refactor: simplify undo and redo logic in GameEngine and removed Hacky Test

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

@@ -144,37 +144,31 @@ class GameEngine extends Observable:
 
   private def performUndo(): Unit =
     if invoker.canUndo then
-      val history = invoker.history
-      val currentIdx = invoker.getCurrentIndex
-      if currentIdx >= 0 && currentIdx < history.size then
-        val cmd = history(currentIdx)
-        (cmd: @unchecked) match
-          case moveCmd: MoveCommand =>
-            if moveCmd.undo() then
-              moveCmd.previousBoard.foreach(currentBoard = _)
-              moveCmd.previousHistory.foreach(currentHistory = _)
-              moveCmd.previousTurn.foreach(currentTurn = _)
-              invoker.undo()
-              notifyObservers(BoardResetEvent(currentBoard, currentHistory, currentTurn))
+      val cmd = invoker.history(invoker.getCurrentIndex)
+      (cmd: @unchecked) match
+        case moveCmd: MoveCommand =>
+          if moveCmd.undo() then
+            moveCmd.previousBoard.foreach(currentBoard = _)
+            moveCmd.previousHistory.foreach(currentHistory = _)
+            moveCmd.previousTurn.foreach(currentTurn = _)
+            invoker.undo()
+            notifyObservers(BoardResetEvent(currentBoard, currentHistory, currentTurn))
     else
       notifyObservers(InvalidMoveEvent(currentBoard, currentHistory, currentTurn, "Nothing to undo."))
 
   private def performRedo(): Unit =
     if invoker.canRedo then
-      val history = invoker.history
-      val nextIdx = invoker.getCurrentIndex + 1
-      if nextIdx >= 0 && nextIdx < history.size then
-        val cmd = history(nextIdx)
-        (cmd: @unchecked) match
-          case moveCmd: MoveCommand =>
-            if moveCmd.execute() then
-              moveCmd.moveResult.foreach {
-                case de.nowchess.chess.command.MoveResult.Successful(newBoard, newHistory, newTurn, captured) =>
-                  updateGameState(newBoard, newHistory, newTurn)
-                  invoker.redo()
-                  emitMoveEvent(moveCmd.from.toString, moveCmd.to.toString, captured, newTurn)
-                case _ => ()
-              }
+      val cmd = invoker.history(invoker.getCurrentIndex + 1)
+      (cmd: @unchecked) match
+        case moveCmd: MoveCommand =>
+          if moveCmd.execute() then
+            moveCmd.moveResult.foreach {
+              case de.nowchess.chess.command.MoveResult.Successful(newBoard, newHistory, newTurn, captured) =>
+                updateGameState(newBoard, newHistory, newTurn)
+                invoker.redo()
+                emitMoveEvent(moveCmd.from.toString, moveCmd.to.toString, captured, newTurn)
+              case _ => ()
+            }
     else
       notifyObservers(InvalidMoveEvent(currentBoard, currentHistory, currentTurn, "Nothing to redo."))
 

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

@@ -1,54 +0,0 @@
-package de.nowchess.chess.engine
-
-import de.nowchess.api.board.{Board, Color}
-import de.nowchess.chess.logic.GameHistory
-import de.nowchess.chess.command.{CommandInvoker, Command}
-import org.scalatest.funsuite.AnyFunSuite
-import org.scalatest.matchers.should.Matchers
-import java.lang.reflect.Field
-
-class GameEngineCoverageHackTest extends AnyFunSuite with Matchers {
-
-  test("Hack: trigger impossible conditions in performUndo and performRedo using reflection") {
-    val engine = new GameEngine()
-    
-    // We need to inject a mock CommandInvoker
-    class MockInvoker extends CommandInvoker {
-      var forceCanUndo = false
-      var forceCanRedo = false
-      var returnedIndex = -1
-      
-      override def canUndo: Boolean = forceCanUndo
-      override def canRedo: Boolean = forceCanRedo
-      override def getCurrentIndex: Int = returnedIndex
-      override def history: List[Command] = List.empty
-    }
-    
-    val mockInvoker = new MockInvoker()
-    
-    // Use reflection to set the private invoker field
-    val field: Field = classOf[GameEngine].getDeclaredField("invoker")
-    field.setAccessible(true)
-    field.set(engine, mockInvoker)
-    
-    // Trigger performUndo where canUndo is true but currentIdx < 0
-    mockInvoker.forceCanUndo = true
-    mockInvoker.returnedIndex = -1 // fails currentIdx >= 0
-    engine.undo() // Hits the unreachable false branch!
-    
-    // Trigger performUndo where currentIdx >= history.size
-    mockInvoker.forceCanUndo = true
-    mockInvoker.returnedIndex = 5 // fails currentIdx < history.size
-    engine.undo() // Hits the unreachable false branch!
-    
-    // Trigger performRedo where nextIdx < 0
-    mockInvoker.forceCanRedo = true
-    mockInvoker.returnedIndex = -5 // nextIdx = -4, fails nextIdx >= 0
-    engine.redo() // Hits unreachable branch!
-    
-    // Trigger performRedo where nextIdx >= history.size
-    mockInvoker.forceCanRedo = true
-    mockInvoker.returnedIndex = 5 // nextIdx = 6, fails nextIdx < history.size
-    engine.redo() // Hits unreachable branch!
-  }
-}