preparing for introduction of castling, en passant and promotion

app/chess_sim/test.py

@@ -65,10 +65,19 @@ class Piece:
         return f"Piece({self.type.name},{self.color.name})"
 
 
+class MoveType(Enum):
+    NORMAL = auto()
+    CASTLING_KINGSIDE = auto()  #todo: implement
+    CASTLING_QUEENSIDE = auto() #todo: implement
+    EN_PASSANT = auto() #todo: implement
+    PROMOTION = auto() #todo: implement
+
 @dataclass
 class BoardMove:
     m_from: BoardPos
     m_to: BoardPos
+    move_type: MoveType = MoveType.NORMAL   #todo: implement and handle
+    promotion_piece: Optional[PieceType] = None #todo: implement and handle
 
     def __str__(self) -> str:
         return f"{self.m_from}->{self.m_to}"
@@ -268,26 +277,35 @@ class ChessBoard:
         
         
         # manually adding castling
-        row_height = 0
-        if color == Color.BLACK:
-            row_height = 7
+        row_height = 7 if color == Color.WHITE else 0
         expected_king_pos = BoardPos((row_height, 4))
 
-        # if the king has moved, return as usual
+        # if king moved
         if self.has_piece_moved(expected_king_pos):
             return moves
 
         expected_lhs_rook_pos = BoardPos((row_height, 0))
         expected_rhs_rook_pos = BoardPos((row_height, 7))
-        lhs_pieces_inbetween = [BoardPos((row_height, i)) for i in range(1, 3)]
-        rhs_pieces_inbetween = [BoardPos((row_height, i)) for i in range(5, 6)]
 
-        # make sure the pieces inbetween are gone and the rook has not moved
-        if not self.has_piece_moved(expected_lhs_rook_pos) and self.are_pieces_none(lhs_pieces_inbetween):
-            #todo: allow castling here
-        if not self.has_piece_moved(expected_rhs_rook_pos) and self.are_pieces_none(rhs_pieces_inbetween):
-            #todo: allow castling here
+        # squares that must be empty between rook and king
+        lhs_pieces_inbetween = [BoardPos((row_height, i)) for i in range(1, 4)]   # cols 1,2,3
+        rhs_pieces_inbetween = [BoardPos((row_height, i)) for i in range(5, 7)]   # cols 5,6
 
+        # squares that must not be attacked by the opponent 
+        lhs_fields_attacked = [BoardPos((row_height, i)) for i in (4, 3, 2)]
+        rhs_fields_attacked = [BoardPos((row_height, i)) for i in (4, 5, 6)]
+
+        if (not self.has_piece_moved(expected_lhs_rook_pos)
+                and self.are_pieces_none(lhs_pieces_inbetween)
+                and not self.are_fields_attacked(lhs_fields_attacked, color.opposite)):
+            # todo: allow castling here
+            pass
+
+        if (not self.has_piece_moved(expected_rhs_rook_pos)
+                and self.are_pieces_none(rhs_pieces_inbetween)
+                and not self.are_fields_attacked(rhs_fields_attacked, color.opposite)):
+            # todo: allow castling here
+            pass
         return moves
 
     def has_piece_moved(self, pos: BoardPos) -> bool:
@@ -330,6 +348,57 @@ class ChessBoard:
                 return pos
         raise ValueError("player has no king")
 
+    # returns true if one field is actively being attacked 
+    def are_fields_attacked(self, fields: List[BoardPos], attacker_color: Color) -> bool:
+        for field in fields:
+            if self.is_field_attacked(field, attacker_color):
+                return True
+        return False
+
+    # checks if the field is being actively attacked by any of the pieces of the attacker color
+    # this "complicated" implementation was necessary to not rely on recursive calls
+    def is_field_attacked(self, pos: BoardPos, attacker_color: Color) -> bool:
+        # iterate opponent pieces and check whether they attack
+        for attacker_pos, attacker in self.iter_pieces():
+            if attacker.color != attacker_color:
+                continue
+
+            rays = self.moves_unchecked(attacker, attacker_pos)
+
+            if attacker.type == PieceType.PAWN:
+                # pawn attacks are the pawn capture rays only
+                forward = -1 if attacker.color == Color.WHITE else 1
+                for dc in (-1, 1):
+                    rr = attacker_pos.x + forward
+                    cc = attacker_pos.y + dc
+                    if not self.on_board(rr, cc):
+                        continue
+                    if BoardPos((rr, cc)) == pos:
+                        return True
+                continue
+
+            if attacker.type in (PieceType.KNIGHT, PieceType.KING):
+                # non-sliding
+                for (rr, cc) in rays[0]:
+                    if not self.on_board(rr, cc):
+                        continue
+                    if BoardPos((rr, cc)) == pos:
+                        return True
+                continue
+
+            # sliding pieces 
+            for ray in rays:
+                for (rr, cc) in ray:
+                    if not self.on_board(rr, cc):
+                        break
+                    if BoardPos((rr, cc)) == pos:
+                        return True
+                    # stop at first occupied square (blocker)
+                    if self.fields[rr][cc].piece is not None:
+                        break
+
+        return False       
+            
     # if a player does not have any moves, it has lost
     def generate_moves(self, color: Color) -> List[BoardMove]: