 = cmd1.hashCode
-    hash1 shouldBe hash2

modules/core/src/test/scala/de/nowchess/chess/command/MoveCommandTest.scala

@@ -0,0 +1,70 @@
+package de.nowchess.chess.command
+
+import de.nowchess.api.board.{Square, File, Rank}
+import de.nowchess.api.game.GameContext
+import org.scalatest.funsuite.AnyFunSuite
+import org.scalatest.matchers.should.Matchers
+
+class MoveCommandTest extends AnyFunSuite with Matchers:
+
+  private def sq(f: File, r: Rank): Square = Square(f, r)
+
+  test("MoveCommand defaults to empty optional state and false execute/undo"):
+    val cmd = MoveCommand(from = sq(File.E, Rank.R2), to = sq(File.E, Rank.R4))
+    cmd.moveResult shouldBe None
+    cmd.previousContext shouldBe None
+    cmd.execute() shouldBe false
+    cmd.undo() shouldBe false
+    cmd.description shouldBe "Move from e2 to e4"
+
+  test("MoveCommand execute/undo succeed when state is present"):
+    val executable = MoveCommand(
+      from = sq(File.E, Rank.R2),
+      to = sq(File.E, Rank.R4),
+      moveResult = Some(MoveResult.Successful(GameContext.initial, None))
+    )
+    executable.execute() shouldBe true
+
+    val undoable = MoveCommand(
+      from = sq(File.E, Rank.R2),
+      to = sq(File.E, Rank.R4),
+      moveResult = Some(MoveResult.Successful(GameContext.initial, None)),
+      previousContext = Some(GameContext.initial)
+    )
+    undoable.undo() shouldBe true
+
+  test("MoveCommand is immutable and preserves equality/hash semantics"):
+    val cmd1 = MoveCommand(from = sq(File.E, Rank.R2), to = sq(File.E, Rank.R4))
+
+    val result = MoveResult.Successful(GameContext.initial, None)
+    val cmd2 = cmd1.copy(
+      moveResult = Some(result),
+      previousContext = Some(GameContext.initial)
+    )
+
+    cmd1.moveResult shouldBe None
+    cmd1.previousContext shouldBe None
+
+    cmd2.moveResult shouldBe Some(result)
+    cmd2.previousContext shouldBe Some(GameContext.initial)
+
+    val eq1 = MoveCommand(
+      from = sq(File.E, Rank.R2),
+      to = sq(File.E, Rank.R4),
+      moveResult = None,
+      previousContext = None
+    )
+
+    val eq2 = MoveCommand(
+      from = sq(File.E, Rank.R2),
+      to = sq(File.E, Rank.R4),
+      moveResult = None,
+      previousContext = None
+    )
+
+    eq1 shouldBe eq2
+    eq1.hashCode shouldBe eq2.hashCode
+
+    val hash1 = eq1.hashCode
+    val hash2 = eq1.hashCode
+    hash1 shouldBe hash2

modules/core/src/test/scala/de/nowchess/chess/controller/GameControllerTest.scala

@@ -1,526 +0,0 @@
-package de.nowchess.chess.controller
-
-import de.nowchess.api.board.*
-import de.nowchess.api.game.CastlingRights
-import de.nowchess.api.move.PromotionPiece
-import de.nowchess.chess.logic.{CastleSide, GameHistory}
-import de.nowchess.chess.notation.FenParser
-import org.scalatest.funsuite.AnyFunSuite
-import org.scalatest.matchers.should.Matchers
-
-class GameControllerTest extends AnyFunSuite with Matchers:
-
-  private def sq(f: File, r: Rank): Square = Square(f, r)
-  private def processMove(board: Board, history: GameHistory, turn: Color, raw: String): MoveResult =
-    GameController.processMove(board, history, turn, raw)
-
-  private def castlingRights(history: GameHistory, color: Color): CastlingRights =
-    de.nowchess.chess.logic.CastlingRightsCalculator.deriveCastlingRights(history, color)
-
-  // ──── processMove ────────────────────────────────────────────────────
-
-  test("processMove: 'quit' input returns Quit"):
-    processMove(Board.initial, GameHistory.empty, Color.White, "quit") shouldBe MoveResult.Quit
-
-  test("processMove: 'q' input returns Quit"):
-    processMove(Board.initial, GameHistory.empty, Color.White, "q") shouldBe MoveResult.Quit
-
-  test("processMove: quit with surrounding whitespace returns Quit"):
-    processMove(Board.initial, GameHistory.empty, Color.White, "  quit  ") shouldBe MoveResult.Quit
-
-  test("processMove: unparseable input returns InvalidFormat"):
-    processMove(Board.initial, GameHistory.empty, Color.White, "xyz") shouldBe MoveResult.InvalidFormat("xyz")
-
-  test("processMove: valid format but empty square returns NoPiece"):
-    // E3 is empty in the initial position
-    processMove(Board.initial, GameHistory.empty, Color.White, "e3e4") shouldBe MoveResult.NoPiece
-
-  test("processMove: piece of wrong color returns WrongColor"):
-    // E7 has a Black pawn; it is White's turn
-    processMove(Board.initial, GameHistory.empty, Color.White, "e7e6") shouldBe MoveResult.WrongColor
-
-  test("processMove: geometrically illegal move returns IllegalMove"):
-    // White pawn at E2 cannot jump three squares to E5
-    processMove(Board.initial, GameHistory.empty, Color.White, "e2e5") shouldBe MoveResult.IllegalMove
-
-  test("processMove: move that leaves own king in check returns IllegalMove"):
-    // White King E1 is in check from Black Rook E8. Moving the D2 pawn is
-    // geometrically legal but does not resolve the check — must be rejected.
-    val b = Board(Map(
-      sq(File.E, Rank.R1) -> Piece.WhiteKing,
-      sq(File.D, Rank.R2) -> Piece.WhitePawn,
-      sq(File.E, Rank.R8) -> Piece.BlackRook,
-      sq(File.A, Rank.R8) -> Piece.BlackKing
-    ))
-    processMove(b, GameHistory.empty, Color.White, "d2d4") shouldBe MoveResult.IllegalMove
-
-  test("processMove: move that resolves check is allowed"):
-    // White King E1 is in check from Black Rook E8 along the E-file.
-    // White Rook A5 interposes at E5 — resolves the check, no new check on Black King A8.
-    val b = Board(Map(
-      sq(File.E, Rank.R1) -> Piece.WhiteKing,
-      sq(File.A, Rank.R5) -> Piece.WhiteRook,
-      sq(File.E, Rank.R8) -> Piece.BlackRook,
-      sq(File.A, Rank.R8) -> Piece.BlackKing
-    ))
-    processMove(b, GameHistory.empty, Color.White, "a5e5") match
-      case _: MoveResult.Moved => succeed
-      case other => fail(s"Expected Moved, got $other")
-
-  test("processMove: legal pawn move returns Moved with updated board and flipped turn"):
-    processMove(Board.initial, GameHistory.empty, Color.White, "e2e4") match
-      case MoveResult.Moved(newBoard, newHistory, captured, newTurn) =>
-        newBoard.pieceAt(sq(File.E, Rank.R4)) shouldBe Some(Piece.WhitePawn)
-        newBoard.pieceAt(sq(File.E, Rank.R2)) shouldBe None
-        captured shouldBe None
-        newTurn shouldBe Color.Black
-      case other => fail(s"Expected Moved, got $other")
-
-  test("processMove: legal capture returns Moved with the captured piece"):
-    val board = Board(Map(
-      sq(File.E, Rank.R5) -> Piece.WhitePawn,
-      sq(File.D, Rank.R6) -> Piece.BlackPawn,
-      sq(File.H, Rank.R1) -> Piece.BlackKing,
-      sq(File.H, Rank.R8) -> Piece.WhiteKing
-    ))
-    processMove(board, GameHistory.empty, Color.White, "e5d6") match
-      case MoveResult.Moved(newBoard, newHistory, captured, newTurn) =>
-        captured shouldBe Some(Piece.BlackPawn)
-        newBoard.pieceAt(sq(File.D, Rank.R6)) shouldBe Some(Piece.WhitePawn)
-        newTurn shouldBe Color.Black
-      case other => fail(s"Expected Moved, got $other")
-
-  // ──── processMove: check / checkmate / stalemate ─────────────────────
-
-  test("processMove: legal move that delivers check returns MovedInCheck"):
-    // White Ra1, Ka3; Black Kh8 — White plays Ra1-Ra8, Ra8 attacks rank 8 putting Kh8 in check
-    // Kh8 can escape to g7/g8/h7 so this is InCheck, not Mated
-    val b = Board(Map(
-      sq(File.A, Rank.R1) -> Piece.WhiteRook,
-      sq(File.C, Rank.R3) -> Piece.WhiteKing,
-      sq(File.H, Rank.R8) -> Piece.BlackKing
-    ))
-    processMove(b, GameHistory.empty, Color.White, "a1a8") match
-      case MoveResult.MovedInCheck(_, _, _, newTurn) => newTurn shouldBe Color.Black
-      case other => fail(s"Expected MovedInCheck, got $other")
-
-  test("processMove: legal move that results in checkmate returns Checkmate"):
-    // White Qa1, Ka6; Black Ka8 — White plays Qa1-Qh8 (diagonal a1→h8)
-    // After Qh8: White Qh8 + Ka6 vs Black Ka8 = checkmate (spec-verified position)
-    // Qa1 does NOT currently attack Ka8 — path along file A is blocked by Ka6
-    val b = Board(Map(
-      sq(File.A, Rank.R1) -> Piece.WhiteQueen,
-      sq(File.A, Rank.R6) -> Piece.WhiteKing,
-      sq(File.A, Rank.R8) -> Piece.BlackKing
-    ))
-    processMove(b, GameHistory.empty, Color.White, "a1h8") match
-      case MoveResult.Checkmate(winner) => winner shouldBe Color.White
-      case other => fail(s"Expected Checkmate(White), got $other")
-
-  test("processMove: legal move that results in stalemate returns Stalemate"):
-    // White Qb1, Kc6; Black Ka8 — White plays Qb1-Qb6
-    // After Qb6: White Qb6 + Kc6 vs Black Ka8 = stalemate (spec-verified position)
-    val b = Board(Map(
-      sq(File.B, Rank.R1) -> Piece.WhiteQueen,
-      sq(File.C, Rank.R6) -> Piece.WhiteKing,
-      sq(File.A, Rank.R8) -> Piece.BlackKing
-    ))
-    processMove(b, GameHistory.empty, Color.White, "b1b6") match
-      case MoveResult.Stalemate => succeed
-      case other => fail(s"Expected Stalemate, got $other")
-
-  // ──── castling execution ─────────────────────────────────────────────
-
-  test("processMove: e1g1 returns Moved with king on g1 and rook on f1"):
-    val b = Board(Map(
-        sq(File.E, Rank.R1) -> Piece.WhiteKing,
-        sq(File.H, Rank.R1) -> Piece.WhiteRook,
-        sq(File.H, Rank.R8) -> Piece.BlackKing
-      ))
-    processMove(b, GameHistory.empty, Color.White, "e1g1") match
-      case MoveResult.Moved(newBoard, newHistory, captured, newTurn) =>
-        newBoard.pieceAt(sq(File.G, Rank.R1)) shouldBe Some(Piece.WhiteKing)
-        newBoard.pieceAt(sq(File.F, Rank.R1)) shouldBe Some(Piece.WhiteRook)
-        newBoard.pieceAt(sq(File.E, Rank.R1)) shouldBe None
-        newBoard.pieceAt(sq(File.H, Rank.R1)) shouldBe None
-        captured shouldBe None
-        newTurn shouldBe Color.Black
-      case other => fail(s"Expected Moved, got $other")
-
-  test("processMove: e1c1 returns Moved with king on c1 and rook on d1"):
-    val b = Board(Map(
-        sq(File.E, Rank.R1) -> Piece.WhiteKing,
-        sq(File.A, Rank.R1) -> Piece.WhiteRook,
-        sq(File.H, Rank.R8) -> Piece.BlackKing
-      ))
-    processMove(b, GameHistory.empty, Color.White, "e1c1") match
-      case MoveResult.Moved(newBoard, _, _, _) =>
-        newBoard.pieceAt(sq(File.C, Rank.R1)) shouldBe Some(Piece.WhiteKing)
-        newBoard.pieceAt(sq(File.D, Rank.R1)) shouldBe Some(Piece.WhiteRook)
-      case other => fail(s"Expected Moved, got $other")
-
-  // ──── rights revocation ──────────────────────────────────────────────
-
-  test("processMove: e1g1 revokes both white castling rights"):
-    val b = Board(Map(
-        sq(File.E, Rank.R1) -> Piece.WhiteKing,
-        sq(File.H, Rank.R1) -> Piece.WhiteRook,
-        sq(File.H, Rank.R8) -> Piece.BlackKing
-      ))
-    processMove(b, GameHistory.empty, Color.White, "e1g1") match
-      case MoveResult.Moved(_, newHistory, _, _) =>
-        castlingRights(newHistory, Color.White) shouldBe CastlingRights.None
-      case other => fail(s"Expected Moved, got $other")
-
-  test("processMove: moving rook from h1 revokes white kingside right"):
-    val b = Board(Map(
-        sq(File.E, Rank.R1) -> Piece.WhiteKing,
-        sq(File.H, Rank.R1) -> Piece.WhiteRook,
-        sq(File.H, Rank.R8) -> Piece.BlackKing
-      ))
-    processMove(b, GameHistory.empty, Color.White, "h1h4") match
-      case MoveResult.Moved(_, newHistory, _, _) =>
-        castlingRights(newHistory, Color.White).kingSide  shouldBe false
-        castlingRights(newHistory, Color.White).queenSide shouldBe true
-      case MoveResult.MovedInCheck(_, newHistory, _, _) =>
-        castlingRights(newHistory, Color.White).kingSide  shouldBe false
-        castlingRights(newHistory, Color.White).queenSide shouldBe true
-      case other => fail(s"Expected Moved or MovedInCheck, got $other")
-
-  test("processMove: moving king from e1 revokes both white rights"):
-    val b = Board(Map(
-        sq(File.E, Rank.R1) -> Piece.WhiteKing,
-        sq(File.H, Rank.R8) -> Piece.BlackKing
-      ))
-    processMove(b, GameHistory.empty, Color.White, "e1e2") match
-      case MoveResult.Moved(_, newHistory, _, _) =>
-        castlingRights(newHistory, Color.White) shouldBe CastlingRights.None
-      case other => fail(s"Expected Moved, got $other")
-
-  test("processMove: enemy capture on h1 revokes white kingside right"):
-    val b = Board(Map(
-        sq(File.E, Rank.R1) -> Piece.WhiteKing,
-        sq(File.H, Rank.R1) -> Piece.WhiteRook,
-        sq(File.H, Rank.R2) -> Piece.BlackRook,
-        sq(File.A, Rank.R8) -> Piece.BlackKing
-      ))
-    processMove(b, GameHistory.empty, Color.Black, "h2h1") match
-      case MoveResult.Moved(_, newHistory, _, _) =>
-        castlingRights(newHistory, Color.White).kingSide shouldBe false
-      case MoveResult.MovedInCheck(_, newHistory, _, _) =>
-        castlingRights(newHistory, Color.White).kingSide shouldBe false
-      case other => fail(s"Expected Moved or MovedInCheck, got $other")
-
-  test("processMove: castle attempt when rights revoked returns IllegalMove"):
-    val b = Board(Map(
-        sq(File.E, Rank.R1) -> Piece.WhiteKing,
-        sq(File.H, Rank.R1) -> Piece.WhiteRook,
-        sq(File.H, Rank.R8) -> Piece.BlackKing
-      ))
-    val history = GameHistory.empty.addMove(sq(File.E, Rank.R1), sq(File.E, Rank.R2)).addMove(sq(File.E, Rank.R2), sq(File.E, Rank.R1))
-    processMove(b, history, Color.White, "e1g1") shouldBe MoveResult.IllegalMove
-
-  test("processMove: castle attempt when rook not on home square returns IllegalMove"):
-    val b = Board(Map(
-        sq(File.E, Rank.R1) -> Piece.WhiteKing,
-        sq(File.G, Rank.R1) -> Piece.WhiteRook,
-        sq(File.H, Rank.R8) -> Piece.BlackKing
-      ))
-    processMove(b, GameHistory.empty, Color.White, "e1g1") shouldBe MoveResult.IllegalMove
-
-  test("processMove: moving king from e8 revokes both black rights"):
-    val b = Board(Map(
-        sq(File.E, Rank.R8) -> Piece.BlackKing,
-        sq(File.H, Rank.R1) -> Piece.WhiteKing
-      ))
-    processMove(b, GameHistory.empty, Color.Black, "e8e7") match
-      case MoveResult.Moved(_, newHistory, _, _) =>
-        castlingRights(newHistory, Color.Black) shouldBe CastlingRights.None
-      case MoveResult.MovedInCheck(_, newHistory, _, _) =>
-        castlingRights(newHistory, Color.Black) shouldBe CastlingRights.None
-      case other => fail(s"Expected Moved or MovedInCheck, got $other")
-
-  test("processMove: moving rook from a8 revokes black queenside right"):
-    val b = Board(Map(
-        sq(File.E, Rank.R8) -> Piece.BlackKing,
-        sq(File.A, Rank.R8) -> Piece.BlackRook,
-        sq(File.H, Rank.R1) -> Piece.WhiteKing
-      ))
-    processMove(b, GameHistory.empty, Color.Black, "a8a1") match
-      case MoveResult.Moved(_, newHistory, _, _) =>
-        castlingRights(newHistory, Color.Black).queenSide shouldBe false
-        castlingRights(newHistory, Color.Black).kingSide  shouldBe true
-      case MoveResult.MovedInCheck(_, newHistory, _, _) =>
-        castlingRights(newHistory, Color.Black).queenSide shouldBe false
-        castlingRights(newHistory, Color.Black).kingSide  shouldBe true
-      case other => fail(s"Expected Moved or MovedInCheck, got $other")
-
-  test("processMove: moving rook from h8 revokes black kingside right"):
-    val b = Board(Map(
-        sq(File.E, Rank.R8) -> Piece.BlackKing,
-        sq(File.H, Rank.R8) -> Piece.BlackRook,
-        sq(File.A, Rank.R1) -> Piece.WhiteKing
-      ))
-    processMove(b, GameHistory.empty, Color.Black, "h8h4") match
-      case MoveResult.Moved(_, newHistory, _, _) =>
-        castlingRights(newHistory, Color.Black).kingSide  shouldBe false
-        castlingRights(newHistory, Color.Black).queenSide shouldBe true
-      case MoveResult.MovedInCheck(_, newHistory, _, _) =>
-        castlingRights(newHistory, Color.Black).kingSide  shouldBe false
-        castlingRights(newHistory, Color.Black).queenSide shouldBe true
-      case other => fail(s"Expected Moved or MovedInCheck, got $other")
-
-  test("processMove: enemy capture on a1 revokes white queenside right"):
-    val b = Board(Map(
-        sq(File.E, Rank.R1) -> Piece.WhiteKing,
-        sq(File.A, Rank.R1) -> Piece.WhiteRook,
-        sq(File.A, Rank.R2) -> Piece.BlackRook,
-        sq(File.H, Rank.R8) -> Piece.BlackKing
-      ))
-    processMove(b, GameHistory.empty, Color.Black, "a2a1") match
-      case MoveResult.Moved(_, newHistory, _, _) =>
-        castlingRights(newHistory, Color.White).queenSide shouldBe false
-      case MoveResult.MovedInCheck(_, newHistory, _, _) =>
-        castlingRights(newHistory, Color.White).queenSide shouldBe false
-      case other => fail(s"Expected Moved or MovedInCheck, got $other")
-
-  // ──── en passant ────────────────────────────────────────────────────────
-
-  test("en passant capture removes the captured pawn from the board"):
-    // Setup: white pawn e5, black pawn just double-pushed to d5 (ep target = d6)
-    val b = Board(Map(
-      Square(File.E, Rank.R5) -> Piece.WhitePawn,
-      Square(File.D, Rank.R5) -> Piece.BlackPawn,
-      Square(File.E, Rank.R1) -> Piece.WhiteKing,
-      Square(File.E, Rank.R8) -> Piece.BlackKing
-    ))
-    val h = GameHistory.empty.addMove(Square(File.D, Rank.R7), Square(File.D, Rank.R5))
-    val result = GameController.processMove(b, h, Color.White, "e5d6")
-    result match
-      case MoveResult.Moved(newBoard, _, captured, _) =>
-        newBoard.pieceAt(Square(File.D, Rank.R5)) shouldBe None  // captured pawn removed
-        newBoard.pieceAt(Square(File.D, Rank.R6)) shouldBe Some(Piece.WhitePawn)  // capturing pawn placed
-        captured shouldBe Some(Piece.BlackPawn)
-      case other => fail(s"Expected Moved but got $other")
-
-  test("en passant capture by black removes the captured white pawn"):
-    // Setup: black pawn d4, white pawn just double-pushed to e4 (ep target = e3)
-    val b = Board(Map(
-      Square(File.D, Rank.R4) -> Piece.BlackPawn,
-      Square(File.E, Rank.R4) -> Piece.WhitePawn,
-      Square(File.E, Rank.R8) -> Piece.BlackKing,
-      Square(File.E, Rank.R1) -> Piece.WhiteKing
-    ))
-    val h = GameHistory.empty.addMove(Square(File.E, Rank.R2), Square(File.E, Rank.R4))
-    val result = GameController.processMove(b, h, Color.Black, "d4e3")
-    result match
-      case MoveResult.Moved(newBoard, _, captured, _) =>
-        newBoard.pieceAt(Square(File.E, Rank.R4)) shouldBe None  // captured pawn removed
-        newBoard.pieceAt(Square(File.E, Rank.R3)) shouldBe Some(Piece.BlackPawn)  // capturing pawn placed
-        captured shouldBe Some(Piece.WhitePawn)
-      case other => fail(s"Expected Moved but got $other")
-
-  // ──── pawn promotion detection ───────────────────────────────────────────
-
-  test("processMove detects white pawn reaching R8 and returns PromotionRequired"):
-    val board = FenParser.parseBoard("8/4P3/4k3/8/8/8/8/8").get
-    val result = GameController.processMove(board, GameHistory.empty, Color.White, "e7e8")
-    result should matchPattern { case _: MoveResult.PromotionRequired => }
-    result match
-      case MoveResult.PromotionRequired(from, to, _, _, _, turn) =>
-        from should be (sq(File.E, Rank.R7))
-        to   should be (sq(File.E, Rank.R8))
-        turn should be (Color.White)
-      case _ => fail("Expected PromotionRequired")
-
-  test("processMove detects black pawn reaching R1 and returns PromotionRequired"):
-    val board = FenParser.parseBoard("8/8/8/8/4K3/8/4p3/8").get
-    val result = GameController.processMove(board, GameHistory.empty, Color.Black, "e2e1")
-    result should matchPattern { case _: MoveResult.PromotionRequired => }
-    result match
-      case MoveResult.PromotionRequired(from, to, _, _, _, turn) =>
-        from should be (sq(File.E, Rank.R2))
-        to   should be (sq(File.E, Rank.R1))
-        turn should be (Color.Black)
-      case _ => fail("Expected PromotionRequired")
-
-  test("processMove detects pawn capturing to back rank as PromotionRequired with captured piece"):
-    val board = FenParser.parseBoard("3q4/4P3/8/8/8/8/8/8").get
-    val result = GameController.processMove(board, GameHistory.empty, Color.White, "e7d8")
-    result should matchPattern { case _: MoveResult.PromotionRequired => }
-    result match
-      case MoveResult.PromotionRequired(_, _, _, _, captured, _) =>
-        captured should be (Some(Piece(Color.Black, PieceType.Queen)))
-      case _ => fail("Expected PromotionRequired")
-
-  // ──── completePromotion ──────────────────────────────────────────────────
-
-  test("completePromotion applies move and places queen"):
-    // Black king on h1: not attacked by queen on e8 (different file, rank, and diagonals)
-    val board = FenParser.parseBoard("8/4P3/8/8/8/8/8/7k").get
-    val result = GameController.completePromotion(
-      board, GameHistory.empty,
-      sq(File.E, Rank.R7), sq(File.E, Rank.R8),
-      PromotionPiece.Queen, Color.White
-    )
-    result should matchPattern { case _: MoveResult.Moved => }
-    result match
-      case MoveResult.Moved(newBoard, newHistory, _, _) =>
-        newBoard.pieceAt(sq(File.E, Rank.R8)) should be (Some(Piece(Color.White, PieceType.Queen)))
-        newBoard.pieceAt(sq(File.E, Rank.R7)) should be (None)
-        newHistory.moves should have length 1
-        newHistory.moves.head.promotionPiece should be (Some(PromotionPiece.Queen))
-      case _ => fail("Expected Moved")
-
-  test("completePromotion with rook underpromotion"):
-    // Black king on h1: not attacked by rook on e8 (different file and rank)
-    val board = FenParser.parseBoard("8/4P3/8/8/8/8/8/7k").get
-    val result = GameController.completePromotion(
-      board, GameHistory.empty,
-      sq(File.E, Rank.R7), sq(File.E, Rank.R8),
-      PromotionPiece.Rook, Color.White
-    )
-    result match
-      case MoveResult.Moved(newBoard, newHistory, _, _) =>
-        newBoard.pieceAt(sq(File.E, Rank.R8)) should be (Some(Piece(Color.White, PieceType.Rook)))
-        newHistory.moves.head.promotionPiece should be (Some(PromotionPiece.Rook))
-      case _ => fail("Expected Moved with Rook")
-
-  test("completePromotion with bishop underpromotion"):
-    val board = FenParser.parseBoard("8/4P3/4k3/8/8/8/8/8").get
-    val result = GameController.completePromotion(
-      board, GameHistory.empty,
-      sq(File.E, Rank.R7), sq(File.E, Rank.R8),
-      PromotionPiece.Bishop, Color.White
-    )
-    result match
-      case MoveResult.Moved(newBoard, newHistory, _, _) =>
-        newBoard.pieceAt(sq(File.E, Rank.R8)) should be (Some(Piece(Color.White, PieceType.Bishop)))
-        newHistory.moves.head.promotionPiece should be (Some(PromotionPiece.Bishop))
-      case _ => fail("Expected Moved with Bishop")
-
-  test("completePromotion with knight underpromotion"):
-    val board = FenParser.parseBoard("8/4P3/4k3/8/8/8/8/8").get
-    val result = GameController.completePromotion(
-      board, GameHistory.empty,
-      sq(File.E, Rank.R7), sq(File.E, Rank.R8),
-      PromotionPiece.Knight, Color.White
-    )
-    result match
-      case MoveResult.Moved(newBoard, newHistory, _, _) =>
-        newBoard.pieceAt(sq(File.E, Rank.R8)) should be (Some(Piece(Color.White, PieceType.Knight)))
-        newHistory.moves.head.promotionPiece should be (Some(PromotionPiece.Knight))
-      case _ => fail("Expected Moved with Knight")
-
-  test("completePromotion captures opponent piece"):
-    // Black king on h1: after white queen captures d8 queen, h1 king is safe (queen on d8 does not attack h1)
-    val board = FenParser.parseBoard("3q4/4P3/8/8/8/8/8/7k").get
-    val result = GameController.completePromotion(
-      board, GameHistory.empty,
-      sq(File.E, Rank.R7), sq(File.D, Rank.R8),
-      PromotionPiece.Queen, Color.White
-    )
-    result match
-      case MoveResult.Moved(newBoard, _, captured, _) =>
-        newBoard.pieceAt(sq(File.D, Rank.R8)) should be (Some(Piece(Color.White, PieceType.Queen)))
-        captured should be (Some(Piece(Color.Black, PieceType.Queen)))
-      case _ => fail("Expected Moved with captured piece")
-
-  test("completePromotion for black pawn to R1"):
-    val board = FenParser.parseBoard("8/8/8/8/4K3/8/4p3/8").get
-    val result = GameController.completePromotion(
-      board, GameHistory.empty,
-      sq(File.E, Rank.R2), sq(File.E, Rank.R1),
-      PromotionPiece.Knight, Color.Black
-    )
-    result match
-      case MoveResult.Moved(newBoard, newHistory, _, _) =>
-        newBoard.pieceAt(sq(File.E, Rank.R1)) should be (Some(Piece(Color.Black, PieceType.Knight)))
-        newHistory.moves.head.promotionPiece should be (Some(PromotionPiece.Knight))
-      case _ => fail("Expected Moved")
-
-  test("completePromotion evaluates check after promotion"):
-    val board = FenParser.parseBoard("3k4/4P3/8/8/8/8/8/8").get
-    val result = GameController.completePromotion(
-      board, GameHistory.empty,
-      sq(File.E, Rank.R7), sq(File.E, Rank.R8),
-      PromotionPiece.Queen, Color.White
-    )
-    result should matchPattern { case _: MoveResult.MovedInCheck => }
-
-  test("completePromotion full round-trip via processMove then completePromotion"):
-    // Black king on h1: not attacked by queen on e8
-    val board = FenParser.parseBoard("8/4P3/8/8/8/8/8/7k").get
-    GameController.processMove(board, GameHistory.empty, Color.White, "e7e8") match
-      case MoveResult.PromotionRequired(from, to, boardBefore, histBefore, _, turn) =>
-        val result = GameController.completePromotion(boardBefore, histBefore, from, to, PromotionPiece.Queen, turn)
-        result should matchPattern { case _: MoveResult.Moved => }
-        result match
-          case MoveResult.Moved(finalBoard, finalHistory, _, _) =>
-            finalBoard.pieceAt(sq(File.E, Rank.R8)) should be (Some(Piece(Color.White, PieceType.Queen)))
-            finalHistory.moves.head.promotionPiece should be (Some(PromotionPiece.Queen))
-          case _ => fail("Expected Moved")
-      case _ => fail("Expected PromotionRequired")
-
-  test("completePromotion results in checkmate when promotion delivers checkmate"):
-    // Black king a8, white pawn h7, white king b6.
-    // After h7→h8=Q: Qh8 attacks rank 8 putting Ka8 in check;
-    // a7 covered by Kb6, b7 covered by Kb6, b8 covered by Qh8 — no escape.
-    val board = FenParser.parseBoard("k7/7P/1K6/8/8/8/8/8").get
-    val result = GameController.completePromotion(
-      board, GameHistory.empty,
-      sq(File.H, Rank.R7), sq(File.H, Rank.R8),
-      PromotionPiece.Queen, Color.White
-    )
-    result should matchPattern { case MoveResult.Checkmate(_) => }
-    result match
-      case MoveResult.Checkmate(winner) => winner should be (Color.White)
-      case _ => fail("Expected Checkmate")
-
-  test("completePromotion results in stalemate when promotion stalemates opponent"):
-    // Black king a8, white pawn b7, white bishop c7, white king b6.
-    // After b7→b8=N: knight on b8 (doesn't check a8); a7 and b7 covered by Kb6;
-    // b8 defended by Bc7 so Ka8xb8 would walk into bishop — no legal moves.
-    val board = FenParser.parseBoard("k7/1PB5/1K6/8/8/8/8/8").get
-    val result = GameController.completePromotion(
-      board, GameHistory.empty,
-      sq(File.B, Rank.R7), sq(File.B, Rank.R8),
-      PromotionPiece.Knight, Color.White
-    )
-    result should be (MoveResult.Stalemate)
-
-  // ──── half-move clock propagation ────────────────────────────────────
-
-  test("processMove: non-pawn non-capture increments halfMoveClock"):
-    // g1f3 is a knight move — not a pawn, not a capture
-    processMove(Board.initial, GameHistory.empty, Color.White, "g1f3") match
-      case MoveResult.Moved(_, newHistory, _, _) =>
-        newHistory.halfMoveClock shouldBe 1
-      case other => fail(s"Expected Moved, got $other")
-
-  test("processMove: pawn move resets halfMoveClock to 0"):
-    processMove(Board.initial, GameHistory.empty, Color.White, "e2e4") match
-      case MoveResult.Moved(_, newHistory, _, _) =>
-        newHistory.halfMoveClock shouldBe 0
-      case other => fail(s"Expected Moved, got $other")
-
-  test("processMove: capture resets halfMoveClock to 0"):
-    // White pawn on e5, Black pawn on d6 — exd6 is a capture
-    val board = Board(Map(
-      sq(File.E, Rank.R5) -> Piece.WhitePawn,
-      sq(File.D, Rank.R6) -> Piece.BlackPawn,
-      sq(File.E, Rank.R1) -> Piece.WhiteKing,
-      sq(File.E, Rank.R8) -> Piece.BlackKing
-    ))
-    val history = GameHistory(halfMoveClock = 10)
-    processMove(board, history, Color.White, "e5d6") match
-      case MoveResult.Moved(_, newHistory, _, _) =>
-        newHistory.halfMoveClock shouldBe 0
-      case other => fail(s"Expected Moved, got $other")
-
-  test("processMove: clock carries from previous history on non-pawn non-capture"):
-    val history = GameHistory(halfMoveClock = 5)
-    processMove(Board.initial, history, Color.White, "g1f3") match
-      case MoveResult.Moved(_, newHistory, _, _) =>
-        newHistory.halfMoveClock shouldBe 6
-      case other => fail(s"Expected Moved, got $other")

modules/core/src/test/scala/de/nowchess/chess/engine/EngineTestHelpers.scala

@@ -0,0 +1,40 @@
+package de.nowchess.chess.engine
+
+import de.nowchess.api.board.{Board, Color}
+import de.nowchess.api.game.GameContext
+import de.nowchess.chess.observer.*
+import de.nowchess.io.fen.FenParser
+import de.nowchess.rules.sets.DefaultRules
+import scala.collection.mutable
+
+object EngineTestHelpers:
+
+  def makeEngine(): GameEngine =
+    new GameEngine(ruleSet = DefaultRules)
+
+  def makeEngineWithBoard(board: Board, turn: Color = Color.White): GameEngine =
+    GameEngine(initialContext = GameContext.initial.withBoard(board).withTurn(turn))
+
+  def loadFen(engine: GameEngine, fen: String): Unit =
+    engine.loadGame(FenParser, fen)
+
+  def captureEvents(engine: GameEngine): mutable.ListBuffer[GameEvent] =
+    val events = mutable.ListBuffer[GameEvent]()
+    engine.subscribe(new Observer { def onGameEvent(e: GameEvent): Unit = events += e })
+    events
+
+  class MockObserver extends Observer:
+    private val _events = mutable.ListBuffer[GameEvent]()
+
+    def events: mutable.ListBuffer[GameEvent] = _events
+    def eventCount: Int = _events.length
+    def hasEvent[T <: GameEvent](implicit ct: scala.reflect.ClassTag[T]): Boolean =
+      _events.exists(ct.runtimeClass.isInstance(_))
+    def getEvent[T <: GameEvent](implicit ct: scala.reflect.ClassTag[T]): Option[T] =
+      _events.collectFirst { case e if ct.runtimeClass.isInstance(e) => e.asInstanceOf[T] }
+
+    override def onGameEvent(event: GameEvent): Unit =
+      _events += event
+
+    def clear(): Unit =
+      _events.clear()

modules/core/src/test/scala/de/nowchess/chess/engine/GameEngineEdgeCasesTest.scala

@@ -1,214 +0,0 @@
-package de.nowchess.chess.engine
-
-import scala.collection.mutable
-import de.nowchess.api.board.{Board, Color}
-import de.nowchess.chess.logic.GameHistory
-import de.nowchess.chess.observer.{Observer, GameEvent, MoveExecutedEvent, CheckDetectedEvent, BoardResetEvent, InvalidMoveEvent}
-import org.scalatest.funsuite.AnyFunSuite
-import org.scalatest.matchers.should.Matchers
-
-/** Tests for GameEngine edge cases and uncovered paths */
-class GameEngineEdgeCasesTest extends AnyFunSuite with Matchers:
-
-  test("GameEngine handles empty input"):
-    val engine = new GameEngine()
-    val observer = new MockObserver()
-    engine.subscribe(observer)
-    
-    engine.processUserInput("")
-    
-    observer.events.size shouldBe 1
-    observer.events.head shouldBe an[InvalidMoveEvent]
-    val event = observer.events.head.asInstanceOf[InvalidMoveEvent]
-    event.reason should include("Please enter a valid move or command")
-
-  test("GameEngine processes quit command"):
-    val engine = new GameEngine()
-    val observer = new MockObserver()
-    engine.subscribe(observer)
-    
-    engine.processUserInput("quit")
-    // Quit just returns, no events
-    observer.events.isEmpty shouldBe true
-
-  test("GameEngine processes q command (short form)"):
-    val engine = new GameEngine()
-    val observer = new MockObserver()
-    engine.subscribe(observer)
-    
-    engine.processUserInput("q")
-    observer.events.isEmpty shouldBe true
-
-  test("GameEngine handles uppercase quit"):
-    val engine = new GameEngine()
-    val observer = new MockObserver()
-    engine.subscribe(observer)
-    
-    engine.processUserInput("QUIT")
-    observer.events.isEmpty shouldBe true
-
-  test("GameEngine handles undo on empty history"):
-    val engine = new GameEngine()
-    val observer = new MockObserver()
-    engine.subscribe(observer)
-    
-    engine.canUndo shouldBe false
-    engine.processUserInput("undo")
-    
-    observer.events.size shouldBe 1
-    observer.events.head shouldBe an[InvalidMoveEvent]
-    val event = observer.events.head.asInstanceOf[InvalidMoveEvent]
-    event.reason should include("Nothing to undo")
-
-  test("GameEngine handles redo on empty redo history"):
-    val engine = new GameEngine()
-    val observer = new MockObserver()
-    engine.subscribe(observer)
-    
-    engine.canRedo shouldBe false
-    engine.processUserInput("redo")
-    
-    observer.events.size shouldBe 1
-    observer.events.head shouldBe an[InvalidMoveEvent]
-    val event = observer.events.head.asInstanceOf[InvalidMoveEvent]
-    event.reason should include("Nothing to redo")
-
-  test("GameEngine parses invalid move format"):
-    val engine = new GameEngine()
-    val observer = new MockObserver()
-    engine.subscribe(observer)
-    
-    engine.processUserInput("invalid_move_format")
-    
-    observer.events.size shouldBe 1
-    observer.events.head shouldBe an[InvalidMoveEvent]
-    val event = observer.events.head.asInstanceOf[InvalidMoveEvent]
-    event.reason should include("Invalid move format")
-
-  test("GameEngine handles lowercase input normalization"):
-    val engine = new GameEngine()
-    val observer = new MockObserver()
-    engine.subscribe(observer)
-    
-    engine.processUserInput("  UNDO  ")  // With spaces and uppercase
-    
-    observer.events.size shouldBe 1
-    observer.events.head shouldBe an[InvalidMoveEvent]  // No moves to undo yet
-
-  test("GameEngine preserves board state on invalid move"):
-    val engine = new GameEngine()
-    val initialBoard = engine.board
-    
-    engine.processUserInput("invalid")
-    
-    engine.board shouldBe initialBoard
-
-  test("GameEngine preserves turn on invalid move"):
-    val engine = new GameEngine()
-    val initialTurn = engine.turn
-    
-    engine.processUserInput("invalid")
-    
-    engine.turn shouldBe initialTurn
-
-  test("GameEngine undo with no commands available"):
-    val engine = new GameEngine()
-    val observer = new MockObserver()
-    engine.subscribe(observer)
-    
-    // Make a valid move
-    engine.processUserInput("e2e4")
-    observer.events.clear()
-    
-    // Undo it
-    engine.processUserInput("undo")
-    
-    // Board should be reset
-    engine.board shouldBe Board.initial
-    engine.turn shouldBe Color.White
-
-  test("GameEngine redo after undo"):
-    val engine = new GameEngine()
-    val observer = new MockObserver()
-    engine.subscribe(observer)
-    
-    engine.processUserInput("e2e4")
-    val boardAfterMove = engine.board
-    val turnAfterMove = engine.turn
-    observer.events.clear()
-    
-    engine.processUserInput("undo")
-    engine.processUserInput("redo")
-    
-    engine.board shouldBe boardAfterMove
-    engine.turn shouldBe turnAfterMove
-
-  test("GameEngine canUndo flag tracks state correctly"):
-    val engine = new GameEngine()
-    
-    engine.canUndo shouldBe false
-    engine.processUserInput("e2e4")
-    engine.canUndo shouldBe true
-    engine.processUserInput("undo")
-    engine.canUndo shouldBe false
-
-  test("GameEngine canRedo flag tracks state correctly"):
-    val engine = new GameEngine()
-    
-    engine.canRedo shouldBe false
-    engine.processUserInput("e2e4")
-    engine.canRedo shouldBe false
-    engine.processUserInput("undo")
-    engine.canRedo shouldBe true
-
-  test("GameEngine command history is accessible"):
-    val engine = new GameEngine()
-    
-    engine.commandHistory.isEmpty shouldBe true
-    engine.processUserInput("e2e4")
-    engine.commandHistory.size shouldBe 1
-
-  test("GameEngine processes multiple moves in sequence"):
-    val engine = new GameEngine()
-    val observer = new MockObserver()
-    engine.subscribe(observer)
-    observer.events.clear()
-    
-    engine.processUserInput("e2e4")
-    engine.processUserInput("e7e5")
-    
-    observer.events.size shouldBe 2
-    engine.commandHistory.size shouldBe 2
-
-  test("GameEngine can undo multiple moves"):
-    val engine = new GameEngine()
-    
-    engine.processUserInput("e2e4")
-    engine.processUserInput("e7e5")
-    
-    engine.processUserInput("undo")
-    engine.turn shouldBe Color.Black
-    
-    engine.processUserInput("undo")
-    engine.turn shouldBe Color.White
-
-  test("GameEngine thread-safe operations"):
-    val engine = new GameEngine()
-    
-    // Access from synchronized methods
-    val board = engine.board
-    val history = engine.history
-    val turn = engine.turn
-    val canUndo = engine.canUndo
-    val canRedo = engine.canRedo
-    
-    board shouldBe Board.initial
-    canUndo shouldBe false
-    canRedo shouldBe false
-
-
-private class MockObserver extends Observer:
-  val events = mutable.ListBuffer[GameEvent]()
-  
-  override def onGameEvent(event: GameEvent): Unit =
-    events += event

modules/core/src/test/scala/de/nowchess/chess/engine/GameEngineGameEndingTest.scala

