feat: NCS-40 Rework Draw System (#34)

Reviewed-on: #34 Reviewed-by: Shahd Lala <shosho996@blackhole.local> Co-authored-by: Janis <janis.e.20@gmx.de> Co-committed-by: Janis <janis.e.20@gmx.de>
2026-04-19 22:44:48 +02:00
parent d16cec176b
commit 33e785d22a
8 changed files with 446 additions and 21 deletions
@@ -31,7 +31,9 @@ class GameEngine(
    else initialContext
  @SuppressWarnings(Array("DisableSyntax.var"))
  private var currentContext: GameContext = contextWithInitialBoard
-  private val invoker                     = new CommandInvoker()
+  @SuppressWarnings(Array("DisableSyntax.var"))
+  private var pendingDrawOffer: Option[Color] = None
+  private val invoker                         = new CommandInvoker()

  private implicit val ec: ExecutionContext = ExecutionContext.global

@@ -77,12 +79,12 @@ class GameEngine(
          notifyObservers(
            InvalidMoveEvent(
              currentContext,
-              "Draw cannot be claimed: neither the 50-move rule nor threefold repetition has been triggered.",
+              InvalidMoveReason.DrawCannotBeClaimed,
            ),
          )

      case "" =>
-        notifyObservers(InvalidMoveEvent(currentContext, "Please enter a valid move or command."))
+        notifyObservers(InvalidMoveEvent(currentContext, InvalidMoveReason.EmptyInput))

      case moveInput =>
        Parser.parseMove(moveInput) match
@@ -90,7 +92,7 @@ class GameEngine(
            notifyObservers(
              InvalidMoveEvent(
                currentContext,
-                s"Invalid move format '$moveInput'. Use coordinate notation, e.g. e2e4.",
+                InvalidMoveReason.InvalidMoveFormat,
              ),
            )
          case Some((from, to, promotionPiece: Option[PromotionPiece])) =>
@@ -100,26 +102,26 @@ class GameEngine(
  private def handleParsedMove(from: Square, to: Square, promotionPiece: Option[PromotionPiece]): Unit =
    currentContext.board.pieceAt(from) match
      case None =>
-        notifyObservers(InvalidMoveEvent(currentContext, "No piece on that square."))
+        notifyObservers(InvalidMoveEvent(currentContext, InvalidMoveReason.NoSourcePiece))
      case Some(piece) if piece.color != currentContext.turn =>
-        notifyObservers(InvalidMoveEvent(currentContext, "That is not your piece."))
+        notifyObservers(InvalidMoveEvent(currentContext, InvalidMoveReason.NotYourPiece))
      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."))
+            notifyObservers(InvalidMoveEvent(currentContext, InvalidMoveReason.IllegalMove))
          case _ if isPromotionMove(piece, to) =>
            if promotionPiece.isEmpty then
              notifyObservers(
-                InvalidMoveEvent(currentContext, "Promotion piece required: append q, r, b, or n to the move."),
+                InvalidMoveEvent(currentContext, InvalidMoveReason.PromotionPieceRequired),
              )
            else
              candidates.find(_.moveType == MoveType.Promotion(promotionPiece.get)) match
                case None =>
                  notifyObservers(
-                    InvalidMoveEvent(currentContext, "Error completing promotion: no matching legal move."),
+                    InvalidMoveEvent(currentContext, InvalidMoveReason.PromotionPieceInvalid),
                  )
                case Some(move) => executeMove(move)
          case move :: _ =>
@@ -137,6 +139,62 @@ class GameEngine(
  /** Redo the last undone move. */
  def redo(): Unit = synchronized(performRedo())

