feat: NCS-40 Rework Draw System

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

@@ -79,12 +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
@@ -92,7 +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])) =>
@@ -102,26 +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 :: _ =>
@@ -141,7 +141,8 @@ class GameEngine(
 
   /** Resign from the game. The opponent wins. */
   def resign(color: Color): Unit = synchronized {
-    if currentContext.result.isDefined then notifyObservers(InvalidMoveEvent(currentContext, "Game is already over."))
+    if currentContext.result.isDefined then
+      notifyObservers(InvalidMoveEvent(currentContext, InvalidMoveReason.GameAlreadyOver))
     else
       currentContext = currentContext.withResult(Some(GameResult.Win(color.opposite)))
       pendingDrawOffer = None
@@ -151,11 +152,12 @@ class GameEngine(
 
   /** Offer a draw. */
   def offerDraw(color: Color): Unit = synchronized {
-    if currentContext.result.isDefined then notifyObservers(InvalidMoveEvent(currentContext, "Game is already over."))
+    if currentContext.result.isDefined then
+      notifyObservers(InvalidMoveEvent(currentContext, InvalidMoveReason.GameAlreadyOver))
     else
       pendingDrawOffer match
         case Some(_) =>
-          notifyObservers(InvalidMoveEvent(currentContext, "A draw offer is already pending."))
+          notifyObservers(InvalidMoveEvent(currentContext, InvalidMoveReason.DrawOfferPending))
         case None =>
           pendingDrawOffer = Some(color)
           notifyObservers(DrawOfferEvent(currentContext, color))
@@ -163,13 +165,14 @@ class GameEngine(
 
   /** Accept a pending draw offer. */
   def acceptDraw(color: Color): Unit = synchronized {
-    if currentContext.result.isDefined then notifyObservers(InvalidMoveEvent(currentContext, "Game is already over."))
+    if currentContext.result.isDefined then
+      notifyObservers(InvalidMoveEvent(currentContext, InvalidMoveReason.GameAlreadyOver))
     else
       pendingDrawOffer match
         case None =>
-          notifyObservers(InvalidMoveEvent(currentContext, "No draw offer to accept."))
+          notifyObservers(InvalidMoveEvent(currentContext, InvalidMoveReason.NoDrawOfferToAccept))
         case Some(offerer) if offerer == color =>
-          notifyObservers(InvalidMoveEvent(currentContext, "Cannot accept your own draw offer."))
+          notifyObservers(InvalidMoveEvent(currentContext, InvalidMoveReason.CannotAcceptOwnDrawOffer))
         case Some(_) =>
           currentContext = currentContext.withResult(Some(GameResult.Draw(DrawReason.Agreement)))
           pendingDrawOffer = None
@@ -179,13 +182,14 @@ class GameEngine(
 
   /** Decline a pending draw offer. */
   def declineDraw(color: Color): Unit = synchronized {
-    if currentContext.result.isDefined then notifyObservers(InvalidMoveEvent(currentContext, "Game is already over."))
+    if currentContext.result.isDefined then
+      notifyObservers(InvalidMoveEvent(currentContext, InvalidMoveReason.GameAlreadyOver))
     else
       pendingDrawOffer match
         case None =>
-          notifyObservers(InvalidMoveEvent(currentContext, "No draw offer to decline."))
+          notifyObservers(InvalidMoveEvent(currentContext, InvalidMoveReason.NoDrawOfferToDecline))
         case Some(offerer) if offerer == color =>
-          notifyObservers(InvalidMoveEvent(currentContext, "Cannot decline your own draw offer."))
+          notifyObservers(InvalidMoveEvent(currentContext, InvalidMoveReason.CannotDeclineOwnDrawOffer))
         case Some(_) =>
           pendingDrawOffer = None
           notifyObservers(DrawOfferDeclinedEvent(currentContext, color))
@@ -380,9 +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 =
@@ -401,7 +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
@@ -421,4 +425,4 @@ class GameEngine(
                 capturedDesc,
               ),
             )
-    else notifyObservers(InvalidMoveEvent(currentContext, "Nothing to redo."))
+    else notifyObservers(InvalidMoveEvent(currentContext, InvalidMoveReason.NothingToRedo))

