1223 lines
49 KiB
Nim
1223 lines
49 KiB
Nim
# Copyright 2023 Mattia Giambirtone & All Contributors
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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import ../util/matrix
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export matrix
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import std/strutils
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import std/strformat
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type
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# Useful type aliases
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Location* = tuple[row, col: int]
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Pieces = tuple[king: Location, queens: seq[Location], rooks: seq[Location],
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bishops: seq[Location], knights: seq[Location],
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pawns: seq[Location]]
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Castling* = tuple[white, black: tuple[queen, king: bool]]
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PieceColor* = enum
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## A piece color enumeration
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None = 0,
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White,
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Black
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PieceKind* = enum
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## A chess piece enumeration
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Empty = '\0', # No piece
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Bishop = 'b',
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King = 'k'
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Knight = 'n',
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Pawn = 'p',
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Queen = 'q',
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Rook = 'r',
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Piece* = object
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## A chess piece
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color*: PieceColor
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kind*: PieceKind
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MoveFlag* = enum
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## An enumeration of move flags
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Default, # Move is a regular move
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XRay, # Move is an X-ray attack
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# Move is a pawn promotion
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PromoteToQueen,
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PromoteToRook,
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PromoteToBishop,
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PromoteToKnight
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Move* = object
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## A chess move
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piece*: Piece
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startSquare*: Location
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targetSquare*: Location
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flag*: MoveFlag
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Position* = ref object
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## A chess position
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move: Move
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# Stores castling metadata
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castling: Castling
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# Number of half-moves that were performed
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# to reach this position starting from the
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# root of the tree
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plyFromRoot: int
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# Number of half moves since
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# last piece capture or pawn movement.
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# Used for the 50-move rule
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halfMoveClock: int
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# Full move counter. Increments
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# every 2 ply
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fullMoveCount: int
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# En passant target square (see https://en.wikipedia.org/wiki/En_passant)
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# If en passant is not possible, both the row and
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# column of the position will be set to -1
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enPassantSquare*: Move
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# Locations of all pieces
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pieces: tuple[white: Pieces, black: Pieces]
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# Potential attacking moves for black and white
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attacked: tuple[white: seq[Move], black: seq[Move]]
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# Has any piece been captured to reach this position?
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captured: Piece
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# Active color
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turn: PieceColor
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ChessBoard* = ref object
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## A chess board object
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grid: Matrix[Piece]
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position: Position
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positionIndex: int
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# List of reached positions
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positions: seq[Position]
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# Initialized only once, copied every time
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var empty: seq[Piece] = @[]
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for _ in countup(0, 63):
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empty.add(Piece(kind: Empty, color: None))
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func emptyPiece*: Piece {.inline.} = Piece(kind: Empty, color: None)
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func emptyLocation*: Location {.inline.} = (-1 , -1)
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func opposite*(c: PieceColor): PieceColor {.inline.} = (if c == White: Black else: White)
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proc algebraicToPosition*(s: string): Location {.inline.}
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proc getCapture*(self: ChessBoard, move: Move): Location
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proc makeMove*(self: ChessBoard, startSquare, targetSquare: string): Move
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proc makeMove*(self: ChessBoard, move: Move): Move
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func emptyMove*: Move {.inline.} = Move(startSquare: emptyLocation(), targetSquare: emptyLocation(), piece: emptyPiece())
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func `+`*(a, b: Location): Location = (a.row + b.row, a.col + b.col)
