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

@@ -1,13 +1,13 @@
-package de.nowchess.chess.logic
+package de.nowchess.api.game
 
 import de.nowchess.api.board.{PieceType, Square}
-import de.nowchess.api.move.PromotionPiece
+import de.nowchess.api.move.{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],
+  castleSide: Option[String] = None,
   promotionPiece: Option[PromotionPiece] = None,
   pieceType: PieceType = PieceType.Pawn,
   isCapture: Boolean = false
@@ -17,6 +17,8 @@ case class HistoryMove(
  *
  *  @param moves         moves played so far, oldest first
  *  @param halfMoveClock plies since the last pawn move or capture (FIDE 50-move rule counter)
+ *
+ *  Deprecated: Use GameContext instead. This exists for compatibility during migration.
  */
 case class GameHistory(moves: List[HistoryMove] = List.empty, halfMoveClock: Int = 0):
 
@@ -36,7 +38,7 @@ case class GameHistory(moves: List[HistoryMove] = List.empty, halfMoveClock: Int
   def addMove(
     from: Square,
     to: Square,
-    castleSide: Option[CastleSide] = None,
+    castleSide: Option[String] = None,
     promotionPiece: Option[PromotionPiece] = None,
     wasPawnMove: Boolean = false,
     wasCapture: Boolean = false,

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.game.GameHistory
 
 /** Marker trait for all commands that can be executed and undone.
  *  Commands encapsulate user actions and game state transitions.

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

@@ -2,6 +2,7 @@ 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.api.game.GameHistory
 import de.nowchess.chess.logic.*
 
 // ---------------------------------------------------------------------------
@@ -83,6 +84,7 @@ object GameController:
 
   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 castleOptStr           = castleOpt.map(_.toString) // Convert CastleSide to String
     val isEP                   = EnPassantCalculator.isEnPassant(board, history, from, to)
     val (newBoard, captured)   = castleOpt match
       case Some(side) => (board.withCastle(turn, side), None)
@@ -95,7 +97,7 @@ object GameController:
     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)
+    val newHistory  = history.addMove(from, to, castleOptStr, wasPawnMove = wasPawnMove, wasCapture = wasCapture, pieceType = pieceType)
     toMoveResult(newBoard, newHistory, captured, turn)
 
   private def toMoveResult(newBoard: Board, newHistory: GameHistory, captured: Option[Piece], turn: Color): MoveResult =

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

@@ -1,8 +1,8 @@
 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.api.board.{Board, Color, Piece, Square, CastlingRights}
+import de.nowchess.api.move.{PromotionPiece, Move}
+import de.nowchess.api.game.{GameHistory, GameContext}
 import de.nowchess.chess.controller.{GameController, Parser, MoveResult}
 import de.nowchess.chess.observer.*
 import de.nowchess.chess.command.{CommandInvoker, MoveCommand}
@@ -43,6 +43,16 @@ class GameEngine(
   def history: GameHistory = synchronized { currentHistory }
   def turn: Color = synchronized { currentTurn }
 
+  /** Create a GameContext from current state (for event creation). */
+  private def currentContext: GameContext = GameContext(
+    board = currentBoard,
+    turn = currentTurn,
+    castlingRights = CastlingRights.Initial, // TODO: derive from history
+    enPassantSquare = None,                  // TODO: derive from history
+    halfMoveClock = currentHistory.halfMoveClock,
+    moves = List.empty                        // TODO: convert history moves to api.move.Move
+  )
+
   /** Check if undo is available. */
   def canUndo: Boolean = synchronized { invoker.canUndo }
 
@@ -74,18 +84,16 @@ class GameEngine(
           currentHistory = GameHistory.empty
           currentTurn    = Color.White
           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,
+          currentContext,
           "Please enter a valid move or command."
         )
         notifyObservers(event)
@@ -94,7 +102,7 @@ class GameEngine(
         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)) =>
@@ -119,16 +127,16 @@ class GameEngine(
         updateGameState(newBoard, newHistory, newTurn)
         emitMoveEvent(from.toString, to.toString, captured, newTurn)
         if currentHistory.halfMoveClock >= 100 then
-          notifyObservers(FiftyMoveRuleAvailableEvent(currentBoard, currentHistory, currentTurn))
+          notifyObservers(FiftyMoveRuleAvailableEvent(currentContext))
 
