enpassant in the editor

lichess-org · Aug 30, 2024 · 92adc76 · 92adc76
1 parent 7dcd9d7
commit 92adc76
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diff --git a/lib/src/model/board_editor/board_editor_controller.dart b/lib/src/model/board_editor/board_editor_controller.dart
@@ -17,6 +17,7 @@ class BoardEditorController extends _$BoardEditorController {
       pieces: readFen(initialFen ?? kInitialFEN).lock,
       unmovedRooks: SquareSet.corners,
       editorPointerMode: EditorPointerMode.drag,
+      enPassantSquare: null,
       pieceToAddOnEdit: null,
     );
   }
@@ -65,6 +66,56 @@ class BoardEditorController extends _$BoardEditorController {
     _updatePosition(readFen(fen).lock);
   }
 
+  /// Calculates the squares where an en passant capture could be possible.
+  SquareSet calculateEnPassantOptions() {
+    final side = state.sideToPlay;
+    final pieces = state.pieces;
+    SquareSet enPassantSquares = SquareSet.empty;
+    final boardFen = writeFen(pieces.unlock);
+    final board = Board.parseFen(boardFen);
+
+    /// For en passant to be possible, there needs to be an adjacent pawn which has moved two squares forward.
+    /// So the two squares behind must be empty
+    void checkEnPassant(Square square, int fileOffset) {
+      final adjacentSquare =
+          Square.fromCoords(square.file.offset(fileOffset)!, square.rank);
+      final targetSquare = Square.fromCoords(
+        square.file.offset(fileOffset)!,
+        square.rank.offset(side == Side.white ? 1 : -1)!,
+      );
+      final originSquare = Square.fromCoords(
+        square.file.offset(fileOffset)!,
+        square.rank.offset(side == Side.white ? 2 : -2)!,
+      );
+
+      if (board.sideAt(adjacentSquare) == side.opposite &&
+          board.roleAt(adjacentSquare) == Role.pawn &&
+          board.sideAt(targetSquare) == null &&
+          board.sideAt(originSquare) == null) {
+        enPassantSquares =
+            enPassantSquares.union(SquareSet.fromSquare(targetSquare));
+      }
+    }
+
+    pieces.forEach((square, piece) {
+      if (piece.color == side && piece.role == Role.pawn) {
+        if ((side == Side.white && square.rank == Rank.fifth) ||
+            (side == Side.black && square.rank == Rank.fourth)) {
+          if (square.file != File.a) checkEnPassant(square, -1);
+          if (square.file != File.h) checkEnPassant(square, 1);
+        }
+      }
+    });
+
+    return enPassantSquares;
+  }
+
+  void toggleEnPassantSquare(Square square) {
+    state = state.copyWith(
+      enPassantSquare: state.enPassantSquare == square ? null : square,
+    );
+  }
+
   void _updatePosition(IMap<Square, Piece> pieces) {
     state = state.copyWith(pieces: pieces);
   }
@@ -105,6 +156,7 @@ class BoardEditorState with _$BoardEditorState {
     required IMap<Square, Piece> pieces,
     required SquareSet unmovedRooks,
     required EditorPointerMode editorPointerMode,
+    required Square? enPassantSquare,
 
     /// When null, clears squares when in edit mode. Has no effect in drag mode.
     required Piece? pieceToAddOnEdit,
@@ -129,6 +181,7 @@ class BoardEditorState with _$BoardEditorState {
       board: board,
       unmovedRooks: unmovedRooks,
       turn: sideToPlay == Side.white ? Side.white : Side.black,
+      epSquare: enPassantSquare,
       halfmoves: 0,
       fullmoves: 1,
     );

diff --git a/lib/src/view/board_editor/board_editor_menu.dart b/lib/src/view/board_editor/board_editor_menu.dart
@@ -15,6 +15,9 @@ class BoardEditorMenu extends ConsumerWidget {
     final editorController = boardEditorControllerProvider(initialFen);
     final editorState = ref.watch(editorController);
 
+    final enPassantSquares =
+        ref.read(editorController.notifier).calculateEnPassantOptions();
+
     return SafeArea(
       child: Padding(
         padding: const EdgeInsets.symmetric(vertical: 16.0, horizontal: 8.0),
@@ -80,6 +83,26 @@ class BoardEditorMenu extends ConsumerWidget {
                   ),
                 );
               }),
+              if (enPassantSquares.isNotEmpty) ...[
+                Padding(
+                  padding: Styles.bodySectionPadding,
+                  child: const Text('En passant', style: Styles.subtitle),
+                ),
+                Wrap(
+                  spacing: 8.0,
+                  children: enPassantSquares.squares.map((square) {
+                    return ChoiceChip(
+                      label: Text(square.name),
+                      selected: editorState.enPassantSquare == square,
+                      onSelected: (selected) {
+                        ref
+                            .read(editorController.notifier)
+                            .toggleEnPassantSquare(square);
+                      },
+                    );
+                  }).toList(),
+                ),
+              ],
             ],
           ),
         ),

diff --git a/test/view/board_editor/board_editor_screen_test.dart b/test/view/board_editor/board_editor_screen_test.dart
@@ -143,6 +143,44 @@ void main() {
       );
     });
 
+    testWidgets('Possible en passant squares are calculated correctly',
+        (tester) async {
+      final app = await buildTestApp(
+        tester,
+        home: const BoardEditorScreen(),
+      );
+      await tester.pumpWidget(app);
+
+      final container = ProviderScope.containerOf(
+        tester.element(find.byType(ChessboardEditor)),
+      );
+      final controllerProvider = boardEditorControllerProvider(null);
+      container
+          .read(controllerProvider.notifier)
+          .loadFen('1nbqkbn1/pppppppp/8/8/8/8/PPPPPPPP/1NBQKBN1');
+
+      expect(
+        container.read(controllerProvider.notifier).calculateEnPassantOptions(),
+        SquareSet.empty,
+      );
+
+      container.read(controllerProvider.notifier).loadFen(
+            'r1bqkbnr/4p1p1/3n4/pPppPppP/8/8/P1PP1P2/RNBQKBNR w KQkq - 0 1',
+          );
+      expect(
+        container.read(controllerProvider.notifier).calculateEnPassantOptions(),
+        SquareSet.fromSquares([Square.a6, Square.c6, Square.f6]),
+      );
+      container.read(controllerProvider.notifier).loadFen(
+            'rnbqkbnr/pp1p1p1p/8/8/PpPpPQpP/8/NPRP1PP1/2B1KBNR b Kkq - 0 1',
+          );
+      container.read(controllerProvider.notifier).setSideToPlay(Side.black);
+      expect(
+        container.read(controllerProvider.notifier).calculateEnPassantOptions(),
+        SquareSet.fromSquares([Square.e3, Square.h3]),
+      );
+    });
+
     testWidgets('Can drag pieces to new squares', (tester) async {
       final app = await buildTestApp(
         tester,