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func isValid*(a: Location): bool = a.row in 0..7 and a.col in 0..7
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proc generateMoves(self: ChessBoard, location: Location): seq[Move]
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# Due to our board layout, directions of movement are reversed for white/black so
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# we need these helpers to avoid going mad with integer tuples and minus signs
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# everywhere
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func topLeftDiagonal(piece: Piece): Location {.inline.} = (if piece.color == White: (-1, -1) else: (1, 1))
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func topRightDiagonal(piece: Piece): Location {.inline.} = (if piece.color == White: (-1, 1) else: (1, -1))
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func bottomLeftDiagonal(piece: Piece): Location {.inline.} = (if piece.color == White: (1, -1) else: (-1, 1))
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func bottomRightDiagonal(piece: Piece): Location {.inline.} = (if piece.color == White: (1, 1) else: (-1, -1))
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func leftSide(piece: Piece): Location {.inline.} = (if piece.color == White: (0, -1) else: (0, 1))
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func rightSide(piece: Piece): Location {.inline.} = (if piece.color == White: (0, 1) else: (0, -1))
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func topSide(piece: Piece): Location {.inline.} = (if piece.color == White: (-1, 0) else: (1, 0))
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func bottomSide(piece: Piece): Location {.inline.} = (if piece.color == White: (1, 0) else: (-1, 0))
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func forward(piece: Piece): Location {.inline.} = (if piece.color == White: (-1, 0) else: (1, 0))
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func doublePush(piece: Piece): Location {.inline.} = (if piece.color == White: (-2, 0) else: (2, 0))
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func bottomLeftKnightMove(piece: Piece, long: bool = true): Location {.inline.} =
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if piece.color == White:
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if long:
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return (-2, 1)
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else:
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return (1, -2)
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elif piece.color == Black:
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if long:
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return (2, -1)
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else:
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return (1, -2)
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func bottomRightKnightMove(piece: Piece, long: bool = true): Location {.inline.} =
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if piece.color == White:
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if long:
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return (2, -1)
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else:
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return (1, 2)
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elif piece.color == Black:
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if long:
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return (2, 1)
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else:
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return (1, 2)
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func topLeftKnightMove(piece: Piece, long: bool = true): Location {.inline.} =
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if piece.color == White:
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if long:
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return (-2, -1)
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else:
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return (-1, -2)
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elif piece.color == Black:
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if long:
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return (2, 1)
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else:
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return (1, 2)
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func topRightKnightMove(piece: Piece, long: bool = true): Location {.inline.} =
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if piece.color == White:
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if long:
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return (-2, 1)
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else:
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return (-1, 2)
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elif piece.color == Black:
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if long:
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return (2, -1)
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else:
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return (-1, 2)
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proc getActiveColor*(self: ChessBoard): PieceColor =
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## Returns the currently active color
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## (turn of who has to move)
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return self.position.turn
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proc getCastlingInformation*(self: ChessBoard): tuple[queen, king: bool] =
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## Returns whether castling is possible
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## for the given color
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case self.getActiveColor():
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of White:
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return self.position.castling.white
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of Black:
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return self.position.castling.black
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else:
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discard
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func getStartRow(piece: Piece): int {.inline.} =
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## Retrieves the starting row of
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## the given piece inside our 8x8
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## grid
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case piece.color:
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of None:
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return -1
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of White:
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case piece.kind:
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of Pawn:
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return 6
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else:
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return 5
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of Black:
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case piece.kind:
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of Pawn:
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return 1
