From ed540e38d6f02f7266f35685e5b737902925bea1 Mon Sep 17 00:00:00 2001
From: Janis <janis.e.20@gmx.de>
Date: Tue, 7 Apr 2026 20:18:47 +0200
Subject: [PATCH] fix: NCS-32 Queenside Castle doesn't care about pieces in the
 way

---
 .../de/nowchess/rules/sets/DefaultRules.scala |  6 ++++-
 .../de/nowchess/rule/DefaultRulesTest.scala   | 24 ++++++++++++++++++-
 2 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/modules/rule/src/main/scala/de/nowchess/rules/sets/DefaultRules.scala b/modules/rule/src/main/scala/de/nowchess/rules/sets/DefaultRules.scala
index dc78274..4de0665 100644
--- a/modules/rule/src/main/scala/de/nowchess/rules/sets/DefaultRules.scala
+++ b/modules/rule/src/main/scala/de/nowchess/rules/sets/DefaultRules.scala
@@ -170,7 +170,11 @@ object DefaultRules extends RuleSet:
     castlingMove: CastlingMove
   ): Unit =
     if castlingRight then
-      val clearSqs = List(castlingMove.middleAlg, castlingMove.kingToAlg).flatMap(Square.fromAlgebraic)
+      // For queenside, also check the square between king destination and rook start
+      val extraSqs = if castlingMove.kingToAlg == "c1" then List("b1")
+                     else if castlingMove.kingToAlg == "c8" then List("b8")
+                     else List.empty
+      val clearSqs = (List(castlingMove.middleAlg, castlingMove.kingToAlg) ++ extraSqs).flatMap(Square.fromAlgebraic)
       if squaresEmpty(context.board, clearSqs) then
         for
           kf <- Square.fromAlgebraic(castlingMove.kingFromAlg)
diff --git a/modules/rule/src/test/scala/de/nowchess/rule/DefaultRulesTest.scala b/modules/rule/src/test/scala/de/nowchess/rule/DefaultRulesTest.scala
index 93d6e8d..5f7425f 100644
--- a/modules/rule/src/test/scala/de/nowchess/rule/DefaultRulesTest.scala
+++ b/modules/rule/src/test/scala/de/nowchess/rule/DefaultRulesTest.scala
@@ -52,7 +52,7 @@ class DefaultRulesTest extends AnyFunSuite with Matchers:
     val moves = rules.allLegalMoves(context)
 
     // King must move; e2 should be valid but d1 might be blocked by rook if still on same file
-    moves.filter(m => m.from == Square(File.E, Rank.R1)).nonEmpty shouldBe true
+    moves.exists(m => m.from == Square(File.E, Rank.R1)) shouldBe true
 
   test("king cannot move to square attacked by opponent"):
     // FEN: white king e1, black rook e2 defended by black king e3
@@ -109,6 +109,28 @@ class DefaultRulesTest extends AnyFunSuite with Matchers:
     val castles = moves.filter(m => m.moveType == MoveType.CastleKingside)
     castles.isEmpty shouldBe true
 
+  test("castling queenside is illegal when knight blocks on b8"):
+    // Black king e8, black rook a8, black knight b8 (blocks queenside path)
+    val board = Board(Map(
+      Square(File.A, Rank.R8) -> Piece(Color.Black, PieceType.Rook),
+      Square(File.B, Rank.R8) -> Piece(Color.Black, PieceType.Knight),
+      Square(File.E, Rank.R8) -> Piece(Color.Black, PieceType.King),
+      Square(File.A, Rank.R1) -> Piece(Color.White, PieceType.Rook),
+      Square(File.E, Rank.R1) -> Piece(Color.White, PieceType.King)
+    ))
+    val context = GameContext(
+      board = board,
+      turn = Color.Black,
+      castlingRights = CastlingRights(whiteKingSide = true, whiteQueenSide = true, blackKingSide = true, blackQueenSide = true),
+      enPassantSquare = None,
+      halfMoveClock = 0,
+      moves = List.empty
+    )
+    val moves = rules.allLegalMoves(context)
+
+    val castles = moves.filter(m => m.moveType == MoveType.CastleQueenside)
+    castles.isEmpty shouldBe true
+
   // ── En passant legality ──────────────────────────────────────────
 
   test("en passant is legal when en passant square is set"):