refactor: NCS-19 Currying (#18)

Summary

  - Curried candidateMoves, legalMoves, and applyMove in the RuleSet trait to separate (context) as the world being
  operated on from the computation parameter
  - Updated DefaultRules overrides and all internal call sites
  - Updated all external call sites: GameEngine, PgnParser, PgnExporter, ChessBoardView, and all affected tests

  Test plan

  - All existing tests pass (./gradlew build)
  - No behaviour changes — pure style refactoring, existing test suite is the regression guard

Co-authored-by: LQ63 <lkhermann@web.de>
Reviewed-on: #18
Reviewed-by: Janis <janis-e@gmx.de>
Co-authored-by: Leon Hermann <lq@blackhole.local>
Co-committed-by: Leon Hermann <lq@blackhole.local>

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

@@ -88,7 +88,7 @@ class GameEngine(
       case Some(piece) if piece.color != currentContext.turn =>
         notifyObservers(InvalidMoveEvent(currentContext, "That is not your piece."))
       case Some(piece) =>
-        val legal = ruleSet.legalMoves(currentContext, from)
+        val legal = ruleSet.legalMoves(currentContext)(from)
         // Find all legal moves going to `to`
         val candidates = legal.filter(_.to == to)
         candidates match
@@ -119,7 +119,7 @@ class GameEngine(
         pendingPromotion = None
         val move = Move(pending.from, pending.to, MoveType.Promotion(piece))
         // Verify it's actually legal
-        val legal = ruleSet.legalMoves(currentContext, pending.from)
+        val legal = ruleSet.legalMoves(currentContext)(pending.from)
         if legal.contains(move) then
           executeMove(move)
         else
@@ -203,7 +203,7 @@ class GameEngine(
 
   private def executeMove(move: Move): Unit =
     val contextBefore = currentContext
-    val nextContext = ruleSet.applyMove(currentContext, move)
+    val nextContext = ruleSet.applyMove(currentContext)(move)
     val captured = computeCaptured(currentContext, move)
 
     val cmd = MoveCommand(

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

@@ -89,8 +89,8 @@ class GameEngineIntegrationTest extends AnyFunSuite with Matchers:
     val promotionMove = Move(sq("e2"), sq("e8"), MoveType.Promotion(PromotionPiece.Queen))
 
     val permissiveRules = new RuleSet:
-      def candidateMoves(context: GameContext, square: Square): List[Move] = legalMoves(context, square)
-      def legalMoves(context: GameContext, square: Square): List[Move] =
+      def candidateMoves(context: GameContext)(square: Square): List[Move] = legalMoves(context)(square)
+      def legalMoves(context: GameContext)(square: Square): List[Move] =
         if square == sq("e2") then List(promotionMove) else List.empty
       def allLegalMoves(context: GameContext): List[Move] = List(promotionMove)
       def isCheck(context: GameContext): Boolean = false
@@ -98,7 +98,7 @@ class GameEngineIntegrationTest extends AnyFunSuite with Matchers:
       def isStalemate(context: GameContext): Boolean = false
       def isInsufficientMaterial(context: GameContext): Boolean = false
       def isFiftyMoveRule(context: GameContext): Boolean = false
-      def applyMove(context: GameContext, move: Move): GameContext = DefaultRules.applyMove(context, move)
+      def applyMove(context: GameContext)(move: Move): GameContext = DefaultRules.applyMove(context)(move)
 
     val engine = new GameEngine(ruleSet = permissiveRules)
     val importer = new GameContextImport:
@@ -111,15 +111,15 @@ class GameEngineIntegrationTest extends AnyFunSuite with Matchers:
   test("loadGame replay restores previous context when promotion cannot be completed"):
     val promotionMove = Move(sq("e2"), sq("e8"), MoveType.Promotion(PromotionPiece.Queen))
     val noLegalMoves = new RuleSet:
-      def candidateMoves(context: GameContext, square: Square): List[Move] = List.empty
-      def legalMoves(context: GameContext, square: Square): List[Move] = List.empty
+      def candidateMoves(context: GameContext)(square: Square): List[Move] = List.empty
+      def legalMoves(context: GameContext)(square: Square): List[Move] = List.empty
       def allLegalMoves(context: GameContext): List[Move] = List.empty
       def isCheck(context: GameContext): Boolean = false
       def isCheckmate(context: GameContext): Boolean = false
       def isStalemate(context: GameContext): Boolean = false
       def isInsufficientMaterial(context: GameContext): Boolean = false
       def isFiftyMoveRule(context: GameContext): Boolean = false
-      def applyMove(context: GameContext, move: Move): GameContext = context
+      def applyMove(context: GameContext)(move: Move): GameContext = context
 
     val engine = new GameEngine(ruleSet = noLegalMoves)
     engine.processUserInput("e2e4")

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

@@ -153,10 +153,10 @@ class GameEnginePromotionTest extends AnyFunSuite with Matchers:
     // This makes completePromotion unable to find Move(from, to, Promotion(Queen)),
     // triggering the "Error completing promotion." branch.
     val delegatingRuleSet: RuleSet = new RuleSet:
-      def candidateMoves(context: GameContext, square: Square): List[Move] =
-        DefaultRules.candidateMoves(context, square)
-      def legalMoves(context: GameContext, square: Square): List[Move] =
-        DefaultRules.legalMoves(context, square).map { m =>
+      def candidateMoves(context: GameContext)(square: Square): List[Move] =
+        DefaultRules.candidateMoves(context)(square)
+      def legalMoves(context: GameContext)(square: Square): List[Move] =
+        DefaultRules.legalMoves(context)(square).map { m =>
           m.moveType match
             case MoveType.Promotion(_) => Move(m.from, m.to, MoveType.Normal())
             case _                     => m
@@ -173,8 +173,8 @@ class GameEnginePromotionTest extends AnyFunSuite with Matchers:
         DefaultRules.isInsufficientMaterial(context)
       def isFiftyMoveRule(context: GameContext): Boolean =
         DefaultRules.isFiftyMoveRule(context)
-      def applyMove(context: GameContext, move: Move): GameContext =
-        DefaultRules.applyMove(context, move)
+      def applyMove(context: GameContext)(move: Move): GameContext =
+        DefaultRules.applyMove(context)(move)
 
     val promotionBoard = FenParser.parseBoard("8/4P3/4k3/8/8/8/8/8").get
     val initialCtx = GameContext.initial.withBoard(promotionBoard).withTurn(Color.White)