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else:
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return 0
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func getLastRow(color: PieceColor): int {.inline.} =
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## Retrieves the location of the last
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## row relative to the given color
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case color:
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of White:
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return 0
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of Black:
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return 7
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else:
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return -1
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proc newChessboard: ChessBoard =
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## Returns a new, empty chessboard
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new(result)
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# Turns our flat sequence into an 8x8 grid
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result.grid = newMatrixFromSeq[Piece](empty, (8, 8))
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result.position = Position(attacked: (@[], @[]),
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enPassantSquare: emptyMove(),
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move: emptyMove(),
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turn: White)
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result.positionIndex = 0
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proc newChessboardFromFEN*(state: string): ChessBoard =
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## Initializes a chessboard with the
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## state encoded by the given FEN string
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result = newChessboard()
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var
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# Current location in the grid
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row = 0
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column = 0
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# Current section in the FEN string
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section = 0
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# Current index into the FEN string
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index = 0
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# Temporary variable to store the piece
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piece: Piece
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# See https://en.wikipedia.org/wiki/Forsyth%E2%80%93Edwards_Notation
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while index <= state.high():
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var c = state[index]
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if c == ' ':
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# Next section
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inc(section)
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inc(index)
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continue
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case section:
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of 0:
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# Piece placement data
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case c.toLowerAscii():
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# Piece
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of 'r', 'n', 'b', 'q', 'k', 'p':
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# We know for a fact these values are in our
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# enumeration, so all is good
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{.push.}
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{.warning[HoleEnumConv]:off.}
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piece = Piece(kind: PieceKind(c.toLowerAscii()), color: if c.isUpperAscii(): White else: Black)
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{.pop.}
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case piece.color:
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of Black:
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case piece.kind:
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of Pawn:
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result.position.pieces.black.pawns.add((row, column))
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of Bishop:
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result.position.pieces.black.bishops.add((row, column))
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of Knight:
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result.position.pieces.black.knights.add((row, column))
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of Rook:
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result.position.pieces.black.rooks.add((row, column))
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of Queen:
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result.position.pieces.black.queens.add((row, column))
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of King:
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result.position.pieces.black.king = (row, column)
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else:
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discard
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of White:
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case piece.kind:
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of Pawn:
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result.position.pieces.white.pawns.add((row, column))
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of Bishop:
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result.position.pieces.white.bishops.add((row, column))
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of Knight:
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result.position.pieces.white.knights.add((row, column))
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of Rook:
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result.position.pieces.white.rooks.add((row, column))
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of Queen:
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result.position.pieces.white.queens.add((row, column))
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of King:
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result.position.pieces.white.king = (row, column)
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else:
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discard
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else:
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discard
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result.grid[row, column] = piece
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inc(column)
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of '/':
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# Next row
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inc(row)
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column = 0
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of '0'..'9':
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# Skip x columns
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let x = int(uint8(c) - uint8('0')) - 1
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if x > 7:
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raise newException(ValueError, "invalid skip value (> 8) in FEN string")
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column += x
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else:
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raise newException(ValueError, "invalid piece identifier in FEN string")
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of 1:
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# Active color
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case c:
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of 'w':
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result.position.turn = White
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of 'b':
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result.position.turn = Black
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else:
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raise newException(ValueError, "invalid active color identifier in FEN string")
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of 2:
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# Castling availability
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case c:
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of '-':
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# Neither side can castle anywhere: do nothing,
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# as the castling metadata is set to this state
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# by default
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discard
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of 'K':
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result.position.castling.white.king = true
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of 'Q':
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result.position.castling.white.queen = true
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of 'k':
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result.position.castling.black.king = true
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of 'q':
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result.position.castling.black.queen = true
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else:
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raise newException(ValueError, "invalid castling availability in FEN string")
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of 3:
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# En passant target square
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case c:
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of '-':
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# Field is already uninitialized to the correct state
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discard
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else:
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result.position.enPassantSquare.targetSquare = state[index..index+1].algebraicToPosition()
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# Just for cleanliness purposes, we fill in the other metadata as
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# well
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result.position.enPassantSquare.piece.color = result.getActiveColor()
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result.position.enPassantSquare.piece.kind = Pawn
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# Square metadata is 2 bytes long
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inc(index)
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of 4:
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# Halfmove clock
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var s = ""
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while not state[index].isSpaceAscii():
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s.add(state[index])
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inc(index)
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# Backtrack so the space is seen by the
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# next iteration of the loop
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dec(index)
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result.position.halfMoveClock = parseInt(s)
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of 5:
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# Fullmove number
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var s = ""
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while index <= state.high():
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s.add(state[index])
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inc(index)
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result.position.fullMoveCount = parseInt(s)
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else:
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raise newException(ValueError, "too many fields in FEN string")
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inc(index)
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proc newDefaultChessboard*: ChessBoard =
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## Initializes a chessboard with the
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## starting position
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return newChessboardFromFEN("rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1")
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proc countPieces*(self: ChessBoard, kind: PieceKind, color: PieceColor): int =
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## Counts the number of pieces with
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## the given color and type
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case color:
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of White:
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case kind:
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of Pawn:
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return self.position.pieces.white.pawns.len()
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of Bishop:
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return self.position.pieces.white.bishops.len()
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of Knight:
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return self.position.pieces.white.knights.len()
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of Rook:
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return self.position.pieces.white.rooks.len()
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of Queen:
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return self.position.pieces.white.queens.len()
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of King:
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# There shall be only one, forever
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return 1
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else:
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discard
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of Black:
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case kind:
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of Pawn:
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return self.position.pieces.black.pawns.len()
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of Bishop:
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return self.position.pieces.black.bishops.len()
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of Knight:
