implemented en passant

src/logic/board.py

@@ -15,8 +15,8 @@ class Board:
         self._white: dict[Position, Piece] = {}
         self._black: dict[Position, Piece] = {}
         self._turn = None
-        self._white_castling_write = set()
-        self._black_castling_write = set()
+        self._white_castling_rights = set()
+        self._black_castling_rights = set()
         self._en_passant_target = None
 
     @staticmethod
@@ -88,13 +88,13 @@ class Board:
             sides = "kq"
             assert c in sides or c in sides.upper(), f"The FEN position is malformed, the castling rights should be either k or q (both either lower- or upper-case), instead is '{c}'"
             if c == "K":
-                ret._white_castling_write.add(CastleSide.King)
+                ret._white_castling_rights.add(CastleSide.King)
             if c == "Q":
-                ret._white_castling_write.add(CastleSide.Queen)
+                ret._white_castling_rights.add(CastleSide.Queen)
             if c == "k":
-                ret._black_castling_write.add(CastleSide.King)
+                ret._black_castling_rights.add(CastleSide.King)
             if c == "q":
-                ret._black_castling_write.add(CastleSide.Queen)
+                ret._black_castling_rights.add(CastleSide.Queen)
 
         # -- En passant target
         if position[index] != "-":
@@ -152,8 +152,8 @@ class Board:
                 return False
         return True
 
-    def castling_writes_for(self, colour: Colour) -> set[CastleSide]:
-        return self._white_castling_write if colour == Colour.WHITE else self._black_castling_write
+    def castling_rights_for(self, colour: Colour) -> set[CastleSide]:
+        return self._white_castling_rights if colour == Colour.WHITE else self._black_castling_rights
 
     def make_move(self, move: Move) -> "Board":
         dest_piece = self.piece_at(move.pos.x, move.pos.y) 
@@ -161,15 +161,18 @@ class Board:
         if dest_piece:
             assert dest_piece.colour != move.piece.colour, "A piece cannot cannot eat another piece of the same colour"
 
+        # -- Copy current state
         ret = Board()
         ret._white = self._white.copy()
         ret._black = self._black.copy()
         ret._turn = Colour.WHITE if self._turn == Colour.BLACK else Colour.BLACK
-        ret._white_castling_write = self._white_castling_write.copy()
-        ret._black_castling_write = self._black_castling_write.copy()
-        ret._en_passant_target = self._en_passant_target
+        ret._white_castling_rights = self._white_castling_rights.copy()
+        ret._black_castling_rights = self._black_castling_rights.copy()
+
 
         piece = move.piece
+
+        # -- Actually make the move
         pieces_moving, other_pieces = (ret._white, ret._black) if piece.colour == Colour.WHITE else (ret._black, ret._white)
 
         del pieces_moving[piece.pos]
@@ -177,6 +180,17 @@ class Board:
         if move.pos in other_pieces:
             del other_pieces[move.pos]
 
+        if move.en_passant:
+            pos_to_remove = Position(move.pos.x, move.pos.y + (1 if self._turn == Colour.BLACK else -1))
+            del other_pieces[pos_to_remove]
+
+        # -- Set en passant target if needed
+        if move.becomes_en_passant_target:
+            ret._en_passant_target = pieces_moving[move.pos]
+        else:
+            ret._en_passant_target = None
+
+        # -- Handle castling (just move the rook over)
         if move.castle_side == CastleSide.King:
             rook_pos = Position(7, piece.pos.y)
             assert rook_pos in pieces_moving and type(pieces_moving[rook_pos]) == Rook, "Either rook is absent from the king side or you are trying to castle with something else than a rook..."
@@ -191,24 +205,25 @@ class Board:
             new_rook_pos = Position(3, piece.pos.y)
             pieces_moving[new_rook_pos] = Rook(new_rook_pos, piece.colour)
 
+        # -- Check for castling rights
         if piece.colour == Colour.WHITE:
             if type(piece) == King:
-                ret._white_castling_write = set()
+                ret._white_castling_rights = set()
 
             if type(piece) == Rook:
-                if piece.pos.x == 0 and CastleSide.Queen in ret._white_castling_write:
-                    ret._white_castling_write.remove(CastleSide.Queen)
-                elif piece.pos.x == 7 and CastleSide.King in ret._white_castling_write:
-                    ret._white_castling_write.remove(CastleSide.King)
+                if piece.pos.x == 0 and CastleSide.Queen in ret._white_castling_rights:
+                    ret._white_castling_rights.remove(CastleSide.Queen)
+                elif piece.pos.x == 7 and CastleSide.King in ret._white_castling_rights:
+                    ret._white_castling_rights.remove(CastleSide.King)
         else:
             if type(piece) == King:
-                ret._black_castling_write = set()
+                ret._black_castling_rights = set()
 