+  /** Resign from the game. The opponent wins. */
+  def resign(color: Color): Unit = synchronized {
+    if currentContext.result.isDefined then
+      notifyObservers(InvalidMoveEvent(currentContext, InvalidMoveReason.GameAlreadyOver))
+    else
+      currentContext = currentContext.withResult(Some(GameResult.Win(color.opposite)))
+      pendingDrawOffer = None
+      invoker.clear()
+      notifyObservers(ResignEvent(currentContext, color))
+  }
+
+  /** Offer a draw. */
+  def offerDraw(color: Color): Unit = synchronized {
+    if currentContext.result.isDefined then
+      notifyObservers(InvalidMoveEvent(currentContext, InvalidMoveReason.GameAlreadyOver))
+    else
+      pendingDrawOffer match
+        case Some(_) =>
+          notifyObservers(InvalidMoveEvent(currentContext, InvalidMoveReason.DrawOfferPending))
+        case None =>
+          pendingDrawOffer = Some(color)
+          notifyObservers(DrawOfferEvent(currentContext, color))
+  }
+
+  /** Accept a pending draw offer. */
+  def acceptDraw(color: Color): Unit = synchronized {
+    if currentContext.result.isDefined then
+      notifyObservers(InvalidMoveEvent(currentContext, InvalidMoveReason.GameAlreadyOver))
+    else
+      pendingDrawOffer match
+        case None =>
+          notifyObservers(InvalidMoveEvent(currentContext, InvalidMoveReason.NoDrawOfferToAccept))
+        case Some(offerer) if offerer == color =>
+          notifyObservers(InvalidMoveEvent(currentContext, InvalidMoveReason.CannotAcceptOwnDrawOffer))
+        case Some(_) =>
+          currentContext = currentContext.withResult(Some(GameResult.Draw(DrawReason.Agreement)))
+          pendingDrawOffer = None
+          invoker.clear()
+          notifyObservers(DrawEvent(currentContext, DrawReason.Agreement))
+  }
+
+  /** Decline a pending draw offer. */
+  def declineDraw(color: Color): Unit = synchronized {
+    if currentContext.result.isDefined then
+      notifyObservers(InvalidMoveEvent(currentContext, InvalidMoveReason.GameAlreadyOver))
+    else
+      pendingDrawOffer match
+        case None =>
+          notifyObservers(InvalidMoveEvent(currentContext, InvalidMoveReason.NoDrawOfferToDecline))
+        case Some(offerer) if offerer == color =>
+          notifyObservers(InvalidMoveEvent(currentContext, InvalidMoveReason.CannotDeclineOwnDrawOffer))
+        case Some(_) =>
+          pendingDrawOffer = None
+          notifyObservers(DrawOfferDeclinedEvent(currentContext, color))
+  }
+
  /** 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.
    */
@@ -145,6 +203,7 @@ class GameEngine(
      case Left(err) => Left(err)
      case Right(ctx) =>
        replayGame(ctx).map { _ =>
+          pendingDrawOffer = None
          notifyObservers(PgnLoadedEvent(currentContext))
        }
  }
@@ -186,6 +245,7 @@ class GameEngine(
      if newContext.moves.isEmpty then newContext.copy(initialBoard = newContext.board)
      else newContext
    currentContext = contextWithInitialBoard
+    pendingDrawOffer = None
    invoker.clear()
    notifyObservers(BoardResetEvent(currentContext))
  }
@@ -193,6 +253,7 @@ class GameEngine(
  /** Reset the board to initial position. */
  def reset(): Unit = synchronized {
    currentContext = GameContext.initial
+    pendingDrawOffer = None
    invoker.clear()
    notifyObservers(BoardResetEvent(currentContext))
  }
@@ -323,9 +384,9 @@ class GameEngine(
          legal.find(m => m.to == to && m.moveType == move.moveType) match
            case Some(legalMove) => executeMove(legalMove)
            case None =>
-              notifyObservers(InvalidMoveEvent(currentContext, s"Bot move ${from}${to} is illegal"))
+              notifyObservers(InvalidMoveEvent(currentContext, InvalidMoveReason.BotMoveIllegal))
        case _ =>
-          notifyObservers(InvalidMoveEvent(currentContext, "Bot move has invalid source square"))
+          notifyObservers(InvalidMoveEvent(currentContext, InvalidMoveReason.BotMoveInvalidSource))
    }

  private def handleBotNoMove(): Unit =
@@ -344,7 +405,7 @@ class GameEngine(
          moveCmd.previousContext.foreach(currentContext = _)
          invoker.undo()
          notifyObservers(MoveUndoneEvent(currentContext, moveCmd.notation))
-    else notifyObservers(InvalidMoveEvent(currentContext, "Nothing to undo."))
+    else notifyObservers(InvalidMoveEvent(currentContext, InvalidMoveReason.NothingToUndo))

  private def performRedo(): Unit =
    if invoker.canRedo then
@@ -364,4 +425,4 @@ class GameEngine(
                capturedDesc,
              ),
            )
-    else notifyObservers(InvalidMoveEvent(currentContext, "Nothing to redo."))
+    else notifyObservers(InvalidMoveEvent(currentContext, InvalidMoveReason.NothingToRedo))
@@ -0,0 +1,21 @@
+package de.nowchess.chess.observer
+
+enum InvalidMoveReason:
+  case GameAlreadyOver
+  case NoSourcePiece
+  case NotYourPiece
+  case IllegalMove
+  case PromotionPieceRequired
+  case PromotionPieceInvalid
+  case InvalidMoveFormat
+  case EmptyInput
+  case DrawCannotBeClaimed
+  case NothingToUndo
+  case NothingToRedo
+  case BotMoveIllegal
+  case BotMoveInvalidSource
+  case DrawOfferPending
+  case NoDrawOfferToAccept
+  case CannotAcceptOwnDrawOffer
+  case NoDrawOfferToDecline
+  case CannotDeclineOwnDrawOffer
@@ -36,7 +36,7 @@ case class DrawEvent(
 /** Fired when a move is invalid. */
 case class InvalidMoveEvent(
    context: GameContext,
-    reason: String,
+    reason: InvalidMoveReason,
 ) extends GameEvent

 /** Fired when the board is reset. */
@@ -74,6 +74,24 @@ case class PgnLoadedEvent(
    context: GameContext,
 ) extends GameEvent

+/** Fired when a player resigns. The opponent wins. */
+case class ResignEvent(
+    context: GameContext,
+    resignedColor: Color,
+) extends GameEvent
+
+/** Fired when a player offers a draw. Waiting for opponent to accept or decline. */
+case class DrawOfferEvent(
+    context: GameContext,
+    offeredBy: Color,
+) extends GameEvent
+
+/** Fired when the opponent declines a draw offer. */
+case class DrawOfferDeclinedEvent(
+    context: GameContext,
+    declinedBy: Color,
+) extends GameEvent
+
 /** Observer trait: implement to receive game state updates. */
 trait Observer:
  def onGameEvent(event: GameEvent): Unit