modules/core/src/main/scala/de/nowchess/chess/observer/InvalidMoveReason.scala

@@ -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

modules/core/src/main/scala/de/nowchess/chess/observer/Observer.scala

@@ -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. */

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

@@ -9,6 +9,7 @@ import de.nowchess.chess.observer.{
   DrawOfferEvent,
   GameEvent,
   InvalidMoveEvent,
+  InvalidMoveReason,
   Observer,
 }
 import org.scalatest.funsuite.AnyFunSuite
@@ -102,7 +103,11 @@ class GameEngineDrawOfferTest extends AnyFunSuite with Matchers:
     engine.acceptDraw(Color.Black)
 
     observer.events should have length 1
-    observer.events.head.getClass.getSimpleName shouldBe "InvalidMoveEvent"
+    observer.events.head match
+      case event: InvalidMoveEvent =>
+        event.reason shouldBe InvalidMoveReason.NoDrawOfferToAccept
+      case other =>
+        fail(s"Expected InvalidMoveEvent, but got $other")
 
   test("Cannot decline draw when no offer pending"):
     val engine   = new GameEngine()
@@ -112,7 +117,11 @@ class GameEngineDrawOfferTest extends AnyFunSuite with Matchers:
     engine.declineDraw(Color.Black)
 
     observer.events should have length 1
-    observer.events.head.getClass.getSimpleName shouldBe "InvalidMoveEvent"
+    observer.events.head match
+      case event: InvalidMoveEvent =>
+        event.reason shouldBe InvalidMoveReason.NoDrawOfferToDecline
+      case other =>
+        fail(s"Expected InvalidMoveEvent, but got $other")
 
   test("Cannot offer draw when game is already over"):
     val engine   = new GameEngine()
@@ -131,7 +140,11 @@ class GameEngineDrawOfferTest extends AnyFunSuite with Matchers:
     engine.offerDraw(Color.White)
 
     observer.events should have length 1
-    observer.events.head.getClass.getSimpleName shouldBe "InvalidMoveEvent"
+    observer.events.head match
+      case event: InvalidMoveEvent =>
+        event.reason shouldBe InvalidMoveReason.GameAlreadyOver
+      case other =>
+        fail(s"Expected InvalidMoveEvent, but got $other")
 
   test("Cannot accept your own draw offer"):
     val engine   = new GameEngine()
@@ -143,7 +156,11 @@ class GameEngineDrawOfferTest extends AnyFunSuite with Matchers:
     engine.acceptDraw(Color.White)
 
     observer.events should have length 1
-    observer.events.head.getClass.getSimpleName shouldBe "InvalidMoveEvent"
+    observer.events.head match
+      case event: InvalidMoveEvent =>
+        event.reason shouldBe InvalidMoveReason.CannotAcceptOwnDrawOffer
+      case other =>
+        fail(s"Expected InvalidMoveEvent, but got $other")
 
   test("Cannot decline your own draw offer"):
     val engine   = new GameEngine()
@@ -155,7 +172,11 @@ class GameEngineDrawOfferTest extends AnyFunSuite with Matchers:
     engine.declineDraw(Color.White)
 
     observer.events should have length 1
-    observer.events.head.getClass.getSimpleName shouldBe "InvalidMoveEvent"
+    observer.events.head match
+      case event: InvalidMoveEvent =>
+        event.reason shouldBe InvalidMoveReason.CannotDeclineOwnDrawOffer
+      case other =>
+        fail(s"Expected InvalidMoveEvent, but got $other")
 
   test("Cannot make second draw offer when one is already pending"):
     val engine   = new GameEngine()
@@ -167,7 +188,11 @@ class GameEngineDrawOfferTest extends AnyFunSuite with Matchers:
     engine.offerDraw(Color.Black)
 
     observer.events should have length 1
-    observer.events.head.getClass.getSimpleName shouldBe "InvalidMoveEvent"
+    observer.events.head match
+      case event: InvalidMoveEvent =>
+        event.reason shouldBe InvalidMoveReason.DrawOfferPending
+      case other =>
+        fail(s"Expected InvalidMoveEvent, but got $other")
 
   test("Draw offer is cleared when game ends by resignation"):
     val engine   = new GameEngine()
@@ -183,7 +208,11 @@ class GameEngineDrawOfferTest extends AnyFunSuite with Matchers:
     engine.acceptDraw(Color.White)
 
     observer.events should have length 1
-    observer.events.head.getClass.getSimpleName shouldBe "InvalidMoveEvent"
+    observer.events.head match
+      case event: InvalidMoveEvent =>
+        event.reason shouldBe InvalidMoveReason.GameAlreadyOver
+      case other =>
+        fail(s"Expected InvalidMoveEvent, but got $other")
 
 private class DrawOfferMockObserver extends Observer:
   val events = mutable.ListBuffer[GameEvent]()