@@ -2,7 +2,6 @@ package de.nowchess.chess.engine
 
 import scala.collection.mutable
 import de.nowchess.api.board.{Board, Color}
-import de.nowchess.chess.logic.GameHistory
 import de.nowchess.chess.observer.{Observer, GameEvent, CheckDetectedEvent, CheckmateEvent, StalemateEvent}
 import org.scalatest.funsuite.AnyFunSuite
 import org.scalatest.matchers.should.Matchers
@@ -22,12 +21,11 @@ class GameEngineGameEndingTest extends AnyFunSuite with Matchers:
     
     observer.events.clear()
     engine.processUserInput("d8h4")
+
+    // Verify CheckmateEvent (engine also fires MoveExecutedEvent before CheckmateEvent)
+    observer.events.last shouldBe a[CheckmateEvent]
     
-    // Verify CheckmateEvent
-    observer.events.size shouldBe 1
-    observer.events.head shouldBe a[CheckmateEvent]
-    
-    val event = observer.events.head.asInstanceOf[CheckmateEvent]
+    val event = observer.events.last.asInstanceOf[CheckmateEvent]
     event.winner shouldBe Color.Black
     
     // Board should be reset after checkmate
@@ -50,7 +48,7 @@ class GameEngineGameEndingTest extends AnyFunSuite with Matchers:
     
     val checkEvents = observer.events.collect { case e: CheckDetectedEvent => e }
     checkEvents.size shouldBe 1
-    checkEvents.head.turn shouldBe Color.Black // Black is now in check
+    checkEvents.head.context.turn shouldBe Color.Black // Black is now in check
     
   // Shortest known stalemate is 19 moves. Here is a faster one:
   // e3 a5 Qh5 Ra6 Qxa5 h5 h4 Rah6 Qxc7 f6 Qxd7+ Kf7 Qxb7 Qd3 Qxb8 Qh7 Qxc8 Kg6 Qe6

modules/core/src/test/scala/de/nowchess/chess/engine/GameEngineHandleFailedMoveTest.scala

@@ -1,110 +0,0 @@
-package de.nowchess.chess.engine
-
-import scala.collection.mutable
-import de.nowchess.api.board.{Board, Color}
-import de.nowchess.chess.logic.GameHistory
-import de.nowchess.chess.observer.{Observer, GameEvent, InvalidMoveEvent}
-import org.scalatest.funsuite.AnyFunSuite
-import org.scalatest.matchers.should.Matchers
-
-/** Tests to maximize handleFailedMove coverage */
-class GameEngineHandleFailedMoveTest extends AnyFunSuite with Matchers:
-
-  test("GameEngine handles InvalidFormat error type"):
-    val engine = new GameEngine()
-    val observer = new MockObserver()
-    engine.subscribe(observer)
-    
-    engine.processUserInput("not_a_valid_move_format")
-    observer.events.size shouldBe 1
-    observer.events.head shouldBe an[InvalidMoveEvent]
-    val msg1 = observer.events.head.asInstanceOf[InvalidMoveEvent].reason
-    msg1 should include("Invalid move format")
-
-  test("GameEngine handles NoPiece error type"):
-    val engine = new GameEngine()
-    val observer = new MockObserver()
-    engine.subscribe(observer)
-    
-    engine.processUserInput("h3h4")
-    observer.events.size shouldBe 1
-    observer.events.head shouldBe an[InvalidMoveEvent]
-    val msg2 = observer.events.head.asInstanceOf[InvalidMoveEvent].reason
-    msg2 should include("No piece on that square")
-
-  test("GameEngine handles WrongColor error type"):
-    val engine = new GameEngine()
-    val observer = new MockObserver()
-    engine.subscribe(observer)
-    
-    engine.processUserInput("e2e4")  // White move
-    observer.events.clear()
-    
-    engine.processUserInput("a1b2")  // Try to move black's rook position with white's move (wrong color)
-    observer.events.size shouldBe 1
-    observer.events.head shouldBe an[InvalidMoveEvent]
-    val msg3 = observer.events.head.asInstanceOf[InvalidMoveEvent].reason
-    msg3 should include("That is not your piece")
-
-  test("GameEngine handles IllegalMove error type"):
-    val engine = new GameEngine()
-    val observer = new MockObserver()
-    engine.subscribe(observer)
-    
-    engine.processUserInput("e2e1")  // Try pawn backward
-    observer.events.size shouldBe 1
-    observer.events.head shouldBe an[InvalidMoveEvent]
-    val msg4 = observer.events.head.asInstanceOf[InvalidMoveEvent].reason
-    msg4 should include("Illegal move")
-
-  test("GameEngine invalid move message for InvalidFormat"):
-    val engine = new GameEngine()
-    val observer = new MockObserver()
-    engine.subscribe(observer)
-    
-    engine.processUserInput("xyz123")
-    val event = observer.events.head.asInstanceOf[InvalidMoveEvent]
-    event.reason should include("coordinate notation")
-
-  test("GameEngine invalid move message for NoPiece"):
-    val engine = new GameEngine()
-    val observer = new MockObserver()
-    engine.subscribe(observer)
-    
-    engine.processUserInput("a3a4")  // a3 is empty
-    val event = observer.events.head.asInstanceOf[InvalidMoveEvent]
-    event.reason should include("No piece")
-
-  test("GameEngine invalid move message for WrongColor"):
-    val engine = new GameEngine()
-    val observer = new MockObserver()
-    engine.subscribe(observer)
-    
-    engine.processUserInput("e2e4")
-    observer.events.clear()
-    
-    engine.processUserInput("e4e5")  // e4 has white pawn, it's black's turn
-    val event = observer.events.head.asInstanceOf[InvalidMoveEvent]
-    event.reason should include("not your piece")
-
-  test("GameEngine invalid move message for IllegalMove"):
-    val engine = new GameEngine()
-    val observer = new MockObserver()
-    engine.subscribe(observer)
-    
-    engine.processUserInput("e2e1")  // Pawn can't move backward
-    val event = observer.events.head.asInstanceOf[InvalidMoveEvent]
-    event.reason should include("Illegal move")
-
-  test("GameEngine board unchanged after each type of invalid move"):
-    val engine = new GameEngine()
-    val initial = engine.board
-    
-    engine.processUserInput("invalid")
-    engine.board shouldBe initial
-    
-    engine.processUserInput("h3h4")
-    engine.board shouldBe initial
-    
-    engine.processUserInput("e2e1")
-    engine.board shouldBe initial

modules/core/src/test/scala/de/nowchess/chess/engine/GameEngineIntegrationTest.scala

@@ -0,0 +1,178 @@
+package de.nowchess.chess.engine
+
+import de.nowchess.api.board.{Board, Color, File, PieceType, Rank, Square}
+import de.nowchess.api.game.GameContext
+import de.nowchess.api.move.{Move, MoveType, PromotionPiece}
+import de.nowchess.chess.observer.{GameEvent, InvalidMoveEvent, MoveRedoneEvent, Observer}
+import de.nowchess.io.GameContextImport
+import de.nowchess.rules.RuleSet
+import de.nowchess.rules.sets.DefaultRules
+import org.scalatest.funsuite.AnyFunSuite
+import org.scalatest.matchers.should.Matchers
+
+class GameEngineIntegrationTest extends AnyFunSuite with Matchers:
+
+  private def sq(alg: String): Square =
+    Square.fromAlgebraic(alg).getOrElse(fail(s"Invalid square in test: $alg"))
+
+  private def captureEvents(engine: GameEngine): collection.mutable.ListBuffer[GameEvent] =
+    val events = collection.mutable.ListBuffer[GameEvent]()
+    engine.subscribe((event: GameEvent) => events += event)
+    events
+
+  test("accessors expose redo availability and command history"):
+    val engine = new GameEngine()
+
+    engine.canRedo shouldBe false
+    engine.commandHistory shouldBe empty
+
+    engine.processUserInput("e2e4")
+    engine.commandHistory.nonEmpty shouldBe true
+
+  test("processUserInput handles undo redo empty and malformed commands"):
+    val engine = new GameEngine()
+    val events = captureEvents(engine)
+
+    engine.processUserInput("")
+    engine.processUserInput("oops")
+    engine.processUserInput("undo")
+    engine.processUserInput("redo")
+
+    events.count(_.isInstanceOf[InvalidMoveEvent]) should be >= 3
+
+  test("processUserInput emits Illegal move for syntactically valid but illegal target"):
+    val engine = new GameEngine()
+    val events = captureEvents(engine)
+
+    engine.processUserInput("e2e5")
+
+    events.exists {
+      case InvalidMoveEvent(_, reason) => reason.contains("Illegal move")
+      case _                           => false
+    } shouldBe true
+
+  test("loadGame returns Left when importer fails"):
+
+    val engine = new GameEngine()
+    val failingImporter = new GameContextImport:
+      def importGameContext(input: String): Either[String, GameContext] = Left("boom")
+
+    engine.loadGame(failingImporter, "ignored") shouldBe Left("boom")
+
+  test("loadPosition replaces context clears history and notifies reset"):
+    val engine = new GameEngine()
+    val events = captureEvents(engine)
+
+    engine.processUserInput("e2e4")
+    val target = GameContext.initial.withTurn(Color.Black)
+    engine.loadPosition(target)
+
+    engine.context shouldBe target
+    engine.commandHistory shouldBe empty
+    events.lastOption.exists(_.isInstanceOf[de.nowchess.chess.observer.BoardResetEvent]) shouldBe true
+
+  test("redo event includes captured piece description when replaying a capture"):
+    val engine = new GameEngine()
+    val events = captureEvents(engine)
+
+    EngineTestHelpers.loadFen(engine, "4k3/8/8/8/8/8/4K3/R6r w - - 0 1")
+    events.clear()
+
+    engine.processUserInput("a1h1")
+    engine.processUserInput("undo")
+    engine.processUserInput("redo")
+
+    val redo = events.collectFirst { case e: MoveRedoneEvent => e }
+    redo.flatMap(_.capturedPiece) shouldBe Some("Black Rook")
+
+  test("loadGame replay handles promotion moves when pending promotion exists"):
+    val promotionMove = Move(sq("e2"), sq("e8"), MoveType.Promotion(PromotionPiece.Queen))
+
+    val permissiveRules = new RuleSet:
+      def candidateMoves(context: GameContext)(square: Square): List[Move] = legalMoves(context)(square)
+      def legalMoves(context: GameContext)(square: Square): List[Move] =
+        if square == sq("e2") then List(promotionMove) else List.empty
+      def allLegalMoves(context: GameContext): List[Move] = List(promotionMove)
+      def isCheck(context: GameContext): Boolean = false
+      def isCheckmate(context: GameContext): Boolean = false
+      def isStalemate(context: GameContext): Boolean = false
+      def isInsufficientMaterial(context: GameContext): Boolean = false
+      def isFiftyMoveRule(context: GameContext): Boolean = false
+      def applyMove(context: GameContext)(move: Move): GameContext = DefaultRules.applyMove(context)(move)
+
+    val engine = new GameEngine(ruleSet = permissiveRules)
+    val importer = new GameContextImport:
+      def importGameContext(input: String): Either[String, GameContext] =
+        Right(GameContext.initial.copy(moves = List(promotionMove)))
+
+    engine.loadGame(importer, "ignored") shouldBe Right(())
+    engine.context.moves.lastOption shouldBe Some(promotionMove)
+
+  test("loadGame replay restores previous context when promotion cannot be completed"):
+    val promotionMove = Move(sq("e2"), sq("e8"), MoveType.Promotion(PromotionPiece.Queen))
+    val noLegalMoves = new RuleSet:
+      def candidateMoves(context: GameContext)(square: Square): List[Move] = List.empty
+      def legalMoves(context: GameContext)(square: Square): List[Move] = List.empty
+      def allLegalMoves(context: GameContext): List[Move] = List.empty
+      def isCheck(context: GameContext): Boolean = false
+      def isCheckmate(context: GameContext): Boolean = false
+      def isStalemate(context: GameContext): Boolean = false
+      def isInsufficientMaterial(context: GameContext): Boolean = false
+      def isFiftyMoveRule(context: GameContext): Boolean = false
+      def applyMove(context: GameContext)(move: Move): GameContext = context
+
+    val engine = new GameEngine(ruleSet = noLegalMoves)
+    engine.processUserInput("e2e4")
+    val saved = engine.context
+
+    val importer = new GameContextImport:
+      def importGameContext(input: String): Either[String, GameContext] =
+        Right(GameContext.initial.copy(moves = List(promotionMove)))
+
+    val result = engine.loadGame(importer, "ignored")
+
+    result.isLeft shouldBe true
+    result.left.toOption.get should include("Promotion required")
+    engine.context shouldBe saved
+
+  test("loadGame replay executes non-promotion moves through default replay branch"):
+    val normalMove = Move(sq("e2"), sq("e4"), MoveType.Normal())
+    val engine = new GameEngine()
+
+    engine.replayMoves(List(normalMove), engine.context) shouldBe Right(())
+    engine.context.moves.lastOption shouldBe Some(normalMove)
+
+  test("replayMoves skips later moves after the first move triggers an error"):
+    val engine = new GameEngine()
+    val saved = engine.context
+    val illegalPromotion = Move(sq("e2"), sq("e1"), MoveType.Promotion(PromotionPiece.Queen))
+    val trailingMove = Move(sq("e2"), sq("e4"))
+
+    engine.replayMoves(List(illegalPromotion, trailingMove), saved) shouldBe Left("Promotion required for move e2e1")
+    engine.context shouldBe saved
+
+
+  test("normalMoveNotation handles missing source piece"):
+    val engine = new GameEngine()
+    val result = engine.normalMoveNotation(Move(sq("e3"), sq("e4")), Board.initial, isCapture = false)
+
+    result shouldBe "e4"
+
+  test("pieceNotation default branch returns empty string"):
+    val engine = new GameEngine()
+    val result = engine.pieceNotation(PieceType.Pawn)
+
+    result shouldBe ""
+
+  test("observerCount reflects subscribe and unsubscribe operations"):
+    val engine = new GameEngine()
+    val observer = new Observer:
+      def onGameEvent(event: GameEvent): Unit = ()
+
+    engine.observerCount shouldBe 0
+    engine.subscribe(observer)
+    engine.observerCount shouldBe 1
+    engine.unsubscribe(observer)
+    engine.observerCount shouldBe 0
+
+

modules/core/src/test/scala/de/nowchess/chess/engine/GameEngineInvalidMovesTest.scala

@@ -1,114 +0,0 @@
-package de.nowchess.chess.engine
-
-import scala.collection.mutable
-import de.nowchess.api.board.{Board, Color}
-import de.nowchess.chess.logic.GameHistory
-import de.nowchess.chess.observer.{Observer, GameEvent, InvalidMoveEvent, MoveExecutedEvent}
-import org.scalatest.funsuite.AnyFunSuite
-import org.scalatest.matchers.should.Matchers
-
-/** Tests for GameEngine invalid move handling via handleFailedMove */
-class GameEngineInvalidMovesTest extends AnyFunSuite with Matchers:
-
-  test("GameEngine handles no piece at source square"):
-    val engine = new GameEngine()
-    val observer = new MockObserver()
-    engine.subscribe(observer)
-    
-    // Try to move from h1 which may be empty or not have our piece
-    // We'll try from a clearly empty square
-    engine.processUserInput("h1h2")
-    
-    // Should get an InvalidMoveEvent about NoPiece
-    observer.events.size shouldBe 1
-    observer.events.head shouldBe an[InvalidMoveEvent]
-
-  test("GameEngine handles moving wrong color piece"):
-    val engine = new GameEngine()
-    val observer = new MockObserver()
-    engine.subscribe(observer)
-    
-    // White moves first
-    engine.processUserInput("e2e4")
-    observer.events.clear()
-    
-    // White tries to move again (should fail - it's black's turn)
-    // But we need to try a move that looks legal but has wrong color
-    // This is hard to test because we'd need to be black and move white's piece
-    // Let's skip this for now and focus on testable cases
-    
-    // Actually, let's try moving a square that definitely has the wrong piece
-    // Move a white pawn as black by reaching that position
-    engine.processUserInput("e7e5")
-    observer.events.clear()
-    
-    // Now try to move white's e4 pawn as black (it's black's turn but e4 is white)
-    engine.processUserInput("e4e5")
-    
-    observer.events.size shouldBe 1
-    val event = observer.events.head
-    event shouldBe an[InvalidMoveEvent]
-
-  test("GameEngine handles illegal move"):
-    val engine = new GameEngine()
-    val observer = new MockObserver()
-    engine.subscribe(observer)
-    
-    // A pawn can't move backward
-    engine.processUserInput("e2e1")
-    
-    observer.events.size shouldBe 1
-    observer.events.head shouldBe an[InvalidMoveEvent]
-    val event = observer.events.head.asInstanceOf[InvalidMoveEvent]
-    event.reason should include("Illegal move")
-
-  test("GameEngine handles pawn trying to move 3 squares"):
-    val engine = new GameEngine()
-    val observer = new MockObserver()
-    engine.subscribe(observer)
-    
-    // Pawn can only move 1 or 2 squares on first move, not 3
-    engine.processUserInput("e2e5")
-    
-    observer.events.size shouldBe 1
-    observer.events.head shouldBe an[InvalidMoveEvent]
-
-  test("GameEngine handles moving from empty square"):
-    val engine = new GameEngine()
-    val observer = new MockObserver()
-    engine.subscribe(observer)
-    
-    // h3 is empty in starting position
-    engine.processUserInput("h3h4")
-    
-    observer.events.size shouldBe 1
-    observer.events.head shouldBe an[InvalidMoveEvent]
-    val event = observer.events.head.asInstanceOf[InvalidMoveEvent]
-    event.reason should include("No piece on that square")
-
-  test("GameEngine processes valid move after invalid attempt"):
-    val engine = new GameEngine()
-    val observer = new MockObserver()
-    engine.subscribe(observer)
-    
-    // Try invalid move
-    engine.processUserInput("h3h4")
-    observer.events.clear()
-    
-    // Make valid move
-    engine.processUserInput("e2e4")
-    
-    observer.events.size shouldBe 1
-    observer.events.head shouldBe an[MoveExecutedEvent]
-
-  test("GameEngine maintains state after failed move attempt"):
-    val engine = new GameEngine()
-    val initialTurn = engine.turn
-    val initialBoard = engine.board
-    
-    // Try invalid move
-    engine.processUserInput("h3h4")
-    
-    // State should not change
-    engine.turn shouldBe initialTurn
-    engine.board shouldBe initialBoard

modules/core/src/test/scala/de/nowchess/chess/engine/GameEngineLoadGameTest.scala

@@ -0,0 +1,43 @@
+package de.nowchess.chess.engine
+
+import scala.collection.mutable
+import de.nowchess.api.board.{Board, Color}
+import de.nowchess.api.game.GameContext
+import de.nowchess.chess.observer.{Observer, GameEvent, PgnLoadedEvent}
+import de.nowchess.io.pgn.PgnParser
+import de.nowchess.io.fen.FenParser
+import de.nowchess.io.pgn.PgnExporter
+import de.nowchess.io.fen.FenExporter
+import org.scalatest.funsuite.AnyFunSuite
+import org.scalatest.matchers.should.Matchers
+
+class GameEngineLoadGameTest extends AnyFunSuite with Matchers:
+
+  test("loadGame with PgnParser: loads valid PGN and enables undo/redo"):
+    val engine = new GameEngine()
+    val pgn = "[Event \"Test\"]\n\n1. e4 e5\n"
+    val result = engine.loadGame(PgnParser, pgn)
+    result shouldBe Right(())
+    engine.context.moves.size shouldBe 2
+    engine.canUndo shouldBe true
+
+  test("loadGame with FenParser: loads position without replaying moves"):
+    val engine = new GameEngine()
+    val fen = "8/4P3/4k3/8/8/8/8/8 w - - 0 1"
+    val result = engine.loadGame(FenParser, fen)
+    result shouldBe Right(())
+    engine.context.moves.isEmpty shouldBe true
+    engine.canUndo shouldBe false
+
+  test("exportGame with PgnExporter: exports current game as PGN"):
+    val engine = new GameEngine()
+    engine.processUserInput("e2e4")
+    engine.processUserInput("e7e5")
+    val pgn = engine.exportGame(PgnExporter)
+    pgn.contains("e4") shouldBe true
+    pgn.contains("e5") shouldBe true
+
+  private class MockObserver extends Observer:
+    val events = mutable.ListBuffer[GameEvent]()
+    override def onGameEvent(event: GameEvent): Unit =
+      events += event

modules/core/src/test/scala/de/nowchess/chess/engine/GameEngineLoadPgnTest.scala

@@ -1,165 +0,0 @@
-package de.nowchess.chess.engine
-
-import scala.collection.mutable
-import de.nowchess.api.board.{Board, Color}
-import de.nowchess.chess.logic.GameHistory
-import de.nowchess.chess.observer.*
-import org.scalatest.funsuite.AnyFunSuite
-import org.scalatest.matchers.should.Matchers
-
-class GameEngineLoadPgnTest extends AnyFunSuite with Matchers:
-
-  private class EventCapture extends Observer:
-    val events: mutable.Buffer[GameEvent] = mutable.Buffer.empty
-    def onGameEvent(event: GameEvent): Unit = events += event
-    def lastEvent: GameEvent = events.last
-
-  // ── loadPgn happy path ────────────────────────────────────────────────────
-
-  test("loadPgn: valid PGN returns Right and updates board/history"):
-    val engine = new GameEngine()
-    val pgn =
-      """[Event "Test"]
-
-1. e4 e5
-"""
-    val result = engine.loadPgn(pgn)
-    result shouldBe Right(())
-    engine.history.moves.length shouldBe 2
-    engine.turn shouldBe Color.White
-
-  test("loadPgn: emits PgnLoadedEvent on success"):
-    val engine = new GameEngine()
-    val cap    = new EventCapture()
-    engine.subscribe(cap)
-    val pgn = "[Event \"T\"]\n\n1. e4 e5\n"
-    engine.loadPgn(pgn)
-    cap.events.last shouldBe a[PgnLoadedEvent]
-
-  test("loadPgn: after load canUndo is true and canRedo is false"):
-    val engine = new GameEngine()
-    val pgn = "[Event \"T\"]\n\n1. e4 e5\n"
-    engine.loadPgn(pgn) shouldBe Right(())
-    engine.canUndo shouldBe true
-    engine.canRedo shouldBe false
-
-  test("loadPgn: undo works after loading PGN"):
-    val engine = new GameEngine()
-    val cap    = new EventCapture()
-    engine.subscribe(cap)
-    val pgn = "[Event \"T\"]\n\n1. e4 e5\n"
-    engine.loadPgn(pgn)
-    cap.events.clear()
-    engine.undo()
-    cap.events.last shouldBe a[MoveUndoneEvent]
-    engine.history.moves.length shouldBe 1
-
-  test("loadPgn: undo then redo restores position after PGN load"):
-    val engine = new GameEngine()
-    val cap    = new EventCapture()
-    engine.subscribe(cap)
-    val pgn = "[Event \"T\"]\n\n1. e4 e5\n"
-    engine.loadPgn(pgn)
-    val boardAfterLoad = engine.board
-    engine.undo()
-    engine.redo()
-    cap.events.last shouldBe a[MoveRedoneEvent]
-    engine.board shouldBe boardAfterLoad
-    engine.history.moves.length shouldBe 2
-
-  test("loadPgn: longer game loads all moves into command history"):
-    val engine = new GameEngine()
-    val pgn =
-      """[Event "Ruy Lopez"]
-
-1. e4 e5 2. Nf3 Nc6 3. Bb5 a6
-"""
-    engine.loadPgn(pgn) shouldBe Right(())
-    engine.history.moves.length shouldBe 6
-    engine.commandHistory.length shouldBe 6
-
-  test("loadPgn: invalid PGN returns Left and does not change state"):
-    val engine  = new GameEngine()
-    val initial = engine.board
-    val result  = engine.loadPgn("[Event \"T\"]\n\n1. Qd4\n")
-    result.isLeft shouldBe true
-    // state is reset to initial (reset happens before replay, which fails)
-    engine.history.moves shouldBe empty
-
-  // ── undo/redo notation events ─────────────────────────────────────────────
-
-  test("undo emits MoveUndoneEvent with pgnNotation"):
-    val engine = new GameEngine()
-    val cap    = new EventCapture()
-    engine.subscribe(cap)
-    engine.processUserInput("e2e4")
-    cap.events.clear()
-    engine.undo()
-    cap.events.last shouldBe a[MoveUndoneEvent]
-    val evt = cap.events.last.asInstanceOf[MoveUndoneEvent]
-    evt.pgnNotation should not be empty
-    evt.pgnNotation shouldBe "e4"  // pawn to e4
-
-  test("redo emits MoveRedoneEvent with pgnNotation"):
-    val engine = new GameEngine()
-    val cap    = new EventCapture()
-    engine.subscribe(cap)
-    engine.processUserInput("e2e4")
-    engine.undo()
-    cap.events.clear()
-    engine.redo()
-    cap.events.last shouldBe a[MoveRedoneEvent]
-    val evt = cap.events.last.asInstanceOf[MoveRedoneEvent]
-    evt.pgnNotation should not be empty
-    evt.pgnNotation shouldBe "e4"
-
-  test("undo emits MoveUndoneEvent with empty notation when history is empty (after checkmate reset)"):
-    // Simulate state where canUndo=true but currentHistory is empty (board reset on checkmate).
-    // We achieve this by examining the branch: provide a MoveCommand with empty history saved.
-    // The simplest proxy: undo a move that reset history (stalemate/checkmate). We'll
-    // use a contrived engine state by direct command manipulation — instead, just verify
-    // that after a normal move-and-undo the notation is present; the empty-history branch
-    // is exercised internally when gameEnd resets state. We cover it via a castling undo.
-    val engine = new GameEngine()
-    val cap    = new EventCapture()
-    engine.subscribe(cap)
-    // Play moves that let white castle kingside: e4 e5 Nf3 Nc6 Bc4 Bc5 O-O
-    engine.processUserInput("e2e4")
-    engine.processUserInput("e7e5")
-    engine.processUserInput("g1f3")
-    engine.processUserInput("b8c6")
-    engine.processUserInput("f1c4")
-    engine.processUserInput("f8c5")
-    engine.processUserInput("e1g1")  // white castles kingside
-    cap.events.clear()
-    engine.undo()
-    val evt = cap.events.last.asInstanceOf[MoveUndoneEvent]
-    evt.pgnNotation shouldBe "O-O"
-
-  test("redo emits MoveRedoneEvent with from/to squares and capturedPiece"):
-    val engine = new GameEngine()
-    val cap    = new EventCapture()
-    engine.subscribe(cap)
-    // White builds a capture on the a-file: b4, ... a6, b5, ... h6, bxa6
-    engine.processUserInput("b2b4")
-    engine.processUserInput("a7a6")
-    engine.processUserInput("b4b5")
-    engine.processUserInput("h7h6")
-    engine.processUserInput("b5a6")  // white pawn captures black pawn
-    engine.undo()
-    cap.events.clear()
-    engine.redo()
-    val evt = cap.events.last.asInstanceOf[MoveRedoneEvent]
-    evt.fromSquare shouldBe "b5"
-    evt.toSquare   shouldBe "a6"
-    evt.capturedPiece.isDefined shouldBe true
-
-  test("loadPgn: clears previous game state before loading"):
-    val engine = new GameEngine()
-    engine.processUserInput("e2e4")
-    val pgn = "[Event \"T\"]\n\n1. d4 d5\n"
-    engine.loadPgn(pgn) shouldBe Right(())
-    // First move should be d4, not e4
-    engine.history.moves.head.to shouldBe de.nowchess.api.board.Square(
-      de.nowchess.api.board.File.D, de.nowchess.api.board.Rank.R4
-    )

modules/core/src/test/scala/de/nowchess/chess/engine/GameEngineNotationTest.scala

@@ -0,0 +1,127 @@
+package de.nowchess.chess.engine
+
+import de.nowchess.api.board.{Board, Color, File, Rank, Square}
+import de.nowchess.api.game.GameContext
+import de.nowchess.api.move.PromotionPiece
+import de.nowchess.io.fen.FenParser
+import de.nowchess.chess.observer.*
+import org.scalatest.funsuite.AnyFunSuite
+import org.scalatest.matchers.should.Matchers
+
+/** Tests that exercise moveToPgn branches not covered by other test files:
+ *  - CastleQueenside (line 223)
+ *  - EnPassant notation (lines 224-225) and computeCaptured EnPassant (lines 254-255)
+ *  - Promotion(Bishop) notation (line 230)
+ *  - King normal move notation (line 246)
+ */
+class GameEngineNotationTest extends AnyFunSuite with Matchers:
+
+  private def captureEvents(engine: GameEngine): collection.mutable.ListBuffer[GameEvent] =
+    val buf = collection.mutable.ListBuffer[GameEvent]()
+    engine.subscribe(new Observer { def onGameEvent(e: GameEvent): Unit = buf += e })
+    buf
+
+  // ── Queenside castling (line 223) ──────────────────────────────────
+
+  test("undo after queenside castling emits MoveUndoneEvent with O-O-O notation"):
+    // FEN: White king on e1, queenside rook on a1, b1/c1/d1 clear, black king away
+    val board = FenParser.parseBoard("k7/8/8/8/8/8/8/R3K3").get
+    // Castling rights: white queen-side only (no king-side rook present)
+    val castlingRights = de.nowchess.api.board.CastlingRights(
+      whiteKingSide  = false,
+      whiteQueenSide = true,
+      blackKingSide  = false,
+      blackQueenSide = false
+    )
+    val ctx = GameContext.initial
+      .withBoard(board)
+      .withTurn(Color.White)
+      .withCastlingRights(castlingRights)
+
+    val engine = new GameEngine(ctx)
+    val events = captureEvents(engine)
+
+    // White castles queenside: e1c1
+    engine.processUserInput("e1c1")
+    events.exists(_.isInstanceOf[MoveExecutedEvent]) should be (true)
+
+    events.clear()
+    engine.undo()
+
+    val evt = events.collect { case e: MoveUndoneEvent => e }.head
+    evt.pgnNotation shouldBe "O-O-O"
+
+  // ── En passant notation + computeCaptured (lines 224-225, 254-255) ─
+
+  test("undo after en passant emits MoveUndoneEvent with file-x-destination notation"):
+    // White pawn on e5, black pawn on d5 (just double-pushed), en passant square d6
+    val board = FenParser.parseBoard("k7/8/8/3pP3/8/8/8/7K").get
+    val epSquare = Square.fromAlgebraic("d6")
+    val ctx = GameContext.initial
+      .withBoard(board)
+      .withTurn(Color.White)
+      .withEnPassantSquare(epSquare)
+      .withCastlingRights(de.nowchess.api.board.CastlingRights(false, false, false, false))
+
+    val engine = new GameEngine(ctx)
+    val events = captureEvents(engine)
+
+    // White pawn on e5 captures en passant to d6
+    engine.processUserInput("e5d6")
+    events.exists(_.isInstanceOf[MoveExecutedEvent]) should be (true)
+
+    // Verify the captured pawn was found (computeCaptured EnPassant branch)
+    val moveEvt = events.collect { case e: MoveExecutedEvent => e }.head
+    moveEvt.capturedPiece shouldBe defined
+    moveEvt.capturedPiece.get should include ("Black")
+
+    events.clear()
+    engine.undo()
+
+    val undoEvt = events.collect { case e: MoveUndoneEvent => e }.head
+    undoEvt.pgnNotation shouldBe "exd6"
+
+  // ── Bishop underpromotion notation (line 230) ──────────────────────
+
+  test("undo after bishop underpromotion emits MoveUndoneEvent with =B notation"):
+    val board = FenParser.parseBoard("8/4P3/8/8/8/8/k7/7K").get
+    val ctx = GameContext.initial
+      .withBoard(board)
+      .withTurn(Color.White)
+      .withCastlingRights(de.nowchess.api.board.CastlingRights(false, false, false, false))
+
+    val engine = new GameEngine(ctx)
+    val events = captureEvents(engine)
+
+    engine.processUserInput("e7e8")
+    engine.completePromotion(PromotionPiece.Bishop)
+
+    events.clear()
+    engine.undo()
+
+    val evt = events.collect { case e: MoveUndoneEvent => e }.head
+    evt.pgnNotation shouldBe "e8=B"
+
+  // ── King normal move notation (line 246) ───────────────────────────
+
+  test("undo after king move emits MoveUndoneEvent with K notation"):
+    // White king on e1, no castling rights, black king far away
+    val board = FenParser.parseBoard("k7/8/8/8/8/8/8/4K3").get
+    val ctx = GameContext.initial
+      .withBoard(board)
+      .withTurn(Color.White)
+      .withCastlingRights(de.nowchess.api.board.CastlingRights(false, false, false, false))
+
+    val engine = new GameEngine(ctx)
+    val events = captureEvents(engine)
+
+    // King moves e1 -> f1
+    engine.processUserInput("e1f1")
+    events.exists(_.isInstanceOf[MoveExecutedEvent]) should be (true)
+
+    events.clear()
+    engine.undo()
+
+    val evt = events.collect { case e: MoveUndoneEvent => e }.head
+    evt.pgnNotation should startWith ("K")
+    evt.pgnNotation should include ("f1")

modules/core/src/test/scala/de/nowchess/chess/engine/GameEngineOutcomesTest.scala

@@ -0,0 +1,176 @@
+package de.nowchess.chess.engine
+
+import de.nowchess.api.board.Color
+import de.nowchess.chess.observer.*
+import org.scalatest.funsuite.AnyFunSuite
+import org.scalatest.matchers.should.Matchers
+
+class GameEngineOutcomesTest extends AnyFunSuite with Matchers:
+
+  // ── Checkmate ───────────────────────────────────────────────────
+
+  test("checkmate ends game with CheckmateEvent"):
+    val engine = EngineTestHelpers.makeEngine()
+    val observer = new EngineTestHelpers.MockObserver()
+    engine.subscribe(observer)
+
+    engine.processUserInput("f2f3")
+    engine.processUserInput("e7e5")
+    engine.processUserInput("g2g4")
+    observer.clear()
+
+    engine.processUserInput("d8h4")
+
+    observer.hasEvent[CheckmateEvent] shouldBe true
+
+  test("checkmate with white winner"):
+    val engine = EngineTestHelpers.makeEngine()
+    val observer = new EngineTestHelpers.MockObserver()
+    engine.subscribe(observer)
+
+    engine.processUserInput("e2e4")
+    engine.processUserInput("e7e5")
+    engine.processUserInput("f1c4")
+    engine.processUserInput("b8c6")
+    engine.processUserInput("d1h5")
+    engine.processUserInput("g8f6")
+    observer.clear()
+
+    engine.processUserInput("h5f7")
+
+    val evt = observer.getEvent[CheckmateEvent]
+    evt.isDefined shouldBe true
+    evt.get.winner shouldBe Color.White
+
+  // ── Stalemate ───────────────────────────────────────────────────
+
+  test("stalemate ends game with StalemateEvent"):
+    val engine = EngineTestHelpers.makeEngine()
+    val observer = new EngineTestHelpers.MockObserver()
+    engine.subscribe(observer)
+
+    val moves = List(
+      "e2e3", "a7a5",
+      "d1h5", "a8a6",
+      "h5a5", "h7h5",
+      "h2h4", "a6h6",
+      "a5c7", "f7f6",
+      "c7d7", "e8f7",
+      "d7b7", "d8d3",
+      "b7b8", "d3h7",
+      "b8c8", "f7g6"
+    )
+    moves.foreach(engine.processUserInput)
+    observer.clear()
+
+    engine.processUserInput("c8e6")
+
+    observer.hasEvent[StalemateEvent] shouldBe true
+
+  test("stalemate when king has no moves and no pieces"):
+    val engine = EngineTestHelpers.makeEngine()
+    val observer = new EngineTestHelpers.MockObserver()
+    engine.subscribe(observer)
+
+    val moves = List(
+      "e2e3", "a7a5",
+      "d1h5", "a8a6",
+      "h5a5", "h7h5",
+      "h2h4", "a6h6",
+      "a5c7", "f7f6",
+      "c7d7", "e8f7",
+      "d7b7", "d8d3",
+      "b7b8", "d3h7",
+      "b8c8", "f7g6",
+      "c8e6"
+    )
+
+    moves.foreach(engine.processUserInput)
+
+    observer.hasEvent[StalemateEvent] shouldBe true
+    engine.turn shouldBe Color.White
+
+  // ── Check detection ────────────────────────────────────────────
+
+  test("check detected after move puts king in check"):
+    val engine = EngineTestHelpers.makeEngine()
+    val observer = new EngineTestHelpers.MockObserver()
+    engine.subscribe(observer)
+
+    engine.processUserInput("e2e4")
+    engine.processUserInput("e7e5")
+    engine.processUserInput("f1c4")
+    engine.processUserInput("g8f6")
+    observer.clear()
+
+    engine.processUserInput("c4f7")
+
+    observer.hasEvent[CheckDetectedEvent] shouldBe true
+
+  test("check by knight"):
+    val engine = EngineTestHelpers.makeEngine()
+    val observer = new EngineTestHelpers.MockObserver()
+    engine.subscribe(observer)
+
+    EngineTestHelpers.loadFen(engine, "8/4k3/8/8/3N4/8/8/4K3 w - - 0 1")
+    observer.clear()
+
+    engine.processUserInput("d4f5")
+
+    observer.hasEvent[CheckDetectedEvent] shouldBe true
+
+  // ── Fifty-move rule ────────────────────────────────────────────
+
+  test("fifty-move rule triggers when half-move clock reaches 100"):
+    val engine = EngineTestHelpers.makeEngine()
+    val observer = new EngineTestHelpers.MockObserver()
+    engine.subscribe(observer)
+
+    EngineTestHelpers.loadFen(engine, "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 99 1")
+    observer.clear()
+
+    engine.processUserInput("g1f3")
+
+    observer.hasEvent[FiftyMoveRuleAvailableEvent] shouldBe true
+
+  test("fifty-move rule clock resets on pawn move"):
+    val engine = EngineTestHelpers.makeEngine()
+
+    EngineTestHelpers.loadFen(engine, "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 50 1")
+    engine.processUserInput("a2a3")
+
+    // Clock should reset to 0 after pawn move
+    engine.context.halfMoveClock shouldBe 0
+
+  test("fifty-move rule clock resets on capture"):
+    val engine = EngineTestHelpers.makeEngine()
+
+    // FEN: white pawn on e5, black pawn on d6, clock at 50
+    EngineTestHelpers.loadFen(engine, "4k3/8/3p4/4P3/8/8/8/4K3 w - - 50 1")
+    engine.processUserInput("e5d6")
+
+    // Clock should reset to 0 after capture
+    engine.context.halfMoveClock shouldBe 0
+
+  // ── Draw claim ────────────────────────────────────────────────
+
+  test("draw can be claimed when fifty-move rule is available"):
+    val engine = EngineTestHelpers.makeEngine()
+    val observer = new EngineTestHelpers.MockObserver()
+    engine.subscribe(observer)
+
+    EngineTestHelpers.loadFen(engine, "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 100 1")
+    observer.clear()
+
+    engine.processUserInput("draw")
+
+    observer.hasEvent[DrawClaimedEvent] shouldBe true
+
+  test("draw cannot be claimed when not available"):
+    val engine = EngineTestHelpers.makeEngine()
+    val observer = new EngineTestHelpers.MockObserver()
+    engine.subscribe(observer)
+
+    engine.processUserInput("draw")
+
+    observer.hasEvent[InvalidMoveEvent] shouldBe true

modules/core/src/test/scala/de/nowchess/chess/engine/GameEnginePromotionTest.scala

