docs(docs): 50 Move rule

Removed docs from this repo and added them to designated repo

modules/api/CHANGELOG.md

@@ -1,3 +1,4 @@
 ##  (2026-03-27)
 ##  (2026-03-28)
 ##  (2026-03-28)
+##  (2026-03-29)

modules/api/versions.env

@@ -1,3 +1,3 @@
 MAJOR=0
 MINOR=0
-PATCH=3
+PATCH=4

modules/core/CHANGELOG.md

@@ -28,3 +28,36 @@
 * 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))
+##  (2026-03-29)
+
+### 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-6 Implementing FEN & PGN ([#7](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/7)) ([f28e69d](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/f28e69dc181416aa2f221fdc4b45c2cda5efbf07))
+* 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))
+##  (2026-03-29)
+
+### 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-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))

modules/core/src/main/scala/de/nowchess/chess/Main.scala

@@ -8,5 +8,5 @@ import de.nowchess.chess.logic.GameHistory
 object Main {
   def main(args: Array[String]): Unit =
     println("NowChess TUI — type moves in coordinate notation (e.g. e2e4). Type 'quit' to exit.")
-    GameController.gameLoop(Board.initial, GameHistory.empty, Color.White)
+    GameController.gameLoop(Board.initial, GameHistory.empty, Color.White, 0)
 }

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

@@ -1,7 +1,7 @@
 package de.nowchess.chess.controller
 
 import scala.io.StdIn
-import de.nowchess.api.board.{Board, Color, File, Piece, Rank, Square}
+import de.nowchess.api.board.{Board, Color, File, Piece, PieceType, Rank, Square}
 import de.nowchess.chess.logic.*
 import de.nowchess.chess.view.Renderer
 
@@ -11,15 +11,16 @@ import de.nowchess.chess.view.Renderer
 
 sealed trait MoveResult
 object MoveResult:
-  case object Quit                                                                       extends MoveResult
+  case object Quit                                                                                              extends MoveResult
-  case class  InvalidFormat(raw: String)                                                extends MoveResult
+  case class  InvalidFormat(raw: String)                                                                       extends MoveResult
-  case object NoPiece                                                                   extends MoveResult
+  case object NoPiece                                                                                          extends MoveResult
-  case object WrongColor                                                                extends MoveResult
+  case object WrongColor                                                                                       extends MoveResult
-  case object IllegalMove                                                               extends MoveResult
+  case object IllegalMove                                                                                      extends MoveResult
-  case class  Moved(newBoard: Board, newHistory: GameHistory, captured: Option[Piece], newTurn: Color)      extends MoveResult
+  case class  Moved(newBoard: Board, newHistory: GameHistory, captured: Option[Piece], newHalfMoveClock: Int, newTurn: Color)        extends MoveResult
-  case class  MovedInCheck(newBoard: Board, newHistory: GameHistory, captured: Option[Piece], newTurn: Color) extends MoveResult
+  case class  MovedInCheck(newBoard: Board, newHistory: GameHistory, captured: Option[Piece], newHalfMoveClock: Int, newTurn: Color) extends MoveResult
-  case class  Checkmate(winner: Color)                                                  extends MoveResult
+  case class  Checkmate(winner: Color)                                                                         extends MoveResult
-  case object Stalemate                                                                 extends MoveResult
+  case object Stalemate                                                                                        extends MoveResult
+  case object DrawClaimed                                                                                      extends MoveResult
 
 // ---------------------------------------------------------------------------
 // Controller
@@ -30,10 +31,13 @@ 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 =
+  def processMove(board: Board, history: GameHistory, turn: Color, halfMoveClock: Int, raw: String): MoveResult =
     raw.trim match
       case "quit" | "q" =>
         MoveResult.Quit
+      case "draw" =>
+        if halfMoveClock >= 100 then MoveResult.DrawClaimed
+        else MoveResult.InvalidFormat("draw")
       case trimmed =>
         Parser.parseMove(trimmed) match
           case None =>
@@ -44,62 +48,84 @@ object GameController:
                 MoveResult.NoPiece
               case Some(piece) if piece.color != turn =>
                 MoveResult.WrongColor
-              case Some(_) =>
+              case Some(piece) =>
                 if !MoveValidator.isLegal(board, history, from, to) then
                   MoveResult.IllegalMove
                 else
                   val castleOpt = if MoveValidator.isCastle(board, from, to)
                                   then Some(MoveValidator.castleSide(from, to))
                                   else None
+                  val isEP = EnPassantCalculator.isEnPassant(board, history, from, to)
                   val (newBoard, captured) = castleOpt match
                     case Some(side) => (board.withCastle(turn, side), None)
-                    case None       => board.withMove(from, to)
+                    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 isReset = piece.pieceType == PieceType.Pawn || captured.isDefined || isEP
+                  val newClock = if isReset then 0 else halfMoveClock + 1
                   val newHistory = history.addMove(from, to, castleOpt)
                   GameRules.gameStatus(newBoard, newHistory, turn.opposite) match
-                    case PositionStatus.Normal  => MoveResult.Moved(newBoard, newHistory, captured, turn.opposite)
+                    case PositionStatus.Normal  => MoveResult.Moved(newBoard, newHistory, captured, newClock, turn.opposite)
-                    case PositionStatus.InCheck => MoveResult.MovedInCheck(newBoard, newHistory, captured, turn.opposite)
+                    case PositionStatus.InCheck => MoveResult.MovedInCheck(newBoard, newHistory, captured, newClock, turn.opposite)
                     case PositionStatus.Mated   => MoveResult.Checkmate(turn)
                     case PositionStatus.Drawn   => MoveResult.Stalemate
 