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

@@ -3,7 +3,7 @@ package de.nowchess.chess.engine
 import de.nowchess.api.board.{Board, Color, File, PieceType, Rank, Square}
 import de.nowchess.api.game.GameContext
 import de.nowchess.api.move.{Move, MoveType, PromotionPiece}
-import de.nowchess.chess.observer.{GameEvent, InvalidMoveEvent, MoveRedoneEvent, Observer}
+import de.nowchess.chess.observer.{GameEvent, InvalidMoveEvent, InvalidMoveReason, MoveRedoneEvent, Observer}
 import de.nowchess.io.GameContextImport
 import de.nowchess.rules.RuleSet
 import de.nowchess.rules.sets.DefaultRules
@@ -50,8 +50,8 @@ class GameEngineIntegrationTest extends AnyFunSuite with Matchers:
     engine.processUserInput("e2e5")
 
     events.exists {
-      case InvalidMoveEvent(_, reason) => reason.contains("Illegal move")
+      case InvalidMoveEvent(_, InvalidMoveReason.IllegalMove) => true
-      case _                           => false
+      case _                                                  => false
     } shouldBe true
 
   test("loadGame returns Left when importer fails"):

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

@@ -4,7 +4,16 @@ import de.nowchess.api.board.{Board, Color, File, Piece, PieceType, Rank, Square
 import de.nowchess.api.game.{DrawReason, GameContext}
 import de.nowchess.api.move.{Move, MoveType, PromotionPiece}
 import de.nowchess.io.fen.FenParser
-import de.nowchess.chess.observer.*
+import de.nowchess.chess.observer.{
+  CheckDetectedEvent,
+  CheckmateEvent,
+  DrawEvent,
+  GameEvent,
+  InvalidMoveEvent,
+  InvalidMoveReason,
+  MoveExecutedEvent,
+  Observer,
+}
 import de.nowchess.rules.RuleSet
 import de.nowchess.rules.sets.DefaultRules
 import org.scalatest.funsuite.AnyFunSuite
@@ -30,8 +39,8 @@ class GameEnginePromotionTest extends AnyFunSuite with Matchers:
     engine.processUserInput("e7e8")
 
     events.exists {
-      case InvalidMoveEvent(_, reason) => reason.contains("Promotion piece required")
+      case InvalidMoveEvent(_, InvalidMoveReason.PromotionPieceRequired) => true
-      case _                           => false
+      case _                                                             => false
     } should be(true)
   }
 
@@ -198,5 +207,5 @@ class GameEnginePromotionTest extends AnyFunSuite with Matchers:
       case _                   => false
     } should be(true)
     val invalidEvt = events.collect { case e: InvalidMoveEvent => e }.last
-    invalidEvt.reason should include("Error completing promotion")
+    invalidEvt.reason shouldBe InvalidMoveReason.PromotionPieceInvalid
   }

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

@@ -3,7 +3,7 @@ package de.nowchess.chess.engine
 import scala.collection.mutable
 import de.nowchess.api.board.Color
 import de.nowchess.api.game.GameResult
-import de.nowchess.chess.observer.{GameEvent, Observer, ResignEvent}
+import de.nowchess.chess.observer.{GameEvent, InvalidMoveEvent, InvalidMoveReason, Observer, ResignEvent}
 import org.scalatest.funsuite.AnyFunSuite
 import org.scalatest.matchers.should.Matchers
 
@@ -55,9 +55,13 @@ class GameEngineResignTest extends AnyFunSuite with Matchers:
     observer.events.clear()
     engine.resign(Color.White)
 
-    // Should get InvalidMoveEvent
+    // Should get InvalidMoveEvent with GameAlreadyOver reason
     observer.events.length shouldBe 1
-    observer.events.head.getClass.getSimpleName shouldBe "InvalidMoveEvent"
+    observer.events.head match
+      case event: InvalidMoveEvent =>
+        event.reason shouldBe InvalidMoveReason.GameAlreadyOver
+      case other =>
+        fail(s"Expected InvalidMoveEvent, but got $other")
 
 private class ResignMockObserver extends Observer:
   val events = mutable.ListBuffer[GameEvent]()