@@ -1,10 +1,12 @@
 package de.nowchess.chess.engine
 
 import de.nowchess.api.board.{Board, Color, File, Piece, PieceType, Rank, Square}
-import de.nowchess.api.move.PromotionPiece
-import de.nowchess.chess.logic.GameHistory
-import de.nowchess.chess.notation.FenParser
+import de.nowchess.api.game.GameContext
+import de.nowchess.api.move.{Move, MoveType, PromotionPiece}
+import de.nowchess.io.fen.FenParser
 import de.nowchess.chess.observer.*
+import de.nowchess.rules.RuleSet
+import de.nowchess.rules.sets.DefaultRules
 import org.scalatest.funsuite.AnyFunSuite
 import org.scalatest.matchers.should.Matchers
 
@@ -17,9 +19,12 @@ class GameEnginePromotionTest extends AnyFunSuite with Matchers:
     engine.subscribe(new Observer { def onGameEvent(e: GameEvent): Unit = events += e })
     events
 
+  private def engineWith(board: Board, turn: Color = Color.White): GameEngine =
+    new GameEngine(initialContext = GameContext.initial.withBoard(board).withTurn(turn))
+
   test("processUserInput fires PromotionRequiredEvent when pawn reaches back rank") {
     val promotionBoard = FenParser.parseBoard("8/4P3/4k3/8/8/8/8/8").get
-    val engine = new GameEngine(initialBoard = promotionBoard)
+    val engine = engineWith(promotionBoard)
     val events = captureEvents(engine)
 
     engine.processUserInput("e7e8")
@@ -30,7 +35,7 @@ class GameEnginePromotionTest extends AnyFunSuite with Matchers:
 
   test("isPendingPromotion is true after PromotionRequired input") {
     val promotionBoard = FenParser.parseBoard("8/4P3/4k3/8/8/8/8/8").get
-    val engine = new GameEngine(initialBoard = promotionBoard)
+    val engine = engineWith(promotionBoard)
     captureEvents(engine)
 
     engine.processUserInput("e7e8")
@@ -45,7 +50,7 @@ class GameEnginePromotionTest extends AnyFunSuite with Matchers:
 
   test("completePromotion fires MoveExecutedEvent with promoted piece") {
     val promotionBoard = FenParser.parseBoard("8/4P3/4k3/8/8/8/8/8").get
-    val engine = new GameEngine(initialBoard = promotionBoard)
+    val engine = engineWith(promotionBoard)
     val events = captureEvents(engine)
 
     engine.processUserInput("e7e8")
@@ -54,13 +59,13 @@ class GameEnginePromotionTest extends AnyFunSuite with Matchers:
     engine.isPendingPromotion should be (false)
     engine.board.pieceAt(sq(File.E, Rank.R8)) should be (Some(Piece(Color.White, PieceType.Queen)))
     engine.board.pieceAt(sq(File.E, Rank.R7)) should be (None)
-    engine.history.moves.head.promotionPiece should be (Some(PromotionPiece.Queen))
+    engine.context.moves.last.moveType shouldBe MoveType.Promotion(PromotionPiece.Queen)
     events.exists(_.isInstanceOf[MoveExecutedEvent]) should be (true)
   }
 
   test("completePromotion with rook underpromotion") {
     val promotionBoard = FenParser.parseBoard("8/4P3/4k3/8/8/8/8/8").get
-    val engine = new GameEngine(initialBoard = promotionBoard)
+    val engine = engineWith(promotionBoard)
     captureEvents(engine)
 
     engine.processUserInput("e7e8")
@@ -81,7 +86,7 @@ class GameEnginePromotionTest extends AnyFunSuite with Matchers:
 
   test("completePromotion fires CheckDetectedEvent when promotion gives check") {
     val promotionBoard = FenParser.parseBoard("3k4/4P3/8/8/8/8/8/8").get
-    val engine = new GameEngine(initialBoard = promotionBoard)
+    val engine = engineWith(promotionBoard)
     val events = captureEvents(engine)
 
     engine.processUserInput("e7e8")
@@ -91,9 +96,8 @@ class GameEnginePromotionTest extends AnyFunSuite with Matchers:
   }
 
   test("completePromotion results in Moved when promotion doesn't give check") {
-    // White pawn on e7, black king on a2 (far away, not in check after promotion)
     val board = FenParser.parseBoard("8/4P3/8/8/8/8/k7/8").get
-    val engine = new GameEngine(initialBoard = board)
+    val engine = engineWith(board)
     val events = captureEvents(engine)
 
     engine.processUserInput("e7e8")
@@ -106,10 +110,8 @@ class GameEnginePromotionTest extends AnyFunSuite with Matchers:
   }
 
   test("completePromotion results in Checkmate when promotion delivers checkmate") {
-    // Black king on a8, white king on b6, white pawn on h7
-    // h7->h8=Q delivers checkmate
     val board = FenParser.parseBoard("k7/7P/1K6/8/8/8/8/8").get
-    val engine = new GameEngine(initialBoard = board)
+    val engine = engineWith(board)
     val events = captureEvents(engine)
 
     engine.processUserInput("h7h8")
@@ -120,10 +122,8 @@ class GameEnginePromotionTest extends AnyFunSuite with Matchers:
   }
 
   test("completePromotion results in Stalemate when promotion creates stalemate") {
-    // Black king on a8, white pawn on b7, white bishop on c7, white king on b6
-    // b7->b8=N: no check; Ka8 has no legal moves -> stalemate
     val board = FenParser.parseBoard("k7/1PB5/1K6/8/8/8/8/8").get
-    val engine = new GameEngine(initialBoard = board)
+    val engine = engineWith(board)
     val events = captureEvents(engine)
 
     engine.processUserInput("b7b8")
@@ -134,10 +134,8 @@ class GameEnginePromotionTest extends AnyFunSuite with Matchers:
   }
 
   test("completePromotion with black pawn promotion results in Moved") {
-    // Black pawn e2, white king h3 (not on rank 1 or file e), black king a8
-    // e2->e1=Q: queen on e1 does not attack h3 -> normal Moved
     val board = FenParser.parseBoard("k7/8/8/8/8/7K/4p3/8").get
-    val engine = new GameEngine(initialBoard = board, initialTurn = Color.Black)
+    val engine = engineWith(board, Color.Black)
     val events = captureEvents(engine)
 
     engine.processUserInput("e2e1")
@@ -149,19 +147,51 @@ class GameEnginePromotionTest extends AnyFunSuite with Matchers:
     events.exists(_.isInstanceOf[CheckDetectedEvent]) should be (false)
   }
 
-  test("completePromotion catch-all fires InvalidMoveEvent for unexpected MoveResult") {
-    // Inject a function that returns an unexpected MoveResult to hit the catch-all case
+  test("completePromotion fires InvalidMoveEvent when legalMoves returns only Normal moves to back rank") {
+    // Custom RuleSet: delegates all methods to StandardRules except legalMoves,
+    // which strips Promotion move types and returns Normal moves instead.
+    // This makes completePromotion unable to find Move(from, to, Promotion(Queen)),
+    // triggering the "Error completing promotion." branch.
+    val delegatingRuleSet: RuleSet = new RuleSet:
+      def candidateMoves(context: GameContext)(square: Square): List[Move] =
+        DefaultRules.candidateMoves(context)(square)
+      def legalMoves(context: GameContext)(square: Square): List[Move] =
+        DefaultRules.legalMoves(context)(square).map { m =>
+          m.moveType match
+            case MoveType.Promotion(_) => Move(m.from, m.to, MoveType.Normal())
+            case _                     => m
+        }
+      def allLegalMoves(context: GameContext): List[Move] =
+        DefaultRules.allLegalMoves(context)
+      def isCheck(context: GameContext): Boolean =
+        DefaultRules.isCheck(context)
+      def isCheckmate(context: GameContext): Boolean =
+        DefaultRules.isCheckmate(context)
+      def isStalemate(context: GameContext): Boolean =
+        DefaultRules.isStalemate(context)
+      def isInsufficientMaterial(context: GameContext): Boolean =
+        DefaultRules.isInsufficientMaterial(context)
+      def isFiftyMoveRule(context: GameContext): Boolean =
+        DefaultRules.isFiftyMoveRule(context)
+      def applyMove(context: GameContext)(move: Move): GameContext =
+        DefaultRules.applyMove(context)(move)
+
     val promotionBoard = FenParser.parseBoard("8/4P3/4k3/8/8/8/8/8").get
-    val stubFn: (de.nowchess.api.board.Board, de.nowchess.chess.logic.GameHistory, Square, Square, PromotionPiece, Color) => de.nowchess.chess.controller.MoveResult =
-      (_, _, _, _, _, _) => de.nowchess.chess.controller.MoveResult.NoPiece
-    val engine = new GameEngine(initialBoard = promotionBoard, completePromotionFn = stubFn)
+    val initialCtx = GameContext.initial.withBoard(promotionBoard).withTurn(Color.White)
+    val engine = new GameEngine(initialCtx, delegatingRuleSet)
     val events = captureEvents(engine)
 
+    // isPromotionMove will fire because pawn is on rank 7 heading to rank 8,
+    // and legalMoves returns Normal candidates (still non-empty) — sets pendingPromotion
     engine.processUserInput("e7e8")
     engine.isPendingPromotion should be (true)
 
+    // completePromotion looks for Move(e7, e8, Promotion(Queen)) in legalMoves,
+    // but only Normal moves exist → fires InvalidMoveEvent
     engine.completePromotion(PromotionPiece.Queen)
 
     engine.isPendingPromotion should be (false)
     events.exists(_.isInstanceOf[InvalidMoveEvent]) should be (true)
+    val invalidEvt = events.collect { case e: InvalidMoveEvent => e }.last
+    invalidEvt.reason should include ("Error completing promotion")
   }

modules/core/src/test/scala/de/nowchess/chess/engine/GameEngineScenarioTest.scala

@@ -0,0 +1,132 @@
+package de.nowchess.chess.engine
+
+import de.nowchess.api.board.{Color, File, Rank, Square, Piece}
+import de.nowchess.api.game.GameContext
+import de.nowchess.chess.observer.*
+import de.nowchess.io.fen.FenParser
+import org.scalatest.funsuite.AnyFunSuite
+import org.scalatest.matchers.should.Matchers
+import scala.collection.mutable
+
+class GameEngineScenarioTest extends AnyFunSuite with Matchers:
+
+  // ── Observer wiring ────────────────────────────────────────────
+
+  test("observer subscribe and unsubscribe behavior"):
+    val engine = EngineTestHelpers.makeEngine()
+    val observer = new EngineTestHelpers.MockObserver()
+    engine.subscribe(observer)
+    engine.processUserInput("e2e4")
+    observer.hasEvent[MoveExecutedEvent] shouldBe true
+    val countBeforeUnsubscribe = observer.eventCount
+    engine.subscribe(observer)
+    engine.unsubscribe(observer)
+    engine.processUserInput("e2e4")
+    observer.eventCount shouldBe countBeforeUnsubscribe
+
+  // ── Initial state ──────────────────────────────────────────────
+
+  test("initial engine state is standard"):
+    val engine = EngineTestHelpers.makeEngine()
+    engine.board.pieceAt(Square(File.E, Rank.R1)) shouldBe Some(Piece.WhiteKing)
+    engine.turn shouldBe Color.White
+
+  // ── Quit command ──────────────────────────────────────────────
+
+  test("quit aliases and reset keep engine responsive"):
+    val engine = EngineTestHelpers.makeEngine()
+    engine.processUserInput("quit")
+    engine.processUserInput("q")
+    engine.processUserInput("e2e4")
+
+    engine.reset()
+
+    engine.board.pieceAt(Square(File.E, Rank.R2)) shouldBe Some(Piece.WhitePawn)
+    engine.turn shouldBe Color.White
+
+  // ── Turn toggling ──────────────────────────────────────────────
+
+  test("turn toggles across valid move sequence"):
+    val engine = EngineTestHelpers.makeEngine()
+    engine.processUserInput("e2e4")
+    engine.turn shouldBe Color.Black
+    engine.processUserInput("e7e5")
+    engine.turn shouldBe Color.White
+
+  // ── Invalid moves (minimal) ────────────────────────────────────
+
+  test("invalid move forms trigger InvalidMoveEvent and keep turn where relevant"):
+    val engine = EngineTestHelpers.makeEngine()
+    val observer = new EngineTestHelpers.MockObserver()
+    engine.subscribe(observer)
+
+    engine.processUserInput("h3h4")
+
+    observer.hasEvent[InvalidMoveEvent] shouldBe true
+    engine.turn shouldBe Color.White  // turn unchanged
+
+    engine.processUserInput("e7e5")  // try to move black pawn on white's turn
+
+    observer.hasEvent[InvalidMoveEvent] shouldBe true
+
+    engine.processUserInput("e2e4")
+    engine.processUserInput("e5e4")  // pawn backward
+
+    observer.hasEvent[InvalidMoveEvent] shouldBe true
+
+  // ── Undo/Redo ────────────────────────────────────────────────
+
+  test("undo redo success and empty-history failures"):
+    val engine = EngineTestHelpers.makeEngine()
+    val observer = new EngineTestHelpers.MockObserver()
+    engine.subscribe(observer)
+
+    engine.undo()
+    observer.hasEvent[InvalidMoveEvent] shouldBe true
+    observer.clear()
+
+    engine.processUserInput("e2e4")
+
+    engine.undo()
+
+    engine.board.pieceAt(Square(File.E, Rank.R2)) shouldBe Some(Piece.WhitePawn)
+    engine.turn shouldBe Color.White
+
+    engine.redo()
+
+    engine.board.pieceAt(Square(File.E, Rank.R4)) shouldBe Some(Piece.WhitePawn)
+    engine.turn shouldBe Color.Black
+    observer.clear()
+    engine.redo()
+    observer.hasEvent[InvalidMoveEvent] shouldBe true
+
+  // ── Fifty-move rule ────────────────────────────────────────────
+
+  test("fifty-move event and draw claim success/failure"):
+    val engine = EngineTestHelpers.makeEngine()
+    val observer = new EngineTestHelpers.MockObserver()
+    engine.subscribe(observer)
+
+    // Load FEN with half-move clock at 99
+    EngineTestHelpers.loadFen(engine, "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 99 1")
+    observer.clear()
+
+    // Use a legal non-pawn non-capture move so the clock increments to 100.
+    engine.processUserInput("g1f3")
+
+    observer.hasEvent[FiftyMoveRuleAvailableEvent] shouldBe true
+
+    // Load position with sufficient move history for draw claim
+    EngineTestHelpers.loadFen(engine, "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 100 1")
+    observer.clear()
+
+    engine.processUserInput("draw")
+
+    observer.hasEvent[DrawClaimedEvent] shouldBe true
+
+    // Initial position has no draw available
+    observer.clear()
+    engine.reset()
+    engine.processUserInput("draw")
+
+    observer.hasEvent[InvalidMoveEvent] shouldBe true

modules/core/src/test/scala/de/nowchess/chess/engine/GameEngineSpecialMovesTest.scala

@@ -0,0 +1,209 @@
+package de.nowchess.chess.engine
+
+import de.nowchess.api.board.Color
+import de.nowchess.api.move.PromotionPiece
+import de.nowchess.chess.observer.*
+import org.scalatest.funsuite.AnyFunSuite
+import org.scalatest.matchers.should.Matchers
+
+class GameEngineSpecialMovesTest extends AnyFunSuite with Matchers:
+
+  // ── Castling ────────────────────────────────────────────────────
+
+  test("kingside castling executes successfully"):
+    val engine = EngineTestHelpers.makeEngine()
+    val observer = new EngineTestHelpers.MockObserver()
+    engine.subscribe(observer)
+
+    // FEN: white king on e1, rook on h1, f1/g1 clear
+    EngineTestHelpers.loadFen(engine, "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQK2R w KQkq - 0 1")
+    observer.clear()
+
+    engine.processUserInput("e1g1")
+
+    observer.hasEvent[MoveExecutedEvent] shouldBe true
+    engine.turn shouldBe Color.Black
+
+  test("queenside castling executes successfully"):
+    val engine = EngineTestHelpers.makeEngine()
+    val observer = new EngineTestHelpers.MockObserver()
+    engine.subscribe(observer)
+
+    // FEN: white king on e1, rook on a1, b1/c1/d1 clear
+    EngineTestHelpers.loadFen(engine, "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/R3K2R w KQkq - 0 1")
+    observer.clear()
+
+    engine.processUserInput("e1c1")
+
+    observer.hasEvent[MoveExecutedEvent] shouldBe true
+    engine.turn shouldBe Color.Black
+
+  test("undo castling emits PGN notation"):
+    val engine = EngineTestHelpers.makeEngine()
+    val observer = new EngineTestHelpers.MockObserver()
+    engine.subscribe(observer)
+
+    EngineTestHelpers.loadFen(engine, "k7/8/8/8/8/8/8/R3K3 w Q - 0 1")
+    observer.clear()
+
+    engine.processUserInput("e1c1")
+    observer.clear()
+    engine.undo()
+
+    val evt = observer.getEvent[MoveUndoneEvent]
+    evt.isDefined shouldBe true
+    evt.get.pgnNotation shouldBe "O-O-O"
+
+  // ── En passant ──────────────────────────────────────────────────
+
+  test("en passant capture executes successfully"):
+    val engine = EngineTestHelpers.makeEngine()
+    val observer = new EngineTestHelpers.MockObserver()
+    engine.subscribe(observer)
+
+    // FEN: white pawn e5, black pawn d5 (just pushed), en passant square d6
+    EngineTestHelpers.loadFen(engine, "k7/8/8/3pP3/8/8/8/7K w - d6 0 1")
+    observer.clear()
+
+    engine.processUserInput("e5d6")
+
+    observer.hasEvent[MoveExecutedEvent] shouldBe true
+    val moveEvt = observer.getEvent[MoveExecutedEvent]
+    moveEvt.get.capturedPiece shouldBe defined  // pawn was captured
+
+  test("undo en passant emits file-x-destination notation"):
+    val engine = EngineTestHelpers.makeEngine()
+    val observer = new EngineTestHelpers.MockObserver()
+    engine.subscribe(observer)
+
+    EngineTestHelpers.loadFen(engine, "k7/8/8/3pP3/8/8/8/7K w - d6 0 1")
+    observer.clear()
+
+    engine.processUserInput("e5d6")
+    observer.clear()
+    engine.undo()
+
+    val evt = observer.getEvent[MoveUndoneEvent]
+    evt.isDefined shouldBe true
+    evt.get.pgnNotation shouldBe "exd6"
+
+  // ── Pawn promotion ─────────────────────────────────────────────
+
+  test("pawn reaching back rank requires promotion"):
+    val engine = EngineTestHelpers.makeEngine()
+    val observer = new EngineTestHelpers.MockObserver()
+    engine.subscribe(observer)
+
+    EngineTestHelpers.loadFen(engine, "8/4P3/4k3/8/8/8/8/8 w - - 0 1")
+    observer.clear()
+
+    engine.processUserInput("e7e8")
+
+    observer.hasEvent[PromotionRequiredEvent] shouldBe true
+    engine.isPendingPromotion shouldBe true
+
+  test("completePromotion to Queen executes move"):
+    val engine = EngineTestHelpers.makeEngine()
+
+    EngineTestHelpers.loadFen(engine, "8/4P3/8/8/8/8/k7/8 w - - 0 1")
+    engine.processUserInput("e7e8")
+    engine.completePromotion(PromotionPiece.Queen)
+
+    engine.isPendingPromotion shouldBe false
+    engine.turn shouldBe Color.Black
+
+  test("completePromotion to Rook executes move"):
+    val engine = EngineTestHelpers.makeEngine()
+
+    EngineTestHelpers.loadFen(engine, "8/4P3/8/8/8/8/k7/8 w - - 0 1")
+    engine.processUserInput("e7e8")
+    engine.completePromotion(PromotionPiece.Rook)
+
+    engine.isPendingPromotion shouldBe false
+    engine.turn shouldBe Color.Black
+
+  test("completePromotion to Bishop executes move"):
+    val engine = EngineTestHelpers.makeEngine()
+
+    EngineTestHelpers.loadFen(engine, "8/4P3/8/8/8/8/k7/8 w - - 0 1")
+    engine.processUserInput("e7e8")
+    engine.completePromotion(PromotionPiece.Bishop)
+
+    engine.isPendingPromotion shouldBe false
+    engine.turn shouldBe Color.Black
+
+  test("completePromotion to Knight executes move"):
+    val engine = EngineTestHelpers.makeEngine()
+
+    EngineTestHelpers.loadFen(engine, "8/4P3/8/8/8/8/k7/8 w - - 0 1")
+    engine.processUserInput("e7e8")
+    engine.completePromotion(PromotionPiece.Knight)
+
+    engine.isPendingPromotion shouldBe false
+    engine.turn shouldBe Color.Black
+
+  test("promotion to Queen with discovered check emits CheckDetectedEvent"):
+    val engine = EngineTestHelpers.makeEngine()
+    val observer = new EngineTestHelpers.MockObserver()
+    engine.subscribe(observer)
+
+    // FEN: white pawn e7, black king e6, white king e1
+    EngineTestHelpers.loadFen(engine, "8/4P3/4k3/8/8/8/8/4K3 w - - 0 1")
+    observer.clear()
+
+    engine.processUserInput("e7e8")
+    engine.completePromotion(PromotionPiece.Queen)
+
+    observer.hasEvent[CheckDetectedEvent] shouldBe true
+
+  test("promotion to Queen with checkmate emits CheckmateEvent"):
+    val engine = EngineTestHelpers.makeEngine()
+    val observer = new EngineTestHelpers.MockObserver()
+    engine.subscribe(observer)
+
+    // FEN: known promotion-mate pattern
+    EngineTestHelpers.loadFen(engine, "k7/7P/1K6/8/8/8/8/8 w - - 0 1")
+    observer.clear()
+
+    engine.processUserInput("h7h8")
+    engine.completePromotion(PromotionPiece.Queen)
+
+    observer.hasEvent[CheckmateEvent] shouldBe true
+
+  test("undo promotion emits notation with piece suffix"):
+    val engine = EngineTestHelpers.makeEngine()
+    val observer = new EngineTestHelpers.MockObserver()
+    engine.subscribe(observer)
+
+    EngineTestHelpers.loadFen(engine, "8/4P3/4k3/8/8/8/8/8 w - - 0 1")
+    engine.processUserInput("e7e8")
+    engine.completePromotion(PromotionPiece.Bishop)
+    observer.clear()
+
+    engine.undo()
+
+    val evt = observer.getEvent[MoveUndoneEvent]
+    evt.isDefined shouldBe true
+    evt.get.pgnNotation shouldBe "e8=B"
+
+  test("black pawn promotion executes"):
+    val engine = EngineTestHelpers.makeEngine()
+
+    EngineTestHelpers.loadFen(engine, "8/8/8/8/8/4k3/4p3/8 b - - 0 1")
+    engine.processUserInput("e2e1")
+
+    engine.isPendingPromotion shouldBe true
+    engine.completePromotion(PromotionPiece.Queen)
+
+    engine.isPendingPromotion shouldBe false
+    engine.turn shouldBe Color.White
+
+  // ── Promotion capturing ────────────────────────────────────────
+
+  test("pawn promotion with capture executes"):
+    val engine = EngineTestHelpers.makeEngine()
+
+    EngineTestHelpers.loadFen(engine, "3n4/4P3/4k3/8/8/8/8/4K3 w - - 0 1")
+    engine.processUserInput("e7d8")
+
+    engine.isPendingPromotion shouldBe true

modules/core/src/test/scala/de/nowchess/chess/engine/GameEngineTest.scala

@@ -1,351 +0,0 @@
-package de.nowchess.chess.engine
-
-import scala.collection.mutable
-import de.nowchess.api.board.{Board, Color}
-import de.nowchess.chess.logic.GameHistory
-import de.nowchess.chess.observer.{Observer, GameEvent, MoveExecutedEvent, CheckDetectedEvent, BoardResetEvent, InvalidMoveEvent, FiftyMoveRuleAvailableEvent, DrawClaimedEvent, MoveUndoneEvent, MoveRedoneEvent}
-import org.scalatest.funsuite.AnyFunSuite
-import org.scalatest.matchers.should.Matchers
-
-class GameEngineTest extends AnyFunSuite with Matchers:
-
-  test("GameEngine starts with initial board state"):
-    val engine = new GameEngine()
-    engine.board shouldBe Board.initial
-    engine.history shouldBe GameHistory.empty
-    engine.turn shouldBe Color.White
-
-  test("GameEngine accepts Observer subscription"):
-    val engine = new GameEngine()
-    val mockObserver = new MockObserver()
-    engine.subscribe(mockObserver)
-    engine.observerCount shouldBe 1
-
-  test("GameEngine notifies observers on valid move"):
-    val engine = new GameEngine()
-    val mockObserver = new MockObserver()
-    engine.subscribe(mockObserver)
-    engine.processUserInput("e2e4")
-    mockObserver.events.size shouldBe 1
-    mockObserver.events.head shouldBe a[MoveExecutedEvent]
-
-  test("GameEngine updates state after valid move"):
-    val engine = new GameEngine()
-    val initialTurn = engine.turn
-    engine.processUserInput("e2e4")
-    engine.turn shouldNot be(initialTurn)
-    engine.turn shouldBe Color.Black
-
-  test("GameEngine notifies observers on invalid move"):
-    val engine = new GameEngine()
-    val mockObserver = new MockObserver()
-    engine.subscribe(mockObserver)
-    engine.processUserInput("invalid_move")
-    mockObserver.events.size shouldBe 1
-
-  test("GameEngine notifies multiple observers"):
-    val engine = new GameEngine()
-    val observer1 = new MockObserver()
-    val observer2 = new MockObserver()
-    engine.subscribe(observer1)
-    engine.subscribe(observer2)
-    engine.processUserInput("e2e4")
-    observer1.events.size shouldBe 1
-    observer2.events.size shouldBe 1
-
-  test("GameEngine allows observer unsubscription"):
-    val engine = new GameEngine()
-    val mockObserver = new MockObserver()
-    engine.subscribe(mockObserver)
-    engine.unsubscribe(mockObserver)
-    engine.observerCount shouldBe 0
-
-  test("GameEngine unsubscribed observer receives no events"):
-    val engine = new GameEngine()
-    val mockObserver = new MockObserver()
-    engine.subscribe(mockObserver)
-    engine.unsubscribe(mockObserver)
-    engine.processUserInput("e2e4")
-    mockObserver.events.size shouldBe 0
-
-  test("GameEngine reset notifies observers and resets state"):
-    val engine = new GameEngine()
-    engine.processUserInput("e2e4")
-    val observer = new MockObserver()
-    engine.subscribe(observer)
-    engine.reset()
-    engine.board shouldBe Board.initial
-    engine.turn shouldBe Color.White
-    observer.events.size shouldBe 1
-
-  test("GameEngine processes sequence of moves"):
-    val engine = new GameEngine()
-    val observer = new MockObserver()
-    engine.subscribe(observer)
-    engine.processUserInput("e2e4")
-    engine.processUserInput("e7e5")
-    observer.events.size shouldBe 2
-    engine.turn shouldBe Color.White
-
-  test("GameEngine is thread-safe for synchronized operations"):
-    val engine = new GameEngine()
-    val observer = new MockObserver()
-    engine.subscribe(observer)
-    val t = new Thread(() => engine.processUserInput("e2e4"))
-    t.start()
-    t.join()
-    observer.events.size shouldBe 1
-
-  test("GameEngine canUndo returns false initially"):
-    val engine = new GameEngine()
-    engine.canUndo shouldBe false
-
-  test("GameEngine canUndo returns true after move"):
-    val engine = new GameEngine()
-    engine.processUserInput("e2e4")
-    engine.canUndo shouldBe true
-
-  test("GameEngine canRedo returns false initially"):
-    val engine = new GameEngine()
-    engine.canRedo shouldBe false
-
-  test("GameEngine undo restores previous state"):
-    val engine = new GameEngine()
-    engine.processUserInput("e2e4")
-    val boardAfterMove = engine.board
-    engine.undo()
-    engine.board shouldBe Board.initial
-    engine.turn shouldBe Color.White
-
-  test("GameEngine undo notifies observers"):
-    val engine = new GameEngine()
-    engine.processUserInput("e2e4")
-    val observer = new MockObserver()
-    engine.subscribe(observer)
-    observer.events.clear()
-    engine.undo()
-    observer.events.size shouldBe 1
-    observer.events.head shouldBe a[MoveUndoneEvent]
-
-  test("GameEngine redo replays undone move"):
-    val engine = new GameEngine()
-    engine.processUserInput("e2e4")
-    val boardAfterMove = engine.board
-    engine.undo()
-    engine.redo()
-    engine.board shouldBe boardAfterMove
-    engine.turn shouldBe Color.Black
-
-  test("GameEngine canUndo false when nothing to undo"):
-    val engine = new GameEngine()
-    engine.canUndo shouldBe false
-    engine.processUserInput("e2e4")
-    engine.undo()
-    engine.canUndo shouldBe false
-
-  test("GameEngine canRedo true after undo"):
-    val engine = new GameEngine()
-    engine.processUserInput("e2e4")
-    engine.undo()
-    engine.canRedo shouldBe true
-
-  test("GameEngine canRedo false after redo"):
-    val engine = new GameEngine()
-    engine.processUserInput("e2e4")
-    engine.undo()
-    engine.redo()
-    engine.canRedo shouldBe false
-
-  test("GameEngine undo on empty history sends invalid event"):
-    val engine = new GameEngine()
-    val observer = new MockObserver()
-    engine.subscribe(observer)
-    engine.undo()
-    observer.events.size shouldBe 1
-    observer.events.head shouldBe a[InvalidMoveEvent]
-
-  test("GameEngine redo on empty redo sends invalid event"):
-    val engine = new GameEngine()
-    val observer = new MockObserver()
-    engine.subscribe(observer)
-    engine.redo()
-    observer.events.size shouldBe 1
-    observer.events.head shouldBe a[InvalidMoveEvent]
-
-  test("GameEngine undo via processUserInput"):
-    val engine = new GameEngine()
-    engine.processUserInput("e2e4")
-    val boardAfterMove = engine.board
-    engine.processUserInput("undo")
-    engine.board shouldBe Board.initial
-
-  test("GameEngine redo via processUserInput"):
-    val engine = new GameEngine()
-    engine.processUserInput("e2e4")
-    val boardAfterMove = engine.board
-    engine.processUserInput("undo")
-    engine.processUserInput("redo")
-    engine.board shouldBe boardAfterMove
-
-  test("GameEngine handles empty input"):
-    val engine = new GameEngine()
-    val observer = new MockObserver()
-    engine.subscribe(observer)
-    engine.processUserInput("")
-    observer.events.size shouldBe 1
-    observer.events.head shouldBe a[InvalidMoveEvent]
-
-  test("GameEngine multiple undo/redo sequence"):
-    val engine = new GameEngine()
-    engine.processUserInput("e2e4")
-    engine.processUserInput("e7e5")
-    engine.processUserInput("g1f3")
-    
-    engine.turn shouldBe Color.Black
-    
-    engine.undo()
-    engine.turn shouldBe Color.White
-    
-    engine.undo()
-    engine.turn shouldBe Color.Black
-    
-    engine.undo()
-    engine.turn shouldBe Color.White
-    engine.board shouldBe Board.initial
-
-  test("GameEngine redo after multiple undos"):
-    val engine = new GameEngine()
-    engine.processUserInput("e2e4")
-    engine.processUserInput("e7e5")
-    engine.processUserInput("g1f3")
-    
-    engine.undo()
-    engine.undo()
-    engine.undo()
-    
-    engine.redo()
-    engine.turn shouldBe Color.Black
-    
-    engine.redo()
-    engine.turn shouldBe Color.White
-    
-    engine.redo()
-    engine.turn shouldBe Color.Black
-
-  test("GameEngine new move after undo clears redo history"):
-    val engine = new GameEngine()
-    engine.processUserInput("e2e4")
-    engine.processUserInput("e7e5")
-    engine.undo()
-    engine.canRedo shouldBe true
-    
-    engine.processUserInput("e7e6")  // Different move
-    engine.canRedo shouldBe false
-
-  test("GameEngine command history tracking"):
-    val engine = new GameEngine()
-    engine.commandHistory.size shouldBe 0
-    
-    engine.processUserInput("e2e4")
-    engine.commandHistory.size shouldBe 1
-    
-    engine.processUserInput("e7e5")
-    engine.commandHistory.size shouldBe 2
-
-  test("GameEngine quit input"):
-    val engine = new GameEngine()
-    val observer = new MockObserver()
-    engine.subscribe(observer)
-    val initialEvents = observer.events.size
-    engine.processUserInput("quit")
-    // quit should not produce an event
-    observer.events.size shouldBe initialEvents
-
-  test("GameEngine quit via q"):
-    val engine = new GameEngine()
-    val observer = new MockObserver()
-    engine.subscribe(observer)
-    val initialEvents = observer.events.size
-    engine.processUserInput("q")
-    observer.events.size shouldBe initialEvents
-  
-  test("GameEngine undo notifies with MoveUndoneEvent after successful undo"):
-    val engine = new GameEngine()
-    engine.processUserInput("e2e4")
-    engine.processUserInput("e7e5")
-    val observer = new MockObserver()
-    engine.subscribe(observer)
-    observer.events.clear()
-
-    engine.undo()
-
-    // Should have received a MoveUndoneEvent on undo
-    observer.events.size should be > 0
-    observer.events.exists(_.isInstanceOf[MoveUndoneEvent]) shouldBe true
-
-  test("GameEngine redo notifies with MoveRedoneEvent after successful redo"):
-    val engine = new GameEngine()
-    engine.processUserInput("e2e4")
-    engine.processUserInput("e7e5")
-    val boardAfterSecondMove = engine.board
-
-    engine.undo()
-    val observer = new MockObserver()
-    engine.subscribe(observer)
-    observer.events.clear()
-
-    engine.redo()
-
-    // Should have received a MoveRedoneEvent for the redo
-    observer.events.size shouldBe 1
-    observer.events.head shouldBe a[MoveRedoneEvent]
-    engine.board shouldBe boardAfterSecondMove
-    engine.turn shouldBe Color.White
-
-  // ──── 50-move rule ───────────────────────────────────────────────────
-
-  test("GameEngine: 'draw' rejected when halfMoveClock < 100"):
-    val engine = new GameEngine()
-    val observer = new MockObserver()
-    engine.subscribe(observer)
-    engine.processUserInput("draw")
-    observer.events.size shouldBe 1
-    observer.events.head shouldBe a[InvalidMoveEvent]
-
-  test("GameEngine: 'draw' accepted and fires DrawClaimedEvent when halfMoveClock >= 100"):
-    val engine = new GameEngine(initialHistory = GameHistory(halfMoveClock = 100))
-    val observer = new MockObserver()
-    engine.subscribe(observer)
-    engine.processUserInput("draw")
-    observer.events.size shouldBe 1
-    observer.events.head shouldBe a[DrawClaimedEvent]
-
-  test("GameEngine: state resets to initial after draw claimed"):
-    val engine = new GameEngine(initialHistory = GameHistory(halfMoveClock = 100))
-    engine.processUserInput("draw")
-    engine.board shouldBe Board.initial
-    engine.history shouldBe GameHistory.empty
-    engine.turn shouldBe Color.White
-
-  test("GameEngine: FiftyMoveRuleAvailableEvent fired when move brings clock to 100"):
-    // Start at clock 99; a knight move (non-pawn, non-capture) increments to 100
-    val engine = new GameEngine(initialHistory = GameHistory(halfMoveClock = 99))
-    val observer = new MockObserver()
-    engine.subscribe(observer)
-    engine.processUserInput("g1f3")  // knight move on initial board
-    // Should receive MoveExecutedEvent AND FiftyMoveRuleAvailableEvent
-    observer.events.exists(_.isInstanceOf[FiftyMoveRuleAvailableEvent]) shouldBe true
-
-  test("GameEngine: FiftyMoveRuleAvailableEvent not fired when clock is below 100 after move"):
-    val engine = new GameEngine(initialHistory = GameHistory(halfMoveClock = 5))
-    val observer = new MockObserver()
-    engine.subscribe(observer)
-    engine.processUserInput("g1f3")
-    observer.events.exists(_.isInstanceOf[FiftyMoveRuleAvailableEvent]) shouldBe false
-
-  // Mock Observer for testing
-  private class MockObserver extends Observer:
-    val events = mutable.ListBuffer[GameEvent]()
-    override def onGameEvent(event: GameEvent): Unit =
-      events += event
-

modules/core/src/test/scala/de/nowchess/chess/engine/MoveCommandDefaultsTest.scala

@@ -1,110 +0,0 @@
-package de.nowchess.chess.command
-
-import de.nowchess.api.board.{Square, File, Rank, Board, Color}
-import de.nowchess.chess.logic.GameHistory
-import org.scalatest.funsuite.AnyFunSuite
-import org.scalatest.matchers.should.Matchers
-
-class MoveCommandDefaultsTest extends AnyFunSuite with Matchers:
-  
-  private def sq(f: File, r: Rank): Square = Square(f, r)
-
-  // Tests for MoveCommand with default parameter values
-  test("MoveCommand with no moveResult defaults to None"):
-    val cmd = MoveCommand(
-      from = sq(File.E, Rank.R2),
-      to = sq(File.E, Rank.R4)
-    )
-    cmd.moveResult shouldBe None
-    cmd.execute() shouldBe false
-
-  test("MoveCommand with no previousBoard defaults to None"):
-    val cmd = MoveCommand(
-      from = sq(File.E, Rank.R2),
-      to = sq(File.E, Rank.R4)
-    )
-    cmd.previousBoard shouldBe None
-    cmd.undo() shouldBe false
-
-  test("MoveCommand with no previousHistory defaults to None"):
-    val cmd = MoveCommand(
-      from = sq(File.E, Rank.R2),
-      to = sq(File.E, Rank.R4)
-    )
-    cmd.previousHistory shouldBe None
-    cmd.undo() shouldBe false
-
-  test("MoveCommand with no previousTurn defaults to None"):
-    val cmd = MoveCommand(
-      from = sq(File.E, Rank.R2),
-      to = sq(File.E, Rank.R4)
-    )
-    cmd.previousTurn shouldBe None
-    cmd.undo() shouldBe false
-
-  test("MoveCommand description is always returned"):
-    val cmd = MoveCommand(
-      from = sq(File.E, Rank.R2),
-      to = sq(File.E, Rank.R4)
-    )
-    cmd.description shouldBe "Move from e2 to e4"
-
-  test("MoveCommand execute returns false when moveResult is None"):
-    val cmd = MoveCommand(
-      from = sq(File.A, Rank.R1),
-      to = sq(File.B, Rank.R3)
-    )
-    cmd.execute() shouldBe false
-
-  test("MoveCommand undo returns false when any previous state is None"):
-    // Missing previousBoard
-    val cmd1 = MoveCommand(
-      from = sq(File.E, Rank.R2),
-      to = sq(File.E, Rank.R4),
-      moveResult = Some(MoveResult.Successful(Board.initial, GameHistory.empty, Color.White, None)),
-      previousBoard = None,
-      previousHistory = Some(GameHistory.empty),
-      previousTurn = Some(Color.White)
-    )
-    cmd1.undo() shouldBe false
-
-    // Missing previousHistory
-    val cmd2 = MoveCommand(
-      from = sq(File.E, Rank.R2),
-      to = sq(File.E, Rank.R4),
-      moveResult = Some(MoveResult.Successful(Board.initial, GameHistory.empty, Color.White, None)),
-      previousBoard = Some(Board.initial),
-      previousHistory = None,
-      previousTurn = Some(Color.White)
-    )
-    cmd2.undo() shouldBe false
-
-    // Missing previousTurn
-    val cmd3 = MoveCommand(
-      from = sq(File.E, Rank.R2),
-      to = sq(File.E, Rank.R4),
-      moveResult = Some(MoveResult.Successful(Board.initial, GameHistory.empty, Color.White, None)),
-      previousBoard = Some(Board.initial),
-      previousHistory = Some(GameHistory.empty),
-      previousTurn = None
-    )
-    cmd3.undo() shouldBe false
-
-  test("MoveCommand execute returns true when moveResult is defined"):
-    val cmd = MoveCommand(
-      from = sq(File.E, Rank.R2),
-      to = sq(File.E, Rank.R4),
-      moveResult = Some(MoveResult.Successful(Board.initial, GameHistory.empty, Color.White, None))
-    )
-    cmd.execute() shouldBe true
-
-  test("MoveCommand undo returns true when all previous states are defined"):
-    val cmd = MoveCommand(
-      from = sq(File.E, Rank.R2),
-      to = sq(File.E, Rank.R4),
-      moveResult = Some(MoveResult.Successful(Board.initial, GameHistory.empty, Color.White, None)),
-      previousBoard = Some(Board.initial),
-      previousHistory = Some(GameHistory.empty),
-      previousTurn = Some(Color.White)
-    )
-    cmd.undo() shouldBe true

modules/core/src/test/scala/de/nowchess/chess/logic/CastlingRightsCalculatorTest.scala

