Alternate castling was forced into normal castling

lib/src/model/common/node.dart

@@ -192,14 +192,24 @@ abstract class Node {
     bool prepend = false,
   }) {
     final pos = nodeAt(path).position;
-    final (newPos, newSan) = pos.makeSan(move);
+    final (newPos, newSan) = pos.makeSan(convertAltCastlingMove(move) ?? move);
     final newNode = Branch(
-      sanMove: SanMove(newSan, move),
+      sanMove: SanMove(newSan, convertAltCastlingMove(move) ?? move),
       position: newPos,
     );
     return addNodeAt(path, newNode, prepend: prepend);
   }
 
+  /// The function `convertAltCastlingMove` checks if a move is an alternative
+  /// castling move and converts it to the corresponding standard castling move if so.
+  Move? convertAltCastlingMove(Move move) {
+    return altCastles.containsValue(move.uci)
+        ? Move.fromUci(
+            altCastles.entries.firstWhere((e) => e.value == move.uci).key,
+          )
+        : move;
+  }
+
   /// Deletes the node at the given path.
   void deleteAt(UciPath path) {
     parentAt(path).children.removeWhere((child) => child.id == path.last);

test/model/common/node_test.dart

@@ -453,6 +453,59 @@ void main() {
         ),
       );
     });
+    group('convert alternative castling move', () {
+      void makeTestAltCastlingMove(String pgn, String alt1, String alt2) {
+        final root = Root.fromPgnGame(PgnGame.parsePgn(pgn));
+        final initialPath = root.mainlinePath;
+        final initialPng = root.makePgn();
+
+        final move = Move.fromUci(alt1);
+        expect(move, isNotNull);
+
+        final newMove = root.convertAltCastlingMove(move!);
+        expect(newMove, isNotNull);
+        expect(newMove, Move.fromUci(alt2));
+        expect(root.mainline.last.sanMove.move, newMove);
+
+        final previousUciPath = root.mainlinePath.penultimate;
+        final (newPath, isNewNode) = root.addMoveAt(previousUciPath, move);
+        expect(newPath, initialPath);
+        expect(isNewNode, isFalse);
+        expect(root.makePgn(), initialPng);
+      }
+
+      test('e1g1 -> e1h1', () {
+        makeTestAltCastlingMove(
+          '1. e4 e5 2. Nf3 Nf6 3. Bc4 Bc5 4. O-O',
+          'e1g1',
+          'e1h1',
+        );
+      });
+
+      test('e8g8 -> e8h8', () {
+        makeTestAltCastlingMove(
+          '1. e4 e5 2. Nf3 Nf6 3. Bc4 Bc5 4. O-O O-O',
+          'e8g8',
+          'e8h8',
+        );
+      });
+
+      test('e1c1 -> e1a1', () {
+        makeTestAltCastlingMove(
+          '1. d4 d5 2. Nc3 Nc6 3. Be3 Be6 4. Qd3 Qd6 5. O-O-O',
+          'e1c1',
+          'e1a1',
+        );
+      });
+
+      test('e8c8 -> e8a8', () {
+        makeTestAltCastlingMove(
+          '1. d4 d5 2. Nc3 Nc6 3. Be3 Be6 4. Qd3 Qd6 5. O-O-O O-O-O',
+          'e8c8',
+          'e8a8',
+        );
+      });
+    });
   });
 }