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

@@ -38,9 +38,10 @@ class GameEngine(
   private implicit val ec: ExecutionContext = ExecutionContext.global
 
   // Synchronized accessors for current state
-  def board: Board         = synchronized(currentContext.board)
-  def turn: Color          = synchronized(currentContext.turn)
-  def context: GameContext = synchronized(currentContext)
+  def board: Board              = synchronized(currentContext.board)
+  def turn: Color               = synchronized(currentContext.turn)
+  def context: GameContext      = synchronized(currentContext)
+  def pendingDrawOfferBy: Option[Color] = synchronized(pendingDrawOffer)
 
   /** Check if undo is available. */
   def canUndo: Boolean = synchronized(invoker.canUndo)
@@ -67,21 +68,7 @@ class GameEngine(
         performRedo()
 
       case "draw" =>
-        if currentContext.halfMoveClock >= 100 then
-          currentContext = currentContext.withResult(Some(GameResult.Draw(DrawReason.FiftyMoveRule)))
-          invoker.clear()
-          notifyObservers(DrawEvent(currentContext, DrawReason.FiftyMoveRule))
-        else if ruleSet.isThreefoldRepetition(currentContext) then
-          currentContext = currentContext.withResult(Some(GameResult.Draw(DrawReason.ThreefoldRepetition)))
-          invoker.clear()
-          notifyObservers(DrawEvent(currentContext, DrawReason.ThreefoldRepetition))
-        else
-          notifyObservers(
-            InvalidMoveEvent(
-              currentContext,
-              InvalidMoveReason.DrawCannotBeClaimed,
-            ),
-          )
+        claimDraw()
 
       case "" =>
         notifyObservers(InvalidMoveEvent(currentContext, InvalidMoveReason.EmptyInput))
@@ -195,6 +182,22 @@ class GameEngine(
           notifyObservers(DrawOfferDeclinedEvent(currentContext, color))
   }
 
+  /** Claim a draw by fifty-move rule or threefold repetition. */
+  def claimDraw(): Unit = synchronized {
+    if currentContext.result.isDefined then
+      notifyObservers(InvalidMoveEvent(currentContext, InvalidMoveReason.GameAlreadyOver))
+    else if currentContext.halfMoveClock >= 100 then
+      currentContext = currentContext.withResult(Some(GameResult.Draw(DrawReason.FiftyMoveRule)))
+      invoker.clear()
+      notifyObservers(DrawEvent(currentContext, DrawReason.FiftyMoveRule))
+    else if ruleSet.isThreefoldRepetition(currentContext) then
+      currentContext = currentContext.withResult(Some(GameResult.Draw(DrawReason.ThreefoldRepetition)))
+      invoker.clear()
+      notifyObservers(DrawEvent(currentContext, DrawReason.ThreefoldRepetition))
+    else
+      notifyObservers(InvalidMoveEvent(currentContext, InvalidMoveReason.DrawCannotBeClaimed))
+  }
+
   /** 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.
     */

modules/core/src/main/scala/de/nowchess/chess/registry/GameEntry.scala

@@ -9,6 +9,5 @@ final case class GameEntry(
     engine: GameEngine,
     white: PlayerInfo,
     black: PlayerInfo,
-    drawOfferedBy: Option[Color] = None,
     resigned: Boolean = false,
 )

modules/core/src/main/scala/de/nowchess/chess/resource/GameResource.scala

@@ -31,7 +31,7 @@ class GameResource(@Inject val registry: GameRegistry, @Inject val objectMapper:
   // ── mapping ──────────────────────────────────────────────────────────────
 
   private def statusOf(entry: GameEntry): String =
-    if entry.drawOfferedBy.isDefined then "drawOffered"
+    if entry.engine.pendingDrawOfferBy.isDefined then "drawOffered"
     else
       val ctx = entry.engine.context
       ctx.result match
@@ -104,7 +104,7 @@ class GameResource(@Inject val registry: GameRegistry, @Inject val objectMapper:
     val error = new AtomicReference[Option[String]](None)
     val obs = new Observer:
       def onGameEvent(e: GameEvent): Unit = e match
-        case InvalidMoveEvent(_, reason) => error.set(Some(reason))
+        case InvalidMoveEvent(_, reason) => error.set(Some(reason.toString))
         case _                           => ()
     engine.subscribe(obs)
     engine.processUserInput(uci)
@@ -230,26 +230,16 @@ class GameResource(@Inject val registry: GameRegistry, @Inject val objectMapper:
     if entry.engine.context.result.isDefined then throw BadRequestException("GAME_OVER", "Game is already over")
     action match
       case "offer" =>
-        registry.update(entry.copy(drawOfferedBy = Some(entry.engine.context.turn)))
+        entry.engine.offerDraw(entry.engine.context.turn)
         ok(OkResponseDto())
       case "accept" =>
-        entry.drawOfferedBy match
-          case None =>
-            throw BadRequestException("NO_DRAW_OFFER", "No draw offer to accept")
-          case Some(offerer) if offerer == entry.engine.context.turn =>
-            throw BadRequestException("CANNOT_ACCEPT_OWN_OFFER", "Cannot accept your own draw offer")
-          case _ =>
-            entry.engine.applyDraw(DrawReason.Agreement)
-            registry.update(entry.copy(drawOfferedBy = None))
-            ok(OkResponseDto())
+        entry.engine.acceptDraw(entry.engine.context.turn)
+        ok(OkResponseDto())
       case "decline" =>
-        if entry.drawOfferedBy.isEmpty then throw BadRequestException("NO_DRAW_OFFER", "No draw offer to decline")
-        registry.update(entry.copy(drawOfferedBy = None))
+        entry.engine.declineDraw(entry.engine.context.turn)
         ok(OkResponseDto())
       case "claim" =>
-        if entry.engine.context.halfMoveClock < 100 then
-          throw BadRequestException("CLAIM_NOT_AVAILABLE", "Fifty-move rule draw is not available")
-        entry.engine.applyDraw(DrawReason.FiftyMoveRule)
+        entry.engine.claimDraw()
         ok(OkResponseDto())
       case _ =>
         throw BadRequestException("INVALID_ACTION", s"Unknown draw action: $action", Some("action"))