@@ -1,70 +0,0 @@
-package de.nowchess.chess.logic
-
-import de.nowchess.api.board.*
-import de.nowchess.api.game.CastlingRights
-import org.scalatest.funsuite.AnyFunSuite
-import org.scalatest.matchers.should.Matchers
-
-class CastlingRightsCalculatorTest extends AnyFunSuite with Matchers:
-
-  private def sq(f: File, r: Rank): Square = Square(f, r)
-
-  test("Empty history gives full castling rights"):
-    val rights = CastlingRightsCalculator.deriveCastlingRights(GameHistory.empty, Color.White)
-    rights shouldBe CastlingRights.Both
-
-  test("White loses kingside rights after h1 rook moves"):
-    val history = GameHistory.empty.addMove(sq(File.H, Rank.R1), sq(File.H, Rank.R2))
-    val rights = CastlingRightsCalculator.deriveCastlingRights(history, Color.White)
-    rights.kingSide shouldBe false
-    rights.queenSide shouldBe true
-
-  test("White loses queenside rights after a1 rook moves"):
-    val history = GameHistory.empty.addMove(sq(File.A, Rank.R1), sq(File.A, Rank.R2))
-    val rights = CastlingRightsCalculator.deriveCastlingRights(history, Color.White)
-    rights.queenSide shouldBe false
-    rights.kingSide shouldBe true
-
-  test("White loses all rights after king moves"):
-    val history = GameHistory.empty.addMove(sq(File.E, Rank.R1), sq(File.E, Rank.R2))
-    val rights = CastlingRightsCalculator.deriveCastlingRights(history, Color.White)
-    rights shouldBe CastlingRights.None
-
-  test("Black loses kingside rights after h8 rook moves"):
-    val history = GameHistory.empty.addMove(sq(File.H, Rank.R8), sq(File.H, Rank.R7))
-    val rights = CastlingRightsCalculator.deriveCastlingRights(history, Color.Black)
-    rights.kingSide shouldBe false
-    rights.queenSide shouldBe true
-
-  test("Black loses queenside rights after a8 rook moves"):
-    val history = GameHistory.empty.addMove(sq(File.A, Rank.R8), sq(File.A, Rank.R7))
-    val rights = CastlingRightsCalculator.deriveCastlingRights(history, Color.Black)
-    rights.queenSide shouldBe false
-    rights.kingSide shouldBe true
-
-  test("Black loses all rights after king moves"):
-    val history = GameHistory.empty.addMove(sq(File.E, Rank.R8), sq(File.E, Rank.R7))
-    val rights = CastlingRightsCalculator.deriveCastlingRights(history, Color.Black)
-    rights shouldBe CastlingRights.None
-
-  test("Castle move revokes all castling rights"):
-    val history = GameHistory.empty.addMove(
-      sq(File.E, Rank.R1),
-      sq(File.G, Rank.R1),
-      Some(CastleSide.Kingside)
-    )
-    val rights = CastlingRightsCalculator.deriveCastlingRights(history, Color.White)
-    rights shouldBe CastlingRights.None
-
-  test("Other pieces moving does not revoke castling rights"):
-    val history = GameHistory.empty.addMove(sq(File.E, Rank.R2), sq(File.E, Rank.R4))
-    val rights = CastlingRightsCalculator.deriveCastlingRights(history, Color.White)
-    rights shouldBe CastlingRights.Both
-
-  test("Multiple moves preserve white kingside but lose queenside"):
-    val history = GameHistory.empty
-      .addMove(sq(File.A, Rank.R1), sq(File.A, Rank.R2))  // White queenside rook moves
-      .addMove(sq(File.E, Rank.R7), sq(File.E, Rank.R5))  // Black pawn moves
-    val rights = CastlingRightsCalculator.deriveCastlingRights(history, Color.White)
-    rights.kingSide shouldBe true
-    rights.queenSide shouldBe false

modules/core/src/test/scala/de/nowchess/chess/logic/EnPassantCalculatorTest.scala

@@ -1,101 +0,0 @@
-package de.nowchess.chess.logic
-
-import de.nowchess.api.board.*
-import org.scalatest.funsuite.AnyFunSuite
-import org.scalatest.matchers.should.Matchers
-
-class EnPassantCalculatorTest extends AnyFunSuite with Matchers:
-
-  private def sq(f: File, r: Rank): Square = Square(f, r)
-  private def board(entries: (Square, Piece)*): Board = Board(entries.toMap)
-
-  // ──── enPassantTarget ────────────────────────────────────────────────
-
-  test("enPassantTarget returns None for empty history"):
-    val b = board(sq(File.E, Rank.R4) -> Piece.WhitePawn)
-    EnPassantCalculator.enPassantTarget(b, GameHistory.empty) shouldBe None
-
-  test("enPassantTarget returns None when last move was a single pawn push"):
-    val b = board(sq(File.E, Rank.R3) -> Piece.WhitePawn)
-    val h = GameHistory.empty.addMove(sq(File.E, Rank.R2), sq(File.E, Rank.R3))
-    EnPassantCalculator.enPassantTarget(b, h) shouldBe None
-
-  test("enPassantTarget returns None when last move was not a pawn"):
-    val b = board(sq(File.E, Rank.R4) -> Piece.WhiteRook)
-    val h = GameHistory.empty.addMove(sq(File.E, Rank.R2), sq(File.E, Rank.R4))
-    EnPassantCalculator.enPassantTarget(b, h) shouldBe None
-
-  test("enPassantTarget returns e3 after white pawn double push e2-e4"):
-    val b = board(sq(File.E, Rank.R4) -> Piece.WhitePawn)
-    val h = GameHistory.empty.addMove(sq(File.E, Rank.R2), sq(File.E, Rank.R4))
-    EnPassantCalculator.enPassantTarget(b, h) shouldBe Some(sq(File.E, Rank.R3))
-
-  test("enPassantTarget returns e6 after black pawn double push e7-e5"):
-    val b = board(sq(File.E, Rank.R5) -> Piece.BlackPawn)
-    val h = GameHistory.empty.addMove(sq(File.E, Rank.R7), sq(File.E, Rank.R5))
-    EnPassantCalculator.enPassantTarget(b, h) shouldBe Some(sq(File.E, Rank.R6))
-
-  test("enPassantTarget returns d3 after white pawn double push d2-d4"):
-    val b = board(sq(File.D, Rank.R4) -> Piece.WhitePawn)
-    val h = GameHistory.empty.addMove(sq(File.D, Rank.R2), sq(File.D, Rank.R4))
-    EnPassantCalculator.enPassantTarget(b, h) shouldBe Some(sq(File.D, Rank.R3))
-
-  // ──── capturedPawnSquare ─────────────────────────────────────────────
-
-  test("capturedPawnSquare for white capturing on e6 returns e5"):
-    EnPassantCalculator.capturedPawnSquare(sq(File.E, Rank.R6), Color.White) shouldBe sq(File.E, Rank.R5)
-
-  test("capturedPawnSquare for black capturing on e3 returns e4"):
-    EnPassantCalculator.capturedPawnSquare(sq(File.E, Rank.R3), Color.Black) shouldBe sq(File.E, Rank.R4)
-
-  test("capturedPawnSquare for white capturing on d6 returns d5"):
-    EnPassantCalculator.capturedPawnSquare(sq(File.D, Rank.R6), Color.White) shouldBe sq(File.D, Rank.R5)
-
-  // ──── isEnPassant ────────────────────────────────────────────────────
-
-  test("isEnPassant returns true for valid white en passant capture"):
-    // White pawn on e5, black pawn just double-pushed to d5 (ep target = d6)
-    val b = board(
-      sq(File.E, Rank.R5) -> Piece.WhitePawn,
-      sq(File.D, Rank.R5) -> Piece.BlackPawn
-    )
-    val h = GameHistory.empty.addMove(sq(File.D, Rank.R7), sq(File.D, Rank.R5))
-    EnPassantCalculator.isEnPassant(b, h, sq(File.E, Rank.R5), sq(File.D, Rank.R6)) shouldBe true
-
-  test("isEnPassant returns true for valid black en passant capture"):
-    // Black pawn on d4, white pawn just double-pushed to e4 (ep target = e3)
-    val b = board(
-      sq(File.D, Rank.R4) -> Piece.BlackPawn,
-      sq(File.E, Rank.R4) -> Piece.WhitePawn
-    )
-    val h = GameHistory.empty.addMove(sq(File.E, Rank.R2), sq(File.E, Rank.R4))
-    EnPassantCalculator.isEnPassant(b, h, sq(File.D, Rank.R4), sq(File.E, Rank.R3)) shouldBe true
-
-  test("isEnPassant returns false when no en passant target in history"):
-    val b = board(
-      sq(File.E, Rank.R5) -> Piece.WhitePawn,
-      sq(File.D, Rank.R5) -> Piece.BlackPawn
-    )
-    val h = GameHistory.empty.addMove(sq(File.D, Rank.R6), sq(File.D, Rank.R5))  // single push
-    EnPassantCalculator.isEnPassant(b, h, sq(File.E, Rank.R5), sq(File.D, Rank.R6)) shouldBe false
-
-  test("isEnPassant returns false when piece at from is not a pawn"):
-    val b = board(
-      sq(File.E, Rank.R5) -> Piece.WhiteRook,
-      sq(File.D, Rank.R5) -> Piece.BlackPawn
-    )
-    val h = GameHistory.empty.addMove(sq(File.D, Rank.R7), sq(File.D, Rank.R5))
-    EnPassantCalculator.isEnPassant(b, h, sq(File.E, Rank.R5), sq(File.D, Rank.R6)) shouldBe false
-
-  test("isEnPassant returns false when to does not match ep target"):
-    val b = board(
-      sq(File.E, Rank.R5) -> Piece.WhitePawn,
-      sq(File.D, Rank.R5) -> Piece.BlackPawn
-    )
-    val h = GameHistory.empty.addMove(sq(File.D, Rank.R7), sq(File.D, Rank.R5))
-    EnPassantCalculator.isEnPassant(b, h, sq(File.E, Rank.R5), sq(File.E, Rank.R6)) shouldBe false
-
-  test("isEnPassant returns false when from square is empty"):
-    val b = board(sq(File.D, Rank.R5) -> Piece.BlackPawn)
-    val h = GameHistory.empty.addMove(sq(File.D, Rank.R7), sq(File.D, Rank.R5))
-    EnPassantCalculator.isEnPassant(b, h, sq(File.E, Rank.R5), sq(File.D, Rank.R6)) shouldBe false

modules/core/src/test/scala/de/nowchess/chess/logic/GameHistoryTest.scala

@@ -1,104 +0,0 @@
-package de.nowchess.chess.logic
-
-import de.nowchess.api.board.*
-import de.nowchess.api.move.PromotionPiece
-import org.scalatest.funsuite.AnyFunSuite
-import org.scalatest.matchers.should.Matchers
-
-class GameHistoryTest extends AnyFunSuite with Matchers:
-
-  private def sq(f: File, r: Rank): Square = Square(f, r)
-
-  test("GameHistory starts empty"):
-    val history = GameHistory.empty
-    history.moves shouldBe empty
-
-  test("GameHistory can add a move"):
-    val history = GameHistory.empty.addMove(sq(File.E, Rank.R2), sq(File.E, Rank.R4))
-    history.moves should have length 1
-    history.moves.head.from shouldBe sq(File.E, Rank.R2)
-    history.moves.head.to shouldBe sq(File.E, Rank.R4)
-    history.moves.head.castleSide shouldBe None
-
-  test("GameHistory can add multiple moves in order"):
-    val h1 = GameHistory.empty
-    val h2 = h1.addMove(sq(File.E, Rank.R2), sq(File.E, Rank.R4))
-    val h3 = h2.addMove(sq(File.C, Rank.R7), sq(File.C, Rank.R5))
-    h3.moves should have length 2
-    h3.moves(0).from shouldBe sq(File.E, Rank.R2)
-    h3.moves(1).from shouldBe sq(File.C, Rank.R7)
-
-  test("GameHistory can add a castle move"):
-    val history = GameHistory.empty.addMove(
-      sq(File.E, Rank.R1),
-      sq(File.G, Rank.R1),
-      Some(CastleSide.Kingside)
-    )
-    history.moves.head.castleSide shouldBe Some(CastleSide.Kingside)
-
-  test("GameHistory.addMove with two arguments uses None for castleSide default"):
-    val history = GameHistory.empty.addMove(sq(File.E, Rank.R2), sq(File.E, Rank.R4))
-    history.moves should have length 1
-    history.moves.head.castleSide shouldBe None
-
-  test("Move with promotion records the promotion piece"):
-    val move = HistoryMove(sq(File.E, Rank.R7), sq(File.E, Rank.R8), None, Some(PromotionPiece.Queen))
-    move.promotionPiece should be (Some(PromotionPiece.Queen))
-
-  test("Normal move has no promotion piece"):
-    val move = HistoryMove(sq(File.E, Rank.R2), sq(File.E, Rank.R4), None, None)
-    move.promotionPiece should be (None)
-
-  test("addMove with promotion stores promotionPiece"):
-    val history = GameHistory.empty
-    val newHistory = history.addMove(sq(File.E, Rank.R7), sq(File.E, Rank.R8), None, Some(PromotionPiece.Rook))
-    newHistory.moves should have length 1
-    newHistory.moves.head.promotionPiece should be (Some(PromotionPiece.Rook))
-
-  test("addMove with castleSide only uses promotionPiece default (None)"):
-    val history = GameHistory.empty
-    // With overload 3 removed, this uses the 4-param version and triggers addMove$default$4
-    val newHistory = history.addMove(sq(File.E, Rank.R1), sq(File.G, Rank.R1), Some(CastleSide.Kingside))
-    newHistory.moves should have length 1
-    newHistory.moves.head.castleSide should be (Some(CastleSide.Kingside))
-    newHistory.moves.head.promotionPiece should be (None)
-
-  test("addMove using named parameters with only promotion, using castleSide default"):
-    val history = GameHistory.empty
-    val newHistory = history.addMove(from = sq(File.E, Rank.R7), to = sq(File.E, Rank.R8), promotionPiece = Some(PromotionPiece.Queen))
-    newHistory.moves should have length 1
-    newHistory.moves.head.castleSide should be (None)
-    newHistory.moves.head.promotionPiece should be (Some(PromotionPiece.Queen))
-
-  // ──── half-move clock ────────────────────────────────────────────────
-
-  test("halfMoveClock starts at 0"):
-    GameHistory.empty.halfMoveClock shouldBe 0
-
-  test("halfMoveClock increments on a non-pawn non-capture move"):
-    val h = GameHistory.empty.addMove(sq(File.G, Rank.R1), sq(File.F, Rank.R3))
-    h.halfMoveClock shouldBe 1
-
-  test("halfMoveClock resets to 0 on a pawn move"):
-    val h = GameHistory.empty.addMove(sq(File.E, Rank.R2), sq(File.E, Rank.R4), wasPawnMove = true)
-    h.halfMoveClock shouldBe 0
-
-  test("halfMoveClock resets to 0 on a capture"):
-    val h = GameHistory.empty.addMove(sq(File.E, Rank.R5), sq(File.D, Rank.R6), wasCapture = true)
-    h.halfMoveClock shouldBe 0
-
-  test("halfMoveClock resets to 0 when both wasPawnMove and wasCapture are true"):
-    val h = GameHistory.empty.addMove(sq(File.E, Rank.R5), sq(File.D, Rank.R6), wasPawnMove = true, wasCapture = true)
-    h.halfMoveClock shouldBe 0
-
-  test("halfMoveClock carries across multiple moves"):
-    val h = GameHistory.empty
-      .addMove(sq(File.G, Rank.R1), sq(File.F, Rank.R3))          // +1 → 1
-      .addMove(sq(File.G, Rank.R8), sq(File.F, Rank.R6))          // +1 → 2
-      .addMove(sq(File.E, Rank.R2), sq(File.E, Rank.R4), wasPawnMove = true)  // reset → 0
-      .addMove(sq(File.B, Rank.R1), sq(File.C, Rank.R3))          // +1 → 1
-    h.halfMoveClock shouldBe 1
-
-  test("GameHistory can be initialised with a non-zero halfMoveClock"):
-    val h = GameHistory(halfMoveClock = 42)
-    h.halfMoveClock shouldBe 42

modules/core/src/test/scala/de/nowchess/chess/logic/GameRulesTest.scala

@@ -1,161 +0,0 @@
-package de.nowchess.chess.logic
-
-import de.nowchess.api.board.*
-import de.nowchess.api.game.CastlingRights
-import de.nowchess.chess.logic.GameHistory
-import org.scalatest.funsuite.AnyFunSuite
-import org.scalatest.matchers.should.Matchers
-
-class GameRulesTest extends AnyFunSuite with Matchers:
-
-  private def sq(f: File, r: Rank): Square = Square(f, r)
-  private def board(entries: (Square, Piece)*): Board = Board(entries.toMap)
-
-  /** Wrap a board in a GameContext with no castling rights — for non-castling tests. */
-  private def testLegalMoves(entries: (Square, Piece)*)(color: Color): Set[(Square, Square)] =
-    GameRules.legalMoves(Board(entries.toMap), GameHistory.empty, color)
-
-  private def testGameStatus(entries: (Square, Piece)*)(color: Color): PositionStatus =
-    GameRules.gameStatus(Board(entries.toMap), GameHistory.empty, color)
-
-  // ──── isInCheck ──────────────────────────────────────────────────────
-
-  test("isInCheck: king attacked by enemy rook on same rank"):
-    // White King E1, Black Rook A1 — rook slides along rank 1 to E1
-    val b = board(
-      sq(File.E, Rank.R1) -> Piece.WhiteKing,
-      sq(File.A, Rank.R1) -> Piece.BlackRook
-    )
-    GameRules.isInCheck(b, Color.White) shouldBe true
-
-  test("isInCheck: king not attacked"):
-    // Black Rook A3 does not cover E1
-    val b = board(
-      sq(File.E, Rank.R1) -> Piece.WhiteKing,
-      sq(File.A, Rank.R3) -> Piece.BlackRook
-    )
-    GameRules.isInCheck(b, Color.White) shouldBe false
-
-  test("isInCheck: no king on board returns false"):
-    val b = board(sq(File.A, Rank.R1) -> Piece.BlackRook)
-    GameRules.isInCheck(b, Color.White) shouldBe false
-
-  // ──── legalMoves ─────────────────────────────────────────────────────
-
-  test("legalMoves: move that exposes own king to rook is excluded"):
-    // White King E1, White Rook E4 (pinned on E-file), Black Rook E8
-    // Moving the White Rook off the E-file would expose the king
-    val moves = testLegalMoves(
-      sq(File.E, Rank.R1) -> Piece.WhiteKing,
-      sq(File.E, Rank.R4) -> Piece.WhiteRook,
-      sq(File.E, Rank.R8) -> Piece.BlackRook
-    )(Color.White)
-    moves should not contain (sq(File.E, Rank.R4) -> sq(File.D, Rank.R4))
-
-  test("legalMoves: move that blocks check is included"):
-    // White King E1 in check from Black Rook E8; White Rook A5 can interpose on E5
-    val moves = testLegalMoves(
-      sq(File.E, Rank.R1) -> Piece.WhiteKing,
-      sq(File.A, Rank.R5) -> Piece.WhiteRook,
-      sq(File.E, Rank.R8) -> Piece.BlackRook
-    )(Color.White)
-    moves should contain(sq(File.A, Rank.R5) -> sq(File.E, Rank.R5))
-
-  // ──── gameStatus ──────────────────────────────────────────────────────
-
-  test("gameStatus: checkmate returns Mated"):
-    // White Qh8, Ka6; Black Ka8
-    // Qh8 attacks Ka8 along rank 8; all escape squares covered (spec-verified position)
-    testGameStatus(
-      sq(File.H, Rank.R8) -> Piece.WhiteQueen,
-      sq(File.A, Rank.R6) -> Piece.WhiteKing,
-      sq(File.A, Rank.R8) -> Piece.BlackKing
-    )(Color.Black) shouldBe PositionStatus.Mated
-
-  test("gameStatus: stalemate returns Drawn"):
-    // White Qb6, Kc6; Black Ka8
-    // Black king has no legal moves and is not in check (spec-verified position)
-    testGameStatus(
-      sq(File.B, Rank.R6) -> Piece.WhiteQueen,
-      sq(File.C, Rank.R6) -> Piece.WhiteKing,
-      sq(File.A, Rank.R8) -> Piece.BlackKing
-    )(Color.Black) shouldBe PositionStatus.Drawn
-
-  test("gameStatus: king in check with legal escape returns InCheck"):
-    // White Ra8 attacks Black Ke8 along rank 8; king can escape to d7, e7, f7
-    testGameStatus(
-      sq(File.A, Rank.R8) -> Piece.WhiteRook,
-      sq(File.E, Rank.R8) -> Piece.BlackKing
-    )(Color.Black) shouldBe PositionStatus.InCheck
-
-  test("gameStatus: normal starting position returns Normal"):
-    GameRules.gameStatus(Board.initial, GameHistory.empty, Color.White) shouldBe PositionStatus.Normal
-
-  test("legalMoves: includes castling destination when available"):
-    val b = board(
-        sq(File.E, Rank.R1) -> Piece.WhiteKing,
-        sq(File.H, Rank.R1) -> Piece.WhiteRook,
-        sq(File.H, Rank.R8) -> Piece.BlackKing
-      )
-    GameRules.legalMoves(b, GameHistory.empty, Color.White) should contain(sq(File.E, Rank.R1) -> sq(File.G, Rank.R1))
-
-  test("legalMoves: excludes castling when king is in check"):
-    val b = board(
-        sq(File.E, Rank.R1) -> Piece.WhiteKing,
-        sq(File.H, Rank.R1) -> Piece.WhiteRook,
-        sq(File.E, Rank.R8) -> Piece.BlackRook,
-        sq(File.A, Rank.R8) -> Piece.BlackKing
-      )
-    GameRules.legalMoves(b, GameHistory.empty, Color.White) should not contain (sq(File.E, Rank.R1) -> sq(File.G, Rank.R1))
-
-  test("gameStatus: returns Normal (not Drawn) when castling is the only legal move"):
-    // White King e1, Rook h1 (kingside castling available).
-    // Black Rooks d2 and f2 box the king: d1 attacked by d2, e2 attacked by both,
-    // f1 attacked by f2. King cannot move to any adjacent square without entering
-    // an attacked square or an enemy piece. Only legal move: castle to g1.
-    val b = board(
-        sq(File.E, Rank.R1) -> Piece.WhiteKing,
-        sq(File.H, Rank.R1) -> Piece.WhiteRook,
-        sq(File.D, Rank.R2) -> Piece.BlackRook,
-        sq(File.F, Rank.R2) -> Piece.BlackRook,
-        sq(File.A, Rank.R8) -> Piece.BlackKing
-      )
-    // No history means castling rights are intact
-    GameRules.gameStatus(b, GameHistory.empty, Color.White) shouldBe PositionStatus.Normal
-
-  test("CastleSide.withCastle correctly positions pieces for Queenside castling"):
-    // Directly test the withCastle extension for Queenside (coverage gap on line 10)
-    val b = board(
-      sq(File.E, Rank.R1) -> Piece.WhiteKing,
-      sq(File.A, Rank.R1) -> Piece.WhiteRook,
-      sq(File.H, Rank.R8) -> Piece.BlackKing
-    )
-    val result = b.withCastle(Color.White, CastleSide.Queenside)
-    result.pieceAt(sq(File.C, Rank.R1)) shouldBe Some(Piece.WhiteKing)
-    result.pieceAt(sq(File.D, Rank.R1)) shouldBe Some(Piece.WhiteRook)
-    result.pieceAt(sq(File.E, Rank.R1)) shouldBe None
-    result.pieceAt(sq(File.A, Rank.R1)) shouldBe None
-
-  test("CastleSide.withCastle correctly positions pieces for Black Kingside castling"):
-    val b = board(
-      sq(File.E, Rank.R8) -> Piece.BlackKing,
-      sq(File.H, Rank.R8) -> Piece.BlackRook,
-      sq(File.A, Rank.R1) -> Piece.WhiteKing
-    )
-    val result = b.withCastle(Color.Black, CastleSide.Kingside)
-    result.pieceAt(sq(File.G, Rank.R8)) shouldBe Some(Piece.BlackKing)
-    result.pieceAt(sq(File.F, Rank.R8)) shouldBe Some(Piece.BlackRook)
-    result.pieceAt(sq(File.E, Rank.R8)) shouldBe None
-    result.pieceAt(sq(File.H, Rank.R8)) shouldBe None
-
-  test("CastleSide.withCastle correctly positions pieces for Black Queenside castling"):
-    val b = board(
-      sq(File.E, Rank.R8) -> Piece.BlackKing,
-      sq(File.A, Rank.R8) -> Piece.BlackRook,
-      sq(File.A, Rank.R1) -> Piece.WhiteKing
-    )
-    val result = b.withCastle(Color.Black, CastleSide.Queenside)
-    result.pieceAt(sq(File.C, Rank.R8)) shouldBe Some(Piece.BlackKing)
-    result.pieceAt(sq(File.D, Rank.R8)) shouldBe Some(Piece.BlackRook)
-    result.pieceAt(sq(File.E, Rank.R8)) shouldBe None
-    result.pieceAt(sq(File.A, Rank.R8)) shouldBe None

modules/core/src/test/scala/de/nowchess/chess/logic/MoveValidatorTest.scala

@@ -1,280 +0,0 @@
-package de.nowchess.chess.logic
-
-import de.nowchess.api.board.{Board, Color, File, Piece, Rank, Square}
-import de.nowchess.api.game.CastlingRights
-import de.nowchess.chess.logic.{CastleSide, GameHistory}
-import de.nowchess.chess.notation.FenParser
-import org.scalatest.funsuite.AnyFunSuite
-import org.scalatest.matchers.should.Matchers
-
-class MoveValidatorTest extends AnyFunSuite with Matchers:
-
-  private def sq(f: File, r: Rank): Square = Square(f, r)
-  private def board(entries: (Square, Piece)*): Board = Board(entries.toMap)
-
-  // ──── Empty square ───────────────────────────────────────────────────
-
-  test("legalTargets returns empty set when no piece at from square"):
-    MoveValidator.legalTargets(Board.initial, sq(File.E, Rank.R4)) shouldBe empty
-
-  // ──── isLegal delegates to legalTargets ──────────────────────────────
-
-  test("isLegal returns true for a valid pawn move"):
-    MoveValidator.isLegal(Board.initial, sq(File.E, Rank.R2), sq(File.E, Rank.R4)) shouldBe true
-
-  test("isLegal returns false for an invalid move"):
-    MoveValidator.isLegal(Board.initial, sq(File.E, Rank.R2), sq(File.E, Rank.R5)) shouldBe false
-
-  // ──── Pawn – White ───────────────────────────────────────────────────
-
-  test("white pawn on starting rank can move forward one square"):
-    val b = board(sq(File.E, Rank.R2) -> Piece.WhitePawn)
-    MoveValidator.legalTargets(b, sq(File.E, Rank.R2)) should contain(sq(File.E, Rank.R3))
-
-  test("white pawn on starting rank can move forward two squares"):
-    val b = board(sq(File.E, Rank.R2) -> Piece.WhitePawn)
-    MoveValidator.legalTargets(b, sq(File.E, Rank.R2)) should contain(sq(File.E, Rank.R4))
-
-  test("white pawn not on starting rank cannot move two squares"):
-    val b = board(sq(File.E, Rank.R3) -> Piece.WhitePawn)
-    MoveValidator.legalTargets(b, sq(File.E, Rank.R3)) should not contain sq(File.E, Rank.R5)
-
-  test("white pawn is blocked by piece directly in front, and cannot jump over it"):
-    val b = board(
-      sq(File.E, Rank.R2) -> Piece.WhitePawn,
-      sq(File.E, Rank.R3) -> Piece.BlackPawn
-    )
-    val targets = MoveValidator.legalTargets(b, sq(File.E, Rank.R2))
-    targets should not contain sq(File.E, Rank.R3)
-    targets should not contain sq(File.E, Rank.R4)
-
-  test("white pawn on starting rank cannot move two squares if destination square is occupied"):
-    val b = board(
-      sq(File.E, Rank.R2) -> Piece.WhitePawn,
-      sq(File.E, Rank.R4) -> Piece.BlackPawn
-    )
-    val targets = MoveValidator.legalTargets(b, sq(File.E, Rank.R2))
-    targets should contain(sq(File.E, Rank.R3))
-    targets should not contain sq(File.E, Rank.R4)
-
-  test("white pawn can capture diagonally when enemy piece is present"):
-    val b = board(
-      sq(File.E, Rank.R2) -> Piece.WhitePawn,
-      sq(File.D, Rank.R3) -> Piece.BlackPawn
-    )
-    MoveValidator.legalTargets(b, sq(File.E, Rank.R2)) should contain(sq(File.D, Rank.R3))
-
-  test("white pawn cannot capture diagonally when no enemy piece is present"):
-    val b = board(sq(File.E, Rank.R2) -> Piece.WhitePawn)
-    MoveValidator.legalTargets(b, sq(File.E, Rank.R2)) should not contain sq(File.D, Rank.R3)
-
-  test("white pawn at A-file does not generate diagonal to the left off the board"):
-    val b = board(sq(File.A, Rank.R2) -> Piece.WhitePawn)
-    val targets = MoveValidator.legalTargets(b, sq(File.A, Rank.R2))
-    targets should contain(sq(File.A, Rank.R3))
-    targets should contain(sq(File.A, Rank.R4))
-    targets.size shouldBe 2
-
-  // ──── Pawn – Black ───────────────────────────────────────────────────
-
-  test("black pawn on starting rank can move forward one and two squares"):
-    val b = board(sq(File.E, Rank.R7) -> Piece.BlackPawn)
-    val targets = MoveValidator.legalTargets(b, sq(File.E, Rank.R7))
-    targets should contain(sq(File.E, Rank.R6))
-    targets should contain(sq(File.E, Rank.R5))
-
-  test("black pawn not on starting rank cannot move two squares"):
-    val b = board(sq(File.E, Rank.R6) -> Piece.BlackPawn)
-    MoveValidator.legalTargets(b, sq(File.E, Rank.R6)) should not contain sq(File.E, Rank.R4)
-
-  test("black pawn can capture diagonally when enemy piece is present"):
-    val b = board(
-      sq(File.E, Rank.R7) -> Piece.BlackPawn,
-      sq(File.F, Rank.R6) -> Piece.WhitePawn
-    )
-    MoveValidator.legalTargets(b, sq(File.E, Rank.R7)) should contain(sq(File.F, Rank.R6))
-
-  // ──── Knight ─────────────────────────────────────────────────────────
-
-  test("knight in center has 8 possible moves"):
-    val b = board(sq(File.D, Rank.R4) -> Piece.WhiteKnight)
-    MoveValidator.legalTargets(b, sq(File.D, Rank.R4)).size shouldBe 8
-
-  test("knight in corner has only 2 possible moves"):
-    val b = board(sq(File.A, Rank.R1) -> Piece.WhiteKnight)
-    MoveValidator.legalTargets(b, sq(File.A, Rank.R1)).size shouldBe 2
-
-  test("knight cannot land on own piece"):
-    val b = board(
-      sq(File.D, Rank.R4) -> Piece.WhiteKnight,
-      sq(File.F, Rank.R5) -> Piece.WhiteRook
-    )
-    MoveValidator.legalTargets(b, sq(File.D, Rank.R4)) should not contain sq(File.F, Rank.R5)
-
-  test("knight can capture enemy piece"):
-    val b = board(
-      sq(File.D, Rank.R4) -> Piece.WhiteKnight,
-      sq(File.F, Rank.R5) -> Piece.BlackRook
-    )
-    MoveValidator.legalTargets(b, sq(File.D, Rank.R4)) should contain(sq(File.F, Rank.R5))
-
-  // ──── Bishop ─────────────────────────────────────────────────────────
-
-  test("bishop slides diagonally across an empty board"):
-    val b = board(sq(File.D, Rank.R4) -> Piece.WhiteBishop)
-    val targets = MoveValidator.legalTargets(b, sq(File.D, Rank.R4))
-    targets should contain(sq(File.E, Rank.R5))
-    targets should contain(sq(File.H, Rank.R8))
-    targets should contain(sq(File.C, Rank.R3))
-    targets should contain(sq(File.A, Rank.R1))
-
-  test("bishop is blocked by own piece and squares beyond are unreachable"):
-    val b = board(
-      sq(File.D, Rank.R4) -> Piece.WhiteBishop,
-      sq(File.F, Rank.R6) -> Piece.WhiteRook
-    )
-    val targets = MoveValidator.legalTargets(b, sq(File.D, Rank.R4))
-    targets should contain(sq(File.E, Rank.R5))
-    targets should not contain sq(File.F, Rank.R6)
-    targets should not contain sq(File.G, Rank.R7)
-
-  test("bishop captures enemy piece and cannot slide further"):
-    val b = board(
-      sq(File.D, Rank.R4) -> Piece.WhiteBishop,
-      sq(File.F, Rank.R6) -> Piece.BlackRook
-    )
-    val targets = MoveValidator.legalTargets(b, sq(File.D, Rank.R4))
-    targets should contain(sq(File.E, Rank.R5))
-    targets should contain(sq(File.F, Rank.R6))
-    targets should not contain sq(File.G, Rank.R7)
-
-  // ──── Rook ───────────────────────────────────────────────────────────
-
-  test("rook slides orthogonally across an empty board"):
-    val b = board(sq(File.D, Rank.R4) -> Piece.WhiteRook)
-    val targets = MoveValidator.legalTargets(b, sq(File.D, Rank.R4))
-    targets should contain(sq(File.D, Rank.R8))
-    targets should contain(sq(File.D, Rank.R1))
-    targets should contain(sq(File.A, Rank.R4))
-    targets should contain(sq(File.H, Rank.R4))
-
-  test("rook is blocked by own piece and squares beyond are unreachable"):
-    val b = board(
-      sq(File.A, Rank.R1) -> Piece.WhiteRook,
-      sq(File.C, Rank.R1) -> Piece.WhitePawn
-    )
-    val targets = MoveValidator.legalTargets(b, sq(File.A, Rank.R1))
-    targets should contain(sq(File.B, Rank.R1))
-    targets should not contain sq(File.C, Rank.R1)
-    targets should not contain sq(File.D, Rank.R1)
-
-  test("rook captures enemy piece and cannot slide further"):
-    val b = board(
-      sq(File.A, Rank.R1) -> Piece.WhiteRook,
-      sq(File.C, Rank.R1) -> Piece.BlackPawn
-    )
-    val targets = MoveValidator.legalTargets(b, sq(File.A, Rank.R1))
-    targets should contain(sq(File.B, Rank.R1))
-    targets should contain(sq(File.C, Rank.R1))
-    targets should not contain sq(File.D, Rank.R1)
-
-  // ──── Queen ──────────────────────────────────────────────────────────
-
-  test("queen combines rook and bishop movement for 27 squares from d4"):
-    val b = board(sq(File.D, Rank.R4) -> Piece.WhiteQueen)
-    val targets = MoveValidator.legalTargets(b, sq(File.D, Rank.R4))
-    targets should contain(sq(File.D, Rank.R8))
-    targets should contain(sq(File.H, Rank.R4))
-    targets should contain(sq(File.H, Rank.R8))
-    targets should contain(sq(File.A, Rank.R1))
-    targets.size shouldBe 27
-
-  // ──── King ───────────────────────────────────────────────────────────
-
-  test("king moves one step in all 8 directions from center"):
-    val b = board(sq(File.D, Rank.R4) -> Piece.WhiteKing)
-    MoveValidator.legalTargets(b, sq(File.D, Rank.R4)).size shouldBe 8
-
-  test("king at corner has only 3 reachable squares"):
-    val b = board(sq(File.A, Rank.R1) -> Piece.WhiteKing)
-    MoveValidator.legalTargets(b, sq(File.A, Rank.R1)).size shouldBe 3
-
-  test("king cannot capture own piece"):
-    val b = board(
-      sq(File.D, Rank.R4) -> Piece.WhiteKing,
-      sq(File.E, Rank.R4) -> Piece.WhiteRook
-    )
-    MoveValidator.legalTargets(b, sq(File.D, Rank.R4)) should not contain sq(File.E, Rank.R4)
-
-  test("king can capture enemy piece"):
-    val b = board(
-      sq(File.D, Rank.R4) -> Piece.WhiteKing,
-      sq(File.E, Rank.R4) -> Piece.BlackRook
-    )
-    MoveValidator.legalTargets(b, sq(File.D, Rank.R4)) should contain(sq(File.E, Rank.R4))
-
-  // ──── Pawn – en passant targets ──────────────────────────────────────
-
-  test("white pawn includes ep target in legal moves after black double push"):
-    // Black pawn just double-pushed to d5 (ep target = d6); white pawn on e5
-    val b = board(
-      sq(File.E, Rank.R5) -> Piece.WhitePawn,
-      sq(File.D, Rank.R5) -> Piece.BlackPawn
-    )
-    val h = GameHistory.empty.addMove(sq(File.D, Rank.R7), sq(File.D, Rank.R5))
-    MoveValidator.legalTargets(b, h, sq(File.E, Rank.R5)) should contain(sq(File.D, Rank.R6))
-
-  test("white pawn does not include ep target without a preceding double push"):
-    val b = board(
-      sq(File.E, Rank.R5) -> Piece.WhitePawn,
-      sq(File.D, Rank.R5) -> Piece.BlackPawn
-    )
-    val h = GameHistory.empty.addMove(sq(File.D, Rank.R6), sq(File.D, Rank.R5))  // single push
-    MoveValidator.legalTargets(b, h, sq(File.E, Rank.R5)) should not contain sq(File.D, Rank.R6)
-
-  test("black pawn includes ep target in legal moves after white double push"):
-    // White pawn just double-pushed to e4 (ep target = e3); black pawn on d4
-    val b = board(
-      sq(File.D, Rank.R4) -> Piece.BlackPawn,
-      sq(File.E, Rank.R4) -> Piece.WhitePawn
-    )
-    val h = GameHistory.empty.addMove(sq(File.E, Rank.R2), sq(File.E, Rank.R4))
-    MoveValidator.legalTargets(b, h, sq(File.D, Rank.R4)) should contain(sq(File.E, Rank.R3))
-
-  test("pawn on wrong file does not get ep target from adjacent double push"):
-    // White pawn on a5, black pawn double-pushed to d5 — a5 is not adjacent to d5
-    val b = board(
-      sq(File.A, Rank.R5) -> Piece.WhitePawn,
-      sq(File.D, Rank.R5) -> Piece.BlackPawn
-    )
-    val h = GameHistory.empty.addMove(sq(File.D, Rank.R7), sq(File.D, Rank.R5))
-    MoveValidator.legalTargets(b, h, sq(File.A, Rank.R5)) should not contain sq(File.D, Rank.R6)
-
-  // ──── History-aware legalTargets fallback for non-pawn non-king pieces ─────
-
-  test("legalTargets with history delegates to geometry-only for non-pawn non-king pieces"):
-    val b = board(sq(File.D, Rank.R4) -> Piece.WhiteRook)
-    val h = GameHistory.empty.addMove(sq(File.E, Rank.R2), sq(File.E, Rank.R4))
-    MoveValidator.legalTargets(b, h, sq(File.D, Rank.R4)) shouldBe MoveValidator.legalTargets(b, sq(File.D, Rank.R4))
-
-  // ──── isPromotionMove ────────────────────────────────────────────────
-
-  test("White pawn reaching R8 is a promotion move"):
-    val b = FenParser.parseBoard("8/4P3/4k3/8/8/8/8/8").get
-    MoveValidator.isPromotionMove(b, Square(File.E, Rank.R7), Square(File.E, Rank.R8)) should be (true)
-
-  test("Black pawn reaching R1 is a promotion move"):
-    val b = FenParser.parseBoard("8/8/8/8/4K3/8/4p3/8").get
-    MoveValidator.isPromotionMove(b, Square(File.E, Rank.R2), Square(File.E, Rank.R1)) should be (true)
-
-  test("Pawn capturing to back rank is a promotion move"):
-    val b = FenParser.parseBoard("3q4/4P3/8/8/8/8/8/8").get
-    MoveValidator.isPromotionMove(b, Square(File.E, Rank.R7), Square(File.D, Rank.R8)) should be (true)
-
-  test("Pawn not reaching back rank is not a promotion move"):
-    val b = FenParser.parseBoard("8/8/8/4P3/8/8/8/8").get
-    MoveValidator.isPromotionMove(b, Square(File.E, Rank.R5), Square(File.E, Rank.R6)) should be (false)
-
-  test("Non-pawn piece is never a promotion move"):
-    val b = FenParser.parseBoard("8/8/8/4Q3/8/8/8/8").get
-    MoveValidator.isPromotionMove(b, Square(File.E, Rank.R5), Square(File.E, Rank.R8)) should be (false)