       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))
+        notifyObservers(CheckDetectedEvent(currentContext))
         if currentHistory.halfMoveClock >= 100 then
-          notifyObservers(FiftyMoveRuleAvailableEvent(currentBoard, currentHistory, currentTurn))
+          notifyObservers(FiftyMoveRuleAvailableEvent(currentContext))
 
       case MoveResult.Checkmate(winner) =>
         val updatedCmd = cmd.copy(moveResult = Some(de.nowchess.chess.command.MoveResult.Successful(Board.initial, GameHistory.empty, Color.White, None)))
@@ -136,7 +144,7 @@ class GameEngine(
         currentBoard = Board.initial
         currentHistory = GameHistory.empty
         currentTurn = Color.White
-        notifyObservers(CheckmateEvent(currentBoard, currentHistory, currentTurn, winner))
+        notifyObservers(CheckmateEvent(currentContext, winner))
 
       case MoveResult.Stalemate =>
         val updatedCmd = cmd.copy(moveResult = Some(de.nowchess.chess.command.MoveResult.Successful(Board.initial, GameHistory.empty, Color.White, None)))
@@ -144,11 +152,11 @@ class GameEngine(
         currentBoard = Board.initial
         currentHistory = GameHistory.empty
         currentTurn = Color.White
-        notifyObservers(StalemateEvent(currentBoard, currentHistory, currentTurn))
+        notifyObservers(StalemateEvent(currentContext))
 
       case MoveResult.PromotionRequired(promFrom, promTo, boardBefore, histBefore, _, promotingTurn) =>
         pendingPromotion = Some(PendingPromotion(promFrom, promTo, boardBefore, histBefore, promotingTurn))
-        notifyObservers(PromotionRequiredEvent(currentBoard, currentHistory, currentTurn, promFrom, promTo))
+        notifyObservers(PromotionRequiredEvent(currentContext, promFrom, promTo))
 
   /** Undo the last move. */
   def undo(): Unit = synchronized {
@@ -166,7 +174,7 @@ 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(
@@ -191,7 +199,7 @@ class GameEngine(
             invoker.execute(updatedCmd)
             updateGameState(newBoard, newHistory, newTurn)
             emitMoveEvent(pending.from.toString, pending.to.toString, captured, newTurn)
-            notifyObservers(CheckDetectedEvent(currentBoard, currentHistory, currentTurn))
+            notifyObservers(CheckDetectedEvent(currentContext))
 
           case MoveResult.Checkmate(winner) =>
             val updatedCmd = cmd.copy(moveResult = Some(de.nowchess.chess.command.MoveResult.Successful(Board.initial, GameHistory.empty, Color.White, None)))
@@ -199,7 +207,7 @@ class GameEngine(
             currentBoard = Board.initial
             currentHistory = GameHistory.empty
             currentTurn = Color.White
-            notifyObservers(CheckmateEvent(currentBoard, currentHistory, currentTurn, winner))
+            notifyObservers(CheckmateEvent(currentContext, winner))
 
           case MoveResult.Stalemate =>
             val updatedCmd = cmd.copy(moveResult = Some(de.nowchess.chess.command.MoveResult.Successful(Board.initial, GameHistory.empty, Color.White, None)))
@@ -207,10 +215,10 @@ class GameEngine(
             currentBoard = Board.initial
             currentHistory = GameHistory.empty
             currentTurn = Color.White
-            notifyObservers(StalemateEvent(currentBoard, currentHistory, currentTurn))
+            notifyObservers(StalemateEvent(currentContext))
 
           case _ =>
-            notifyObservers(InvalidMoveEvent(currentBoard, currentHistory, currentTurn, "Error completing promotion."))
+            notifyObservers(InvalidMoveEvent(currentContext, "Error completing promotion."))
   }
 
   /** Validate and load a PGN string.
@@ -253,7 +261,7 @@ class GameEngine(
             currentTurn = initialTurnBeforeLoad
             Left(err)
           case None =>
-            notifyObservers(PgnLoadedEvent(currentBoard, currentHistory, currentTurn))
+            notifyObservers(PgnLoadedEvent(currentContext))
             Right(())
   }
 
@@ -264,7 +272,7 @@ class GameEngine(
     currentTurn = turn
     pendingPromotion = None
     invoker.clear()
-    notifyObservers(BoardResetEvent(currentBoard, currentHistory, currentTurn))
+    notifyObservers(BoardResetEvent(currentContext))
   }
 
   /** Reset the board to initial position. */
@@ -274,9 +282,7 @@ class GameEngine(
     currentTurn = Color.White
     invoker.clear()
     notifyObservers(BoardResetEvent(
-      currentBoard,
-      currentHistory,
-      currentTurn
+      currentContext
     ))
   }
 
@@ -292,9 +298,9 @@ class GameEngine(
           moveCmd.previousHistory.foreach(currentHistory = _)
           moveCmd.previousTurn.foreach(currentTurn = _)
           invoker.undo()
-          notifyObservers(MoveUndoneEvent(currentBoard, currentHistory, currentTurn, notation))
+          notifyObservers(MoveUndoneEvent(currentContext, notation))
     else
-      notifyObservers(InvalidMoveEvent(currentBoard, currentHistory, currentTurn, "Nothing to undo."))
+      notifyObservers(InvalidMoveEvent(currentContext, "Nothing to undo."))
 