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return self.position.pieces.black.knights.len()
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of Rook:
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return self.position.pieces.black.rooks.len()
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of Queen:
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return self.position.pieces.black.queens.len()
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of King:
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# In perpetuity
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return 1
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else:
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discard
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of None:
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raise newException(ValueError, "invalid piece type")
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proc countPieces*(self: ChessBoard, piece: Piece): int =
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## Returns the number of pieces on the board that
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## are of the same type and color of the given piece
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return self.countPieces(piece.kind, piece.color)
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func rankToColumn(rank: int): int =
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## Converts a chess rank (1-indexed)
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## into a 0-indexed column value for our
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## board. This converter is necessary because
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## chess positions are indexed differently with
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## respect to our internal representation
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const indeces = [7, 6, 5, 4, 3, 2, 1, 0]
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return indeces[rank - 1]
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proc algebraicToPosition*(s: string): Location {.inline.} =
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## Converts a square location from algebraic
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## notation to its corresponding row and column
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## in the chess grid (0 indexed)
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if len(s) != 2:
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raise newException(ValueError, "algebraic position must be of length 2")
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var s = s.toLowerAscii()
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if s[0] notin 'a'..'h':
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raise newException(ValueError, &"algebraic position has invalid first character ('{s[0]}')")
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if s[1] notin '1'..'8':
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raise newException(ValueError, &"algebraic position has invalid second character ('{s[1]}')")
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let file = int(uint8(s[0]) - uint8('a'))
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# Convert the rank character to a number
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let rank = rankToColumn(int(uint8(s[1]) - uint8('0')))
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return (rank, file)
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proc getPiece*(self: ChessBoard, square: string): Piece =
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## Gets the piece on the given square
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## in algebraic notation
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let loc = square.algebraicToPosition()
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return self.grid[loc.row, loc.col]
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proc getCapture*(self: ChessBoard, move: Move): Location =
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## Returns the location that would be captured if this
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## move were played on the board, taking en passant and
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## other things into account (the move is assumed to be
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## already valid). An empty location is returned if no
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## piece is captured by the given move
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result = emptyLocation()
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let target = self.grid[move.targetSquare.row, move.targetSquare.col]
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if target.color == None:
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if move.targetSquare != self.position.enPassantSquare.targetSquare:
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return
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else:
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return ((if move.piece.color == White: move.targetSquare.row + 1 else: move.targetSquare.row - 1), move.targetSquare.col)
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if target.color == move.piece.color.opposite():
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return move.targetSquare
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proc isCapture*(self: ChessBoard, move: Move): bool {.inline.} =
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## Returns whether the given move is a capture
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## or not
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return self.getCapture(move) != emptyLocation()
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proc generatePawnMoves(self: ChessBoard, location: Location): seq[Move] =
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## Generates the possible moves for the pawn in the given
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## location
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var
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piece = self.grid[location.row, location.col]
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locations: seq[Location] = @[]
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doAssert piece.kind == Pawn, &"generatePawnMoves called on a {piece.kind}"
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# Pawns can move forward one square
|
|
let forwardOffset = piece.forward()
|
|
let forward = (forwardOffset + location)
|
|
if forward.isValid() and self.grid[forward.row, forward.col].color == None:
|
|
locations.add(forwardOffset)
|
|
# If the pawn is on its first rank, it can push two squares
|
|
if location.row == piece.getStartRow():
|
|
locations.add(piece.doublePush())
|
|
if self.position.enPassantSquare.piece.color == piece.color.opposite:
|
|
if abs(self.position.enPassantSquare.targetSquare.col - location.col) == 1 and abs(self.position.enPassantSquare.targetSquare.row - location.row) == 1:
|
|
# Only viable if the piece is on the diagonal of the target
|
|
locations.add(self.position.enPassantSquare.targetSquare)
|
|
# They can also move on either diagonal one
|
|
# square, but only to capture
|
|
if location.col in 1..6:
|
|
# Top right diagonal
|
|
locations.add(piece.topRightDiagonal())
|
|
if location.row in 1..6:
|
|
# Top left diagonal
|
|
locations.add(piece.topLeftDiagonal())
|
|
|
|
# Pawn is at the right side, can only capture
|
|
# on the left one
|
|
if location.col == 7 and location.row < 7:
|
|
locations.add(piece.topLeftDiagonal())
|
|
# Pawn is at the left side, can only capture
|
|
# on the right one
|
|
if location.col == 0 and location.row < 7:
|
|
locations.add(piece.topRightDiagonal())
|
|
var
|
|
newLocation: Location
|
|
targetPiece: Piece
|
|
for target in locations:
|
|
newLocation = location + target
|
|
if not newLocation.isValid():
|
|
continue
|
|
targetPiece = self.grid[newLocation.row, newLocation.col]
|
|
if targetPiece.color == piece.color:
|
|
# Can't move over a friendly piece
|
|
continue
|
|
if location.col != newLocation.col and not self.isCapture(Move(piece: piece, startSquare: location, targetSquare: newLocation)):
|
|
# Can only move diagonally when capturing
|
|
continue
|
|
if newLocation.row == piece.color.getLastRow():
|
|
# Generate all promotion moves
|
|
for promotionType in [PromoteToKnight, PromoteToBishop, PromoteToRook, PromoteToQueen]:
|
|
result.add(Move(startSquare: location, targetSquare: newLocation, piece: piece, flag: promotionType))
|
|
continue
|
|
# Move is just a pawn push
|
|
result.add(Move(startSquare: location, targetSquare: newLocation, piece: piece))
|
|
|
|
|
|
proc generateSlidingMoves(self: ChessBoard, location: Location): seq[Move] =
|
|
## Generates moves for the sliding piece in the given location
|
|
var
|
|
piece = self.grid[location.row, location.col]
|
|
doAssert piece.kind in [Bishop, Rook, Queen], &"generateSlidingMoves called on a {piece.kind}"
|
|
var directions: seq[Location] = @[]
|
|
# Only check in the right directions for the chosen piece
|
|
if piece.kind in [Bishop, Queen]:
|
|
directions.add(piece.topLeftDiagonal())
|
|
directions.add(piece.topRightDiagonal())
|
|
directions.add(piece.bottomLeftDiagonal())
|
|
directions.add(piece.bottomRightDiagonal())
|
|
if piece.kind in [Queen, Rook]:
|
|
directions.add(piece.topSide())
|
|
directions.add(piece.bottomSide())
|
|
directions.add(piece.rightSide())
|
|
directions.add(piece.leftSide())
|
|
for direction in directions:
|
|
# Slide in this direction as long as it's possible
|
|
var
|
|
square: Location = location
|
|
otherPiece: Piece
|
|
while true:
|
|
square = square + direction
|
|
# End of board reached
|
|
if not square.isValid():
|
|
break
|
|
otherPiece = self.grid[square.row, square.col]
|
|
# A friendly piece is in the way
|
|
if otherPiece.color == piece.color:
|
|
break
|
|
if otherPiece.color == piece.color.opposite:
|
|
# Target square contains an enemy piece: capture
|
|
# it and stop going any further
|
|
result.add(Move(startSquare: location, targetSquare: square, piece: piece))
|
|
break
|
|
# Target square is empty
|
|
result.add(Move(startSquare: location, targetSquare: square, piece: piece))
|
|
|
|
|
|
proc generateKingMoves(self: ChessBoard, location: Location): seq[Move] =
|
|
## Generates moves for the king in the given location
|
|
var
|
|
piece = self.grid[location.row, location.col]
|
|
doAssert piece.kind == King, &"generateKingMoves called on a {piece.kind}"
|
|
var directions: seq[Location] = @[piece.topLeftDiagonal(),
|
|
piece.topRightDiagonal(),
|
|
piece.bottomRightDiagonal(),
|
|
piece.bottomLeftDiagonal(),
|
|
piece.topSide(),
|
|
piece.bottomSide(),
|
|
piece.leftSide(),
|
|
piece.rightSide()]
|
|
for direction in directions:
|
|
# Step in this direction once
|
|
let square: Location = location + direction
|
|
# End of board reached
|
|
if not square.isValid():
|
|
continue
|
|
let otherPiece = self.grid[square.row, square.col]
|
|
# A friendly piece is in the way
|
|
if otherPiece.color == piece.color:
|
|
continue
|
|
if otherPiece.color == piece.color.opposite:
|
|
# Target square contains an enemy piece: capture
|
|
# it
|
|
result.add(Move(startSquare: location, targetSquare: square, piece: piece))
|
|
continue
|
|
# Target square is empty
|
|
result.add(Move(startSquare: location, targetSquare: square, piece: piece))
|
|
|
|
|
|
proc generateKnightMoves(self: ChessBoard, location: Location): seq[Move] =
|
|
## Generates moves for the knight in the given location
|
|
var
|
|
piece = self.grid[location.row, location.col]
|
|
doAssert piece.kind == Knight, &"generateKnightMoves called on a {piece.kind}"
|
|
var directions: seq[Location] = @[piece.bottomLeftKnightMove(),
|
|
piece.bottomRightKnightMove(),
|
|
piece.topLeftKnightMove(),
|
|
piece.topRightKnightMove(),
|
|
piece.bottomLeftKnightMove(long=false),
|
|
piece.bottomRightKnightMove(long=false),
|
|
piece.topLeftKnightMove(long=false),
|
|
piece.topRightKnightMove(long=false)]
|
|
for direction in directions:
|
|
# Jump to this square
|
|
let square: Location = location + direction
|
|
# End of board reached
|
|
if not square.isValid():
|
|
continue
|
|
let otherPiece = self.grid[square.row, square.col]
|
|
# A friendly piece is in the way
|
|
if otherPiece.color == piece.color:
|
|
continue
|
|
if otherPiece.color == piece.color.opposite:
|
|
# Target square contains an enemy piece: capture
|
|
# it
|
|
result.add(Move(startSquare: location, targetSquare: square, piece: piece))
|
|
continue
|
|
# Target square is empty
|
|
result.add(Move(startSquare: location, targetSquare: square, piece: piece))
|
|
|
|
|
|
proc generateMoves(self: ChessBoard, location: Location): seq[Move] =
|
|
## Returns the list of possible legal chess moves for the
|
|
## piece in the given location
|
|
let piece = self.grid[location.row, location.col]
|
|
case piece.kind:
|
|
of Queen, Bishop, Rook:
|
|
return self.generateSlidingMoves(location)
|
|
of Pawn:
|
|
return self.generatePawnMoves(location)
|
|
of King:
|
|
return self.generateKingMoves(location)
|
|
of Knight:
|
|
return self.generateKnightMoves(location)
|
|
else:
|
|
return @[]
|
|
|
|
|
|
proc getAttackers*(self: ChessBoard, square: string): seq[Piece] =
|
|
## Returns all the attackers of the given square
|
|
let loc = square.algebraicToPosition()
|
|
for move in self.position.attacked.black:
|
|
if move.targetSquare == loc:
|
|
result.add(move.piece)
|
|
for move in self.position.attacked.white:
|
|
if move.targetSquare == loc:
|
|
result.add(move.piece)
|
|
|
|
|
|
proc getAttackersFor*(self: ChessBoard, square: string, color: PieceColor): seq[Piece] =
|
|
## Returns all the attackers of the given square
|
|
## for the given color
|
|
let loc = square.algebraicToPosition()
|
|
case color:
|
|
of White:
|
|
for move in self.position.attacked.black:
|
|
if move.targetSquare == loc:
|
|
result.add(move.piece)
|
|
of Black:
|
|
for move in self.position.attacked.white:
|
|
if move.targetSquare == loc:
|
|
result.add(move.piece)
|
|
else:
|
|
discard
|
|
|
|
# We don't use getAttackers because this one only cares about whether
|
|
# the square is attacked or not (and can therefore exit earlier than
|
|
# getAttackers)
|
|
proc isAttacked*(self: ChessBoard, loc: Location): bool =
|
|
## Returns whether the given location is attacked
|
|
## by the opponent. If the location is empty, this
|
|
## function returns true regardless of which color
|
|
## the attackers are
|
|
let piece = self.grid[loc.row, loc.col]
|
|
case piece.color:
|
|
of White:
|
|
for move in self.position.attacked.black:
|
|
if move.targetSquare == loc:
|
|
return true
|
|
of Black:
|
|
for move in self.position.attacked.white:
|
|
if move.targetSquare == loc:
|
|
return true
|
|
of None:
|
|
case self.getActiveColor():
|
|
of White:
|
|
for move in self.position.attacked.black:
|
|
if move.targetSquare == loc:
|
|
return true
|
|
of Black:
|
|
for move in self.position.attacked.white:
|
|
if move.targetSquare == loc:
|
|
return true
|
|
else:
|
|
discard
|
|
|
|
|
|
proc isAttacked*(self: ChessBoard, square: string): bool =
|
|
## Returns whether the given square is attacked
|
|
## by its opponent
|
|
return self.isAttacked(square.algebraicToPosition())