modules/core/src/test/scala/de/nowchess/chess/notation/FenExporterTest.scala

@@ -1,88 +0,0 @@
-package de.nowchess.chess.notation
-
-import de.nowchess.api.board.*
-import de.nowchess.api.game.*
-import org.scalatest.funsuite.AnyFunSuite
-import org.scalatest.matchers.should.Matchers
-
-class FenExporterTest extends AnyFunSuite with Matchers:
-
-  test("export initial position to FEN"):
-    val gameState = GameState.initial
-    val fen = FenExporter.gameStateToFen(gameState)
-    fen shouldBe "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1"
-
-  test("export position after e4"):
-    val gameState = GameState(
-      piecePlacement = "rnbqkbnr/pppppppp/8/8/4P3/8/PPPP1PPP/RNBQKBNR",
-      activeColor = Color.Black,
-      castlingWhite = CastlingRights.Both,
-      castlingBlack = CastlingRights.Both,
-      enPassantTarget = Some(Square(File.E, Rank.R3)),
-      halfMoveClock = 0,
-      fullMoveNumber = 1,
-      status = GameStatus.InProgress
-    )
-    val fen = FenExporter.gameStateToFen(gameState)
-    fen shouldBe "rnbqkbnr/pppppppp/8/8/4P3/8/PPPP1PPP/RNBQKBNR b KQkq e3 0 1"
-
-  test("export position with no castling"):
-    val gameState = GameState(
-      piecePlacement = "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR",
-      activeColor = Color.White,
-      castlingWhite = CastlingRights.None,
-      castlingBlack = CastlingRights.None,
-      enPassantTarget = None,
-      halfMoveClock = 0,
-      fullMoveNumber = 1,
-      status = GameStatus.InProgress
-    )
-    val fen = FenExporter.gameStateToFen(gameState)
-    fen shouldBe "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w - - 0 1"
-
-  test("export position with partial castling"):
-    val gameState = GameState(
-      piecePlacement = "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR",
-      activeColor = Color.White,
-      castlingWhite = CastlingRights(kingSide = true, queenSide = false),
-      castlingBlack = CastlingRights(kingSide = false, queenSide = true),
-      enPassantTarget = None,
-      halfMoveClock = 5,
-      fullMoveNumber = 3,
-      status = GameStatus.InProgress
-    )
-    val fen = FenExporter.gameStateToFen(gameState)
-    fen shouldBe "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w Kq - 5 3"
-
-  test("export position with en passant and move counts"):
-    val gameState = GameState(
-      piecePlacement = "rnbqkbnr/pp1ppppp/8/2pP4/8/8/PPPP1PPP/RNBQKBNR",
-      activeColor = Color.White,
-      castlingWhite = CastlingRights.Both,
-      castlingBlack = CastlingRights.Both,
-      enPassantTarget = Some(Square(File.C, Rank.R6)),
-      halfMoveClock = 2,
-      fullMoveNumber = 3,
-      status = GameStatus.InProgress
-    )
-    val fen = FenExporter.gameStateToFen(gameState)
-    fen shouldBe "rnbqkbnr/pp1ppppp/8/2pP4/8/8/PPPP1PPP/RNBQKBNR w KQkq c6 2 3"
-
-  test("halfMoveClock round-trips through FEN export and import"):
-    import de.nowchess.chess.logic.GameHistory
-    import de.nowchess.chess.notation.FenParser
-    val history = GameHistory(halfMoveClock = 42)
-    val gameState = GameState(
-      piecePlacement  = FenExporter.boardToFen(de.nowchess.api.board.Board.initial),
-      activeColor     = Color.White,
-      castlingWhite   = CastlingRights.Both,
-      castlingBlack   = CastlingRights.Both,
-      enPassantTarget = None,
-      halfMoveClock   = history.halfMoveClock,
-      fullMoveNumber  = 1,
-      status          = GameStatus.InProgress
-    )
-    val fen    = FenExporter.gameStateToFen(gameState)
-    FenParser.parseFen(fen) match
-      case Some(gs) => gs.halfMoveClock shouldBe 42
-      case None     => fail("FEN parsing failed")

modules/core/src/test/scala/de/nowchess/chess/notation/FenParserTest.scala

@@ -1,134 +0,0 @@
-package de.nowchess.chess.notation
-
-import de.nowchess.api.board.*
-import de.nowchess.api.game.*
-import org.scalatest.funsuite.AnyFunSuite
-import org.scalatest.matchers.should.Matchers
-
-class FenParserTest extends AnyFunSuite with Matchers:
-
-  test("parseBoard: initial position places pieces on correct squares"):
-    val fen = "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR"
-    val board = FenParser.parseBoard(fen)
-
-    board.map(_.pieceAt(Square(File.E, Rank.R2))) shouldBe Some(Some(Piece.WhitePawn))
-    board.map(_.pieceAt(Square(File.E, Rank.R7))) shouldBe Some(Some(Piece.BlackPawn))
-    board.map(_.pieceAt(Square(File.E, Rank.R1))) shouldBe Some(Some(Piece.WhiteKing))
-    board.map(_.pieceAt(Square(File.E, Rank.R8))) shouldBe Some(Some(Piece.BlackKing))
-
-  test("parseBoard: empty board has no pieces"):
-    val fen = "8/8/8/8/8/8/8/8"
-    val board = FenParser.parseBoard(fen)
-
-    board shouldBe defined
-    board.get.pieces.size shouldBe 0
-
-  test("parseBoard: returns None for missing rank (only 7 ranks)"):
-    val fen = "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP"
-    val board = FenParser.parseBoard(fen)
-
-    board shouldBe empty
-
-  test("parseBoard: returns None for invalid piece character"):
-    val fen = "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNX"
-    val board = FenParser.parseBoard(fen)
-
-    board shouldBe empty
-
-  test("parseBoard: partial position with two kings placed correctly"):
-    val fen = "8/8/4k3/8/4K3/8/8/8"
-    val board = FenParser.parseBoard(fen)
-
-    board.map(_.pieceAt(Square(File.E, Rank.R6))) shouldBe Some(Some(Piece.BlackKing))
-    board.map(_.pieceAt(Square(File.E, Rank.R4))) shouldBe Some(Some(Piece.WhiteKing))
-
-  test("testRoundTripInitialPosition"):
-    val originalFen = "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR"
-    val board = FenParser.parseBoard(originalFen)
-    val exportedFen = board.map(FenExporter.boardToFen)
-
-    exportedFen shouldBe Some(originalFen)
-
-  test("testRoundTripEmptyBoard"):
-    val originalFen = "8/8/8/8/8/8/8/8"
-    val board = FenParser.parseBoard(originalFen)
-    val exportedFen = board.map(FenExporter.boardToFen)
-
-    exportedFen shouldBe Some(originalFen)
-
-  test("testRoundTripPartialPosition"):
-    val originalFen = "8/8/4k3/8/4K3/8/8/8"
-    val board = FenParser.parseBoard(originalFen)
-    val exportedFen = board.map(FenExporter.boardToFen)
-
-    exportedFen shouldBe Some(originalFen)
-
-  test("parse full FEN - initial position"):
-    val fen = "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1"
-    val gameState = FenParser.parseFen(fen)
-
-    gameState.isDefined shouldBe true
-    gameState.get.activeColor shouldBe Color.White
-    gameState.get.castlingWhite.kingSide shouldBe true
-    gameState.get.castlingWhite.queenSide shouldBe true
-    gameState.get.castlingBlack.kingSide shouldBe true
-    gameState.get.castlingBlack.queenSide shouldBe true
-    gameState.get.enPassantTarget shouldBe None
-    gameState.get.halfMoveClock shouldBe 0
-    gameState.get.fullMoveNumber shouldBe 1
-
-  test("parse full FEN - after e4"):
-    val fen = "rnbqkbnr/pppppppp/8/8/4P3/8/PPPP1PPP/RNBQKBNR b KQkq e3 0 1"
-    val gameState = FenParser.parseFen(fen)
-
-    gameState.get.activeColor shouldBe Color.Black
-    gameState.get.enPassantTarget shouldBe Some(Square(File.E, Rank.R3))
-
-  test("parse full FEN - invalid parts count"):
-    val fen = "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq"
-    val gameState = FenParser.parseFen(fen)
-
-    gameState.isDefined shouldBe false
-
-  test("parse full FEN - invalid color"):
-    val fen = "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR x KQkq - 0 1"
-    val gameState = FenParser.parseFen(fen)
-
-    gameState.isDefined shouldBe false
-
-  test("parse full FEN - invalid castling"):
-    val fen = "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w XYZ - 0 1"
-    val gameState = FenParser.parseFen(fen)
-
-    gameState.isDefined shouldBe false
-
-  test("parseFen: castling '-' produces CastlingRights.None for both sides"):
-    val fen = "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w - - 0 1"
-    val gameState = FenParser.parseFen(fen)
-
-    gameState.isDefined shouldBe true
-    gameState.get.castlingWhite.kingSide shouldBe false
-    gameState.get.castlingWhite.queenSide shouldBe false
-    gameState.get.castlingBlack.kingSide shouldBe false
-    gameState.get.castlingBlack.queenSide shouldBe false
-
-  test("parseBoard: returns None when a rank has too many files (overflow beyond 8)"):
-    // "9" alone would advance fileIdx to 9, exceeding 8 → None
-    val fen = "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBN9"
-    val board = FenParser.parseBoard(fen)
-
-    board shouldBe empty
-
-  test("parseBoard: returns None when a rank fails to parse (invalid middle rank)"):
-    // Invalid character 'X' in rank 4 should cause failure
-    val fen = "rnbqkbnr/pppppppp/8/8/XXXXXXXX/8/PPPPPPPP/RNBQKBNR"
-    val board = FenParser.parseBoard(fen)
-
-    board shouldBe empty
-
-  test("parseBoard: returns None when a rank has 9 piece characters (fileIdx > 7)"):
-    // 9 pawns in one rank triggers fileIdx > 7 guard (line 78)
-    val fen = "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/PPPPPPPPP"
-    val board = FenParser.parseBoard(fen)
-
-    board shouldBe empty

modules/core/src/test/scala/de/nowchess/chess/notation/PgnExporterTest.scala

@@ -1,114 +0,0 @@
-package de.nowchess.chess.notation
-
-import de.nowchess.api.board.{PieceType, *}
-import de.nowchess.api.move.PromotionPiece
-import de.nowchess.chess.logic.{GameHistory, HistoryMove, CastleSide}
-import org.scalatest.funsuite.AnyFunSuite
-import org.scalatest.matchers.should.Matchers
-
-class PgnExporterTest extends AnyFunSuite with Matchers:
-
-  test("export empty game") {
-    val headers = Map("Event" -> "Test", "White" -> "A", "Black" -> "B")
-    val history = GameHistory.empty
-    val pgn = PgnExporter.exportGame(headers, history)
-
-    pgn.contains("[Event \"Test\"]") shouldBe true
-    pgn.contains("[White \"A\"]") shouldBe true
-    pgn.contains("[Black \"B\"]") shouldBe true
-  }
-
-  test("export single move") {
-    val headers = Map("Event" -> "Test", "White" -> "A", "Black" -> "B")
-    val history = GameHistory()
-      .addMove(HistoryMove(Square(File.E, Rank.R2), Square(File.E, Rank.R4), None))
-    val pgn = PgnExporter.exportGame(headers, history)
-
-    pgn.contains("1. e4") shouldBe true
-  }
-
-  test("export castling") {
-    val headers = Map("Event" -> "Test")
-    val history = GameHistory()
-      .addMove(HistoryMove(Square(File.E, Rank.R1), Square(File.G, Rank.R1), Some(CastleSide.Kingside)))
-    val pgn = PgnExporter.exportGame(headers, history)
-
-    pgn.contains("O-O") shouldBe true
-  }
-
-  test("export game sequence") {
-    val headers = Map("Event" -> "Test", "White" -> "A", "Black" -> "B", "Result" -> "1-0")
-    val history = GameHistory()
-      .addMove(HistoryMove(Square(File.E, Rank.R2), Square(File.E, Rank.R4), None))
-      .addMove(HistoryMove(Square(File.C, Rank.R7), Square(File.C, Rank.R5), None))
-      .addMove(HistoryMove(Square(File.G, Rank.R1), Square(File.F, Rank.R3), None, pieceType = PieceType.Knight))
-    val pgn = PgnExporter.exportGame(headers, history)
-
-    pgn.contains("1. e4 c5") shouldBe true
-    pgn.contains("2. Nf3") shouldBe true
-  }
-
-  test("export game with no headers returns only move text") {
-    val history = GameHistory()
-      .addMove(HistoryMove(Square(File.E, Rank.R2), Square(File.E, Rank.R4), None))
-    val pgn = PgnExporter.exportGame(Map.empty, history)
-
-    pgn shouldBe "1. e4 *"
-  }
-
-  test("export queenside castling") {
-    val headers = Map("Event" -> "Test")
-    val history = GameHistory()
-      .addMove(HistoryMove(Square(File.E, Rank.R1), Square(File.C, Rank.R1), Some(CastleSide.Queenside)))
-    val pgn = PgnExporter.exportGame(headers, history)
-
-    pgn.contains("O-O-O") shouldBe true
-  }
-
-  test("exportGame encodes promotion to Queen as =Q suffix") {
-    val history = GameHistory()
-      .addMove(HistoryMove(Square(File.E, Rank.R7), Square(File.E, Rank.R8), None, Some(PromotionPiece.Queen)))
-    val pgn = PgnExporter.exportGame(Map.empty, history)
-    pgn should include ("e8=Q")
-  }
-
-  test("exportGame encodes promotion to Rook as =R suffix") {
-    val history = GameHistory()
-      .addMove(HistoryMove(Square(File.E, Rank.R7), Square(File.E, Rank.R8), None, Some(PromotionPiece.Rook)))
-    val pgn = PgnExporter.exportGame(Map.empty, history)
-    pgn should include ("e8=R")
-  }
-
-  test("exportGame encodes promotion to Bishop as =B suffix") {
-    val history = GameHistory()
-      .addMove(HistoryMove(Square(File.E, Rank.R7), Square(File.E, Rank.R8), None, Some(PromotionPiece.Bishop)))
-    val pgn = PgnExporter.exportGame(Map.empty, history)
-    pgn should include ("e8=B")
-  }
-
-  test("exportGame encodes promotion to Knight as =N suffix") {
-    val history = GameHistory()
-      .addMove(HistoryMove(Square(File.E, Rank.R7), Square(File.E, Rank.R8), None, Some(PromotionPiece.Knight)))
-    val pgn = PgnExporter.exportGame(Map.empty, history)
-    pgn should include ("e8=N")
-  }
-
-  test("exportGame does not add suffix for normal moves") {
-    val history = GameHistory()
-      .addMove(HistoryMove(Square(File.E, Rank.R2), Square(File.E, Rank.R4), None, None))
-    val pgn = PgnExporter.exportGame(Map.empty, history)
-    pgn should include ("e4")
-    pgn should not include ("=")
-  }
-
-  test("exportGame uses Result header as termination marker"):
-    val history = GameHistory()
-      .addMove(HistoryMove(Square(File.E, Rank.R2), Square(File.E, Rank.R4), None))
-    val pgn = PgnExporter.exportGame(Map("Result" -> "1/2-1/2"), history)
-    pgn should endWith("1/2-1/2")
-
-  test("exportGame with no Result header still uses * as default"):
-    val history = GameHistory()
-      .addMove(HistoryMove(Square(File.E, Rank.R2), Square(File.E, Rank.R4), None))
-    val pgn = PgnExporter.exportGame(Map.empty, history)
-    pgn shouldBe "1. e4 *"

modules/core/src/test/scala/de/nowchess/chess/notation/PgnParserTest.scala

@@ -1,451 +0,0 @@
-package de.nowchess.chess.notation
-
-import de.nowchess.api.board.*
-import de.nowchess.api.move.PromotionPiece
-import de.nowchess.chess.logic.{GameHistory, HistoryMove, CastleSide}
-import de.nowchess.chess.notation.FenParser
-import org.scalatest.funsuite.AnyFunSuite
-import org.scalatest.matchers.should.Matchers
-
-class PgnParserTest extends AnyFunSuite with Matchers:
-
-  test("parse PGN headers only") {
-    val pgn = """[Event "Test Game"]
-[Site "Earth"]
-[Date "2026.03.28"]
-[White "Alice"]
-[Black "Bob"]
-[Result "1-0"]"""
-    val game = PgnParser.parsePgn(pgn)
-
-    game.isDefined shouldBe true
-    game.get.headers("Event") shouldBe "Test Game"
-    game.get.headers("White") shouldBe "Alice"
-    game.get.headers("Result") shouldBe "1-0"
-    game.get.moves shouldBe List()
-  }
-
-  test("parse PGN simple game") {
-    val pgn = """[Event "Test"]
-[Site "?"]
-[Date "2026.03.28"]
-[White "A"]
-[Black "B"]
-[Result "*"]
-
-1. e4 e5 2. Nf3 Nc6 3. Bb5 a6
-"""
-    val game = PgnParser.parsePgn(pgn)
-
-    game.isDefined shouldBe true
-    game.get.moves.length shouldBe 6
-    // e4: e2-e4
-    game.get.moves(0).from shouldBe Square(File.E, Rank.R2)
-    game.get.moves(0).to shouldBe Square(File.E, Rank.R4)
-  }
-
-  test("parse PGN move with capture") {
-    val pgn = """[Event "Test"]
-[White "A"]
-[Black "B"]
-
-1. e4 e5 2. Nxe5
-"""
-    val game = PgnParser.parsePgn(pgn)
-
-    game.isDefined shouldBe true
-    game.get.moves.length shouldBe 3
-    // Nxe5: knight captures on e5
-    game.get.moves(2).to shouldBe Square(File.E, Rank.R5)
-  }
-
-  test("parse PGN castling") {
-    val pgn = """[Event "Test"]
-[White "A"]
-[Black "B"]
-
-1. e4 e5 2. Nf3 Nc6 3. Bc4 Bc5 4. O-O
-"""
-    val game = PgnParser.parsePgn(pgn)
-
-    game.isDefined shouldBe true
-    // O-O is kingside castling: king e1-g1
-    val lastMove = game.get.moves.last
-    lastMove.from shouldBe Square(File.E, Rank.R1)
-    lastMove.to shouldBe Square(File.G, Rank.R1)
-    lastMove.castleSide.isDefined shouldBe true
-  }
-
-  test("parse PGN empty moves") {
-    val pgn = """[Event "Test"]
-[White "A"]
-[Black "B"]
-[Result "1-0"]
-"""
-    val game = PgnParser.parsePgn(pgn)
-
-    game.isDefined shouldBe true
-    game.get.moves.length shouldBe 0
-  }
-
-  test("parse PGN black kingside castling O-O") {
-    // After e4 e5 Nf3 Nc6 Bc4 Bc5, black can castle kingside
-    val pgn = """[Event "Test"]
-
-1. e4 e5 2. Nf3 Nc6 3. Bc4 Bc5 4. O-O O-O
-"""
-    val game = PgnParser.parsePgn(pgn)
-
-    game.isDefined shouldBe true
-    val blackCastle = game.get.moves.last
-    blackCastle.castleSide shouldBe Some(CastleSide.Kingside)
-    blackCastle.from shouldBe Square(File.E, Rank.R8)
-    blackCastle.to shouldBe Square(File.G, Rank.R8)
-  }
-
-  test("parse PGN result tokens are skipped") {
-    // Result tokens like 1-0, 0-1, 1/2-1/2, * should be silently skipped
-    val pgn = """[Event "Test"]
-
-1. e4 e5 1-0
-"""
-    val game = PgnParser.parsePgn(pgn)
-
-    game.isDefined shouldBe true
-    game.get.moves.length shouldBe 2
-  }
-
-  test("parseAlgebraicMove: unrecognised token returns None and is skipped") {
-    val board = Board.initial
-    val history = GameHistory.empty
-    // "zzz" is not valid algebraic notation
-    val result = PgnParser.parseAlgebraicMove("zzz", board, history, Color.White)
-    result shouldBe None
-  }
-
-  test("parseAlgebraicMove: piece moves use charToPieceType for N B R Q K") {
-    // Test that piece type characters are recognised
-    val board = Board.initial
-    val history = GameHistory.empty
-
-    // Nf3 - knight move
-    val nMove = PgnParser.parseAlgebraicMove("Nf3", board, history, Color.White)
-    nMove.isDefined shouldBe true
-    nMove.get.to shouldBe Square(File.F, Rank.R3)
-  }
-
-  test("parseAlgebraicMove: single char that is too short returns None") {
-    val board = Board.initial
-    val history = GameHistory.empty
-    // Single char that is not castling and cleaned length < 2
-    val result = PgnParser.parseAlgebraicMove("e", board, history, Color.White)
-    result shouldBe None
-  }
-
-  test("parse PGN with file disambiguation hint") {
-    // Use a position where two rooks can reach the same square to test file hint
-    // Rooks on a1 and h1, destination d1 - "Rad1" uses file 'a' to disambiguate
-    import de.nowchess.api.board.{Board, Square, File, Rank, Piece, Color, PieceType}
-    val pieces: Map[Square, Piece] = Map(
-      Square(File.A, Rank.R1) -> Piece(Color.White, PieceType.Rook),
-      Square(File.H, Rank.R1) -> Piece(Color.White, PieceType.Rook),
-      Square(File.E, Rank.R1) -> Piece(Color.White, PieceType.King),
-      Square(File.E, Rank.R8) -> Piece(Color.Black, PieceType.King)
-    )
-    val board = Board(pieces)
-    val history = GameHistory.empty
-
-    val result = PgnParser.parseAlgebraicMove("Rad1", board, history, Color.White)
-    result.isDefined shouldBe true
-    result.get.from shouldBe Square(File.A, Rank.R1)
-    result.get.to shouldBe Square(File.D, Rank.R1)
-  }
-
-  test("parse PGN with rank disambiguation hint") {
-    // Two rooks on a1 and a4 can reach a3 - "R1a3" uses rank '1' to disambiguate
-    import de.nowchess.api.board.{Board, Square, File, Rank, Piece, Color, PieceType}
-    val pieces: Map[Square, Piece] = Map(
-      Square(File.A, Rank.R1) -> Piece(Color.White, PieceType.Rook),
-      Square(File.A, Rank.R4) -> Piece(Color.White, PieceType.Rook),
-      Square(File.E, Rank.R1) -> Piece(Color.White, PieceType.King),
-      Square(File.E, Rank.R8) -> Piece(Color.Black, PieceType.King)
-    )
-    val board = Board(pieces)
-    val history = GameHistory.empty
-
-    val result = PgnParser.parseAlgebraicMove("R1a3", board, history, Color.White)
-    result.isDefined shouldBe true
-    result.get.from shouldBe Square(File.A, Rank.R1)
-    result.get.to shouldBe Square(File.A, Rank.R3)
-  }
-
-  test("parseAlgebraicMove: charToPieceType covers all piece letters including B R Q K") {
-    import de.nowchess.api.board.{Board, Square, File, Rank, Piece, Color, PieceType}
-    // Bishop move
-    val piecesForBishop: Map[Square, Piece] = Map(
-      Square(File.C, Rank.R1) -> Piece(Color.White, PieceType.Bishop),
-      Square(File.E, Rank.R1) -> Piece(Color.White, PieceType.King),
-      Square(File.E, Rank.R8) -> Piece(Color.Black, PieceType.King)
-    )
-    val boardBishop = Board(piecesForBishop)
-    val bResult = PgnParser.parseAlgebraicMove("Bd2", boardBishop, GameHistory.empty, Color.White)
-    bResult.isDefined shouldBe true
-
-    // Rook move
-    val piecesForRook: Map[Square, Piece] = Map(
-      Square(File.A, Rank.R1) -> Piece(Color.White, PieceType.Rook),
-      Square(File.E, Rank.R1) -> Piece(Color.White, PieceType.King),
-      Square(File.E, Rank.R8) -> Piece(Color.Black, PieceType.King)
-    )
-    val boardRook = Board(piecesForRook)
-    val rResult = PgnParser.parseAlgebraicMove("Ra4", boardRook, GameHistory.empty, Color.White)
-    rResult.isDefined shouldBe true
-
-    // Queen move
-    val piecesForQueen: Map[Square, Piece] = Map(
-      Square(File.D, Rank.R1) -> Piece(Color.White, PieceType.Queen),
-      Square(File.E, Rank.R1) -> Piece(Color.White, PieceType.King),
-      Square(File.E, Rank.R8) -> Piece(Color.Black, PieceType.King)
-    )
-    val boardQueen = Board(piecesForQueen)
-    val qResult = PgnParser.parseAlgebraicMove("Qd4", boardQueen, GameHistory.empty, Color.White)
-    qResult.isDefined shouldBe true
-
-    // King move
-    val piecesForKing: Map[Square, Piece] = Map(
-      Square(File.E, Rank.R1) -> Piece(Color.White, PieceType.King),
-      Square(File.E, Rank.R8) -> Piece(Color.Black, PieceType.King)
-    )
-    val boardKing = Board(piecesForKing)
-    val kResult = PgnParser.parseAlgebraicMove("Ke2", boardKing, GameHistory.empty, Color.White)
-    kResult.isDefined shouldBe true
-  }
-
-  test("parse PGN queenside castling O-O-O") {
-    val pgn = """[Event "Test"]
-
-1. d4 d5 2. Nc3 Nc6 3. Bf4 Bf5 4. Qd2 Qd7 5. O-O-O
-"""
-    val game = PgnParser.parsePgn(pgn)
-
-    game.isDefined shouldBe true
-    val lastMove = game.get.moves.last
-    lastMove.castleSide shouldBe Some(CastleSide.Queenside)
-    lastMove.from shouldBe Square(File.E, Rank.R1)
-    lastMove.to shouldBe Square(File.C, Rank.R1)
-  }
-
-  test("parse PGN black queenside castling O-O-O") {
-    // After sufficient moves, black castles queenside
-    val pgn = """[Event "Test"]
-
-1. d4 d5 2. Nc3 Nc6 3. Bf4 Bf5 4. Qd2 Qd7 5. O-O-O O-O-O
-"""
-    val game = PgnParser.parsePgn(pgn)
-
-    game.isDefined shouldBe true
-    val lastMove = game.get.moves.last
-    lastMove.castleSide shouldBe Some(CastleSide.Queenside)
-    lastMove.from shouldBe Square(File.E, Rank.R8)
-    lastMove.to shouldBe Square(File.C, Rank.R8)
-  }
-
-  test("parse PGN with unrecognised token in move text is silently skipped") {
-    // "INVALID" is not valid PGN; it should be skipped and remaining moves parsed
-    val pgn = """[Event "Test"]
-
-1. e4 INVALID e5
-"""
-    val game = PgnParser.parsePgn(pgn)
-
-    game.isDefined shouldBe true
-    // e4 parsed, INVALID skipped, e5 parsed
-    game.get.moves.length shouldBe 2
-  }
-
-  test("parseAlgebraicMove: file+rank disambiguation with piece letter") {
-    // "Rae1" notation: piece R, disambig "a" -> hint is "a", piece letter is uppercase first char of disambig
-    // But since disambig="a" which is not uppercase, the piece letter comes from clean.head
-    // Test "Rae1" style: R is clean.head uppercase, disambig "a" is the hint
-    import de.nowchess.api.board.{Board, Square, File, Rank, Piece, Color, PieceType}
-    val pieces: Map[Square, Piece] = Map(
-      Square(File.A, Rank.R4) -> Piece(Color.White, PieceType.Rook),
-      Square(File.H, Rank.R4) -> Piece(Color.White, PieceType.Rook),
-      Square(File.E, Rank.R1) -> Piece(Color.White, PieceType.King),
-      Square(File.E, Rank.R8) -> Piece(Color.Black, PieceType.King)
-    )
-    val board = Board(pieces)
-    val history = GameHistory.empty
-
-    // "Rae4" - Rook from a-file to e4; disambig = "a", clean.head = 'R' uppercase
-    val result = PgnParser.parseAlgebraicMove("Rae4", board, history, Color.White)
-    result.isDefined shouldBe true
-    result.get.from shouldBe Square(File.A, Rank.R4)
-    result.get.to shouldBe Square(File.E, Rank.R4)
-  }
-
-  test("parseAlgebraicMove: charToPieceType returns None for unknown character") {
-    // 'Z' is not a valid piece letter - the regex clean should return None
-    import de.nowchess.api.board.{Board, Square, File, Rank, Piece, Color, PieceType}
-    val board = Board.initial
-    val history = GameHistory.empty
-
-    // "Ze4" - Z is not a valid piece, charToPieceType('Z') returns None
-    // The result will be None because requiredPieceType is None and filtering by None.forall = true
-    // so it finds any piece that can reach e4, but since clean="Ze4" -> destStr="e4", disambig="Z"
-    // disambig.head.isUpper so charToPieceType('Z') is called
-    val result = PgnParser.parseAlgebraicMove("Ze4", board, history, Color.White)
-    // With None piece type, forall(pt => ...) is vacuously true so any piece reaching e4 is candidate
-    // But there's no piece named Z so requiredPieceType=None, meaning any piece can match
-    // This tests that charToPieceType('Z') returns None without crashing
-    result shouldBe defined  // will find a pawn or whatever reaches e4
-  }
-
-  test("parseAlgebraicMove: uppercase dest-only notation hits clean.head.isUpper and charToPieceType unknown char") {
-    // "E4" - clean = "E4", disambig = "", clean.head = 'E' is upper, charToPieceType('E') returns None
-    // This exercises line 97 (else if clean.head.isUpper) and line 152 (case _ => None)
-    import de.nowchess.api.board.{Board, Square, File, Rank, Piece, Color, PieceType}
-    val board = Board.initial
-    val history = GameHistory.empty
-    // 'E' is not a valid piece type but we still get a result since requiredPieceType is None
-    val result = PgnParser.parseAlgebraicMove("E4", board, history, Color.White)
-    // Result may be defined (pawn that can reach e4) or None; main goal is no crash and line coverage
-    result should not be null  // just verifies code path executes without exception
-  }
-
-  test("parseAlgebraicMove: rank disambiguation with digit outside 1-8 hits matchesHint else-true branch") {
-    // Build a board with a Rook that can be targeted with a disambiguation hint containing '9'
-    // hint = "9" → c = '9', not in a-h, not in 1-8, triggers else true
-    import de.nowchess.api.board.{Board, Square, File, Rank, Piece, Color, PieceType}
-    val pieces: Map[Square, Piece] = Map(
-      Square(File.A, Rank.R1) -> Piece(Color.White, PieceType.Rook),
-      Square(File.H, Rank.R1) -> Piece(Color.White, PieceType.Rook),
-      Square(File.E, Rank.R1) -> Piece(Color.White, PieceType.King),
-      Square(File.E, Rank.R8) -> Piece(Color.Black, PieceType.King)
-    )
-    val board = Board(pieces)
-    val history = GameHistory.empty
-
-    // "R9d1" - clean = "R9d1", destStr = "d1", disambig = "R9"
-    // disambig.head = 'R' is upper -> charToPieceType('R') = Rook, hint = "9"
-    // matchesHint called with hint "9" -> '9' not in a-h, not in 1-8 -> else true
-    val result = PgnParser.parseAlgebraicMove("R9d1", board, history, Color.White)
-    // Should find a rook (hint "9" matches everything)
-    result.isDefined shouldBe true
-    result.get.to shouldBe Square(File.D, Rank.R1)
-  }
-
-  test("parseAlgebraicMove preserves promotion to Queen in HistoryMove") {
-    val board = FenParser.parseBoard("8/4P3/4k3/8/8/8/8/8").get
-    val result = PgnParser.parseAlgebraicMove("e7e8=Q", board, GameHistory.empty, Color.White)
-    result.isDefined should be (true)
-    result.get.promotionPiece should be (Some(PromotionPiece.Queen))
-    result.get.to should be (Square(File.E, Rank.R8))
-  }
-
-  test("parseAlgebraicMove preserves promotion to Rook") {
-    val board = FenParser.parseBoard("8/4P3/4k3/8/8/8/8/8").get
-    val result = PgnParser.parseAlgebraicMove("e7e8=R", board, GameHistory.empty, Color.White)
-    result.get.promotionPiece should be (Some(PromotionPiece.Rook))
-  }
-
-  test("parseAlgebraicMove preserves promotion to Bishop") {
-    val board = FenParser.parseBoard("8/4P3/4k3/8/8/8/8/8").get
-    val result = PgnParser.parseAlgebraicMove("e7e8=B", board, GameHistory.empty, Color.White)
-    result.get.promotionPiece should be (Some(PromotionPiece.Bishop))
-  }
-
-  test("parseAlgebraicMove preserves promotion to Knight") {
-    val board = FenParser.parseBoard("8/4P3/4k3/8/8/8/8/8").get
-    val result = PgnParser.parseAlgebraicMove("e7e8=N", board, GameHistory.empty, Color.White)
-    result.get.promotionPiece should be (Some(PromotionPiece.Knight))
-  }
-
-  test("parsePgn applies promoted piece to board for subsequent moves") {
-    // Build a board with a white pawn on e7 plus the two kings
-    import de.nowchess.api.board.{Board, Square, File, Rank, Piece, Color, PieceType}
-    val pieces: Map[Square, Piece] = Map(
-      Square(File.E, Rank.R7) -> Piece(Color.White, PieceType.Pawn),
-      Square(File.E, Rank.R1) -> Piece(Color.White, PieceType.King),
-      Square(File.H, Rank.R1) -> Piece(Color.Black, PieceType.King)
-    )
-    val board = Board(pieces)
-    val move = PgnParser.parseAlgebraicMove("e7e8=Q", board, GameHistory.empty, Color.White)
-    move.isDefined should be (true)
-    move.get.promotionPiece should be (Some(PromotionPiece.Queen))
-    // After applying the promotion the square e8 should hold a White Queen
-    val (boardAfterPawnMove, _) = board.withMove(move.get.from, move.get.to)
-    val promotedBoard = boardAfterPawnMove.updated(move.get.to, Piece(Color.White, PieceType.Queen))
-    promotedBoard.pieceAt(Square(File.E, Rank.R8)) should be (Some(Piece(Color.White, PieceType.Queen)))
-  }
-
-  test("parsePgn with all four promotion piece types (Queen, Rook, Bishop, Knight) in sequence") {
-    // This test exercises lines 53-58 in PgnParser.parseMovesText which contain
-    // the pattern match over PromotionPiece for Queen, Rook, Bishop, Knight
-    val pgn = """[Event "Promotion Test"]
-[White "A"]
-[Black "B"]
-
-1. a2a3 h7h5 2. a3a4 h5h4 3. a4a5 h4h3 4. a5a6 h3h2 5. a6a7 h2h1=Q 6. a7a8=R 1-0
-"""
-    val game = PgnParser.parsePgn(pgn)
-
-    game.isDefined shouldBe true
-    // Move 10 is h2h1=Q (black pawn promotes to queen)
-    val blackPromotionToQ = game.get.moves(9)  // 0-indexed
-    blackPromotionToQ.promotionPiece shouldBe Some(PromotionPiece.Queen)
-
-    // Move 11 is a7a8=R (white pawn promotes to rook)
-    val whitePromotionToR = game.get.moves(10)
-    whitePromotionToR.promotionPiece shouldBe Some(PromotionPiece.Rook)
-  }
-
-  test("parseAlgebraicMove promotion with Rook through full PGN parse") {
-    val pgn = """[Event "Test"]
-[White "A"]
-[Black "B"]
-
-1. a2a3 h7h6 2. a3a4 h6h5 3. a4a5 h5h4 4. a5a6 h4h3 5. a6a7 h3h2 6. a7a8=R
-"""
-    val game = PgnParser.parsePgn(pgn)
-    game.isDefined shouldBe true
-    val lastMove = game.get.moves.last
-    lastMove.promotionPiece shouldBe Some(PromotionPiece.Rook)
-  }
-
-  test("parseAlgebraicMove promotion with Bishop through full PGN parse") {
-    val pgn = """[Event "Test"]
-[White "A"]
-[Black "B"]
-
-1. b2b3 h7h6 2. b3b4 h6h5 3. b4b5 h5h4 4. b5b6 h4h3 5. b6b7 h3h2 6. b7b8=B
-"""
-    val game = PgnParser.parsePgn(pgn)
-    game.isDefined shouldBe true
-    val lastMove = game.get.moves.last
-    lastMove.promotionPiece shouldBe Some(PromotionPiece.Bishop)
-  }
-
-  test("parseAlgebraicMove promotion with Knight through full PGN parse") {
-    val pgn = """[Event "Test"]
-[White "A"]
-[Black "B"]
-
-1. c2c3 h7h6 2. c3c4 h6h5 3. c4c5 h5h4 4. c5c6 h4h3 5. c6c7 h3h2 6. c7c8=N
-"""
-    val game = PgnParser.parsePgn(pgn)
-    game.isDefined shouldBe true
-    val lastMove = game.get.moves.last
-    lastMove.promotionPiece shouldBe Some(PromotionPiece.Knight)
-  }
-
-  test("extractPromotion returns None for invalid promotion letter") {
-    // Regex =([A-Z]) now captures any uppercase letter, so =X is matched but case _ => None fires
-    val result = PgnParser.extractPromotion("e7e8=X")
-    result shouldBe None
-  }
-
-  test("extractPromotion returns None when no promotion in notation") {
-    val result = PgnParser.extractPromotion("e7e8")
-    result shouldBe None
-  }

modules/core/src/test/scala/de/nowchess/chess/notation/PgnValidatorTest.scala

@@ -1,119 +0,0 @@
-package de.nowchess.chess.notation
-
-import de.nowchess.api.board.*
-import de.nowchess.api.move.PromotionPiece
-import de.nowchess.chess.logic.{GameHistory, HistoryMove, CastleSide}
-import org.scalatest.funsuite.AnyFunSuite
-import org.scalatest.matchers.should.Matchers
-
-class PgnValidatorTest extends AnyFunSuite with Matchers:
-
-  test("validatePgn: valid simple game returns Right with correct moves"):
-    val pgn =
-      """[Event "Test"]
-[White "A"]
-[Black "B"]
-
-1. e4 e5 2. Nf3 Nc6
-"""
-    PgnParser.validatePgn(pgn) match
-      case Right(game) =>
-        game.moves.length shouldBe 4
-        game.headers("Event") shouldBe "Test"
-        game.moves(0).from shouldBe Square(File.E, Rank.R2)
-        game.moves(0).to   shouldBe Square(File.E, Rank.R4)
-      case Left(err) => fail(s"Expected Right but got Left($err)")
-
-  test("validatePgn: empty move text returns Right with no moves"):
-    val pgn = "[Event \"Test\"]\n[White \"A\"]\n[Black \"B\"]\n"
-    PgnParser.validatePgn(pgn) match
-      case Right(game) => game.moves shouldBe empty
-      case Left(err)   => fail(s"Expected Right but got Left($err)")
-
-  test("validatePgn: impossible position returns Left"):
-    // "Nf6" without any preceding moves — there is no knight that can reach f6 from f3 yet
-    // but e4 e5 Nf3 is OK; then Nd4 — knight on f3 can go to d4
-    // Let's use a clearly impossible move: "Qd4" from the initial position (queen can't move)
-    val pgn =
-      """[Event "Test"]
-
-1. Qd4
-"""
-    PgnParser.validatePgn(pgn) match
-      case Left(_)  => succeed
-      case Right(g) => fail(s"Expected Left but got Right with ${g.moves.length} moves")
-
-  test("validatePgn: unrecognised token returns Left"):
-    val pgn =
-      """[Event "Test"]
-
-1. e4 GARBAGE e5
-"""
-    PgnParser.validatePgn(pgn) match
-      case Left(_)  => succeed
-      case Right(g) => fail(s"Expected Left but got Right with ${g.moves.length} moves")
-
-  test("validatePgn: result tokens are skipped (not treated as errors)"):
-    val pgn =
-      """[Event "Test"]
-
-1. e4 e5 1-0
-"""
-    PgnParser.validatePgn(pgn) match
-      case Right(game) => game.moves.length shouldBe 2
-      case Left(err)   => fail(s"Expected Right but got Left($err)")
-
-  test("validatePgn: valid kingside castling is accepted"):
-    val pgn =
-      """[Event "Test"]
-
-1. e4 e5 2. Nf3 Nc6 3. Bc4 Bc5 4. O-O
-"""
-    PgnParser.validatePgn(pgn) match
-      case Right(game) =>
-        game.moves.last.castleSide shouldBe Some(CastleSide.Kingside)
-      case Left(err) => fail(s"Expected Right but got Left($err)")
-
-  test("validatePgn: castling when not legal returns Left"):
-    // Try to castle on move 1 — impossible from initial position (pieces in the way)
-    val pgn =
-      """[Event "Test"]
-
-1. O-O
-"""
-    PgnParser.validatePgn(pgn) match
-      case Left(_)  => succeed
-      case Right(g) => fail(s"Expected Left but got Right with ${g.moves.length} moves")
-
-  test("validatePgn: valid queenside castling is accepted"):
-    val pgn =
-      """[Event "Test"]
-
-1. d4 d5 2. Nc3 Nc6 3. Bf4 Bf5 4. Qd2 Qd7 5. O-O-O
-"""
-    PgnParser.validatePgn(pgn) match
-      case Right(game) =>
-        game.moves.last.castleSide shouldBe Some(CastleSide.Queenside)
-      case Left(err) => fail(s"Expected Right but got Left($err)")
-
-  test("validatePgn: disambiguation with two rooks is accepted"):
-    val pieces: Map[Square, Piece] = Map(
-      Square(File.A, Rank.R1) -> Piece(Color.White, PieceType.Rook),
-      Square(File.H, Rank.R1) -> Piece(Color.White, PieceType.Rook),
-      Square(File.E, Rank.R4) -> Piece(Color.White, PieceType.King),
-      Square(File.E, Rank.R8) -> Piece(Color.Black, PieceType.King)
-    )
-    // Build PGN from this custom board is hard, so test strictParseAlgebraicMove directly
-    val board = Board(pieces)
-    // Both rooks can reach d1 — "Rad1" should pick the a-file rook
-    val result = PgnParser.validatePgn("[Event \"T\"]\n\n1. e4")
-    // This tests the main flow; below we test disambiguation in isolation
-    result.isRight shouldBe true
-
-  test("validatePgn: ambiguous move without disambiguation returns Left"):
-    // Set up a position where two identical pieces can reach the same square
-    // We can test this via the strict path: two rooks, target square, no disambiguation hint
-    // Build it through a sequence that leads to two rooks on same file targeting same square
-    // This is hard to construct via PGN alone; verify via a known impossible disambiguation
-    val pgn = "[Event \"T\"]\n\n1. e4"
-    PgnParser.validatePgn(pgn).isRight shouldBe true

modules/core/src/test/scala/de/nowchess/chess/observer/ObservableThreadSafetyTest.scala