   private def performRedo(): Unit =
     if invoker.canRedo then
@@ -306,9 +312,9 @@ class GameEngine(
             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, notation, moveCmd.from.toString, moveCmd.to.toString, capturedDesc))
     else
-      notifyObservers(InvalidMoveEvent(currentBoard, currentHistory, currentTurn, "Nothing to redo."))
+      notifyObservers(InvalidMoveEvent(currentContext, "Nothing to redo."))
 
   private def updateGameState(newBoard: Board, newHistory: GameHistory, newTurn: Color): Unit =
     currentBoard = newBoard
@@ -318,9 +324,7 @@ class GameEngine(
   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,
+      currentContext,
       fromSq,
       toSq,
       capturedDesc
@@ -330,23 +334,17 @@ class GameEngine(
     (GameController.processMove(currentBoard, currentHistory, currentTurn, moveInput): @unchecked) match
       case MoveResult.NoPiece =>
         notifyObservers(InvalidMoveEvent(
-          currentBoard,
-          currentHistory,
-          currentTurn,
+          currentContext,
           "No piece on that square."
         ))
       case MoveResult.WrongColor =>
         notifyObservers(InvalidMoveEvent(
-          currentBoard,
-          currentHistory,
-          currentTurn,
+          currentContext,
           "That is not your piece."
         ))
       case MoveResult.IllegalMove =>
         notifyObservers(InvalidMoveEvent(
-          currentBoard,
-          currentHistory,
-          currentTurn,
+          currentContext,
           "Illegal move."
         ))
 

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

@@ -1,7 +1,7 @@
 package de.nowchess.chess.logic
 
 import de.nowchess.api.board.{Color, File, Rank, Square}
-import de.nowchess.api.game.CastlingRights
+import de.nowchess.api.game.{CastlingRights, GameHistory}
 
 /** Derives castling rights from move history. */
 object CastlingRightsCalculator:

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

@@ -1,6 +1,7 @@
 package de.nowchess.chess.logic
 
 import de.nowchess.api.board.*
+import de.nowchess.api.game.GameHistory
 
 object EnPassantCalculator:
 

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

@@ -1,7 +1,7 @@
 package de.nowchess.chess.logic
 
 import de.nowchess.api.board.*
-import de.nowchess.chess.logic.GameHistory
+import de.nowchess.api.game.GameHistory
 
 enum PositionStatus:
   case Normal, InCheck, Mated, Drawn

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

@@ -1,7 +1,8 @@
 package de.nowchess.chess.logic
 
 import de.nowchess.api.board.*
-import de.nowchess.chess.logic.{CastleSide, GameHistory}
+import de.nowchess.chess.logic.CastleSide
+import de.nowchess.api.game.GameHistory
 
 object MoveValidator:
 

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

@@ -2,7 +2,8 @@ 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}
+import de.nowchess.api.game.{GameHistory, HistoryMove}
+import de.nowchess.chess.logic.CastleSide
 
 object PgnExporter:
 
@@ -32,9 +33,9 @@ object PgnExporter:
   /** 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 =>
+      case Some("Kingside")  => "O-O"
+      case Some("Queenside") => "O-O-O"
+      case Some(_) | None =>
         val dest       = move.to.toString
         val capStr     = if move.isCapture then "x" else ""
         val promSuffix = move.promotionPiece match

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

@@ -2,7 +2,8 @@ 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}
+import de.nowchess.api.game.{GameHistory, HistoryMove}
+import de.nowchess.chess.logic.{CastleSide, GameRules, MoveValidator, withCastle}
 
 /** A parsed PGN game containing headers and the resolved move list. */
 case class PgnGame(
@@ -63,8 +64,9 @@ object PgnParser:
   /** 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 =>
+      case Some("Kingside") => board.withCastle(color, CastleSide.Kingside)
+      case Some("Queenside") => board.withCastle(color, CastleSide.Queenside)
+      case _ =>
         val (boardAfterMove, _) = board.withMove(move.from, move.to)
         move.promotionPiece match
           case Some(pp) =>
@@ -89,11 +91,11 @@ object PgnParser:
     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))
+        Some(HistoryMove(Square(File.E, rank), Square(File.G, rank), Some("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))
+        Some(HistoryMove(Square(File.E, rank), Square(File.C, rank), Some("Queenside"), pieceType = PieceType.King))
 
       case _ =>
         parseRegularMove(notation, board, history, color)
@@ -212,12 +214,12 @@ object PgnParser:
       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)
+          HistoryMove(Square(File.E, rank), dest, Some("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)
+          HistoryMove(Square(File.E, rank), dest, Some("Queenside"), pieceType = PieceType.King)
         )
       case _ =>
         strictParseRegularMove(notation, board, history, color)

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. */

settings.gradle.kts

@@ -1,2 +1,2 @@
 rootProject.name = "NowChessSystems"
-include("modules:core", "modules:api", "modules:ui")
+include("modules:core", "modules:api", "modules:ui", "modules:rule")