refactor(core): integrate Rule module and update GameContext handling

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

@@ -6,9 +6,9 @@ import de.nowchess.api.game.GameContext
 import de.nowchess.chess.controller.Parser
 import de.nowchess.chess.observer.*
 import de.nowchess.chess.command.{CommandInvoker, MoveCommand, MoveResult}
-import de.nowchess.chess.notation.{PgnExporter, PgnParser}
+import de.nowchess.io.pgn.PgnParser
 import de.nowchess.rules.RuleSet
-import de.nowchess.rules.sets.StandardRules
+import de.nowchess.rules.sets.DefaultRules
 
 /** Pure game engine that manages game state and notifies observers of state changes.
  *  All rule queries delegate to the injected RuleSet.
@@ -16,7 +16,7 @@ import de.nowchess.rules.sets.StandardRules
  */
 class GameEngine(
   initialContext: GameContext = GameContext.initial,
-  ruleSet: RuleSet = StandardRules
+  ruleSet: RuleSet = DefaultRules
 ) extends Observable:
   private var currentContext: GameContext = initialContext
   private val invoker = new CommandInvoker()
@@ -146,25 +146,16 @@ class GameEngine(
         invoker.clear()
 
         var error: Option[String] = None
-        import scala.util.control.Breaks._
+        game.moves.foreach: histMove =>
-        breakable {
-          game.moves.foreach { histMove =>
           handleParsedMove(histMove.from, histMove.to)
           histMove.promotionPiece.foreach(completePromotion)
-            // $COVERAGE-OFF$ unreachable: PgnParser.validatePgn ensures promotion annotation is present
           if pendingPromotion.isDefined && histMove.promotionPiece.isEmpty then
             error = Some(s"Promotion required for move ${histMove.from}${histMove.to}")
-              break()
-          // $COVERAGE-ON$
-          }
-        }
 
         error match
-          // $COVERAGE-OFF$ unreachable: error is only set in the unreachable block above
           case Some(err) =>
             currentContext = savedContext
             Left(err)
-          // $COVERAGE-ON$
           case None =>
             notifyObservers(PgnLoadedEvent(currentContext))
             Right(())

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

@@ -151,7 +151,7 @@ class GameEngineLoadPgnTest extends AnyFunSuite with Matchers:
   test("loadPosition: fires BoardResetEvent and updates context"):
     import de.nowchess.api.board.{Board, Color}
     import de.nowchess.api.game.GameContext
-    import de.nowchess.chess.notation.FenParser
+    import de.nowchess.io.fen.FenParser
 
     val engine = new GameEngine()
     val cap    = new EventCapture()

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

@@ -3,7 +3,7 @@ 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.chess.notation.FenParser
+import de.nowchess.io.fen.FenParser
 import de.nowchess.chess.observer.*
 import org.scalatest.funsuite.AnyFunSuite
 import org.scalatest.matchers.should.Matchers

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

@@ -3,10 +3,10 @@ package de.nowchess.chess.engine
 import de.nowchess.api.board.{Board, Color, File, Piece, PieceType, Rank, Square}
 import de.nowchess.api.game.GameContext
 import de.nowchess.api.move.{Move, MoveType, PromotionPiece}
-import de.nowchess.chess.notation.FenParser
+import de.nowchess.io.fen.FenParser
 import de.nowchess.chess.observer.*
 import de.nowchess.rules.RuleSet
-import de.nowchess.rules.sets.StandardRules
+import de.nowchess.rules.sets.DefaultRules
 import org.scalatest.funsuite.AnyFunSuite
 import org.scalatest.matchers.should.Matchers
 
@@ -154,27 +154,27 @@ class GameEnginePromotionTest extends AnyFunSuite with Matchers:
     // triggering the "Error completing promotion." branch.
     val delegatingRuleSet: RuleSet = new RuleSet:
       def candidateMoves(context: GameContext, square: Square): List[Move] =
-        StandardRules.candidateMoves(context, square)
+        DefaultRules.candidateMoves(context, square)
       def legalMoves(context: GameContext, square: Square): List[Move] =
-        StandardRules.legalMoves(context, square).map { m =>
+        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] =
-        StandardRules.allLegalMoves(context)
+        DefaultRules.allLegalMoves(context)
       def isCheck(context: GameContext): Boolean =
-        StandardRules.isCheck(context)
+        DefaultRules.isCheck(context)
       def isCheckmate(context: GameContext): Boolean =
-        StandardRules.isCheckmate(context)
+        DefaultRules.isCheckmate(context)
       def isStalemate(context: GameContext): Boolean =
-        StandardRules.isStalemate(context)
+        DefaultRules.isStalemate(context)
       def isInsufficientMaterial(context: GameContext): Boolean =
-        StandardRules.isInsufficientMaterial(context)
+        DefaultRules.isInsufficientMaterial(context)
       def isFiftyMoveRule(context: GameContext): Boolean =
-        StandardRules.isFiftyMoveRule(context)
+        DefaultRules.isFiftyMoveRule(context)
       def applyMove(context: GameContext, move: Move): GameContext =
-        StandardRules.applyMove(context, move)
+        DefaultRules.applyMove(context, move)
 
     val promotionBoard = FenParser.parseBoard("8/4P3/4k3/8/8/8/8/8").get
     val initialCtx = GameContext.initial.withBoard(promotionBoard).withTurn(Color.White)

modules/io/build.gradle.kts

@@ -39,6 +39,7 @@ dependencies {
     }
 
     implementation(project(":modules:api"))
+    implementation(project(":modules:rule"))
 
     testImplementation(platform("org.junit:junit-bom:5.13.4"))
     testImplementation("org.junit.jupiter:junit-jupiter")

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

@@ -4,6 +4,6 @@ import de.nowchess.api.game.GameContext
 
 trait GameContextImport {
 
-  def importGameContext(input: String): GameContext
+  def importGameContext(input: String): Option[GameContext]
 
 }

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

@@ -1,9 +1,10 @@
-package de.nowchess.chess.notation
+package de.nowchess.io.fen
 
 import de.nowchess.api.board.*
 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 =
@@ -23,7 +24,7 @@ object FenExporter:
           if emptyCount > 0 then
             rankChars += emptyCount.toString.charAt(0)
             emptyCount = 0
-          rankChars += pieceToPgnChar(piece)
+          rankChars += pieceToFenChar(piece)
         case None =>
           emptyCount += 1
 
@@ -39,6 +40,8 @@ object FenExporter:
     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(rights: CastlingRights): String =
     val wk = if rights.whiteKingSide then "K" else ""
@@ -49,7 +52,7 @@ object FenExporter:
     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

@@ -1,9 +1,10 @@
-package de.nowchess.chess.notation
+package de.nowchess.io.fen
 
 import de.nowchess.api.board.*
 import de.nowchess.api.game.GameContext
+import de.nowchess.io.GameContextImport
 
-object FenParser:
+object FenParser extends GameContextImport:
 
   /** Parse a complete FEN string into a GameContext.
    *  Returns None if the format is invalid. */
@@ -27,6 +28,8 @@ object FenParser:
         moves = List.empty
       )
 
+  def importGameContext(input: String): Option[GameContext] = parseFen(input)
+
   /** Parse active color ("w" or "b"). */
   private def parseColor(s: String): Option[Color] =
     if s == "w" then Some(Color.White)
@@ -102,3 +105,4 @@ 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

@@ -1,6 +1,6 @@
-package de.nowchess.chess.notation
+package de.nowchess.io.pgn
 
-import de.nowchess.api.board.{PieceType, *}
+import de.nowchess.api.board.*
 import de.nowchess.api.move.PromotionPiece
 import de.nowchess.api.game.{GameHistory, HistoryMove}
 
@@ -52,3 +52,5 @@ object PgnExporter:
           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/io/src/main/scala/de/nowchess/io/pgn/PgnParser.scala

@@ -1,9 +1,9 @@
-package de.nowchess.chess.notation
+package de.nowchess.io.pgn
 
 import de.nowchess.api.board.*
 import de.nowchess.api.move.{Move, MoveType, PromotionPiece}
 import de.nowchess.api.game.{GameContext, HistoryMove}
-import de.nowchess.rules.sets.StandardRules
+import de.nowchess.rules.sets.DefaultRules
 
 /** A parsed PGN game containing headers and the resolved move list. */
 case class PgnGame(
@@ -35,7 +35,7 @@ object PgnParser:
 
   /** Parse PGN header lines of the form [Key "Value"]. */
   private def parseHeaders(lines: Array[String]): Map[String, String] =
-    val pattern = """^\[(\w+)\s+"([^"]*)"\s*\]$""".r
+    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. */
@@ -51,7 +51,7 @@ object PgnParser:
             case None       => state
             case Some(move) =>
               val histMove   = toHistoryMove(move, ctx, color)
-              val nextCtx    = StandardRules.applyMove(ctx, move)
+              val nextCtx    = DefaultRules.applyMove(ctx, move)
               (nextCtx, color.opposite, acc :+ histMove)
     moves
 