@@ -1,168 +0,0 @@
-package de.nowchess.chess.observer
-
-import de.nowchess.api.board.{Board, Color}
-import de.nowchess.chess.logic.GameHistory
-import org.scalatest.funsuite.AnyFunSuite
-import org.scalatest.matchers.should.Matchers
-import scala.collection.mutable
-
-class ObservableThreadSafetyTest extends AnyFunSuite with Matchers:
-
-  private class TestObservable extends Observable:
-    def testNotifyObservers(event: GameEvent): Unit =
-      notifyObservers(event)
-
-  private class CountingObserver extends Observer:
-    @volatile private var eventCount = 0
-    @volatile private var lastEvent: Option[GameEvent] = None
-
-    def onGameEvent(event: GameEvent): Unit =
-      eventCount += 1
-      lastEvent = Some(event)
-
-  private def createTestEvent(): GameEvent =
-    BoardResetEvent(
-      board = Board.initial,
-      history = GameHistory.empty,
-      turn = Color.White
-    )
-
-  test("Observable is thread-safe for concurrent subscribe and notify"):
-    val observable = new TestObservable()
-    val testEvent = createTestEvent()
-    @volatile var raceConditionCaught = false
-
-    // Thread 1: repeatedly notifies observers with long iteration
-    val notifierThread = new Thread(new Runnable {
-      def run(): Unit = {
-        try {
-          for _ <- 1 to 500000 do
-            observable.testNotifyObservers(testEvent)
-        } catch {
-          case _: java.util.ConcurrentModificationException =>
-            raceConditionCaught = true
-        }
-      }
-    })
-
-    // Thread 2: rapidly subscribes/unsubscribes observers during notify
-    val subscriberThread = new Thread(new Runnable {
-      def run(): Unit = {
-        try {
-          for _ <- 1 to 500000 do
-            val obs = new CountingObserver()
-            observable.subscribe(obs)
-            observable.unsubscribe(obs)
-        } catch {
-          case _: java.util.ConcurrentModificationException =>
-            raceConditionCaught = true
-        }
-      }
-    })
-
-    notifierThread.start()
-    subscriberThread.start()
-    notifierThread.join()
-    subscriberThread.join()
-
-    raceConditionCaught shouldBe false
-
-  test("Observable is thread-safe for concurrent subscribe, unsubscribe, and notify"):
-    val observable = new TestObservable()
-    val testEvent = createTestEvent()
-    val exceptions = mutable.ListBuffer[Exception]()
-    val observers = mutable.ListBuffer[CountingObserver]()
-
-    // Pre-subscribe some observers
-    for _ <- 1 to 10 do
-      val obs = new CountingObserver()
-      observers += obs
-      observable.subscribe(obs)
-
-    // Thread 1: notifies observers
-    val notifierThread = new Thread(new Runnable {
-      def run(): Unit = {
-        try {
-          for _ <- 1 to 5000 do
-            observable.testNotifyObservers(testEvent)
-        } catch {
-          case e: Exception => exceptions += e
-        }
-      }
-    })
-
-    // Thread 2: subscribes new observers
-    val subscriberThread = new Thread(new Runnable {
-      def run(): Unit = {
-        try {
-          for _ <- 1 to 5000 do
-            val obs = new CountingObserver()
-            observable.subscribe(obs)
-        } catch {
-          case e: Exception => exceptions += e
-        }
-      }
-    })
-
-    // Thread 3: unsubscribes observers
-    val unsubscriberThread = new Thread(new Runnable {
-      def run(): Unit = {
-        try {
-          for i <- 1 to 5000 do
-            if observers.nonEmpty then
-              val obs = observers(i % observers.size)
-              observable.unsubscribe(obs)
-        } catch {
-          case e: Exception => exceptions += e
-        }
-      }
-    })
-
-    notifierThread.start()
-    subscriberThread.start()
-    unsubscriberThread.start()
-    notifierThread.join()
-    subscriberThread.join()
-    unsubscriberThread.join()
-
-    exceptions.isEmpty shouldBe true
-
-  test("Observable.observerCount is thread-safe during concurrent modifications"):
-    val observable = new TestObservable()
-    val exceptions = mutable.ListBuffer[Exception]()
-    val countResults = mutable.ListBuffer[Int]()
-
-    // Thread 1: subscribes observers
-    val subscriberThread = new Thread(new Runnable {
-      def run(): Unit = {
-        try {
-          for _ <- 1 to 500 do
-            observable.subscribe(new CountingObserver())
-        } catch {
-          case e: Exception => exceptions += e
-        }
-      }
-    })
-
-    // Thread 2: reads observer count
-    val readerThread = new Thread(new Runnable {
-      def run(): Unit = {
-        try {
-          for _ <- 1 to 500 do
-            val count = observable.observerCount
-            countResults += count
-        } catch {
-          case e: Exception => exceptions += e
-        }
-      }
-    })
-
-    subscriberThread.start()
-    readerThread.start()
-    subscriberThread.join()
-    readerThread.join()
-
-    exceptions.isEmpty shouldBe true
-    // Count should never go backwards
-    for i <- 1 until countResults.size do
-      countResults(i) >= countResults(i - 1) shouldBe true

modules/core/src/test/scala/de/nowchess/chess/view/PieceUnicodeTest.scala

@@ -1,43 +0,0 @@
-package de.nowchess.chess.view
-
-import de.nowchess.api.board.Piece
-import org.scalatest.funsuite.AnyFunSuite
-import org.scalatest.matchers.should.Matchers
-
-class PieceUnicodeTest extends AnyFunSuite with Matchers:
-
-  test("White King maps to ♔"):
-    Piece.WhiteKing.unicode shouldBe "\u2654"
-
-  test("White Queen maps to ♕"):
-    Piece.WhiteQueen.unicode shouldBe "\u2655"
-
-  test("White Rook maps to ♖"):
-    Piece.WhiteRook.unicode shouldBe "\u2656"
-
-  test("White Bishop maps to ♗"):
-    Piece.WhiteBishop.unicode shouldBe "\u2657"
-
-  test("White Knight maps to ♘"):
-    Piece.WhiteKnight.unicode shouldBe "\u2658"
-
-  test("White Pawn maps to ♙"):
-    Piece.WhitePawn.unicode shouldBe "\u2659"
-
-  test("Black King maps to ♚"):
-    Piece.BlackKing.unicode shouldBe "\u265A"
-
-  test("Black Queen maps to ♛"):
-    Piece.BlackQueen.unicode shouldBe "\u265B"
-
-  test("Black Rook maps to ♜"):
-    Piece.BlackRook.unicode shouldBe "\u265C"
-
-  test("Black Bishop maps to ♝"):
-    Piece.BlackBishop.unicode shouldBe "\u265D"
-
-  test("Black Knight maps to ♞"):
-    Piece.BlackKnight.unicode shouldBe "\u265E"
-
-  test("Black Pawn maps to ♟"):
-    Piece.BlackPawn.unicode shouldBe "\u265F"

modules/core/src/test/scala/de/nowchess/chess/view/RendererTest.scala

@@ -1,41 +0,0 @@
-package de.nowchess.chess.view
-
-import de.nowchess.api.board.{Board, File, Piece, Rank, Square}
-import org.scalatest.funsuite.AnyFunSuite
-import org.scalatest.matchers.should.Matchers
-
-class RendererTest extends AnyFunSuite with Matchers:
-
-  test("render contains column header with all file labels"):
-    Renderer.render(Board.initial) should include("a  b  c  d  e  f  g  h")
-
-  test("render output begins with the column header"):
-    Renderer.render(Board.initial) should startWith("  a  b  c  d  e  f  g  h")
-
-  test("render contains rank labels 1 through 8"):
-    val output = Renderer.render(Board.initial)
-    for rank <- 1 to 8 do output should include(s"$rank ")
-
-  test("render shows white king unicode symbol for initial board"):
-    Renderer.render(Board.initial) should include("\u2654")
-
-  test("render shows black king unicode symbol for initial board"):
-    Renderer.render(Board.initial) should include("\u265A")
-
-  test("render contains ANSI light-square background code"):
-    Renderer.render(Board.initial) should include("\u001b[48;5;223m")
-
-  test("render contains ANSI dark-square background code"):
-    Renderer.render(Board.initial) should include("\u001b[48;5;130m")
-
-  test("render uses white-piece foreground color for white pieces"):
-    Renderer.render(Board.initial) should include("\u001b[97m")
-
-  test("render uses black-piece foreground color for black pieces"):
-    Renderer.render(Board.initial) should include("\u001b[30m")
-
-  test("render of empty board contains no piece unicode"):
-    val output = Renderer.render(Board(Map.empty))
-    output should include("a  b  c  d  e  f  g  h")
-    output should not include "\u2654"
-    output should not include "\u265A"

modules/core/versions.env

@@ -1,3 +1,3 @@
 MAJOR=0
-MINOR=8
+MINOR=10
 PATCH=0

modules/io/CHANGELOG.md

@@ -0,0 +1 @@
+##  (2026-04-06)

modules/io/build.gradle.kts

@@ -0,0 +1,63 @@
+plugins {
+    id("scala")
+    id("org.scoverage") version "8.1"
+}
+
+group = "de.nowchess"
+version = "1.0-SNAPSHOT"
+
+@Suppress("UNCHECKED_CAST")
+val versions = rootProject.extra["VERSIONS"] as Map<String, String>
+
+repositories {
+    mavenCentral()
+}
+
+scala {
+    scalaVersion = versions["SCALA3"]!!
+}
+
+scoverage {
+    scoverageVersion.set(versions["SCOVERAGE"]!!)
+}
+
+tasks.withType<ScalaCompile> {
+    scalaCompileOptions.additionalParameters = listOf("-encoding", "UTF-8")
+}
+
+dependencies {
+
+    implementation("org.scala-lang:scala3-compiler_3") {
+        version {
+            strictly(versions["SCALA3"]!!)
+        }
+    }
+    implementation("org.scala-lang:scala3-library_3") {
+        version {
+            strictly(versions["SCALA3"]!!)
+        }
+    }
+
+    implementation(project(":modules:api"))
+    implementation(project(":modules:rule"))
+
+    testImplementation(platform("org.junit:junit-bom:5.13.4"))
+    testImplementation("org.junit.jupiter:junit-jupiter")
+    testImplementation("org.scalatest:scalatest_3:${versions["SCALATEST"]!!}")
+    testImplementation("co.helmethair:scalatest-junit-runner:${versions["SCALATEST_JUNIT"]!!}")
+
+    testRuntimeOnly("org.junit.platform:junit-platform-launcher")
+}
+
+tasks.test {
+    useJUnitPlatform {
+        includeEngines("scalatest")
+        testLogging {
+            events("skipped", "failed")
+        }
+    }
+    finalizedBy(tasks.reportScoverage)
+}
+tasks.reportScoverage {
+    dependsOn(tasks.test)
+}

modules/io/src/main/scala/de/nowchess/io/GameContextExport.scala

@@ -0,0 +1,7 @@
+package de.nowchess.io
+
+import de.nowchess.api.game.GameContext
+
+trait GameContextExport:
+
+  def exportGameContext(context: GameContext): String

modules/io/src/main/scala/de/nowchess/io/GameContextImport.scala

@@ -0,0 +1,7 @@
+package de.nowchess.io
+
+import de.nowchess.api.game.GameContext
+
+trait GameContextImport:
+
+  def importGameContext(input: String): Either[String, GameContext]

modules/io/src/main/scala/de/nowchess/io/fen/FenExporter.scala

@@ -1,10 +1,10 @@
-package de.nowchess.chess.notation
+package de.nowchess.io.fen
 
 import de.nowchess.api.board.*
-import de.nowchess.api.game.{CastlingRights, GameState}
-import de.nowchess.api.board.Color
+import de.nowchess.api.game.GameContext
+import de.nowchess.io.GameContextExport
 
-object FenExporter:
+object FenExporter extends GameContextExport:
 
   /** Convert a Board to FEN piece-placement string (rank 8 to rank 1, separated by '/'). */
   def boardToFen(board: Board): String =
@@ -24,32 +24,35 @@ object FenExporter:
           if emptyCount > 0 then
             rankChars += emptyCount.toString.charAt(0)
             emptyCount = 0
-          rankChars += pieceToPgnChar(piece)
+          rankChars += pieceToFenChar(piece)
         case None =>
           emptyCount += 1
 
     if emptyCount > 0 then rankChars += emptyCount.toString.charAt(0)
     rankChars.mkString
 
-  /** Convert a GameState to a complete FEN string. */
-  def gameStateToFen(state: GameState): String =
-    val piecePlacement = state.piecePlacement
-    val activeColor = if state.activeColor == Color.White then "w" else "b"
-    val castling = castlingString(state.castlingWhite, state.castlingBlack)
-    val enPassant = state.enPassantTarget.map(_.toString).getOrElse("-")
-    s"$piecePlacement $activeColor $castling $enPassant ${state.halfMoveClock} ${state.fullMoveNumber}"
+  /** Convert a GameContext to a complete FEN string. */
+  def gameContextToFen(context: GameContext): String =
+    val piecePlacement = boardToFen(context.board)
+    val activeColor = if context.turn == Color.White then "w" else "b"
+    val castling = castlingString(context.castlingRights)
+    val enPassant = context.enPassantSquare.map(_.toString).getOrElse("-")
+    val fullMoveNumber = 1 + (context.moves.length / 2)
+    s"$piecePlacement $activeColor $castling $enPassant ${context.halfMoveClock} $fullMoveNumber"
+
+  def exportGameContext(context: GameContext): String = gameContextToFen(context)
 
   /** Convert castling rights to FEN notation. */
-  private def castlingString(white: CastlingRights, black: CastlingRights): String =
-    val wk = if white.kingSide then "K" else ""
-    val wq = if white.queenSide then "Q" else ""
-    val bk = if black.kingSide then "k" else ""
-    val bq = if black.queenSide then "q" else ""
+  private def castlingString(rights: CastlingRights): String =
+    val wk = if rights.whiteKingSide then "K" else ""
+    val wq = if rights.whiteQueenSide then "Q" else ""
+    val bk = if rights.blackKingSide then "k" else ""
+    val bq = if rights.blackQueenSide then "q" else ""
     val result = s"$wk$wq$bk$bq"
     if result.isEmpty then "-" else result
 
   /** Convert a Piece to its FEN character (uppercase = White, lowercase = Black). */
-  private def pieceToPgnChar(piece: Piece): Char =
+  private def pieceToFenChar(piece: Piece): Char =
     val base = piece.pieceType match
       case PieceType.Pawn   => 'p'
       case PieceType.Knight => 'n'
@@ -58,3 +61,4 @@ object FenExporter:
       case PieceType.Queen  => 'q'
       case PieceType.King   => 'k'
     if piece.color == Color.White then base.toUpper else base
+

modules/io/src/main/scala/de/nowchess/io/fen/FenParser.scala

@@ -1,48 +1,55 @@
-package de.nowchess.chess.notation
+package de.nowchess.io.fen
 
 import de.nowchess.api.board.*
-import de.nowchess.api.game.{CastlingRights, GameState, GameStatus}
+import de.nowchess.api.game.GameContext
+import de.nowchess.io.GameContextImport
 
-object FenParser:
+object FenParser extends GameContextImport:
 
-  /** Parse a complete FEN string into a GameState.
-   *  Returns None if the format is invalid. */
-  def parseFen(fen: String): Option[GameState] =
+  /** Parse a complete FEN string into a GameContext.
+   *  Returns Left with error message if the format is invalid. */
+  def parseFen(fen: String): Either[String, GameContext] =
     val parts = fen.trim.split("\\s+")
-    Option.when(parts.length == 6)(parts).flatMap: parts =>
+    if parts.length != 6 then
+      Left(s"Invalid FEN: expected 6 space-separated fields, got ${parts.length}")
+    else
       for
-        _ <- parseBoard(parts(0))
-        activeColor <- parseColor(parts(1))
-        castlingRights <- parseCastling(parts(2))
-        enPassant <- parseEnPassant(parts(3))
-        halfMoveClock <- parts(4).toIntOption
-        fullMoveNumber <- parts(5).toIntOption
-        if halfMoveClock >= 0 && fullMoveNumber >= 1
-      yield GameState(
-        piecePlacement = parts(0),
-        activeColor = activeColor,
-        castlingWhite = castlingRights._1,
-        castlingBlack = castlingRights._2,
-        enPassantTarget = enPassant,
+        board <- parseBoard(parts(0)).toRight("Invalid FEN: invalid board position")
+        activeColor <- parseColor(parts(1)).toRight("Invalid FEN: invalid active color (expected 'w' or 'b')")
+        castlingRights <- parseCastling(parts(2)).toRight("Invalid FEN: invalid castling rights")
+        enPassant <- parseEnPassant(parts(3)).toRight("Invalid FEN: invalid en passant square")
+        halfMoveClock <- parts(4).toIntOption.toRight("Invalid FEN: invalid half-move clock (expected integer)")
+        fullMoveNumber <- parts(5).toIntOption.toRight("Invalid FEN: invalid full move number (expected integer)")
+        _ <- Either.cond(halfMoveClock >= 0 && fullMoveNumber >= 1, (), "Invalid FEN: invalid move counts")
+      yield GameContext(
+        board = board,
+        turn = activeColor,
+        castlingRights = castlingRights,
+        enPassantSquare = enPassant,
         halfMoveClock = halfMoveClock,
-        fullMoveNumber = fullMoveNumber,
-        status = GameStatus.InProgress
+        moves = List.empty
       )
 
+  def importGameContext(input: String): Either[String, GameContext] =
+    parseFen(input)
+
   /** Parse active color ("w" or "b"). */
   private def parseColor(s: String): Option[Color] =
     if s == "w" then Some(Color.White)
     else if s == "b" then Some(Color.Black)
     else None
 
-  /** Parse castling rights string (e.g. "KQkq", "K", "-") into rights for White and Black. */
-  private def parseCastling(s: String): Option[(CastlingRights, CastlingRights)] =
+  /** Parse castling rights string (e.g. "KQkq", "K", "-") into unified castling rights. */
+  private def parseCastling(s: String): Option[CastlingRights] =
     if s == "-" then
-      Some((CastlingRights.None, CastlingRights.None))
+      Some(CastlingRights.None)
     else if s.length <= 4 && s.forall(c => "KQkq".contains(c)) then
-      val white = CastlingRights(kingSide = s.contains('K'), queenSide = s.contains('Q'))
-      val black = CastlingRights(kingSide = s.contains('k'), queenSide = s.contains('q'))
-      Some((white, black))
+      Some(CastlingRights(
+        whiteKingSide = s.contains('K'),
+        whiteQueenSide = s.contains('Q'),
+        blackKingSide = s.contains('k'),
+        blackQueenSide = s.contains('q')
+      ))
     else
       None
 
@@ -101,3 +108,4 @@ object FenParser:
       case 'k' => Some(PieceType.King)
       case _   => None
     pieceTypeOpt.map(pt => Piece(color, pt))
+

modules/io/src/main/scala/de/nowchess/io/pgn/PgnExporter.scala

@@ -0,0 +1,80 @@
+package de.nowchess.io.pgn
+
+import de.nowchess.api.board.*
+import de.nowchess.api.move.{Move, MoveType, PromotionPiece}
+import de.nowchess.api.game.GameContext
+import de.nowchess.io.GameContextExport
+import de.nowchess.rules.sets.DefaultRules
+
+object PgnExporter extends GameContextExport:
+
+  /** Export a GameContext to PGN format. */
+  def exportGameContext(context: GameContext): String =
+    val headers = Map(
+      "Event" -> "?",
+      "White" -> "?",
+      "Black" -> "?",
+      "Result" -> "*"
+    )
+
+    exportGame(headers, context.moves)
+
+  /** Export a game with headers and moves to PGN format. */
+  def exportGame(headers: Map[String, String], moves: List[Move]): String =
+    val headerLines = headers.map { case (key, value) =>
+      s"""[$key "$value"]"""
+    }.mkString("\n")
+
+    val moveText = if moves.isEmpty then ""
+    else
+      var ctx = GameContext.initial
+      val sanMoves = moves.map { move =>
+        val algebraic = moveToAlgebraic(move, ctx.board)
+        ctx = DefaultRules.applyMove(ctx)(move)
+        algebraic
+      }
+
+      val groupedMoves = sanMoves.zipWithIndex.groupBy(_._2 / 2)
+      val moveLines = for (moveNumber, movePairs) <- groupedMoves.toList.sortBy(_._1) yield
+        val moveNum = moveNumber + 1
+        val whiteMoveStr = movePairs.find(_._2 % 2 == 0).map(_._1).getOrElse("")
+        val blackMoveStr = movePairs.find(_._2 % 2 == 1).map(_._1).getOrElse("")
+        if blackMoveStr.isEmpty then s"$moveNum. $whiteMoveStr"
+        else s"$moveNum. $whiteMoveStr $blackMoveStr"
+
+      val termination = headers.getOrElse("Result", "*")
+      moveLines.mkString(" ") + s" $termination"
+
+    if headerLines.isEmpty then moveText
+    else if moveText.isEmpty then headerLines
+    else s"$headerLines\n\n$moveText"
+
+  /** Convert a Move to Standard Algebraic Notation using the board state before the move. */
+  private def moveToAlgebraic(move: Move, boardBefore: Board): String =
+    move.moveType match
+      case MoveType.CastleKingside  => "O-O"
+      case MoveType.CastleQueenside => "O-O-O"
+      case MoveType.EnPassant       => s"${move.from.file.toString.toLowerCase}x${move.to}"
+      case MoveType.Promotion(pp)   =>
+        val promSuffix = pp match
+          case PromotionPiece.Queen  => "=Q"
+          case PromotionPiece.Rook   => "=R"
+          case PromotionPiece.Bishop => "=B"
+          case PromotionPiece.Knight => "=N"
+        val isCapture = boardBefore.pieceAt(move.to).isDefined
+        if isCapture then s"${move.from.file.toString.toLowerCase}x${move.to}$promSuffix"
+        else s"${move.to}$promSuffix"
+      case MoveType.Normal(isCapture) =>
+        val dest   = move.to.toString
+        val capStr = if isCapture then "x" else ""
+        boardBefore.pieceAt(move.from).map(_.pieceType).getOrElse(PieceType.Pawn) match
+          case PieceType.Pawn =>
+            if isCapture then s"${move.from.file.toString.toLowerCase}x$dest"
+            else dest
+          case PieceType.Knight => s"N$capStr$dest"
+          case PieceType.Bishop => s"B$capStr$dest"
+          case PieceType.Rook   => s"R$capStr$dest"
+          case PieceType.Queen  => s"Q$capStr$dest"
+          case PieceType.King   => s"K$capStr$dest"
+
+

modules/io/src/main/scala/de/nowchess/io/pgn/PgnParser.scala

@@ -0,0 +1,184 @@
+package de.nowchess.io.pgn
+
+import de.nowchess.api.board.*
+import de.nowchess.api.move.{Move, MoveType, PromotionPiece}
+import de.nowchess.api.game.GameContext
+import de.nowchess.io.GameContextImport
+import de.nowchess.rules.sets.DefaultRules
+
+/** A parsed PGN game containing headers and the resolved move list. */
+case class PgnGame(
+  headers: Map[String, String],
+  moves: List[Move]
+)
+
+object PgnParser extends GameContextImport:
+
+  /** Strictly validate a PGN text.
+   *  Returns Right(PgnGame) if every move token is a legal move in the evolving position.
+   *  Returns Left(error message) on the first illegal or impossible move, or any unrecognised token. */
+  def validatePgn(pgn: String): Either[String, PgnGame] =
+    val lines = pgn.split("\n").map(_.trim)
+    val (headerLines, rest) = lines.span(_.startsWith("["))
+    val headers  = parseHeaders(headerLines)
+    val moveText = rest.mkString(" ")
+    validateMovesText(moveText).map(moves => PgnGame(headers, moves))
+
+  /** Import a PGN text into a GameContext by validating and replaying all moves.
+   *  Returns Right(GameContext) with all moves applied and .moves populated.
+   *  Returns Left(error message) if validation fails or move replay encounters an issue. */
+  def importGameContext(input: String): Either[String, GameContext] =
+    validatePgn(input).flatMap { game =>
+      Right(game.moves.foldLeft(GameContext.initial)((ctx, move) => DefaultRules.applyMove(ctx)(move)))
+    }
+
+  /** Parse a complete PGN text into a PgnGame with headers and moves.
+   *  Always succeeds (returns Some); malformed tokens are silently skipped. */
+  def parsePgn(pgn: String): Option[PgnGame] =
+    val lines = pgn.split("\n").map(_.trim)
+    val (headerLines, rest) = lines.span(_.startsWith("["))
+    val headers  = parseHeaders(headerLines)
+    val moveText = rest.mkString(" ")
+    val moves    = parseMovesText(moveText)
+    Some(PgnGame(headers, moves))
+
+  /** Parse PGN header lines of the form [Key "Value"]. */
+  private def parseHeaders(lines: Array[String]): Map[String, String] =
+    val pattern = """^\[(\w+)\s+"([^"]*)"\s*]$""".r
+    lines.flatMap(line => pattern.findFirstMatchIn(line).map(m => m.group(1) -> m.group(2))).toMap
+
+  /** Parse the move-text section (e.g. "1. e4 e5 2. Nf3") into resolved Moves. */
+  private def parseMovesText(moveText: String): List[Move] =
+    val tokens = moveText.split("\\s+").filter(_.nonEmpty)
+    val (_, _, moves) = tokens.foldLeft(
+      (GameContext.initial, Color.White, List.empty[Move])
+    ):
+      case (state @ (ctx, color, acc), token) =>
+        if isMoveNumberOrResult(token) then state
+        else
+          parseAlgebraicMove(token, ctx, color) match
+            case None       => state
+            case Some(move) =>
+              val nextCtx    = DefaultRules.applyMove(ctx)(move)
+              (nextCtx, color.opposite, acc :+ move)
+    moves
+
+  /** True for move-number tokens ("1.", "12.") and PGN result tokens. */
+  private def isMoveNumberOrResult(token: String): Boolean =
+    token.matches("""\d+\.""") ||
+    token == "*"               ||
+    token == "1-0"             ||
+    token == "0-1"             ||
+    token == "1/2-1/2"
+
+  /** Parse a single algebraic notation token into a Move, given the current game context. */
+  def parseAlgebraicMove(notation: String, ctx: GameContext, color: Color): Option[Move] =
+    notation match
+      case "O-O" | "O-O+" | "O-O#" =>
+        val rank = if color == Color.White then Rank.R1 else Rank.R8
+        val move = Move(Square(File.E, rank), Square(File.G, rank), MoveType.CastleKingside)
+        Option.when(DefaultRules.legalMoves(ctx)(Square(File.E, rank)).contains(move))(move)
+
+      case "O-O-O" | "O-O-O+" | "O-O-O#" =>
+        val rank = if color == Color.White then Rank.R1 else Rank.R8
+        val move = Move(Square(File.E, rank), Square(File.C, rank), MoveType.CastleQueenside)
+        Option.when(DefaultRules.legalMoves(ctx)(Square(File.E, rank)).contains(move))(move)
+
+      case _ =>
+        parseRegularMove(notation, ctx, color)
+
+  /** Parse regular algebraic notation (pawn moves, piece moves, captures, disambiguation). */
+  private def parseRegularMove(notation: String, ctx: GameContext, color: Color): Option[Move] =
+    val clean = notation
+      .replace("+", "")
+      .replace("#", "")
+      .replace("x", "")
+      .replaceAll("=[NBRQ]$", "")
+
+    if clean.length < 2 then None
+    else
+      val destStr = clean.takeRight(2)
+      Square.fromAlgebraic(destStr).flatMap: toSquare =>
+        val disambig = clean.dropRight(2)
+
+        val requiredPieceType: Option[PieceType] =
+          if disambig.nonEmpty && disambig.head.isUpper then charToPieceType(disambig.head)
+          else if clean.head.isUpper then charToPieceType(clean.head)
+          else Some(PieceType.Pawn)
+
+        val hint =
+          if disambig.nonEmpty && disambig.head.isUpper then disambig.tail
+          else disambig
+
+        val promotion = extractPromotion(notation)
+
+        // Get all legal moves for this color that reach toSquare
+        val allLegal = DefaultRules.allLegalMoves(ctx)
+        val candidates = allLegal.filter { move =>
+          move.to == toSquare &&
+          ctx.board.pieceAt(move.from).exists(p =>
+            p.color == color &&
+            requiredPieceType.forall(_ == p.pieceType)
+          ) &&
+          (hint.isEmpty || matchesHint(move.from, hint)) &&
+          promotionMatches(move, promotion)
+        }
+
+        candidates.headOption
+
+  /** True if `sq` matches a disambiguation hint (file letter, rank digit, or both). */
+  private def matchesHint(sq: Square, hint: String): Boolean =
+    hint.forall(c =>
+      if c >= 'a' && c <= 'h' then sq.file.toString.equalsIgnoreCase(c.toString)
+      else if c >= '1' && c <= '8' then sq.rank.ordinal == (c - '1')
+      else true
+    )
+
+  private def promotionMatches(move: Move, promotion: Option[PromotionPiece]): Boolean =
+    promotion match
+      case None     => move.moveType match
+                         case MoveType.Normal(_) | MoveType.EnPassant | MoveType.CastleKingside | MoveType.CastleQueenside => true
+                         case _ => false
+      case Some(pp) => move.moveType == MoveType.Promotion(pp)
+
+  /** Extract a promotion piece from a notation string containing =Q/=R/=B/=N. */
+  private[pgn] def extractPromotion(notation: String): Option[PromotionPiece] =
+    val promotionPattern = """=([A-Z])""".r
+    promotionPattern.findFirstMatchIn(notation).flatMap { m =>
+      m.group(1) match
+        case "Q" => Some(PromotionPiece.Queen)
+        case "R" => Some(PromotionPiece.Rook)
+        case "B" => Some(PromotionPiece.Bishop)
+        case "N" => Some(PromotionPiece.Knight)
+        case _   => None
+    }
+
+  /** Convert a piece-letter character to a PieceType. */
+  private def charToPieceType(c: Char): Option[PieceType] =
+    c match
+      case 'N' => Some(PieceType.Knight)
+      case 'B' => Some(PieceType.Bishop)
+      case 'R' => Some(PieceType.Rook)
+      case 'Q' => Some(PieceType.Queen)
+      case 'K' => Some(PieceType.King)
+      case _   => None
+
+  // ── Strict validation helpers ─────────────────────────────────────────────
+
+  /** Walk all move tokens, failing immediately on any unresolvable or illegal move. */
+  private def validateMovesText(moveText: String): Either[String, List[Move]] =
+    val tokens = moveText.split("\\s+").filter(_.nonEmpty)
+    tokens.foldLeft(Right((GameContext.initial, Color.White, List.empty[Move])): Either[String, (GameContext, Color, List[Move])]) {
+      case (acc, token) =>
+        acc.flatMap { case (ctx, color, moves) =>
+          if isMoveNumberOrResult(token) then Right((ctx, color, moves))
+          else
+            parseAlgebraicMove(token, ctx, color) match
+              case None       => Left(s"Illegal or impossible move: '$token'")
+              case Some(move) =>
+                val nextCtx  = DefaultRules.applyMove(ctx)(move)
+                Right((nextCtx, color.opposite, moves :+ move))
+        }
+    }.map(_._3)
+
+

modules/io/src/test/scala/de/nowchess/io/fen/FenExporterTest.scala

@@ -0,0 +1,104 @@
+package de.nowchess.io.fen
+
+import de.nowchess.api.board.*
+import de.nowchess.api.game.GameContext
+import de.nowchess.api.move.Move
+import org.scalatest.funsuite.AnyFunSuite
+import org.scalatest.matchers.should.Matchers
+
+class FenExporterTest extends AnyFunSuite with Matchers:
+
+  private def context(
+    piecePlacement: String,
+    turn: Color,
+    castlingRights: CastlingRights,
+    enPassantSquare: Option[Square],
+    halfMoveClock: Int,
+    moveCount: Int
+  ): GameContext =
+    val board = FenParser.parseBoard(piecePlacement).getOrElse(
+      fail(s"Invalid test board FEN: $piecePlacement")
+    )
+    val dummyMove = Move(Square(File.A, Rank.R2), Square(File.A, Rank.R3))
+    GameContext(
+      board = board,
+      turn = turn,
+      castlingRights = castlingRights,
+      enPassantSquare = enPassantSquare,
+      halfMoveClock = halfMoveClock,
+      moves = List.fill(moveCount)(dummyMove)
+    )
+
+  test("exportGameContextToFen handles initial and typical developed position"):
+    FenExporter.gameContextToFen(GameContext.initial) shouldBe
+      "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1"
+
+    val gameContext = context(
+      piecePlacement = "rnbqkbnr/pppppppp/8/8/4P3/8/PPPP1PPP/RNBQKBNR",
+      turn = Color.Black,
+      castlingRights = CastlingRights.All,
+      enPassantSquare = Some(Square(File.E, Rank.R3)),
+      halfMoveClock = 0,
+      moveCount = 0
+    )
+    FenExporter.gameContextToFen(gameContext) shouldBe
+      "rnbqkbnr/pppppppp/8/8/4P3/8/PPPP1PPP/RNBQKBNR b KQkq e3 0 1"
+
+  test("export handles castling rights variants and en-passant with counters"):
+    val noCastling = context(
+      piecePlacement = "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR",
+      turn = Color.White,
+      castlingRights = CastlingRights.None,
+      enPassantSquare = None,
+      halfMoveClock = 0,
+      moveCount = 0
+    )
+    FenExporter.gameContextToFen(noCastling) shouldBe
+      "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w - - 0 1"
+
+    val partialCastling = context(
+      piecePlacement = "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR",
+      turn = Color.White,
+      castlingRights = CastlingRights(
+        whiteKingSide = true,
+        whiteQueenSide = false,
+        blackKingSide = false,
+        blackQueenSide = true
+      ),
+      enPassantSquare = None,
+      halfMoveClock = 5,
+      moveCount = 4
+    )
+    FenExporter.gameContextToFen(partialCastling) shouldBe
+      "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w Kq - 5 3"
+
+    val withEnPassant = context(
+      piecePlacement = "rnbqkbnr/pp1ppppp/8/2pP4/8/8/PPPP1PPP/RNBQKBNR",
+      turn = Color.White,
+      castlingRights = CastlingRights.All,
+      enPassantSquare = Some(Square(File.C, Rank.R6)),
+      halfMoveClock = 2,
+      moveCount = 4
+    )
+    FenExporter.gameContextToFen(withEnPassant) shouldBe
+      "rnbqkbnr/pp1ppppp/8/2pP4/8/8/PPPP1PPP/RNBQKBNR w KQkq c6 2 3"
+
+  test("halfMoveClock round-trips through FEN export and import"):
+    val gameContext = GameContext(
+      board = Board.initial,
+      turn = Color.White,
+      castlingRights = CastlingRights.All,
+      enPassantSquare = None,
+      halfMoveClock = 42,
+      moves = List.empty
+    )
+    val fen = FenExporter.gameContextToFen(gameContext)
+    FenParser.parseFen(fen) match
+      case Right(ctx) => ctx.halfMoveClock shouldBe 42
+      case Left(err)  => fail(s"FEN parsing failed: $err")
+
+  test("exportGameContext forwards to gameContextToFen"):
+    val ctx = GameContext.initial
+
+    FenExporter.exportGameContext(ctx) shouldBe FenExporter.gameContextToFen(ctx)
+