   /** Thin I/O shell: renders the board, reads a line, delegates to processMove,
    *  prints the outcome, and recurses until the game ends.
    */
-  def gameLoop(board: Board, history: GameHistory, turn: Color): Unit =
+  def gameLoop(board: Board, history: GameHistory, turn: Color, halfMoveClock: Int): Unit =
     println()
     print(Renderer.render(board))
-    println(s"${turn.label}'s turn. Enter move: ")
+    val input =
-    val input = Option(StdIn.readLine()).getOrElse("quit").trim
+      if halfMoveClock >= 100 then
-    processMove(board, history, turn, input) match
+        println(s"[50-move rule] ${turn.label} may claim a draw, or continue playing.")
+        println("  1. Claim draw")
+        println("  2. Continue")
+        Option(StdIn.readLine()).getOrElse("2").trim match
+          case "1" => "draw"
+          case _   =>
+            println(s"${turn.label}'s turn. Enter move: ")
+            Option(StdIn.readLine()).getOrElse("quit").trim
+      else
+        println(s"${turn.label}'s turn. Enter move: ")
+        Option(StdIn.readLine()).getOrElse("quit").trim
+    processMove(board, history, turn, halfMoveClock, input) match
       case MoveResult.Quit =>
         println("Game over. Goodbye!")
+      case MoveResult.DrawClaimed =>
+        println("Draw claimed by 50-move rule.")
+        gameLoop(Board.initial, GameHistory.empty, Color.White, 0)
       case MoveResult.InvalidFormat(raw) =>
         println(s"Invalid move format '$raw'. Use coordinate notation, e.g. e2e4.")
-        gameLoop(board, history, turn)
+        gameLoop(board, history, turn, halfMoveClock)
       case MoveResult.NoPiece =>
         println(s"No piece on ${Parser.parseMove(input).map(_._1).fold("?")(_.toString)}.")
-        gameLoop(board, history, turn)
+        gameLoop(board, history, turn, halfMoveClock)
       case MoveResult.WrongColor =>
         println(s"That is not your piece.")
-        gameLoop(board, history, turn)
+        gameLoop(board, history, turn, halfMoveClock)
       case MoveResult.IllegalMove =>
         println(s"Illegal move.")
-        gameLoop(board, history, turn)
+        gameLoop(board, history, turn, halfMoveClock)
-      case MoveResult.Moved(newBoard, newHistory, captured, newTurn) =>
+      case MoveResult.Moved(newBoard, newHistory, captured, newClock, newTurn) =>
         val prevTurn = newTurn.opposite
         captured.foreach: cap =>
           val toSq = Parser.parseMove(input).map(_._2).fold("?")(_.toString)
           println(s"${prevTurn.label} captures ${cap.color.label} ${cap.pieceType.label} on $toSq")
-        gameLoop(newBoard, newHistory, newTurn)
+        gameLoop(newBoard, newHistory, newTurn, newClock)
-      case MoveResult.MovedInCheck(newBoard, newHistory, captured, newTurn) =>
+      case MoveResult.MovedInCheck(newBoard, newHistory, captured, newClock, newTurn) =>
         val prevTurn = newTurn.opposite
         captured.foreach: cap =>
           val toSq = Parser.parseMove(input).map(_._2).fold("?")(_.toString)
           println(s"${prevTurn.label} captures ${cap.color.label} ${cap.pieceType.label} on $toSq")
         println(s"${newTurn.label} is in check!")
-        gameLoop(newBoard, newHistory, newTurn)
+        gameLoop(newBoard, newHistory, newTurn, newClock)
       case MoveResult.Checkmate(winner) =>
         println(s"Checkmate! ${winner.label} wins.")
-        gameLoop(Board.initial, GameHistory.empty, Color.White)
+        gameLoop(Board.initial, GameHistory.empty, Color.White, 0)
       case MoveResult.Stalemate =>
         println("Stalemate! The game is a draw.")
-        gameLoop(Board.initial, GameHistory.empty, Color.White)
+        gameLoop(Board.initial, GameHistory.empty, Color.White, 0)

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

@@ -0,0 +1,32 @@
+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/MoveValidator.scala

@@ -155,8 +155,21 @@ object MoveValidator:
     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)

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

@@ -11,11 +11,11 @@ import java.io.ByteArrayInputStream
 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 =
+  private def processMove(board: Board, history: GameHistory, turn: Color, raw: String, halfMoveClock: Int = 0): MoveResult =
-    GameController.processMove(board, history, turn, raw)
+    GameController.processMove(board, history, turn, halfMoveClock, raw)
 
-  private def gameLoop(board: Board, history: GameHistory, turn: Color): Unit =
+  private def gameLoop(board: Board, history: GameHistory, turn: Color, halfMoveClock: Int = 0): Unit =
-    GameController.gameLoop(board, history, turn)
+    GameController.gameLoop(board, history, turn, halfMoveClock)
 
   private def castlingRights(history: GameHistory, color: Color): CastlingRights =
     de.nowchess.chess.logic.CastlingRightsCalculator.deriveCastlingRights(history, color)
@@ -48,7 +48,7 @@ class GameControllerTest extends AnyFunSuite with Matchers:
 
   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) =>
+      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
@@ -63,7 +63,7 @@ class GameControllerTest extends AnyFunSuite with Matchers:
       sq(File.H, Rank.R8) -> Piece.WhiteKing
     ))
     processMove(board, GameHistory.empty, Color.White, "e5d6") match
-      case MoveResult.Moved(newBoard, newHistory, captured, newTurn) =>
+      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
@@ -133,7 +133,7 @@ class GameControllerTest extends AnyFunSuite with Matchers:
       sq(File.H, Rank.R8) -> Piece.BlackKing
     ))
     processMove(b, GameHistory.empty, Color.White, "a1a8") match
-      case MoveResult.MovedInCheck(_, _, _, newTurn) => newTurn shouldBe Color.Black
+      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"):
@@ -220,7 +220,7 @@ class GameControllerTest extends AnyFunSuite with Matchers:
         sq(File.H, Rank.R8) -> Piece.BlackKing
       ))
     processMove(b, GameHistory.empty, Color.White, "e1g1") match
-      case MoveResult.Moved(newBoard, newHistory, captured, newTurn) =>
+      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
@@ -236,7 +236,7 @@ class GameControllerTest extends AnyFunSuite with Matchers:
         sq(File.H, Rank.R8) -> Piece.BlackKing
       ))
     processMove(b, GameHistory.empty, Color.White, "e1c1") match
-      case MoveResult.Moved(newBoard, _, _, _) =>
+      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")
@@ -250,7 +250,7 @@ class GameControllerTest extends AnyFunSuite with Matchers:
         sq(File.H, Rank.R8) -> Piece.BlackKing
       ))
     processMove(b, GameHistory.empty, Color.White, "e1g1") match
-      case MoveResult.Moved(_, newHistory, _, _) =>
+      case MoveResult.Moved(_, newHistory, _, _, _) =>
         castlingRights(newHistory, Color.White) shouldBe CastlingRights.None
       case other => fail(s"Expected Moved, got $other")
 
@@ -261,10 +261,10 @@ class GameControllerTest extends AnyFunSuite with Matchers:
         sq(File.H, Rank.R8) -> Piece.BlackKing
       ))
     processMove(b, GameHistory.empty, Color.White, "h1h4") match
-      case MoveResult.Moved(_, newHistory, _, _) =>
+      case MoveResult.Moved(_, newHistory, _, _, _) =>
         castlingRights(newHistory, Color.White).kingSide  shouldBe false
         castlingRights(newHistory, Color.White).queenSide shouldBe true
-      case MoveResult.MovedInCheck(_, newHistory, _, _) =>
+      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")
@@ -275,7 +275,7 @@ class GameControllerTest extends AnyFunSuite with Matchers:
         sq(File.H, Rank.R8) -> Piece.BlackKing
       ))
     processMove(b, GameHistory.empty, Color.White, "e1e2") match
-      case MoveResult.Moved(_, newHistory, _, _) =>
+      case MoveResult.Moved(_, newHistory, _, _, _) =>
         castlingRights(newHistory, Color.White) shouldBe CastlingRights.None
       case other => fail(s"Expected Moved, got $other")
 