             if type(piece) == Rook:
-                if piece.pos.x == 0 and CastleSide.Queen in ret._black_castling_write:
-                    ret._black_castling_write.remove(CastleSide.Queen)
-                elif piece.pos.x == 7 and CastleSide.King in ret._black_castling_write:
-                    ret._black_castling_write.remove(CastleSide.King)
+                if piece.pos.x == 0 and CastleSide.Queen in ret._black_castling_rights:
+                    ret._black_castling_rights.remove(CastleSide.Queen)
+                elif piece.pos.x == 7 and CastleSide.King in ret._black_castling_rights:
+                    ret._black_castling_rights.remove(CastleSide.King)
 
 
         return ret

src/logic/move.py

@@ -8,11 +8,13 @@ class CastleSide(Enum):
     Queen = "O-O-O"
 
 class Move:
-    def __init__(self, piece: "Piece", pos: Position,/, is_capturing: bool = False, castle_side: CastleSide = CastleSide.Neither) -> None:
+    def __init__(self, piece: "Piece", pos: Position,/, is_capturing: bool = False, castle_side: CastleSide = CastleSide.Neither, en_passant: bool = False, becomes_en_passant_target: bool = False) -> None:
         self.piece = piece
         self.pos = pos
         self.is_capturing = is_capturing
         self.castle_side = castle_side
+        self.becomes_en_passant_target = becomes_en_passant_target
+        self.en_passant = en_passant
 
     def to_algebraic(self) -> str:
         raise NotImplementedError("The move can't be translated to algbraic notation, as it was not implemented")

src/logic/pieces/king.py

@@ -23,11 +23,11 @@ class King(Piece):
             return self.keep_only_blocking(ret, board)
 
         # -- Castles
-        castling_writes = board.castling_writes_for(self.colour)
-        if len(castling_writes) == 0:
+        castling_rights = board.castling_rights_for(self.colour)
+        if len(castling_rights) == 0:
             return ret
 
-        if CastleSide.King in castling_writes:
+        if CastleSide.King in castling_rights:
             clear = True
             for dx in range(1, 3):
                 x = self.pos.x + dx
@@ -45,7 +45,7 @@ class King(Piece):
             if clear:
                 ret.append(Move(self, Position(6, self.pos.y), castle_side=CastleSide.King))
 
-        if CastleSide.Queen in castling_writes:
+        if CastleSide.Queen in castling_rights:
             clear = True
             for dx in range(1, 3):
                 x = self.pos.x - dx

src/logic/pieces/pawn.py

@@ -24,18 +24,30 @@ class Pawn(Piece):
             if capturable_piece.colour != self.colour:
                 ret.append(Move(self, capturable_piece.pos, is_capturing = True))
 
+        # -- Can we capture en passant?
+        if board._en_passant_target is not None and \
+            board._en_passant_target.pos.y == self.pos.y and (
+                board._en_passant_target.pos.x == self.pos.x - 1
+                or board._en_passant_target.pos.x == self.pos.x + 1
+        ):
+            if board._en_passant_target.colour != self.colour:
+                old_pos = board._en_passant_target.pos
+                new_pos = Position(old_pos.x, old_pos.y + (1 if self.colour == Colour.WHITE else -1))
+                ret.append(Move(self, new_pos, is_capturing = True, en_passant = True))
+
+        # -- Normal moves
         if self.colour == Colour.WHITE:
             for dy in range(1, 3 if self.pos.y == 1 else 2):
                 if self.pos.y + dy > 7 or board.piece_at(self.pos.x, self.pos.y + dy):
                     break
                 pos = Position(self.pos.x, self.pos.y + dy)
-                ret.append(Move(self, pos))
+                ret.append(Move(self, pos, becomes_en_passant_target=dy==2))
         else:
             for dy in range(1, 3 if self.pos.y == 6 else 2):
                 if self.pos.y - dy < 0 or board.piece_at(self.pos.x, self.pos.y - dy):
                     break
                 pos = Position(self.pos.x, self.pos.y - dy)
-                ret.append(Move(self, pos))
+                ret.append(Move(self, pos, becomes_en_passant_target=dy==2))
 
         if not looking_for_check and board.is_check_for(self.colour):
             return self.keep_only_blocking(ret, board)