modules/io/src/test/scala/de/nowchess/io/fen/FenParserTest.scala

@@ -0,0 +1,55 @@
+package de.nowchess.io.fen
+
+import de.nowchess.api.board.*
+import org.scalatest.funsuite.AnyFunSuite
+import org.scalatest.matchers.should.Matchers
+
+class FenParserTest extends AnyFunSuite with Matchers:
+
+  test("parseBoard parses canonical positions and supports round-trip"):
+    val initial = "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR"
+    val empty = "8/8/8/8/8/8/8/8"
+    val partial = "8/8/4k3/8/4K3/8/8/8"
+
+    FenParser.parseBoard(initial).map(_.pieceAt(Square(File.E, Rank.R2))) shouldBe Some(Some(Piece.WhitePawn))
+    FenParser.parseBoard(initial).map(_.pieceAt(Square(File.E, Rank.R8))) shouldBe Some(Some(Piece.BlackKing))
+    FenParser.parseBoard(empty).map(_.pieces.size) shouldBe Some(0)
+    FenParser.parseBoard(partial).map(_.pieceAt(Square(File.E, Rank.R6))) shouldBe Some(Some(Piece.BlackKing))
+
+    FenParser.parseBoard(initial).map(FenExporter.boardToFen) shouldBe Some(initial)
+    FenParser.parseBoard(empty).map(FenExporter.boardToFen) shouldBe Some(empty)
+
+  test("parseFen parses full state for common valid inputs"):
+    FenParser.parseFen("rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1").fold(_ => fail(), ctx =>
+      ctx.turn shouldBe Color.White
+      ctx.castlingRights.whiteKingSide shouldBe true
+      ctx.enPassantSquare shouldBe None
+      ctx.halfMoveClock shouldBe 0
+    )
+
+    FenParser.parseFen("rnbqkbnr/pppppppp/8/8/4P3/8/PPPP1PPP/RNBQKBNR b KQkq e3 0 1").fold(_ => fail(), ctx =>
+      ctx.turn shouldBe Color.Black
+      ctx.enPassantSquare shouldBe Some(Square(File.E, Rank.R3))
+    )
+
+    FenParser.parseFen("rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w - - 0 1").fold(_ => fail(), ctx =>
+      ctx.castlingRights.whiteKingSide shouldBe false
+      ctx.castlingRights.blackQueenSide shouldBe false
+    )
+
+  test("parseFen rejects invalid color and castling tokens"):
+    FenParser.parseFen("rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR x KQkq - 0 1").isLeft shouldBe true
+    FenParser.parseFen("rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w XYZ - 0 1").isLeft shouldBe true
+
+  test("importGameContext returns Right for valid and Left for invalid FEN"):
+    val fen = "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1"
+    FenParser.importGameContext(fen).isRight shouldBe true
+    FenParser.importGameContext("invalid fen string").isLeft shouldBe true
+
+  test("parseBoard rejects malformed board shapes and invalid piece symbols"):
+    FenParser.parseBoard("8/8/8/8/8/8/8") shouldBe None
+    FenParser.parseBoard("9/8/8/8/8/8/8/8") shouldBe None
+    FenParser.parseBoard("8p/8/8/8/8/8/8/8") shouldBe None
+    FenParser.parseBoard("7/8/8/8/8/8/8/8") shouldBe None
+    FenParser.parseBoard("8/8/8/8/8/8/8/7X") shouldBe None
+

modules/io/src/test/scala/de/nowchess/io/pgn/PgnExporterTest.scala

@@ -0,0 +1,108 @@
+package de.nowchess.io.pgn
+
+import de.nowchess.api.board.*
+import de.nowchess.api.game.GameContext
+import de.nowchess.api.move.{Move, MoveType, PromotionPiece}
+import org.scalatest.funsuite.AnyFunSuite
+import org.scalatest.matchers.should.Matchers
+
+class PgnExporterTest extends AnyFunSuite with Matchers:
+
+  test("exportGame renders headers and basic move text"):
+    val headers = Map("Event" -> "Test", "White" -> "A", "Black" -> "B")
+    val emptyPgn = PgnExporter.exportGame(headers, List.empty)
+    emptyPgn.contains("[Event \"Test\"]") shouldBe true
+    emptyPgn.contains("[White \"A\"]") shouldBe true
+    emptyPgn.contains("[Black \"B\"]") shouldBe true
+
+    val moves = List(Move(Square(File.E, Rank.R2), Square(File.E, Rank.R4), MoveType.Normal()))
+    PgnExporter.exportGame(headers, moves).contains("1. e4") shouldBe true
+
+  test("exportGame renders castling grouping and result markers"):
+    PgnExporter.exportGame(Map("Event" -> "Test"), List(Move(Square(File.E, Rank.R1), Square(File.G, Rank.R1), MoveType.CastleKingside))) should include("O-O")
+    PgnExporter.exportGame(Map("Event" -> "Test"), List(Move(Square(File.E, Rank.R1), Square(File.C, Rank.R1), MoveType.CastleQueenside))) should include("O-O-O")
+
+    val seq = List(
+      Move(Square(File.E, Rank.R2), Square(File.E, Rank.R4), MoveType.Normal()),
+      Move(Square(File.C, Rank.R7), Square(File.C, Rank.R5), MoveType.Normal()),
+      Move(Square(File.G, Rank.R1), Square(File.F, Rank.R3), MoveType.Normal())
+    )
+    val grouped = PgnExporter.exportGame(Map("Result" -> "1-0"), seq)
+    grouped should include("1. e4 c5")
+    grouped should include("2. Nf3")
+
+    val oneMove = List(Move(Square(File.E, Rank.R2), Square(File.E, Rank.R4), MoveType.Normal()))
+    PgnExporter.exportGame(Map.empty, oneMove) shouldBe "1. e4 *"
+    PgnExporter.exportGame(Map("Result" -> "1/2-1/2"), oneMove) should endWith("1/2-1/2")
+
+  test("exportGame handles promotion suffixes and normal move formatting"):
+    List(
+      PromotionPiece.Queen -> "=Q",
+      PromotionPiece.Rook -> "=R",
+      PromotionPiece.Bishop -> "=B",
+      PromotionPiece.Knight -> "=N"
+    ).foreach { (piece, suffix) =>
+      val move = Move(Square(File.E, Rank.R7), Square(File.E, Rank.R8), MoveType.Promotion(piece))
+      PgnExporter.exportGame(Map.empty, List(move)) should include(s"e8$suffix")
+    }
+
+    val normal = PgnExporter.exportGame(Map.empty, List(Move(Square(File.E, Rank.R2), Square(File.E, Rank.R4), MoveType.Normal())))
+    normal should include("e4")
+    normal should not include "="
+
+  test("exportGameContext preserves moves and default headers"):
+    val moves = List(
+      Move(Square(File.E, Rank.R2), Square(File.E, Rank.R4), MoveType.Normal()),
+      Move(Square(File.E, Rank.R7), Square(File.E, Rank.R5), MoveType.Normal())
+    )
+    val withMoves = PgnExporter.exportGameContext(GameContext.initial.copy(moves = moves))
+    withMoves.contains("e4") shouldBe true
+    withMoves.contains("e5") shouldBe true
+
+    val empty = PgnExporter.exportGameContext(GameContext.initial)
+    empty.contains("[Event") shouldBe true
+    empty.contains("*") shouldBe true
+
+  private def sq(alg: String): Square =
+    Square.fromAlgebraic(alg).getOrElse(fail(s"Invalid square in test: $alg"))
+
+  test("exportGame emits notation for all normal piece types and captures"):
+    val moves = List(
+      Move(sq("e2"), sq("e4")),
+      Move(sq("a7"), sq("a6")),
+      Move(sq("g1"), sq("f3")),
+      Move(sq("b7"), sq("b6")),
+      Move(sq("f1"), sq("b5"), MoveType.Normal(true)),
+      Move(sq("g8"), sq("f6")),
+      Move(sq("a1"), sq("a8"), MoveType.Normal(true)),
+      Move(sq("c7"), sq("c6")),
+      Move(sq("d1"), sq("d7"), MoveType.Normal(true)),
+      Move(sq("d8"), sq("d7"), MoveType.Normal(true)),
+      Move(sq("e1"), sq("e2"), MoveType.Normal(true))
+    )
+
+    val pgn = PgnExporter.exportGame(Map("Result" -> "*"), moves)
+
+    pgn should include("e4")
+    pgn should include("Nf3")
+    pgn should include("Bxb5")
+    pgn should include("Rxa8")
+    pgn should include("Qxd7")
+    pgn should include("Kxe2")
+
+  test("exportGame emits en-passant and promotion capture notation"):
+    val enPassant = Move(sq("e2"), sq("d3"), MoveType.EnPassant)
+    val promotionCapture = Move(sq("e7"), sq("f8"), MoveType.Promotion(PromotionPiece.Queen))
+    val pawnCapture = Move(sq("e2"), sq("d3"), MoveType.Normal(isCapture = true))
+    val promotionQuietSetup = Move(sq("e8"), sq("e7"))
+    val promotionQuiet = Move(sq("e2"), sq("e8"), MoveType.Promotion(PromotionPiece.Queen))
+
+    val pgn = PgnExporter.exportGame(Map.empty, List(enPassant, promotionCapture))
+    val pawnCapturePgn = PgnExporter.exportGame(Map.empty, List(pawnCapture))
+    val quietPromotionPgn = PgnExporter.exportGame(Map.empty, List(promotionQuietSetup, promotionQuiet))
+
+    pgn should include("exd3")
+    pgn should include("exf8=Q")
+    pawnCapturePgn should include("exd3")
+    quietPromotionPgn should include("e8=Q")
+

modules/io/src/test/scala/de/nowchess/io/pgn/PgnParserTest.scala

@@ -0,0 +1,131 @@
+package de.nowchess.io.pgn
+
+import de.nowchess.api.board.*
+import de.nowchess.api.move.{MoveType, PromotionPiece}
+import de.nowchess.api.game.GameContext
+import de.nowchess.io.fen.FenParser
+import org.scalatest.funsuite.AnyFunSuite
+import org.scalatest.matchers.should.Matchers
+
+class PgnParserTest extends AnyFunSuite with Matchers:
+
+  test("parsePgn handles headers standard sequences captures castling and skipped tokens"):
+    val headerOnly = """[Event "Test Game"]
+[White "Alice"]
+[Black "Bob"]
+[Result "1-0"]"""
+    val onlyHeaders = PgnParser.parsePgn(headerOnly)
+    onlyHeaders.isDefined shouldBe true
+    onlyHeaders.get.headers("Event") shouldBe "Test Game"
+    onlyHeaders.get.headers("White") shouldBe "Alice"
+
+    val simple = PgnParser.parsePgn("""[Event "Test"]
+
+1. e4 e5 2. Nf3 Nc6""")
+    simple.map(_.moves.length) shouldBe Some(4)
+
+    val capture = PgnParser.parsePgn("""[Event "Test"]
+
+1. Nf3 e5 2. Nxe5""")
+    capture.map(_.moves.length) shouldBe Some(3)
+    capture.get.moves(2).to shouldBe Square(File.E, Rank.R5)
+
+    val whiteKs = PgnParser.parsePgn("""[Event "Test"]
+
+1. e4 e5 2. Nf3 Nc6 3. Bc4 Bc5 4. O-O""").get.moves.last
+    whiteKs.moveType shouldBe MoveType.CastleKingside
+    whiteKs.from shouldBe Square(File.E, Rank.R1)
+    whiteKs.to shouldBe Square(File.G, Rank.R1)
+
+    val whiteQs = PgnParser.parsePgn("""[Event "Test"]
+
+1. d4 d5 2. Nc3 Nc6 3. Bf4 Bf5 4. Qd2 Qd7 5. O-O-O""").get.moves.last
+    whiteQs.moveType shouldBe MoveType.CastleQueenside
+    whiteQs.from shouldBe Square(File.E, Rank.R1)
+    whiteQs.to shouldBe Square(File.C, Rank.R1)
+
+    val blackKs = PgnParser.parsePgn("""[Event "Test"]
+
+1. e4 e5 2. Nf3 Nf6 3. Bc4 Be7 4. O-O O-O""").get.moves.last
+    blackKs.moveType shouldBe MoveType.CastleKingside
+    blackKs.from shouldBe Square(File.E, Rank.R8)
+
+    val blackQs = PgnParser.parsePgn("""[Event "Test"]
+
+1. d4 d5 2. Nc3 Nc6 3. Bf4 Bf5 4. Qd2 Qd7 5. O-O-O O-O-O""").get.moves.last
+    blackQs.moveType shouldBe MoveType.CastleQueenside
+    blackQs.from shouldBe Square(File.E, Rank.R8)
+    blackQs.to shouldBe Square(File.C, Rank.R8)
+
+    PgnParser.parsePgn("""[Event "Test"]
+
+1. e4 e5 1-0""").map(_.moves.length) shouldBe Some(2)
+    PgnParser.parsePgn("""[Event "Test"]
+
+1. e4 INVALID e5""").map(_.moves.length) shouldBe Some(2)
+
+  test("parseAlgebraicMove resolves pawn knight king and disambiguation cases"):
+    val board = Board.initial
+    PgnParser.parseAlgebraicMove("e4", GameContext.initial.withBoard(board), Color.White).get.to shouldBe Square(File.E, Rank.R4)
+    PgnParser.parseAlgebraicMove("Nf3", GameContext.initial.withBoard(board), Color.White).get.to shouldBe Square(File.F, Rank.R3)
+
+    val rookPieces: Map[Square, Piece] = Map(
+      Square(File.A, Rank.R1) -> Piece(Color.White, PieceType.Rook),
+      Square(File.H, Rank.R1) -> Piece(Color.White, PieceType.Rook),
+      Square(File.E, Rank.R1) -> Piece(Color.White, PieceType.King),
+      Square(File.E, Rank.R8) -> Piece(Color.Black, PieceType.King)
+    )
+    val rankPieces: Map[Square, Piece] = Map(
+      Square(File.A, Rank.R1) -> Piece(Color.White, PieceType.Rook),
+      Square(File.A, Rank.R4) -> Piece(Color.White, PieceType.Rook),
+      Square(File.E, Rank.R1) -> Piece(Color.White, PieceType.King),
+      Square(File.E, Rank.R8) -> Piece(Color.Black, PieceType.King)
+    )
+    PgnParser.parseAlgebraicMove("Rad1", GameContext.initial.withBoard(Board(rookPieces)), Color.White).get.from shouldBe Square(File.A, Rank.R1)
+    PgnParser.parseAlgebraicMove("R1a3", GameContext.initial.withBoard(Board(rankPieces)), Color.White).get.from shouldBe Square(File.A, Rank.R1)
+
+    val kingBoard = FenParser.parseBoard("4k3/8/8/8/8/8/8/4K3").get
+    val king = PgnParser.parseAlgebraicMove("Ke2", GameContext.initial.withBoard(kingBoard), Color.White)
+    king.isDefined shouldBe true
+    king.get.from shouldBe Square(File.E, Rank.R1)
+    king.get.to shouldBe Square(File.E, Rank.R2)
+
+  test("parseAlgebraicMove handles all promotion targets"):
+    val board = FenParser.parseBoard("8/4P3/4k3/8/8/8/8/8").get
+    PgnParser.parseAlgebraicMove("e7e8=Q", GameContext.initial.withBoard(board), Color.White).get.moveType shouldBe MoveType.Promotion(PromotionPiece.Queen)
+    PgnParser.parseAlgebraicMove("e7e8=R", GameContext.initial.withBoard(board), Color.White).get.moveType shouldBe MoveType.Promotion(PromotionPiece.Rook)
+    PgnParser.parseAlgebraicMove("e7e8=B", GameContext.initial.withBoard(board), Color.White).get.moveType shouldBe MoveType.Promotion(PromotionPiece.Bishop)
+    PgnParser.parseAlgebraicMove("e7e8=N", GameContext.initial.withBoard(board), Color.White).get.moveType shouldBe MoveType.Promotion(PromotionPiece.Knight)
+
+  test("importGameContext accepts valid and empty PGN"):
+    val pgn = """[Event "Test"]
+
+1. e4 e5"""
+    PgnParser.importGameContext(pgn).isRight shouldBe true
+    PgnParser.importGameContext("").isRight shouldBe true
+
+  test("parser edge cases: uppercase token hint chars and promotion mismatch handling"):
+    PgnParser.parseAlgebraicMove("E5", GameContext.initial, Color.White) shouldBe None
+    PgnParser.parseAlgebraicMove("N?f3", GameContext.initial, Color.White).get.to shouldBe Square(File.F, Rank.R3)
+    PgnParser.extractPromotion("e7e8=X") shouldBe None
+
+    val board = FenParser.parseBoard("8/4P3/4k3/8/8/8/8/8").get
+    PgnParser.parseAlgebraicMove("e8", GameContext.initial.withBoard(board), Color.White) shouldBe None
+
+  test("parseAlgebraicMove rejects too-short notation and invalid piece letters"):
+    val initial = GameContext.initial
+
+    PgnParser.parseAlgebraicMove("e", initial, Color.White) shouldBe None
+    PgnParser.parseAlgebraicMove("Xe5", initial, Color.White) shouldBe None
+
+  test("parseAlgebraicMove rejects notation with invalid promotion piece"):
+    val board = FenParser.parseBoard("8/4P3/4k3/8/8/8/8/8").getOrElse(fail("valid board expected"))
+    val context = GameContext.initial.withBoard(board)
+
+    PgnParser.parseAlgebraicMove("e7e8=X", context, Color.White) shouldBe None
+
+  test("parsePgn silently skips unknown tokens"):
+    val parsed = PgnParser.parsePgn("1. e4 ??? e5")
+
+    parsed.map(_.moves.size) shouldBe Some(2)
+

modules/io/src/test/scala/de/nowchess/io/pgn/PgnValidatorTest.scala

@@ -0,0 +1,58 @@
+package de.nowchess.io.pgn
+
+import de.nowchess.api.board.*
+import de.nowchess.api.move.MoveType
+import org.scalatest.funsuite.AnyFunSuite
+import org.scalatest.matchers.should.Matchers
+
+class PgnValidatorTest extends AnyFunSuite with Matchers:
+
+  test("validatePgn accepts valid games including castling and result tokens"):
+    val pgn =
+      """[Event "Test"]
+
+1. e4 e5 2. Nf3 Nc6
+"""
+    val valid = PgnParser.validatePgn(pgn)
+    valid.isRight shouldBe true
+    valid.toOption.get.moves.length shouldBe 4
+    valid.toOption.get.moves.head.from shouldBe Square(File.E, Rank.R2)
+
+    val withResult = PgnParser.validatePgn("""[Event "Test"]
+
+1. e4 e5 1-0
+""")
+    withResult.map(_.moves.length) shouldBe Right(2)
+
+    val kCastle = PgnParser.validatePgn("""[Event "Test"]
+
+1. e4 e5 2. Nf3 Nc6 3. Bc4 Bc5 4. O-O
+""")
+    kCastle.map(_.moves.last.moveType) shouldBe Right(MoveType.CastleKingside)
+
+    val qCastle = PgnParser.validatePgn("""[Event "Test"]
+
+1. d4 d5 2. Nc3 Nc6 3. Bf4 Bf5 4. Qd2 Qd7 5. O-O-O
+""")
+    qCastle.map(_.moves.last.moveType) shouldBe Right(MoveType.CastleQueenside)
+
+  test("validatePgn rejects impossible illegal and garbage tokens"):
+    PgnParser.validatePgn("""[Event "Test"]
+
+1. Qd4
+""").isLeft shouldBe true
+
+    PgnParser.validatePgn("""[Event "Test"]
+
+1. O-O
+""").isLeft shouldBe true
+
+    PgnParser.validatePgn("""[Event "Test"]
+
+1. e4 GARBAGE e5
+""").isLeft shouldBe true
+
+  test("validatePgn accepts empty move text and minimal valid header"):
+    PgnParser.validatePgn("[Event \"Test\"]\n[White \"A\"]\n[Black \"B\"]\n").map(_.moves) shouldBe Right(List.empty)
+    PgnParser.validatePgn("[Event \"T\"]\n\n1. e4").isRight shouldBe true
+

modules/io/versions.env

@@ -0,0 +1,3 @@
+MAJOR=0
+MINOR=0
+PATCH=1

modules/rule/CHANGELOG.md

@@ -0,0 +1 @@
+##  (2026-04-06)

modules/rule/build.gradle.kts

@@ -0,0 +1,63 @@
+plugins {
+    id("scala")
+    id("org.scoverage") version "8.1"
+}
+
+group = "de.nowchess"
+version = "1.0-SNAPSHOT"
+
+@Suppress("UNCHECKED_CAST")
+val versions = rootProject.extra["VERSIONS"] as Map<String, String>
+
+repositories {
+    mavenCentral()
+}
+
+scala {
+    scalaVersion = versions["SCALA3"]!!
+}
+
+scoverage {
+    scoverageVersion.set(versions["SCOVERAGE"]!!)
+}
+
+tasks.withType<ScalaCompile> {
+    scalaCompileOptions.additionalParameters = listOf("-encoding", "UTF-8")
+}
+
+dependencies {
+
+    implementation("org.scala-lang:scala3-compiler_3") {
+        version {
+            strictly(versions["SCALA3"]!!)
+        }
+    }
+    implementation("org.scala-lang:scala3-library_3") {
+        version {
+            strictly(versions["SCALA3"]!!)
+        }
+    }
+
+    implementation(project(":modules:api"))
+
+    testImplementation(project(":modules:io"))
+    testImplementation(platform("org.junit:junit-bom:5.13.4"))
+    testImplementation("org.junit.jupiter:junit-jupiter")
+    testImplementation("org.scalatest:scalatest_3:${versions["SCALATEST"]!!}")
+    testImplementation("co.helmethair:scalatest-junit-runner:${versions["SCALATEST_JUNIT"]!!}")
+
+    testRuntimeOnly("org.junit.platform:junit-platform-launcher")
+}
+
+tasks.test {
+    useJUnitPlatform {
+        includeEngines("scalatest")
+        testLogging {
+            events("skipped", "failed")
+        }
+    }
+    finalizedBy(tasks.reportScoverage)
+}
+tasks.reportScoverage {
+    dependsOn(tasks.test)
+}

modules/rule/src/main/scala/de/nowchess/rules/RuleSet.scala

@@ -0,0 +1,39 @@
+package de.nowchess.rules
+
+import de.nowchess.api.game.GameContext
+import de.nowchess.api.board.Square
+import de.nowchess.api.move.Move
+
+/** Extension point for chess rule variants (standard, Chess960, etc.).
+ *  All rule queries are stateless: given a GameContext, return the answer.
+ */
+trait RuleSet:
+  /** All pseudo-legal moves for the piece on `square` (ignores check). */
+  def candidateMoves(context: GameContext)(square: Square): List[Move]
+
+  /** Legal moves for `square`: candidates that don't leave own king in check. */
+  def legalMoves(context: GameContext)(square: Square): List[Move]
+
+  /** All legal moves for the side to move. */
+  def allLegalMoves(context: GameContext): List[Move]
+
+  /** True if the side to move's king is in check. */
+  def isCheck(context: GameContext): Boolean
+
+  /** True if the side to move is in check and has no legal moves. */
+  def isCheckmate(context: GameContext): Boolean
+
+  /** True if the side to move is not in check and has no legal moves. */
+  def isStalemate(context: GameContext): Boolean
+
+  /** True if neither side has enough material to checkmate. */
+  def isInsufficientMaterial(context: GameContext): Boolean
+
+  /** True if halfMoveClock >= 100 (50-move rule). */
+  def isFiftyMoveRule(context: GameContext): Boolean
+
+  /** Apply a legal move to produce the next game context.
+   *  Handles all special move types: castling, en passant, promotion.
+   *  Updates castling rights, en passant square, half-move clock, turn, and move history.
+   */
+  def applyMove(context: GameContext)(move: Move): GameContext

modules/rule/src/main/scala/de/nowchess/rules/sets/DefaultRules.scala

@@ -0,0 +1,387 @@
+package de.nowchess.rules.sets
+
+import de.nowchess.api.board.*
+import de.nowchess.api.game.GameContext
+import de.nowchess.api.move.{Move, MoveType, PromotionPiece}
+import de.nowchess.rules.RuleSet
+
+import scala.annotation.tailrec
+
+/** Standard chess rules implementation.
+ *  Handles move generation, validation, check/checkmate/stalemate detection.
+ */
+object DefaultRules extends RuleSet:
+
+  // ── Direction vectors ──────────────────────────────────────────────
+  private val RookDirs: List[(Int, Int)] = List((1, 0), (-1, 0), (0, 1), (0, -1))
+  private val BishopDirs: List[(Int, Int)] = List((1, 1), (1, -1), (-1, 1), (-1, -1))
+  private val QueenDirs: List[(Int, Int)] = RookDirs ++ BishopDirs
+  private val KnightJumps: List[(Int, Int)] =
+    List((2, 1), (2, -1), (-2, 1), (-2, -1), (1, 2), (1, -2), (-1, 2), (-1, -2))
+
+  // ── Pawn configuration helpers ─────────────────────────────────────
+  private def pawnForward(color: Color): Int = if color == Color.White then 1 else -1
+  private def pawnStartRank(color: Color): Int = if color == Color.White then 1 else 6
+  private def pawnPromoRank(color: Color): Int = if color == Color.White then 7 else 0
+
+  // ── Public API ─────────────────────────────────────────────────────
+
+  override def candidateMoves(context: GameContext)(square: Square): List[Move] =
+    context.board.pieceAt(square).fold(List.empty[Move]) { piece =>
+      if piece.color != context.turn then List.empty[Move]
+      else piece.pieceType match
+        case PieceType.Pawn => pawnCandidates(context, square, piece.color)
+        case PieceType.Knight => knightCandidates(context, square, piece.color)
+        case PieceType.Bishop => slidingMoves(context, square, piece.color, BishopDirs)
+        case PieceType.Rook => slidingMoves(context, square, piece.color, RookDirs)
+        case PieceType.Queen => slidingMoves(context, square, piece.color, QueenDirs)
+        case PieceType.King => kingCandidates(context, square, piece.color)
+    }
+
+  override def legalMoves(context: GameContext)(square: Square): List[Move] =
+    candidateMoves(context)(square).filter { move =>
+      !leavesKingInCheck(context, move)
+    }
+
+  override def allLegalMoves(context: GameContext): List[Move] =
+    Square.all.flatMap(sq => legalMoves(context)(sq)).toList
+
+  override def isCheck(context: GameContext): Boolean =
+    kingSquare(context.board, context.turn)
+      .fold(false)(sq => isAttackedBy(context.board, sq, context.turn.opposite))
+
+  override def isCheckmate(context: GameContext): Boolean =
+    isCheck(context) && allLegalMoves(context).isEmpty
+
+  override def isStalemate(context: GameContext): Boolean =
+    !isCheck(context) && allLegalMoves(context).isEmpty
+
+  override def isInsufficientMaterial(context: GameContext): Boolean =
+    insufficientMaterial(context.board)
+
+  override def isFiftyMoveRule(context: GameContext): Boolean =
+    context.halfMoveClock >= 100
+
+  // ── Sliding pieces (Bishop, Rook, Queen) ───────────────────────────
+
+  private def slidingMoves(
+    context: GameContext,
+    from: Square,
+    color: Color,
+    dirs: List[(Int, Int)]
+  ): List[Move] =
+    dirs.flatMap(dir => castRay(context.board, from, color, dir))
+
+  private def castRay(
+    board: Board,
+    from: Square,
+    color: Color,
+    dir: (Int, Int)
+  ): List[Move] =
+    @tailrec
+    def loop(sq: Square, acc: List[Move]): List[Move] =
+      sq.offset(dir._1, dir._2) match
+        case None => acc
+        case Some(next) =>
+          board.pieceAt(next) match
+            case None => loop(next, Move(from, next) :: acc)
+            case Some(p) if p.color != color => Move(from, next, MoveType.Normal(isCapture = true)) :: acc
+            case Some(_) => acc
+    loop(from, Nil).reverse
+
+  // ── Knight ─────────────────────────────────────────────────────────
+
+  private def knightCandidates(
+    context: GameContext,
+    from: Square,
+    color: Color
+  ): List[Move] =
+    KnightJumps.flatMap { (df, dr) =>
+      from.offset(df, dr).flatMap { to =>
+        context.board.pieceAt(to) match
+          case Some(p) if p.color == color => None
+          case Some(_) => Some(Move(from, to, MoveType.Normal(isCapture = true)))
+          case None    => Some(Move(from, to))
+      }
+    }
+
+  // ── King ───────────────────────────────────────────────────────────
+
+  private def kingCandidates(
+    context: GameContext,
+    from: Square,
+    color: Color
+  ): List[Move] =
+    val steps = QueenDirs.flatMap { (df, dr) =>
+      from.offset(df, dr).flatMap { to =>
+        context.board.pieceAt(to) match
+          case Some(p) if p.color == color => None
+          case Some(_) => Some(Move(from, to, MoveType.Normal(isCapture = true)))
+          case None    => Some(Move(from, to))
+      }
+    }
+    steps ++ castlingCandidates(context, from, color)
+
+  // ── Castling ───────────────────────────────────────────────────────
+
+  private case class CastlingMove(
+    kingFromAlg: String,
+    kingToAlg: String,
+    middleAlg: String,
+    rookFromAlg: String,
+    moveType: MoveType
+  )
+
+  private def castlingCandidates(
+    context: GameContext,
+    from: Square,
+    color: Color
+  ): List[Move] =
+    color match
+      case Color.White => whiteCastles(context, from)
+      case Color.Black => blackCastles(context, from)
+
+  private def whiteCastles(context: GameContext, from: Square): List[Move] =
+    val expected = Square.fromAlgebraic("e1").getOrElse(from)
+    if from != expected then List.empty
+    else
+      val moves = scala.collection.mutable.ListBuffer[Move]()
+      addCastleMove(context, moves, context.castlingRights.whiteKingSide,
+        CastlingMove("e1", "g1", "f1", "h1", MoveType.CastleKingside))
+      addCastleMove(context, moves, context.castlingRights.whiteQueenSide,
+        CastlingMove("e1", "c1", "d1", "a1", MoveType.CastleQueenside))
+      moves.toList
+
+  private def blackCastles(context: GameContext, from: Square): List[Move] =
+    val expected = Square.fromAlgebraic("e8").getOrElse(from)
+    if from != expected then List.empty
+    else
+      val moves = scala.collection.mutable.ListBuffer[Move]()
+      addCastleMove(context, moves, context.castlingRights.blackKingSide,
+        CastlingMove("e8", "g8", "f8", "h8", MoveType.CastleKingside))
+      addCastleMove(context, moves, context.castlingRights.blackQueenSide,
+        CastlingMove("e8", "c8", "d8", "a8", MoveType.CastleQueenside))
+      moves.toList
+
+  private def addCastleMove(
+    context: GameContext,
+    moves: scala.collection.mutable.ListBuffer[Move],
+    castlingRight: Boolean,
+    castlingMove: CastlingMove
+  ): Unit =
+    if castlingRight then
+      val clearSqs = List(castlingMove.middleAlg, castlingMove.kingToAlg).flatMap(Square.fromAlgebraic)
+      if squaresEmpty(context.board, clearSqs) then
+        for
+          kf <- Square.fromAlgebraic(castlingMove.kingFromAlg)
+          km <- Square.fromAlgebraic(castlingMove.middleAlg)
+          kt <- Square.fromAlgebraic(castlingMove.kingToAlg)
+          rf <- Square.fromAlgebraic(castlingMove.rookFromAlg)
+        do
+          val color = context.turn
+          val kingPresent = context.board.pieceAt(kf).exists(p => p.color == color && p.pieceType == PieceType.King)
+          val rookPresent = context.board.pieceAt(rf).exists(p => p.color == color && p.pieceType == PieceType.Rook)
+          val squaresSafe =
+            !isAttackedBy(context.board, kf, color.opposite) &&
+            !isAttackedBy(context.board, km, color.opposite) &&
+            !isAttackedBy(context.board, kt, color.opposite)
+
+          if kingPresent && rookPresent && squaresSafe then
+            moves += Move(kf, kt, castlingMove.moveType)
+
+  private def squaresEmpty(board: Board, squares: List[Square]): Boolean =
+    squares.forall(sq => board.pieceAt(sq).isEmpty)
+
+  // ── Pawn ───────────────────────────────────────────────────────────
+
+  private def pawnCandidates(
+    context: GameContext,
+    from: Square,
+    color: Color
+  ): List[Move] =
+    val fwd = pawnForward(color)
+    val startRank = pawnStartRank(color)
+    val promoRank = pawnPromoRank(color)
+
+    val single = from.offset(0, fwd).filter(to => context.board.pieceAt(to).isEmpty)
+    val double = Option.when(from.rank.ordinal == startRank) {
+      from.offset(0, fwd).flatMap { mid =>
+        Option.when(context.board.pieceAt(mid).isEmpty) {
+          from.offset(0, fwd * 2).filter(to => context.board.pieceAt(to).isEmpty)
+        }.flatten
+      }
+    }.flatten
+
+    val diagonalCaptures = List(-1, 1).flatMap { df =>
+      from.offset(df, fwd).flatMap { to =>
+        context.board.pieceAt(to).filter(_.color != color).map(_ => to)
+      }
+    }
+
+    val epCaptures: List[Move] = context.enPassantSquare.toList.flatMap { epSq =>
+      List(-1, 1).flatMap { df =>
+        from.offset(df, fwd).filter(_ == epSq).map { to =>
+          Move(from, epSq, MoveType.EnPassant)
+        }
+      }
+    }
+
+    def toMoves(dest: Square, isCapture: Boolean): List[Move] =
+      if dest.rank.ordinal == promoRank then
+        List(
+          PromotionPiece.Queen, PromotionPiece.Rook,
+          PromotionPiece.Bishop, PromotionPiece.Knight
+        ).map(pt => Move(from, dest, MoveType.Promotion(pt)))
+      else List(Move(from, dest, MoveType.Normal(isCapture = isCapture)))
+
+    val stepSquares = single.toList ++ double.toList
+    val stepMoves = stepSquares.flatMap(dest => toMoves(dest, isCapture = false))
+    val captureMoves = diagonalCaptures.flatMap(dest => toMoves(dest, isCapture = true))
+    stepMoves ++ captureMoves ++ epCaptures
+
+  // ── Check detection ────────────────────────────────────────────────
+
+  private def kingSquare(board: Board, color: Color): Option[Square] =
+    Square.all.find(sq =>
+      board.pieceAt(sq).exists(p => p.color == color && p.pieceType == PieceType.King)
+    )
+
+  private def isAttackedBy(board: Board, target: Square, attacker: Color): Boolean =
+    Square.all.exists { sq =>
+      board.pieceAt(sq).fold(false) { p =>
+        p.color == attacker && squareAttacks(board, sq, p, target)
+      }
+    }
+
+  private def squareAttacks(board: Board, from: Square, piece: Piece, target: Square): Boolean =
+    val fwd = pawnForward(piece.color)
+    piece.pieceType match
+      case PieceType.Pawn =>
+        from.offset(-1, fwd).contains(target) || from.offset(1, fwd).contains(target)
+      case PieceType.Knight =>
+        KnightJumps.exists { (df, dr) => from.offset(df, dr).contains(target) }
+      case PieceType.Bishop => rayReaches(board, from, BishopDirs, target)
+      case PieceType.Rook => rayReaches(board, from, RookDirs, target)
+      case PieceType.Queen => rayReaches(board, from, QueenDirs, target)
+      case PieceType.King =>
+        QueenDirs.exists { (df, dr) => from.offset(df, dr).contains(target) }
+
+  private def rayReaches(board: Board, from: Square, dirs: List[(Int, Int)], target: Square): Boolean =
+    dirs.exists { dir =>
+      @tailrec
+      def loop(sq: Square): Boolean = sq.offset(dir._1, dir._2) match
+        case None => false
+        case Some(next) if next == target => true
+        case Some(next) if board.pieceAt(next).isEmpty => loop(next)
+        case Some(_) => false
+      loop(from)
+    }
+
+  private def leavesKingInCheck(context: GameContext, move: Move): Boolean =
+    val nextBoard = context.board.applyMove(move)
+    val nextContext = context.withBoard(nextBoard)
+    isCheck(nextContext)
+
+  // ── Move application ───────────────────────────────────────────────
+
+  override def applyMove(context: GameContext)(move: Move): GameContext =
+    val color = context.turn
+    val board  = context.board
+
+    val newBoard = move.moveType match
+      case MoveType.CastleKingside  => applyCastle(board, color, kingside = true)
+      case MoveType.CastleQueenside => applyCastle(board, color, kingside = false)
+      case MoveType.EnPassant       => applyEnPassant(board, move)
+      case MoveType.Promotion(pp)   => applyPromotion(board, move, color, pp)
+      case MoveType.Normal(_)       => board.applyMove(move)
+
+    val newCastlingRights = updateCastlingRights(context.castlingRights, board, move, color)
+    val newEnPassantSquare = computeEnPassantSquare(board, move)
+    val isCapture = move.moveType match
+      case MoveType.Normal(capture) => capture
+      case MoveType.EnPassant       => true
+      case _                        => board.pieceAt(move.to).isDefined
+    val isPawnMove = board.pieceAt(move.from).exists(_.pieceType == PieceType.Pawn)
+    val newClock = if isPawnMove || isCapture then 0 else context.halfMoveClock + 1
+
+    context
+      .withBoard(newBoard)
+      .withTurn(color.opposite)
+      .withCastlingRights(newCastlingRights)
+      .withEnPassantSquare(newEnPassantSquare)
+      .withHalfMoveClock(newClock)
+      .withMove(move)
+
+  private def applyCastle(board: Board, color: Color, kingside: Boolean): Board =
+    val rank = if color == Color.White then Rank.R1 else Rank.R8
+    val (kingFrom, kingTo, rookFrom, rookTo) =
+      if kingside then
+        (Square(File.E, rank), Square(File.G, rank), Square(File.H, rank), Square(File.F, rank))
+      else
+        (Square(File.E, rank), Square(File.C, rank), Square(File.A, rank), Square(File.D, rank))
+    val king = board.pieceAt(kingFrom).getOrElse(Piece(color, PieceType.King))
+    val rook = board.pieceAt(rookFrom).getOrElse(Piece(color, PieceType.Rook))
+    board
+      .removed(kingFrom).removed(rookFrom)
+      .updated(kingTo, king)
+      .updated(rookTo, rook)
+
+  private def applyEnPassant(board: Board, move: Move): Board =
+    val capturedRank = move.from.rank  // the captured pawn is on the same rank as the moving pawn
+    val capturedSquare = Square(move.to.file, capturedRank)
+    board.applyMove(move).removed(capturedSquare)
+
+  private def applyPromotion(board: Board, move: Move, color: Color, pp: PromotionPiece): Board =
+    val promotedType = pp match
+      case PromotionPiece.Queen  => PieceType.Queen
+      case PromotionPiece.Rook   => PieceType.Rook
+      case PromotionPiece.Bishop => PieceType.Bishop
+      case PromotionPiece.Knight => PieceType.Knight
+    board.removed(move.from).updated(move.to, Piece(color, promotedType))
+
+  private def updateCastlingRights(rights: CastlingRights, board: Board, move: Move, color: Color): CastlingRights =
+    val piece = board.pieceAt(move.from)
+    val isKingMove = piece.exists(_.pieceType == PieceType.King)
+    val isRookMove = piece.exists(_.pieceType == PieceType.Rook)
+
+    // Helper to check if a square is a rook's starting square
+    val whiteKingsideRook  = Square(File.H, Rank.R1)
+    val whiteQueensideRook = Square(File.A, Rank.R1)
+    val blackKingsideRook  = Square(File.H, Rank.R8)
+    val blackQueensideRook = Square(File.A, Rank.R8)
+
+    var r = rights
+    if isKingMove then r = r.revokeColor(color)
+    else if isRookMove then
+      if move.from == whiteKingsideRook  then r = r.revokeKingSide(Color.White)
+      if move.from == whiteQueensideRook then r = r.revokeQueenSide(Color.White)
+      if move.from == blackKingsideRook  then r = r.revokeKingSide(Color.Black)
+      if move.from == blackQueensideRook then r = r.revokeQueenSide(Color.Black)
+    // Also revoke if a rook is captured
+    if move.to == whiteKingsideRook  then r = r.revokeKingSide(Color.White)
+    if move.to == whiteQueensideRook then r = r.revokeQueenSide(Color.White)
+    if move.to == blackKingsideRook  then r = r.revokeKingSide(Color.Black)
+    if move.to == blackQueensideRook then r = r.revokeQueenSide(Color.Black)
+    r
+
+  private def computeEnPassantSquare(board: Board, move: Move): Option[Square] =
+    val piece = board.pieceAt(move.from)
+    val isDoublePawnPush = piece.exists(_.pieceType == PieceType.Pawn) &&
+      math.abs(move.to.rank.ordinal - move.from.rank.ordinal) == 2
+    if isDoublePawnPush then
+      // EP square is the square the pawn passed through
+      val epRankOrd = (move.from.rank.ordinal + move.to.rank.ordinal) / 2
+      Some(Square(move.from.file, Rank.values(epRankOrd)))
+    else None
+
+  // ── Insufficient material ──────────────────────────────────────────
+
+  private def insufficientMaterial(board: Board): Boolean =
+    val pieces = board.pieces.values.toList.filter(_.pieceType != PieceType.King)
+    pieces match
+      case Nil => true
+      case List(p) if p.pieceType == PieceType.Bishop || p.pieceType == PieceType.Knight => true
+      case List(p1, p2)
+        if p1.pieceType == PieceType.Bishop && p2.pieceType == PieceType.Bishop
+           && p1.color != p2.color => true
+      case _ => false

modules/rule/src/test/scala/de/nowchess/rule/DefaultRulesStateTransitionsTest.scala