@@ -287,9 +287,9 @@ class GameControllerTest extends AnyFunSuite with Matchers:
         sq(File.A, Rank.R8) -> Piece.BlackKing
       ))
     processMove(b, GameHistory.empty, Color.Black, "h2h1") match
-      case MoveResult.Moved(_, newHistory, _, _) =>
+      case MoveResult.Moved(_, newHistory, _, _, _) =>
         castlingRights(newHistory, Color.White).kingSide shouldBe false
-      case MoveResult.MovedInCheck(_, newHistory, _, _) =>
+      case MoveResult.MovedInCheck(_, newHistory, _, _, _) =>
         castlingRights(newHistory, Color.White).kingSide shouldBe false
       case other => fail(s"Expected Moved or MovedInCheck, got $other")
 
@@ -316,9 +316,9 @@ class GameControllerTest extends AnyFunSuite with Matchers:
         sq(File.H, Rank.R1) -> Piece.WhiteKing
       ))
     processMove(b, GameHistory.empty, Color.Black, "e8e7") match
-      case MoveResult.Moved(_, newHistory, _, _) =>
+      case MoveResult.Moved(_, newHistory, _, _, _) =>
         castlingRights(newHistory, Color.Black) shouldBe CastlingRights.None
-      case MoveResult.MovedInCheck(_, newHistory, _, _) =>
+      case MoveResult.MovedInCheck(_, newHistory, _, _, _) =>
         castlingRights(newHistory, Color.Black) shouldBe CastlingRights.None
       case other => fail(s"Expected Moved or MovedInCheck, got $other")
 