@@ -82,12 +82,12 @@ object PgnParser:
       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(StandardRules.legalMoves(ctx, Square(File.E, rank)).contains(move))(move)
+        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(StandardRules.legalMoves(ctx, Square(File.E, rank)).contains(move))(move)
+        Option.when(DefaultRules.legalMoves(ctx, Square(File.E, rank)).contains(move))(move)
 
       case _ =>
         parseRegularMove(notation, ctx, color)
@@ -118,7 +118,7 @@ object PgnParser:
         val promotion = extractPromotion(notation)
 
         // Get all legal moves for this color that reach toSquare
-        val allLegal = StandardRules.allLegalMoves(ctx)
+        val allLegal = DefaultRules.allLegalMoves(ctx)
         val candidates = allLegal.filter { move =>
           move.to == toSquare &&
           ctx.board.pieceAt(move.from).exists(p =>
@@ -146,7 +146,7 @@ object PgnParser:
       case Some(pp) => move.moveType == MoveType.Promotion(pp)
 
   /** Extract a promotion piece from a notation string containing =Q/=R/=B/=N. */
-  private[notation] def extractPromotion(notation: String): Option[PromotionPiece] =
+  private[pgn] def extractPromotion(notation: String): Option[PromotionPiece] =
     val promotionPattern = """=([A-Z])""".r
     promotionPattern.findFirstMatchIn(notation).flatMap { m =>
       m.group(1) match
@@ -181,7 +181,9 @@ object PgnParser:
               case None       => Left(s"Illegal or impossible move: '$token'")
               case Some(move) =>
                 val histMove = toHistoryMove(move, ctx, color)
-                val nextCtx  = StandardRules.applyMove(ctx, move)
+                val nextCtx  = DefaultRules.applyMove(ctx, move)
                 Right((nextCtx, color.opposite, moves :+ histMove))
         }
     }.map(_._3)
+
+

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

@@ -1,4 +1,4 @@
-package de.nowchess.chess.notation
+package de.nowchess.io.fen
 
 import de.nowchess.api.board.*
 import de.nowchess.api.game.GameContext
@@ -99,3 +99,4 @@ class FenExporterTest extends AnyFunSuite with Matchers:
     FenParser.parseFen(fen) match
       case Some(ctx) => ctx.halfMoveClock shouldBe 42
       case None     => fail("FEN parsing failed")
+

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

@@ -1,4 +1,4 @@
-package de.nowchess.chess.notation
+package de.nowchess.io.fen
 
 import de.nowchess.api.board.*
 import org.scalatest.funsuite.AnyFunSuite
@@ -130,3 +130,4 @@ class FenParserTest extends AnyFunSuite with Matchers:
     val board = FenParser.parseBoard(fen)
 
     board shouldBe empty
+

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

@@ -1,4 +1,4 @@
-package de.nowchess.chess.notation
+package de.nowchess.io.pgn
 
 import de.nowchess.api.board.{PieceType, *}
 import de.nowchess.api.move.PromotionPiece
@@ -112,3 +112,4 @@ class PgnExporterTest extends AnyFunSuite with Matchers:
       .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/io/src/test/scala/de/nowchess/io/pgn/PgnParserTest.scala

@@ -1,9 +1,9 @@
-package de.nowchess.chess.notation
+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.chess.notation.FenParser
+import de.nowchess.io.fen.FenParser
 import org.scalatest.funsuite.AnyFunSuite
 import org.scalatest.matchers.should.Matchers
 
@@ -437,3 +437,4 @@ class PgnParserTest extends AnyFunSuite with Matchers:
     val result = PgnParser.extractPromotion("e7e8")
     result shouldBe None
   }
+

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

@@ -1,4 +1,4 @@
-package de.nowchess.chess.notation
+package de.nowchess.io.pgn
 
 import de.nowchess.api.board.*
 import de.nowchess.api.move.PromotionPiece
@@ -117,3 +117,4 @@ class PgnValidatorTest extends AnyFunSuite with Matchers:
     // 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/rule/src/main/scala/de/nowchess/rules/sets/DefaultRules.scala

@@ -10,7 +10,7 @@ import scala.annotation.tailrec
 /** Standard chess rules implementation.
  *  Handles move generation, validation, check/checkmate/stalemate detection.
  */
-object StandardRules extends RuleSet:
+object DefaultRules extends RuleSet:
 
   // ── Direction vectors ──────────────────────────────────────────────
   private val RookDirs: List[(Int, Int)] = List((1, 0), (-1, 0), (0, 1), (0, -1))