feat: NCS-41 Bot Platform (#33)

Co-authored-by: Janis <janis@nowchess.de>
Reviewed-on: #33
Co-authored-by: Janis <janis.e.20@gmx.de>
Co-committed-by: Janis <janis.e.20@gmx.de>

modules/rule/src/main/scala/de/nowchess/rules/sets/DefaultRules.scala

@@ -81,8 +81,7 @@ object DefaultRules extends RuleSet:
 
   private def countPositionOccurrences(context: GameContext, targetPosition: Position): Int =
     try
-      var count     = 0
-      var tempCtx   = GameContext(
+      val initialCtx = GameContext(
         board = context.initialBoard,
         turn = Color.White,
         castlingRights = CastlingRights.Initial,
@@ -91,20 +90,24 @@ object DefaultRules extends RuleSet:
         moves = List.empty,
         initialBoard = context.initialBoard,
       )
-      var tempPos   = Position(tempCtx.board, tempCtx.turn, tempCtx.castlingRights, tempCtx.enPassantSquare)
-      if tempPos == targetPosition then count += 1
 
-      for move <- context.moves do
-        tempCtx = applyMove(tempCtx)(move)
-        tempPos = Position(
-          board = tempCtx.board,
-          turn = tempCtx.turn,
-          castlingRights = tempCtx.castlingRights,
-          enPassantSquare = tempCtx.enPassantSquare,
+      def positionOf(ctx: GameContext): Position =
+        Position(
+          board = ctx.board,
+          turn = ctx.turn,
+          castlingRights = ctx.castlingRights,
+          enPassantSquare = ctx.enPassantSquare,
         )
-        if tempPos == targetPosition then count += 1
 
-      count
+      val initialCount = if positionOf(initialCtx) == targetPosition then 1 else 0
+
+      context.moves
+        .foldLeft((initialCtx, initialCount)) { case ((tempCtx, count), move) =>
+          val nextCtx   = applyMove(tempCtx)(move)
+          val nextCount = if positionOf(nextCtx) == targetPosition then count + 1 else count
+          (nextCtx, nextCount)
+        }
+        ._2
     catch
       case _: Exception =>
         // If replay fails, conservatively count only the current position (never triggers a draw)

modules/rule/src/test/scala/de/nowchess/rule/DefaultRulesTest.scala

@@ -29,10 +29,12 @@ class DefaultRulesTest extends AnyFunSuite with Matchers:
 
   test("pawn can capture diagonally"):
     // FEN: white pawn e4, black pawn d5
-    val fen      = "8/8/8/3p4/4P3/8/8/8 w - - 0 1"
-    val context  = FenParser.parseFen(fen).fold(_ => fail(), identity)
-    val moves    = rules.allLegalMoves(context)
-    val captures = moves.filter(m => m.from == Square(File.E, Rank.R4) && (m.moveType match { case _: MoveType.Normal => true; case _ => false }))
+    val fen     = "8/8/8/3p4/4P3/8/8/8 w - - 0 1"
+    val context = FenParser.parseFen(fen).fold(_ => fail(), identity)
+    val moves   = rules.allLegalMoves(context)
+    val captures = moves.filter(m =>
+      m.from == Square(File.E, Rank.R4) && (m.moveType match { case _: MoveType.Normal => true; case _ => false }),
+    )
     captures.exists(m => m.to == Square(File.D, Rank.R5)) shouldBe true
 
   test("pawn cannot move backward"):
@@ -208,7 +210,7 @@ class DefaultRulesTest extends AnyFunSuite with Matchers:
 
   test("threefold repetition catch block returns false for inconsistent context"):
     // A context whose moves cannot be replayed from initialBoard (forces the catch path)
-    val m = Move(Square(File.E, Rank.R5), Square(File.E, Rank.R6))  // e5→e6, no pawn there in initial board
+    val m = Move(Square(File.E, Rank.R5), Square(File.E, Rank.R6)) // e5→e6, no pawn there in initial board
     val brokenCtx = GameContext(
       board = Board.initial,
       turn = Color.White,