@@ -329,10 +329,10 @@ class GameControllerTest extends AnyFunSuite with Matchers:
         sq(File.H, Rank.R1) -> Piece.WhiteKing
       ))
     processMove(b, GameHistory.empty, Color.Black, "a8a1") match
-      case MoveResult.Moved(_, newHistory, _, _) =>
+      case MoveResult.Moved(_, newHistory, _, _, _) =>
         castlingRights(newHistory, Color.Black).queenSide shouldBe false
         castlingRights(newHistory, Color.Black).kingSide  shouldBe true
-      case MoveResult.MovedInCheck(_, newHistory, _, _) =>
+      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")
@@ -344,10 +344,10 @@ class GameControllerTest extends AnyFunSuite with Matchers:
         sq(File.A, Rank.R1) -> Piece.WhiteKing
       ))
     processMove(b, GameHistory.empty, Color.Black, "h8h4") match
-      case MoveResult.Moved(_, newHistory, _, _) =>
+      case MoveResult.Moved(_, newHistory, _, _, _) =>
         castlingRights(newHistory, Color.Black).kingSide  shouldBe false
         castlingRights(newHistory, Color.Black).queenSide shouldBe true
-      case MoveResult.MovedInCheck(_, newHistory, _, _) =>
+      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")
@@ -360,8 +360,140 @@ class GameControllerTest extends AnyFunSuite with Matchers:
         sq(File.H, Rank.R8) -> Piece.BlackKing
       ))
     processMove(b, GameHistory.empty, Color.Black, "a2a1") match
-      case MoveResult.Moved(_, newHistory, _, _) =>
+      case MoveResult.Moved(_, newHistory, _, _, _) =>
         castlingRights(newHistory, Color.White).queenSide shouldBe false
-      case MoveResult.MovedInCheck(_, newHistory, _, _) =>
+      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, 0, "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, 0, "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")
+
+  // ──── processMove: 50-move rule draw claim ───────────────────────────────
+
+  test("processMove: 'draw' with halfMoveClock = 100 returns DrawClaimed"):
+    val b = Board(Map(
+      sq(File.E, Rank.R1) -> Piece.WhiteKing,
+      sq(File.E, Rank.R8) -> Piece.BlackKing
+    ))
+    GameController.processMove(b, GameHistory.empty, Color.White, 100, "draw") shouldBe MoveResult.DrawClaimed
+
+  test("processMove: 'draw' with halfMoveClock = 99 returns InvalidFormat"):
+    val b = Board(Map(
+      sq(File.E, Rank.R1) -> Piece.WhiteKing,
+      sq(File.E, Rank.R8) -> Piece.BlackKing
+    ))
+    GameController.processMove(b, GameHistory.empty, Color.White, 99, "draw") shouldBe MoveResult.InvalidFormat("draw")
+
+  // ──── processMove: halfMoveClock update ──────────────────────────────────
+
+  test("processMove: pawn move resets halfMoveClock to 0"):
+    GameController.processMove(Board.initial, GameHistory.empty, Color.White, 10, "e2e4") match
+      case MoveResult.Moved(_, _, _, newClock, _) => newClock shouldBe 0
+      case other => fail(s"Expected Moved, got $other")
+
+  test("processMove: capture resets halfMoveClock to 0"):
+    val b = Board(Map(
+      sq(File.A, Rank.R5) -> Piece.WhiteRook,
+      sq(File.D, Rank.R5) -> Piece.BlackPawn,
+      sq(File.H, Rank.R1) -> Piece.WhiteKing,
+      sq(File.H, Rank.R8) -> Piece.BlackKing
+    ))
+    GameController.processMove(b, GameHistory.empty, Color.White, 15, "a5d5") match
+      case MoveResult.Moved(_, _, _, newClock, _) => newClock shouldBe 0
+      case other => fail(s"Expected Moved, got $other")
+
+  test("processMove: en passant capture resets halfMoveClock to 0"):
+    val b = Board(Map(
+      sq(File.E, Rank.R5) -> Piece.WhitePawn,
+      sq(File.D, Rank.R5) -> Piece.BlackPawn,
+      sq(File.E, Rank.R1) -> Piece.WhiteKing,
+      sq(File.E, Rank.R8) -> Piece.BlackKing
+    ))
+    val h = GameHistory.empty.addMove(sq(File.D, Rank.R7), sq(File.D, Rank.R5))
+    GameController.processMove(b, h, Color.White, 20, "e5d6") match
+      case MoveResult.Moved(_, _, _, newClock, _) => newClock shouldBe 0
+      case other => fail(s"Expected Moved, got $other")
+
+  test("processMove: quiet piece move increments halfMoveClock"):
+    val b = Board(Map(
+      sq(File.A, Rank.R1) -> Piece.WhiteRook,
+      sq(File.E, Rank.R1) -> Piece.WhiteKing,
+      sq(File.E, Rank.R8) -> Piece.BlackKing
+    ))
+    GameController.processMove(b, GameHistory.empty, Color.White, 10, "a1a5") match
+      case MoveResult.Moved(_, _, _, newClock, _) => newClock shouldBe 11
+      case other => fail(s"Expected Moved, got $other")
+
+  test("processMove: MovedInCheck carries updated halfMoveClock"):
+    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
+    ))
+    GameController.processMove(b, GameHistory.empty, Color.White, 7, "a1a8") match
+      case MoveResult.MovedInCheck(_, _, _, newClock, _) => newClock shouldBe 8
+      case other => fail(s"Expected MovedInCheck, got $other")
+
+  // ──── gameLoop: 50-move rule menu ────────────────────────────────────────
+
+  test("gameLoop: shows 50-move rule menu when halfMoveClock >= 100 and draw claimed"):
+    val b = Board(Map(
+      sq(File.E, Rank.R1) -> Piece.WhiteKing,
+      sq(File.E, Rank.R8) -> Piece.BlackKing
+    ))
+    val output = captureOutput:
+      withInput("1\nquit\n"):
+        GameController.gameLoop(b, GameHistory.empty, Color.White, 100)
+    output should include("50-move rule")
+    output should include("Draw claimed by 50-move rule.")
+
+  test("gameLoop: shows 50-move rule menu when halfMoveClock >= 100 and player continues"):
+    val b = Board(Map(
+      sq(File.E, Rank.R1) -> Piece.WhiteKing,
+      sq(File.E, Rank.R8) -> Piece.BlackKing
+    ))
+    val output = captureOutput:
+      withInput("2\nquit\n"):
+        GameController.gameLoop(b, GameHistory.empty, Color.White, 100)
+    output should include("50-move rule")
+    output should include("White's turn")
+
+  test("gameLoop: no 50-move rule menu when halfMoveClock < 100"):
+    val output = captureOutput:
+      withInput("quit\n"):
+        GameController.gameLoop(Board.initial, GameHistory.empty, Color.White, 99)
+    output should not include "50-move rule"

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

@@ -0,0 +1,101 @@
+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/MoveValidatorTest.scala

@@ -211,3 +211,47 @@ class MoveValidatorTest extends AnyFunSuite with Matchers:
       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))

modules/core/versions.env

@@ -1,3 +1,3 @@
 MAJOR=0
-MINOR=2
+MINOR=4
 PATCH=0