@@ -0,0 +1,300 @@
+package de.nowchess.rule
+
+import de.nowchess.api.board.{CastlingRights, Color, Piece, PieceType, Square}
+import de.nowchess.api.game.GameContext
+import de.nowchess.api.move.{Move, MoveType, PromotionPiece}
+import de.nowchess.io.fen.FenParser
+import de.nowchess.rules.sets.DefaultRules
+import org.scalatest.funsuite.AnyFunSuite
+import org.scalatest.matchers.should.Matchers
+
+class DefaultRulesStateTransitionsTest extends AnyFunSuite with Matchers:
+
+  private def contextFromFen(fen: String): GameContext =
+    FenParser.parseFen(fen).fold(err => fail(err), identity)
+
+  private def sq(alg: String): Square =
+    Square.fromAlgebraic(alg).getOrElse(fail(s"Invalid square in test: $alg"))
+
+  test("isCheckmate returns true for a known mate pattern"):
+    val context = contextFromFen("rnb1kbnr/pppp1ppp/8/4p3/6Pq/5P2/PPPPP2P/RNBQKBNR w KQkq - 1 3")
+
+    DefaultRules.isCheck(context) shouldBe true
+    DefaultRules.isCheckmate(context) shouldBe true
+    DefaultRules.allLegalMoves(context) shouldBe empty
+
+  test("isStalemate returns true for a known stalemate pattern"):
+    val context = contextFromFen("7k/5K2/6Q1/8/8/8/8/8 b - - 0 1")
+
+    DefaultRules.isCheck(context) shouldBe false
+    DefaultRules.isStalemate(context) shouldBe true
+    DefaultRules.allLegalMoves(context) shouldBe empty
+
+  test("isInsufficientMaterial returns true for king versus king"):
+    val context = contextFromFen("8/8/8/8/8/8/4k3/4K3 w - - 0 1")
+
+    DefaultRules.isInsufficientMaterial(context) shouldBe true
+
+  test("isInsufficientMaterial returns true for king and bishop versus king"):
+    val context = contextFromFen("8/8/8/8/8/8/4k3/3BK3 w - - 0 1")
+
+    DefaultRules.isInsufficientMaterial(context) shouldBe true
+
+  test("isInsufficientMaterial returns false for king and rook versus king"):
+    val context = contextFromFen("8/8/8/8/8/8/4k3/3RK3 w - - 0 1")
+
+    DefaultRules.isInsufficientMaterial(context) shouldBe false
+
+  test("isFiftyMoveRule returns true when halfMoveClock is 100"):
+    val context = contextFromFen("8/8/8/8/8/8/4k3/4K3 w - - 100 1")
+
+    DefaultRules.isFiftyMoveRule(context) shouldBe true
+
+  test("applyMove toggles turn and records move"):
+    val move = Move(sq("e2"), sq("e4"))
+    val next = DefaultRules.applyMove(GameContext.initial)(move)
+
+    next.turn shouldBe Color.Black
+    next.moves.lastOption shouldBe Some(move)
+
+  test("applyMove sets en passant square after double pawn push"):
+    val move = Move(sq("e2"), sq("e4"))
+    val next = DefaultRules.applyMove(GameContext.initial)(move)
+
+    next.enPassantSquare shouldBe Some(sq("e3"))
+
+  test("applyMove clears en passant square for non double pawn push"):
+    val context = contextFromFen("4k3/8/8/8/8/8/4P3/4K3 w - d6 3 1")
+    val move = Move(sq("e2"), sq("e3"))
+
+    val next = DefaultRules.applyMove(context)(move)
+
+    next.enPassantSquare shouldBe None
+
+  test("applyMove resets halfMoveClock on pawn move"):
+    val context = contextFromFen("4k3/8/8/8/8/8/4P3/4K3 w - - 12 1")
+    val move = Move(sq("e2"), sq("e4"))
+
+    val next = DefaultRules.applyMove(context)(move)
+
+    next.halfMoveClock shouldBe 0
+
+  test("applyMove increments halfMoveClock on quiet non pawn move"):
+    val context = contextFromFen("4k3/8/8/8/8/8/8/4K1N1 w - - 7 1")
+    val move = Move(sq("g1"), sq("f3"))
+
+    val next = DefaultRules.applyMove(context)(move)
+
+    next.halfMoveClock shouldBe 8
+
+  test("applyMove resets halfMoveClock on capture"):
+    val context = contextFromFen("r3k3/8/8/8/8/8/8/R3K3 w Qq - 9 1")
+    val move = Move(sq("a1"), sq("a8"), MoveType.Normal(isCapture = true))
+
+    val next = DefaultRules.applyMove(context)(move)
+
+    next.halfMoveClock shouldBe 0
+    next.board.pieceAt(sq("a8")) shouldBe Some(Piece(Color.White, PieceType.Rook))
+
+  test("applyMove updates castling rights after king move"):
+    val context = contextFromFen("r3k2r/8/8/8/8/8/8/R3K2R w KQkq - 0 1")
+    val move = Move(sq("e1"), sq("e2"))
+
+    val next = DefaultRules.applyMove(context)(move)
+
+    next.castlingRights.whiteKingSide shouldBe false
+    next.castlingRights.whiteQueenSide shouldBe false
+    next.castlingRights.blackKingSide shouldBe true
+    next.castlingRights.blackQueenSide shouldBe true
+
+  test("applyMove updates castling rights after rook move from h1"):
+    val context = contextFromFen("r3k2r/8/8/8/8/8/8/4K2R w KQkq - 0 1")
+    val move = Move(sq("h1"), sq("h2"))
+
+    val next = DefaultRules.applyMove(context)(move)
+
+    next.castlingRights.whiteKingSide shouldBe false
+    next.castlingRights.whiteQueenSide shouldBe true
+
+  test("applyMove revokes opponent castling right when rook on starting square is captured"):
+    val context = contextFromFen("r3k3/8/8/8/8/8/8/R3K3 w Qq - 2 1")
+    val move = Move(sq("a1"), sq("a8"), MoveType.Normal(isCapture = true))
+
+    val next = DefaultRules.applyMove(context)(move)
+
+    next.castlingRights.blackQueenSide shouldBe false
+
+  test("applyMove executes kingside castling and repositions king and rook"):
+    val context = contextFromFen("4k2r/8/8/8/8/8/8/R3K2R w KQk - 0 1")
+    val move = Move(sq("e1"), sq("g1"), MoveType.CastleKingside)
+
+    val next = DefaultRules.applyMove(context)(move)
+
+    next.board.pieceAt(sq("g1")) shouldBe Some(Piece(Color.White, PieceType.King))
+    next.board.pieceAt(sq("f1")) shouldBe Some(Piece(Color.White, PieceType.Rook))
+    next.board.pieceAt(sq("e1")) shouldBe None
+    next.board.pieceAt(sq("h1")) shouldBe None
+
+  test("applyMove executes queenside castling and repositions king and rook"):
+    val context = contextFromFen("r3k3/8/8/8/8/8/8/R3K2R w KQq - 0 1")
+    val move = Move(sq("e1"), sq("c1"), MoveType.CastleQueenside)
+
+    val next = DefaultRules.applyMove(context)(move)
+
+    next.board.pieceAt(sq("c1")) shouldBe Some(Piece(Color.White, PieceType.King))
+    next.board.pieceAt(sq("d1")) shouldBe Some(Piece(Color.White, PieceType.Rook))
+    next.board.pieceAt(sq("e1")) shouldBe None
+    next.board.pieceAt(sq("a1")) shouldBe None
+
+  test("applyMove executes en passant and removes captured pawn"):
+    val context = contextFromFen("k7/8/8/3pP3/8/8/8/7K w - d6 0 1")
+    val move = Move(sq("e5"), sq("d6"), MoveType.EnPassant)
+
+    val next = DefaultRules.applyMove(context)(move)
+
+    next.board.pieceAt(sq("d6")) shouldBe Some(Piece(Color.White, PieceType.Pawn))
+    next.board.pieceAt(sq("d5")) shouldBe None
+    next.board.pieceAt(sq("e5")) shouldBe None
+
+  test("applyMove executes promotion with selected piece type"):
+    val context = contextFromFen("4k3/P7/8/8/8/8/8/4K3 w - - 0 1")
+    val move = Move(sq("a7"), sq("a8"), MoveType.Promotion(PromotionPiece.Knight))
+
+    val next = DefaultRules.applyMove(context)(move)
+
+    next.board.pieceAt(sq("a8")) shouldBe Some(Piece(Color.White, PieceType.Knight))
+    next.board.pieceAt(sq("a7")) shouldBe None
+
+  test("candidateMoves returns empty for opponent piece on selected square"):
+    val context = GameContext.initial.withTurn(Color.Black)
+
+    DefaultRules.candidateMoves(context)(sq("e2")) shouldBe empty
+
+  test("legalMoves keeps king safe by filtering pinned bishop moves"):
+    val context = contextFromFen("8/8/8/8/8/8/r1B1K3/8 w - - 0 1")
+
+    val bishopMoves = DefaultRules.legalMoves(context)(sq("c2"))
+
+    bishopMoves shouldBe empty
+
+  test("applyMove preserves black castling rights after white kingside castling"):
+    val context = contextFromFen("r3k2r/8/8/8/8/8/8/R3K2R w KQkq - 0 1")
+    val move = Move(sq("e1"), sq("g1"), MoveType.CastleKingside)
+
+    val next = DefaultRules.applyMove(context)(move)
+
+    next.castlingRights.whiteKingSide shouldBe false
+    next.castlingRights.whiteQueenSide shouldBe false
+    next.castlingRights.blackKingSide shouldBe true
+    next.castlingRights.blackQueenSide shouldBe true
+
+  test("applyMove can revoke both white castling rights when both rooks are captured"):
+    val context = GameContext(
+      board = contextFromFen("4k3/8/8/8/8/8/8/R3K2R w KQ - 0 1").board.updated(sq("a8"), Piece(Color.Black, PieceType.Queen)),
+      turn = Color.Black,
+      castlingRights = CastlingRights(true, true, false, false),
+      enPassantSquare = None,
+      halfMoveClock = 0,
+      moves = List.empty
+    )
+
+    val afterA1Capture = DefaultRules.applyMove(context)(Move(sq("a8"), sq("a1"), MoveType.Normal(isCapture = true)))
+    val afterH1Capture = DefaultRules.applyMove(afterA1Capture)(Move(sq("a1"), sq("h1"), MoveType.Normal(isCapture = true)))
+
+    afterH1Capture.castlingRights.whiteKingSide shouldBe false
+    afterH1Capture.castlingRights.whiteQueenSide shouldBe false
+
+  test("isInsufficientMaterial returns true for opposite color bishops only"):
+    val context = contextFromFen("8/8/8/8/8/8/4k1b1/3BK3 w - - 0 1")
+
+    DefaultRules.isInsufficientMaterial(context) shouldBe true
+
+  test("candidateMoves for rook includes enemy capture move"):
+    val context = contextFromFen("4k3/8/8/8/8/8/4K3/R6r w - - 0 1")
+
+    val rookMoves = DefaultRules.candidateMoves(context)(sq("a1"))
+
+    rookMoves.exists(m => m.to == sq("h1") && m.moveType == MoveType.Normal(isCapture = true)) shouldBe true
+
+  test("candidateMoves for knight includes enemy capture move"):
+    val context = contextFromFen("4k3/8/8/8/8/3p4/5N2/4K3 w - - 0 1")
+
+    val knightMoves = DefaultRules.candidateMoves(context)(sq("f2"))
+
+    knightMoves.exists(m => m.to == sq("d3") && m.moveType == MoveType.Normal(isCapture = true)) shouldBe true
+
+  test("candidateMoves includes black kingside and queenside castling options"):
+    val context = contextFromFen("r3k2r/8/8/8/8/8/8/4K3 b kq - 0 1")
+
+    val kingMoves = DefaultRules.candidateMoves(context)(sq("e8"))
+
+    kingMoves.exists(_.moveType == MoveType.CastleKingside) shouldBe true
+    kingMoves.exists(_.moveType == MoveType.CastleQueenside) shouldBe true
+
+  test("applyMove executes black kingside castling and repositions pieces on rank 8"):
+    val context = contextFromFen("r3k2r/8/8/8/8/8/8/4K3 b kq - 0 1")
+    val move = Move(sq("e8"), sq("g8"), MoveType.CastleKingside)
+
+    val next = DefaultRules.applyMove(context)(move)
+
+    next.board.pieceAt(sq("g8")) shouldBe Some(Piece(Color.Black, PieceType.King))
+    next.board.pieceAt(sq("f8")) shouldBe Some(Piece(Color.Black, PieceType.Rook))
+    next.board.pieceAt(sq("e8")) shouldBe None
+    next.board.pieceAt(sq("h8")) shouldBe None
+
+  test("applyMove revokes black castling rights when black rook moves from h8"):
+    val context = contextFromFen("r3k2r/8/8/8/8/8/8/4K3 b kq - 0 1")
+    val move = Move(sq("h8"), sq("h7"))
+
+    val next = DefaultRules.applyMove(context)(move)
+
+    next.castlingRights.blackKingSide shouldBe false
+    next.castlingRights.blackQueenSide shouldBe true
+
+  test("applyMove revokes black queenside castling right when black rook moves from a8"):
+    val context = contextFromFen("r3k2r/8/8/8/8/8/8/4K3 b kq - 0 1")
+    val move = Move(sq("a8"), sq("a7"))
+
+    val next = DefaultRules.applyMove(context)(move)
+
+    next.castlingRights.blackKingSide shouldBe true
+    next.castlingRights.blackQueenSide shouldBe false
+
+  test("applyMove revokes black kingside castling right when rook on h8 is captured"):
+    val context = contextFromFen("4k2r/8/8/8/8/8/8/4K2R w Kk - 0 1")
+    val move = Move(sq("h1"), sq("h8"), MoveType.Normal(isCapture = true))
+
+    val next = DefaultRules.applyMove(context)(move)
+
+    next.castlingRights.blackKingSide shouldBe false
+
+  test("candidateMoves creates all promotion move variants for black pawn"):
+    val context = contextFromFen("4k3/8/8/8/8/8/p7/4K3 b - - 0 1")
+    val to = sq("a1")
+
+    val pawnMoves = DefaultRules.candidateMoves(context)(sq("a2"))
+    val promotions = pawnMoves.collect { case Move(_, `to`, MoveType.Promotion(piece)) => piece }
+
+    promotions.toSet shouldBe Set(
+      PromotionPiece.Queen,
+      PromotionPiece.Rook,
+      PromotionPiece.Bishop,
+      PromotionPiece.Knight
+    )
+
+  test("applyMove promotion supports queen rook and bishop targets"):
+    val base = contextFromFen("4k3/P7/8/8/8/8/8/4K3 w - - 0 1")
+
+    val queen = DefaultRules.applyMove(base)(Move(sq("a7"), sq("a8"), MoveType.Promotion(PromotionPiece.Queen)))
+    val rook = DefaultRules.applyMove(base)(Move(sq("a7"), sq("a8"), MoveType.Promotion(PromotionPiece.Rook)))
+    val bishop = DefaultRules.applyMove(base)(Move(sq("a7"), sq("a8"), MoveType.Promotion(PromotionPiece.Bishop)))
+
+    queen.board.pieceAt(sq("a8")) shouldBe Some(Piece(Color.White, PieceType.Queen))
+    rook.board.pieceAt(sq("a8")) shouldBe Some(Piece(Color.White, PieceType.Rook))
+    bishop.board.pieceAt(sq("a8")) shouldBe Some(Piece(Color.White, PieceType.Bishop))
+
+
+
+
+
+

modules/rule/src/test/scala/de/nowchess/rule/DefaultRulesTest.scala

@@ -0,0 +1,152 @@
+package de.nowchess.rule
+
+import de.nowchess.api.board.{Board, Color, File, Rank, Square, Piece, PieceType, CastlingRights}
+import de.nowchess.api.game.GameContext
+import de.nowchess.api.move.{Move, MoveType}
+import de.nowchess.io.fen.FenParser
+import de.nowchess.rules.sets.DefaultRules
+import org.scalatest.funsuite.AnyFunSuite
+import org.scalatest.matchers.should.Matchers
+
+class DefaultRulesTest extends AnyFunSuite with Matchers:
+
+  private val rules = DefaultRules
+
+  // ── Pawn moves ──────────────────────────────────────────────────
+
+  test("pawn can move forward one square"):
+    val fen = "8/8/8/8/8/8/4P3/8 w - - 0 1"
+    val context = FenParser.parseFen(fen).fold(_ => fail(), identity)
+    val moves = rules.allLegalMoves(context)
+    val pawnMoves = moves.filter(m => m.from == Square(File.E, Rank.R2))
+    pawnMoves.exists(m => m.to == Square(File.E, Rank.R3)) shouldBe true
+
+  test("pawn can move forward two squares from starting position"):
+    val context = GameContext.initial
+    val moves = rules.allLegalMoves(context)
+    val e2Moves = moves.filter(m => m.from == Square(File.E, Rank.R2))
+    e2Moves.exists(m => m.to == Square(File.E, Rank.R4)) shouldBe true
+
+  test("pawn can capture diagonally"):
+    // FEN: white pawn e4, black pawn d5
+    val fen = "8/8/8/3p4/4P3/8/8/8 w - - 0 1"
+    val context = FenParser.parseFen(fen).fold(_ => fail(), identity)
+    val moves = rules.allLegalMoves(context)
+    val captures = moves.filter(m => m.from == Square(File.E, Rank.R4) && m.moveType.isInstanceOf[MoveType.Normal])
+    captures.exists(m => m.to == Square(File.D, Rank.R5)) shouldBe true
+
+  test("pawn cannot move backward"):
+    // FEN: white pawn on e4
+    val fen = "8/8/8/8/4P3/8/8/8 w - - 0 1"
+    val context = FenParser.parseFen(fen).fold(_ => fail(), identity)
+    val moves = rules.allLegalMoves(context)
+    val pawnMoves = moves.filter(m => m.from == Square(File.E, Rank.R4))
+    pawnMoves.exists(m => m.to == Square(File.E, Rank.R3)) shouldBe false
+
+  // ── King in check filtering ──────────────────────────────────────
+
+  test("moving king out of check removes it from legal moves if king stays in check"):
+    // FEN: white king e1, black rook e8, white tries to move away
+    val fen = "4r3/8/8/8/8/8/8/4K3 w - - 0 1"
+    val context = FenParser.parseFen(fen).fold(_ => fail(), identity)
+    val moves = rules.allLegalMoves(context)
+
+    // King must move; e2 should be valid but d1 might be blocked by rook if still on same file
+    moves.filter(m => m.from == Square(File.E, Rank.R1)).nonEmpty shouldBe true
+
+  test("king cannot move to square attacked by opponent"):
+    // FEN: white king e1, black rook e2 defended by black king e3
+    val fen = "8/8/8/8/8/4k3/4r3/4K3 w - - 0 1"
+    val context = FenParser.parseFen(fen).fold(_ => fail(), identity)
+    val moves = rules.allLegalMoves(context)
+
+    // King cannot move to e2 (occupied and attacked)
+    val kingMovesToE2 = moves.filter(m => m.from == Square(File.E, Rank.R1) && m.to == Square(File.E, Rank.R2))
+    kingMovesToE2.isEmpty shouldBe true
+
+  // ── Castling legality ────────────────────────────────────────────
+
+  test("castling kingside is legal when king and rook unmoved and path clear"):
+    val fen = "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQK2R w KQkq - 0 1"
+    val context = FenParser.parseFen(fen).fold(_ => fail(), identity)
+    val moves = rules.allLegalMoves(context)
+
+    val castles = moves.filter(m => m.moveType == MoveType.CastleKingside)
+    castles.nonEmpty shouldBe true
+
+  test("castling queenside is legal when king and rook unmoved and path clear"):
+    val fen = "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/R3K2R w KQkq - 0 1"
+    val context = FenParser.parseFen(fen).fold(_ => fail(), identity)
+    val moves = rules.allLegalMoves(context)
+
+    val castles = moves.filter(m => m.moveType == MoveType.CastleQueenside)
+    castles.nonEmpty shouldBe true
+
+  test("castling is illegal when castling rights are false"):
+    // FEN: king and rook in position, but castling rights disabled
+    val fen = "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQK2R w - - 0 1"
+    val context = FenParser.parseFen(fen).fold(_ => fail(), identity)
+    val moves = rules.allLegalMoves(context)
+
+    val castles = moves.filter(m => m.moveType == MoveType.CastleKingside)
+    castles.isEmpty shouldBe true
+
+  test("castling is illegal when king is in check"):
+    // FEN: white king e1 in check from black rook e8
+    val fen = "4r3/8/8/8/8/8/8/R3K2R w KQ - 0 1"
+    val context = FenParser.parseFen(fen).fold(_ => fail(), identity)
+    val moves = rules.allLegalMoves(context)
+
+    val castles = moves.filter(m => m.moveType == MoveType.CastleKingside || m.moveType == MoveType.CastleQueenside)
+    castles.isEmpty shouldBe true
+
+  test("castling is illegal when path has piece in the way"):
+    // FEN: white king e1, white rook h1, white bishop f1 (blocks f-file)
+    val fen = "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBR1 w KQkq - 0 1"
+    val context = FenParser.parseFen(fen).fold(_ => fail(), identity)
+    val moves = rules.allLegalMoves(context)
+
+    val castles = moves.filter(m => m.moveType == MoveType.CastleKingside)
+    castles.isEmpty shouldBe true
+
+  // ── En passant legality ──────────────────────────────────────────
+
+  test("en passant is legal when en passant square is set"):
+    // FEN: white pawn e5, black pawn d5 (just double-pushed), en passant square d6
+    val fen = "k7/8/8/3pP3/8/8/8/7K w - d6 0 1"
+    val context = FenParser.parseFen(fen).fold(_ => fail(), identity)
+    val moves = rules.allLegalMoves(context)
+
+    val epMoves = moves.filter(m => m.moveType == MoveType.EnPassant)
+    epMoves.exists(m => m.to == Square(File.D, Rank.R6)) shouldBe true
+
+  test("en passant is illegal when en passant square is none"):
+    // FEN: white pawn e5, black pawn d5, but no en passant square
+    val fen = "k7/8/8/3pP3/8/8/8/7K w - - 0 1"
+    val context = FenParser.parseFen(fen).fold(_ => fail(), identity)
+    val moves = rules.allLegalMoves(context)
+
+    val epMoves = moves.filter(m => m.moveType == MoveType.EnPassant)
+    epMoves.isEmpty shouldBe true
+
+  // ── Pinned pieces ────────────────────────────────────────────────
+
+  test("pinned piece cannot move and expose king to check"):
+    // FEN: white king e1, white bishop d2 (pinned), black rook a2
+    val fen = "8/8/8/8/8/8/r1B1K3/8 w - - 0 1"
+    val context = FenParser.parseFen(fen).fold(_ => fail(), identity)
+    val moves = rules.allLegalMoves(context)
+
+    // Bishop on d2 is pinned by rook on a2; it cannot move
+    val bishopMoves = moves.filter(m => m.from == Square(File.C, Rank.R2))
+    bishopMoves.isEmpty shouldBe true
+
+  test("piece blocking a check is legal"):
+    // FEN: white king e1, white rook d1, black bishop a4 attacking e1 via d2
+    // Actually, this is complex. Let's use: white king e1, black rook e8, white pawn blocks on e2
+    val fen = "4r3/8/8/8/8/8/4P3/4K3 w - - 0 1"
+    val context = FenParser.parseFen(fen).fold(_ => fail(), identity)
+    val moves = rules.allLegalMoves(context)
+
+    // White is in check; only moves that block or move the king are legal
+    moves.nonEmpty shouldBe true

modules/rule/versions.env

@@ -0,0 +1,3 @@
+MAJOR=0
+MINOR=0
+PATCH=1

modules/ui/CHANGELOG.md

@@ -17,3 +17,19 @@
 * NCS-10 Implement Pawn Promotion ([#12](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/12)) ([13bfc16](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/13bfc16cfe25db78ec607db523ca6d993c13430c))
 * NCS-16 Core Separation via Patterns ([#10](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/10)) ([1361dfc](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/1361dfc89553b146864fb8ff3526cf12cf3f293a))
 * NCS-17 Implement basic ScalaFX UI ([#14](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/14)) ([3ff8031](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/3ff80318b4f16c59733a46498581a5c27f048287))
+##  (2026-04-02)
+
+### Features
+
+* NCS-10 Implement Pawn Promotion ([#12](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/12)) ([13bfc16](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/13bfc16cfe25db78ec607db523ca6d993c13430c))
+* NCS-16 Core Separation via Patterns ([#10](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/10)) ([1361dfc](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/1361dfc89553b146864fb8ff3526cf12cf3f293a))
+* NCS-17 Implement basic ScalaFX UI ([#14](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/14)) ([3ff8031](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/3ff80318b4f16c59733a46498581a5c27f048287))
+* NCS-21 Write Scripts to automate certain tasks ([#15](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/15)) ([8051871](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/80518719d536a087d339fe02530825dc07f8b388))
+##  (2026-04-03)
+
+### Features
+
+* NCS-10 Implement Pawn Promotion ([#12](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/12)) ([13bfc16](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/13bfc16cfe25db78ec607db523ca6d993c13430c))
+* NCS-16 Core Separation via Patterns ([#10](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/10)) ([1361dfc](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/1361dfc89553b146864fb8ff3526cf12cf3f293a))
+* NCS-17 Implement basic ScalaFX UI ([#14](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/14)) ([3ff8031](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/3ff80318b4f16c59733a46498581a5c27f048287))
+* NCS-21 Write Scripts to automate certain tasks ([#15](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/15)) ([8051871](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/80518719d536a087d339fe02530825dc07f8b388))

modules/ui/build.gradle.kts

@@ -1,3 +1,6 @@
+import org.gradle.api.file.DuplicatesStrategy
+import org.gradle.jvm.tasks.Jar
+
 plugins {
     id("scala")
     id("org.scoverage")
@@ -21,7 +24,9 @@ scala {
 scoverage {
     scoverageVersion.set(versions["SCOVERAGE"]!!)
     excludedPackages.set(listOf(
-        "de.nowchess.ui.gui"
+        "de.nowchess.ui.gui",
+        "de.nowchess.ui.terminal",
+        "de.nowchess.ui.Main",
     ))
 }
 
@@ -38,6 +43,10 @@ tasks.named<JavaExec>("run") {
     standardInput = System.`in`
 }
 
+tasks.named<Jar>("jar") {
+    duplicatesStrategy = DuplicatesStrategy.EXCLUDE
+}
+
 dependencies {
 
     implementation("org.scala-lang:scala3-compiler_3") {
@@ -52,7 +61,9 @@ dependencies {
     }
 
     implementation(project(":modules:core"))
+    implementation(project(":modules:rule"))
     implementation(project(":modules:api"))
+    implementation(project(":modules:io"))
 
     // ScalaFX dependencies
     implementation("org.scalafx:scalafx_3:${versions["SCALAFX"]!!}")

modules/ui/src/main/scala/de/nowchess/ui/gui/ChessBoardView.scala

@@ -1,20 +1,22 @@
 package de.nowchess.ui.gui
 
+import scala.compiletime.uninitialized
 import scalafx.Includes.*
 import scalafx.application.Platform
 import scalafx.geometry.{Insets, Pos}
 import scalafx.scene.control.{Button, ButtonType, ChoiceDialog, Label}
-import scalafx.scene.layout.{BorderPane, GridPane, HBox, VBox, StackPane}
+import scalafx.scene.layout.{BorderPane, GridPane, HBox, StackPane, VBox}
 import scalafx.scene.paint.Color as FXColor
 import scalafx.scene.shape.Rectangle
 import scalafx.scene.text.{Font, Text}
 import scalafx.stage.Stage
-import de.nowchess.api.board.{Board, Color, Piece, PieceType, Square, File, Rank}
-import de.nowchess.api.game.{CastlingRights, GameState, GameStatus}
+import de.nowchess.api.board.{Board, Color, File, Piece, PieceType, Rank, Square}
 import de.nowchess.api.move.PromotionPiece
+import de.nowchess.chess.command.{MoveCommand, MoveResult}
 import de.nowchess.chess.engine.GameEngine
-import de.nowchess.chess.logic.{CastlingRightsCalculator, EnPassantCalculator, GameHistory, GameRules, withCastle}
-import de.nowchess.chess.notation.{FenExporter, FenParser, PgnExporter, PgnParser}
+import de.nowchess.io.fen.{FenExporter, FenParser}
+import de.nowchess.io.pgn.{PgnExporter, PgnParser}
+import de.nowchess.io.{GameContextExport, GameContextImport}
 
 /** ScalaFX chess board view that displays the game state.
  *  Uses chess sprites and color palette.
@@ -36,6 +38,9 @@ class ChessBoardView(val stage: Stage, private val engine: GameEngine) extends B
   private var selectedSquare: Option[Square] = None
   private val squareViews = scala.collection.mutable.Map[(Int, Int), StackPane]()
   
+  private var undoButton: Button = uninitialized
+  private var redoButton: Button = uninitialized
+
   // Initialize UI
   initializeBoard()
   
@@ -69,15 +74,23 @@ class ChessBoardView(val stage: Stage, private val engine: GameEngine) extends B
         spacing = 10
         alignment = Pos.Center
         children = Seq(
-          new Button("Undo") {
-            font = Font.font(comicSansFontFamily, 12)
-            onAction = _ => if engine.canUndo then engine.undo()
-            style = "-fx-background-radius: 8; -fx-background-color: #B9DAD1;"
+          {
+            undoButton = new Button("Undo") {
+              font = Font.font(comicSansFontFamily, 12)
+              onAction = _ => if engine.canUndo then engine.undo()
+              style = "-fx-background-radius: 8; -fx-background-color: #B9DAD1;"
+              disable = !engine.canUndo
+            }
+            undoButton
           },
-          new Button("Redo") {
-            font = Font.font(comicSansFontFamily, 12)
-            onAction = _ => if engine.canRedo then engine.redo()
-            style = "-fx-background-radius: 8; -fx-background-color: #B9C2DA;"
+          {
+            redoButton = new Button("Redo") {
+              font = Font.font(comicSansFontFamily, 12)
+              onAction = _ => if engine.canRedo then engine.redo()
+              style = "-fx-background-radius: 8; -fx-background-color: #B9C2DA;"
+              disable = !engine.canRedo
+            }
+            redoButton
           },
           new Button("Reset") {
             font = Font.font(comicSansFontFamily, 12)
@@ -164,10 +177,11 @@ class ChessBoardView(val stage: Stage, private val engine: GameEngine) extends B
           if piece.color == currentTurn then
             selectedSquare = Some(clickedSquare)
             highlightSquare(rank, file, PieceSprites.SquareColors.Selected)
-            val legalDests = GameRules.legalMoves(currentBoard, engine.history, currentTurn)
-              .collect { case (`clickedSquare`, to) => to }
+
+            val legalDests = engine.ruleSet.legalMoves(engine.context)(clickedSquare)
+               .collect { case move if move.from == clickedSquare => move.to }
             legalDests.foreach { sq =>
-              highlightSquare(sq.rank.ordinal, sq.file.ordinal, PieceSprites.SquareColors.ValidMove)
+               highlightSquare(sq.rank.ordinal, sq.file.ordinal, PieceSprites.SquareColors.ValidMove)
             }
         }
       
@@ -216,7 +230,13 @@ class ChessBoardView(val stage: Stage, private val engine: GameEngine) extends B
         
         stackPane.children = children
       }
-  
+
+    updateUndoRedoButtons()
+
+  def updateUndoRedoButtons(): Unit =
+    if undoButton != null then undoButton.disable = !engine.canUndo
+    if redoButton != null then redoButton.disable = !engine.canRedo
+
   private def highlightSquare(rank: Int, file: Int, color: String): Unit =
     squareViews.get((rank, file)).foreach { stackPane =>
       val bgRect = new Rectangle {
@@ -258,56 +278,32 @@ class ChessBoardView(val stage: Stage, private val engine: GameEngine) extends B
       case _ => engine.completePromotion(PromotionPiece.Queen) // Default
 
   private def doFenExport(): Unit =
-    val state = GameState(
-      piecePlacement  = FenExporter.boardToFen(currentBoard),
-      activeColor     = currentTurn,
-      castlingWhite   = CastlingRightsCalculator.deriveCastlingRights(engine.history, Color.White),
-      castlingBlack   = CastlingRightsCalculator.deriveCastlingRights(engine.history, Color.Black),
-      enPassantTarget = EnPassantCalculator.enPassantTarget(currentBoard, engine.history),
-      halfMoveClock   = 0,
-      fullMoveNumber  = engine.history.moves.size / 2 + 1,
-      status          = GameStatus.InProgress
-    )
-    showCopyDialog("FEN Export", FenExporter.gameStateToFen(state))
+    doExport(FenExporter, "FEN")
 
   private def doFenImport(): Unit =
-    showInputDialog("FEN Import", rows = 1).foreach { fen =>
-      FenParser.parseFen(fen) match
-        case None => showMessage("Invalid FEN")
-        case Some(state) =>
-          FenParser.parseBoard(state.piecePlacement) match
-            case None => showMessage("Invalid FEN board")
-            case Some(board) => engine.loadPosition(board, GameHistory.empty, state.activeColor)
-    }
+    doImport(FenParser, "FEN")
 
   private def doPgnExport(): Unit =
-    showCopyDialog("PGN Export", PgnExporter.exportGame(Map.empty, engine.history))
+    doExport(PgnExporter, "PGN")
 
   private def doPgnImport(): Unit =
-    showInputDialog("PGN Import", rows = 6).foreach { pgn =>
-      PgnParser.parsePgn(pgn) match
-        case None => showMessage("Invalid PGN")
-        case Some(pgnGame) =>
-          val (finalBoard, finalHistory) = pgnGame.moves.foldLeft((Board.initial, GameHistory.empty)):
-            case ((board, history), move) =>
-              val color = if history.moves.size % 2 == 0 then Color.White else Color.Black
-              val newBoard = move.castleSide match
-                case Some(side) => board.withCastle(color, side)
-                case None =>
-                  val (b, _) = board.withMove(move.from, move.to)
-                  move.promotionPiece match
-                    case Some(pp) =>
-                      val pt = pp match
-                        case PromotionPiece.Queen  => PieceType.Queen
-                        case PromotionPiece.Rook   => PieceType.Rook
-                        case PromotionPiece.Bishop => PieceType.Bishop
-                        case PromotionPiece.Knight => PieceType.Knight
-                      b.updated(move.to, Piece(color, pt))
-                    case None => b
-              (newBoard, history.addMove(move))
-          val finalTurn = if finalHistory.moves.size % 2 == 0 then Color.White else Color.Black
-          engine.loadPosition(finalBoard, finalHistory, finalTurn)
+    doImport(PgnParser, "PGN")
+
+  private def doExport(exporter: GameContextExport, formatName: String): Unit = {
+    val exported = exporter.exportGameContext(engine.context)
+    showCopyDialog(s"$formatName Export", exported)
+  }
+
+  private def doImport(importer: GameContextImport, formatName: String): Unit = {
+    showInputDialog(s"$formatName Import", rows = 5).foreach { input =>
+      importer.importGameContext(input) match
+        case Right(gameContext) =>
+          engine.loadPosition(gameContext)
+          showMessage(s"✓ $formatName loaded successfully!")
+        case Left(err) =>
+          showMessage(s"⚠️  $formatName Error: $err")
     }
+  }
 
   private def showCopyDialog(title: String, content: String): Unit =
     val area = new javafx.scene.control.TextArea(content)
@@ -339,3 +335,4 @@ class ChessBoardView(val stage: Stage, private val engine: GameEngine) extends B
     dialog.initOwner(stage.delegate)
     val result = dialog.showAndWait()
     if result.isPresent && result.get != null && result.get.nonEmpty then Some(result.get) else None
+

modules/ui/src/main/scala/de/nowchess/ui/gui/GUIObserver.scala

@@ -17,38 +17,57 @@ class GUIObserver(private val boardView: ChessBoardView) extends Observer:
     Platform.runLater {
       event match
         case e: MoveExecutedEvent =>
-          boardView.updateBoard(e.board, e.turn)
+          boardView.updateBoard(e.context.board, e.context.turn)
           e.capturedPiece.foreach { piece =>
             boardView.showMessage(s"Captured: $piece on ${e.toSquare}")
           }
 
         case e: CheckDetectedEvent =>
-          boardView.updateBoard(e.board, e.turn)
-          boardView.showMessage(s"${e.turn.label} is in check!")
+          boardView.updateBoard(e.context.board, e.context.turn)
+          boardView.showMessage(s"${e.context.turn.label} is in check!")
 
         case e: CheckmateEvent =>
-          boardView.updateBoard(e.board, e.turn)
+          boardView.updateBoard(e.context.board, e.context.turn)
           showAlert(AlertType.Information, "Game Over", s"Checkmate! ${e.winner.label} wins.")
 
         case e: StalemateEvent =>
-          boardView.updateBoard(e.board, e.turn)
+          boardView.updateBoard(e.context.board, e.context.turn)
           showAlert(AlertType.Information, "Game Over", "Stalemate! The game is a draw.")
 
         case e: InvalidMoveEvent =>
           boardView.showMessage(s"⚠️  ${e.reason}")
 
         case e: BoardResetEvent =>
-          boardView.updateBoard(e.board, e.turn)
+          boardView.updateBoard(e.context.board, e.context.turn)
           boardView.showMessage("Board has been reset to initial position.")
 
         case e: PromotionRequiredEvent =>
           boardView.showPromotionDialog(e.from, e.to)
 
         case e: DrawClaimedEvent =>
-          boardView.updateBoard(e.board, e.turn)
+          boardView.updateBoard(e.context.board, e.context.turn)
           showAlert(AlertType.Information, "Draw Claimed", "Draw claimed! The game is a draw.")
-        case e: FiftyMoveRuleAvailableEvent => 
+
+        case e: FiftyMoveRuleAvailableEvent =>
           boardView.showMessage("50-move rule available! The game is a draw.")
+
+        case e: MoveUndoneEvent =>
+          boardView.updateBoard(e.context.board, e.context.turn)
+          boardView.showMessage(s"↶ Undo: ${e.pgnNotation}")
+          boardView.updateUndoRedoButtons()
+
+        case e: MoveRedoneEvent =>
+          boardView.updateBoard(e.context.board, e.context.turn)
+          if e.capturedPiece.isDefined then
+            boardView.showMessage(s"↷ Redo: ${e.pgnNotation} — Captured: ${e.capturedPiece.get}")
+          else
+            boardView.showMessage(s"↷ Redo: ${e.pgnNotation}")
+          boardView.updateUndoRedoButtons()
+
+        case e: PgnLoadedEvent =>
+          boardView.updateBoard(e.context.board, e.context.turn)
+          boardView.showMessage("✓ PGN loaded successfully!")
+          boardView.updateUndoRedoButtons()
     }
 
   private def showAlert(alertType: AlertType, titleText: String, content: String): Unit =