refactor(50-move-rule): extract handleParsedMove to reduce cognitive complexity in processUserInput

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

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

@@ -90,19 +90,17 @@ class GameEngine(
         notifyObservers(event)
 
       case moveInput =>
-        // Try to parse as a move
         Parser.parseMove(moveInput) match
           case None =>
-            val event = InvalidMoveEvent(
+            notifyObservers(InvalidMoveEvent(
-              currentBoard,
+              currentBoard, currentHistory, currentTurn,
-              currentHistory,
-              currentTurn,
               s"Invalid move format '$moveInput'. Use coordinate notation, e.g. e2e4."
-            )
+            ))
-            notifyObservers(event)
-
           case Some((from, to)) =>
-            // Create a move command with current state snapshot
+            handleParsedMove(from, to, moveInput)
+  }
+
+  private def handleParsedMove(from: Square, to: Square, moveInput: String): Unit =
     val cmd = MoveCommand(
       from = from,
       to = to,
@@ -110,14 +108,11 @@ class GameEngine(
       previousHistory = Some(currentHistory),
       previousTurn = Some(currentTurn)
     )
-
-            // Execute the move through GameController
     GameController.processMove(currentBoard, currentHistory, currentTurn, moveInput) match
       case MoveResult.InvalidFormat(_) | MoveResult.NoPiece | MoveResult.WrongColor | MoveResult.IllegalMove | MoveResult.Quit =>
         handleFailedMove(moveInput)
 
       case MoveResult.Moved(newBoard, newHistory, captured, newTurn) =>
-                // Move succeeded - store result and execute through invoker
         val updatedCmd = cmd.copy(moveResult = Some(de.nowchess.chess.command.MoveResult.Successful(newBoard, newHistory, newTurn, captured)))
         invoker.execute(updatedCmd)
         updateGameState(newBoard, newHistory, newTurn)
@@ -126,7 +121,6 @@ class GameEngine(
           notifyObservers(FiftyMoveRuleAvailableEvent(currentBoard, currentHistory, currentTurn))
 
       case MoveResult.MovedInCheck(newBoard, newHistory, captured, newTurn) =>
-                // Move succeeded with check
         val updatedCmd = cmd.copy(moveResult = Some(de.nowchess.chess.command.MoveResult.Successful(newBoard, newHistory, newTurn, captured)))
         invoker.execute(updatedCmd)
         updateGameState(newBoard, newHistory, newTurn)
@@ -136,7 +130,6 @@ class GameEngine(
           notifyObservers(FiftyMoveRuleAvailableEvent(currentBoard, currentHistory, currentTurn))
 
       case MoveResult.Checkmate(winner) =>
-                // Move resulted in checkmate
         val updatedCmd = cmd.copy(moveResult = Some(de.nowchess.chess.command.MoveResult.Successful(Board.initial, GameHistory.empty, Color.White, None)))
         invoker.execute(updatedCmd)
         currentBoard = Board.initial
@@ -145,7 +138,6 @@ class GameEngine(
         notifyObservers(CheckmateEvent(currentBoard, currentHistory, currentTurn, winner))
 
       case MoveResult.Stalemate =>
-                // Move resulted in stalemate
         val updatedCmd = cmd.copy(moveResult = Some(de.nowchess.chess.command.MoveResult.Successful(Board.initial, GameHistory.empty, Color.White, None)))
         invoker.execute(updatedCmd)
         currentBoard = Board.initial
@@ -156,7 +148,6 @@ class GameEngine(
       case MoveResult.PromotionRequired(promFrom, promTo, boardBefore, histBefore, _, promotingTurn) =>
         pendingPromotion = Some(PendingPromotion(promFrom, promTo, boardBefore, histBefore, promotingTurn))
         notifyObservers(PromotionRequiredEvent(currentBoard, currentHistory, currentTurn, promFrom, promTo))
-  }
 
   /** Undo the last move. */
   def undo(): Unit = synchronized {