From 45113e97379819f1069d72bfbd10619eecd9aa93 Mon Sep 17 00:00:00 2001
From: Alex Baker <iamalexbaker@gmail.com>
Date: Sun, 23 Jun 2024 20:29:29 +0700
Subject: [PATCH] Chess960 castling bug (K-B1, R-C1)

---
 lib/src/game/game.dart  | 9 +++++++--
 test/castling_test.dart | 9 +++++++++
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/lib/src/game/game.dart b/lib/src/game/game.dart
index 387981e..26854de 100644
--- a/lib/src/game/game.dart
+++ b/lib/src/game/game.dart
@@ -418,23 +418,28 @@ class Game {
         int rookTargetFile = i == 0 ? targetFile - 1 : targetFile + 1;
         int rookTargetSq =
             size.square(rookTargetFile, royalRank); // where the rook lands
+
         // Check rook target square is empty (or occupied by the rook/king already)
         if (board[rookTargetSq].isNotEmpty &&
             rookTargetSq != rookSq &&
             rookTargetSq != from) {
           continue;
         }
+
         // Check king target square is empty (or occupied by the castling rook)
         if (board[targetSq].isNotEmpty &&
             targetSq != rookSq &&
-            targetSq != square) continue;
+            targetSq != square) {
+          continue;
+        }
+
         int numMidSqs = (targetFile - castlingFile!).abs();
         bool valid = true;
         if (!options.ignorePieces) {
           int numRookMidSquares = (targetFile - rookFile).abs();
           if (numRookMidSquares > 1) {
             for (int j = 1; j <= numRookMidSquares; j++) {
-              int midFile = rookFile + (i == 0 ? -j : j);
+              int midFile = rookFile + (rookFile > targetFile ? -j : j);
               int midSq = size.square(midFile, royalRank);
               if (board[midSq].isNotEmpty && midFile != castlingFile) {
                 valid = false;
diff --git a/test/castling_test.dart b/test/castling_test.dart
index c540889..cd3ae0d 100644
--- a/test/castling_test.dart
+++ b/test/castling_test.dart
@@ -21,6 +21,15 @@ void main() {
       expect(moves.from(g.size.squareNumber('c1')).length, 3);
     });
     // https://github.com/alexobviously/bishop/issues/77
+    test('Chess960 K-B1:R-C1 castling', () {
+      final g = Game(
+        variant: CommonVariants.chess960(),
+        fen: 'rkr4n/ppppqbpp/3bpp1n/8/8/2BPPN2/PPPQBPPP/RKR4N w KQkq - 6 7',
+      );
+      final moves = g.generateLegalMoves();
+      expect(moves.castlingMoves.length, 1);
+      expect(moves.from(g.size.squareNumber('b1')).length, 1);
+    });
     test('Castling rights when a rook takes a rook', () {
       final g = Game(
         fen: 'rnbqk1nr/ppp1ppb1/6p1/3p4/8/2N5/PPPPPPP1/R1BQKBNR w KQkq - 0 5',