|
|
|
|
|
|
proc updateAttackedSquares(self: ChessBoard) =
|
|
## Updates internal metadata about which squares
|
|
## are attacked. Called internally by doMove
|
|
|
|
# We refresh the attack metadata at every move. This is an
|
|
# O(1) operation, because we're only updating the length
|
|
# field without deallocating the memory, which will promptly
|
|
# be reused by us again. Neat!
|
|
self.position.attacked.white.setLen(0)
|
|
self.position.attacked.black.setLen(0)
|
|
# Go over each piece one by one and see which squares
|
|
# it currently attacks
|
|
|
|
# Pawns
|
|
for loc in self.position.pieces.white.pawns:
|
|
for move in self.generateMoves(loc):
|
|
self.position.attacked.white.add(move)
|
|
# Bishops
|
|
for loc in self.position.pieces.white.bishops:
|
|
for move in self.generateMoves(loc):
|
|
self.position.attacked.white.add(move)
|
|
# Rooks
|
|
for loc in self.position.pieces.white.rooks:
|
|
for move in self.generateMoves(loc):
|
|
self.position.attacked.white.add(move)
|
|
# Queens
|
|
for loc in self.position.pieces.white.queens:
|
|
for move in self.generateMoves(loc):
|
|
self.position.attacked.white.add(move)
|
|
# King
|
|
for move in self.generateMoves(self.position.pieces.white.king):
|
|
self.position.attacked.white.add(move)
|
|
|
|
# Same for black
|
|
for loc in self.position.pieces.black.pawns:
|
|
for move in self.generateMoves(loc):
|
|
self.position.attacked.black.add(move)
|
|
for loc in self.position.pieces.black.bishops:
|
|
for move in self.generateMoves(loc):
|
|
self.position.attacked.black.add(move)
|
|
for loc in self.position.pieces.black.rooks:
|
|
for move in self.generateMoves(loc):
|
|
self.position.attacked.black.add(move)
|
|
for loc in self.position.pieces.black.queens:
|
|
for move in self.generateMoves(loc):
|
|
self.position.attacked.black.add(move)
|
|
for move in self.generateMoves(self.position.pieces.black.king):
|
|
self.position.attacked.black.add(move)
|
|
|
|
|
|
proc removePiece(self: ChessBoard, location: Location) =
|
|
## Removes a piece from the board, updating necessary
|
|
## metadata
|
|
var piece = self.grid[location.row, location.col]
|
|
self.grid[location.row, location.col] = emptyPiece()
|
|
case piece.color:
|
|
of White:
|
|
case piece.kind:
|
|
of Pawn:
|
|
self.position.pieces.white.pawns.delete(self.position.pieces.white.pawns.find(location))
|
|
of Bishop:
|
|
self.position.pieces.white.pawns.delete(self.position.pieces.white.bishops.find(location))
|
|
of Knight:
|
|
self.position.pieces.white.pawns.delete(self.position.pieces.white.knights.find(location))
|
|
of Rook:
|
|
self.position.pieces.white.rooks.delete(self.position.pieces.white.rooks.find(location))
|
|
of Queen:
|
|
self.position.pieces.white.queens.delete(self.position.pieces.white.queens.find(location))
|
|
of King:
|
|
doAssert false, "removePiece: attempted to remove the white king"
|
|
else:
|
|
discard
|
|
of Black:
|
|
case piece.kind:
|
|
of Pawn:
|
|
self.position.pieces.black.pawns.delete(self.position.pieces.white.pawns.find(location))
|
|
of Bishop:
|
|
self.position.pieces.black.bishops.delete(self.position.pieces.black.bishops.find(location))
|
|
of Knight:
|
|
self.position.pieces.black.knights.delete(self.position.pieces.black.knights.find(location))
|
|
of Rook:
|
|
self.position.pieces.black.rooks.delete(self.position.pieces.black.rooks.find(location))
|
|
of Queen:
|
|
self.position.pieces.black.queens.delete(self.position.pieces.black.queens.find(location))
|
|
of King:
|
|
doAssert false, "removePiece: attempted to remove the black king"
|
|
else:
|
|
discard
|
|
else:
|
|
discard
|
|
|
|
|
|
proc handleCapture(self: ChessBoard, move: Move) =
|
|
## Handles capturing (assumes the move is valid)
|
|
let targetPiece = self.grid[move.targetSquare.row, move.targetSquare.col]
|
|
assert self.position.captured == emptyPiece(), "capture: last capture is non-empty"
|
|
self.position.captured = move.piece
|
|
self.removePiece(move.targetSquare)
|
|
|
|
|
|
proc movePiece(self: ChessBoard, move: Move) =
|
|
## Internal helper to move a piece. Does
|
|
## not update attacked squares, just position
|
|
## metadata and the grid itself
|
|
case move.piece.color:
|
|
of White:
|
|
case move.piece.kind:
|
|
of Pawn:
|
|
# The way things are structured, we don't care about the order
|
|
# of this list, so we can add and remove entries as we please
|
|
self.position.pieces.white.pawns.delete(self.position.pieces.white.pawns.find(move.startSquare))
|
|
self.position.pieces.white.pawns.add(move.targetSquare)
|
|
of Bishop:
|
|
self.position.pieces.white.bishops.delete(self.position.pieces.white.bishops.find(move.startSquare))
|
|
self.position.pieces.white.bishops.add(move.targetSquare)
|
|
of Knight:
|
|
self.position.pieces.white.knights.delete(self.position.pieces.white.knights.find(move.startSquare))
|
|
self.position.pieces.white.knights.add(move.targetSquare)
|
|
of Rook:
|
|
self.position.pieces.white.rooks.delete(self.position.pieces.white.rooks.find(move.startSquare))
|
|
self.position.pieces.white.rooks.add(move.targetSquare)
|
|
of Queen:
|
|
try:
|
|
self.position.pieces.white.queens.delete(self.position.pieces.white.queens.find(move.startSquare))
|
|
except:
|
|
echo self.position.pieces.white.queens
|
|
echo move.startSquare
|
|
raise getCurrentException()
|
|
self.position.pieces.white.queens.add(move.targetSquare)
|
|
of King:
|
|
self.position.pieces.white.king = move.targetSquare
|
|
else:
|
|
discard
|
|
of Black:
|
|
case move.piece.kind:
|
|
of Pawn:
|
|
self.position.pieces.black.pawns.delete(self.position.pieces.black.pawns.find(move.startSquare))
|
|
self.position.pieces.black.pawns.add(move.targetSquare)
|
|
of Bishop:
|
|
self.position.pieces.black.bishops.delete(self.position.pieces.black.bishops.find(move.startSquare))
|
|
self.position.pieces.black.bishops.add(move.targetSquare)
|
|
of Knight:
|
|
self.position.pieces.black.knights.delete(self.position.pieces.black.knights.find(move.startSquare))
|
|
self.position.pieces.black.knights.add(move.targetSquare)
|
|
of Rook:
|
|
self.position.pieces.black.rooks.delete(self.position.pieces.black.rooks.find(move.startSquare))
|
|
self.position.pieces.black.rooks.add(move.targetSquare)
|
|
of Queen:
|
|
self.position.pieces.black.queens.delete(self.position.pieces.black.queens.find(move.startSquare))
|
|
self.position.pieces.black.queens.add(move.targetSquare)
|
|
of King:
|
|
self.position.pieces.black.king = move.targetSquare
|
|
else:
|
|
discard
|
|
else:
|
|
discard
|
|
# Empty out the starting square
|
|
self.grid[move.startSquare.row, move.startSquare.col] = emptyPiece()
|
|
# Actually move the piece
|
|
self.grid[move.targetSquare.row, move.targetSquare.col] = move.piece
|
|
|
|
|
|
proc updatePositions(self: ChessBoard, move: Move) =
|
|
## Internal helper to update the position of
|
|
## the pieces on the board after a move
|
|
let capture = self.getCapture(move)
|
|
if capture != emptyLocation():
|
|
# Move has captured a piece: remove it as well. We call a helper instead
|
|
# of doing it ourselves because there's a bunch of metadata that needs
|
|
# to be updated to do this properly and I thought it'd fit into its neat
|
|
# little function
|
|
self.handleCapture(move)
|
|
# Update the positional metadata of the moving piece
|
|
self.movePiece(move)
|
|
|
|
|
|
proc inCheck*(self: ChessBoard, color: PieceColor = None): bool =
|
|
## Returns whether the given color's
|
|
## king is in check. If the color is
|
|
## set to None, checks are checked
|
|
## for the active color's king
|
|
case color:
|
|
of White:
|
|
return self.isAttacked(self.position.pieces.white.king)
|
|
of Black:
|
|
return self.isAttacked(self.position.pieces.black.king)
|
|
of None:
|
|
case self.getActiveColor():
|
|
of White:
|
|
return self.isAttacked(self.position.pieces.white.king)
|
|
of Black:
|
|
return self.isAttacked(self.position.pieces.black.king)
|
|
else:
|
|
# Unreachable
|
|
discard
|
|
|
|
|
|
proc doMove(self: ChessBoard, move: Move) =
|
|
## Internal function called by makeMove after
|
|
## performing legality checks on the given move. Can
|
|
## be used in performance-critical paths where
|
|
## a move is already known to be legal
|
|
|
|
# Final checks
|
|
|
|
# Needed to detect draw by the 50 move rule
|
|
if move.piece.kind != Pawn and not self.isCapture(move):
|
|
inc(self.position.halfMoveClock)
|
|
else:
|
|
self.position.halfMoveClock = 0
|
|
if (self.position.halfMoveClock and 1) == 0: # Equivalent to (x mod 2) == 0, just much faster
|
|
inc(self.position.fullMoveCount)
|
|
# En passant is possible only immediately after the
|
|
# pawn has moved
|
|
if self.position.enPassantSquare != emptyMove() and self.position.enPassantSquare.piece.color == self.getActiveColor().opposite():
|
|
self.position.enPassantSquare = emptyMove()
|
|
# TODO: Castling
|
|
|
|
self.position.move = move
|
|
|
|
# Update position and attack metadata
|
|
self.updatePositions(move)
|
|
self.updateAttackedSquares()
|
|
|
|
# Record final position for future reference
|
|
self.positions.add(self.position)
|
|
# Create new position with
|
|
var newPos = Position(plyFromRoot: self.position.plyFromRoot + 1,
|
|
captured: emptyPiece(),
|
|
turn: self.position.turn.opposite(),
|
|
# Inherit values from current position
|
|
# (they are already up to date by this point)
|
|
castling: self.position.castling,
|
|
enPassantSquare: self.position.enPassantSquare,
|
|
attacked: (@[], @[])
|
|
)
|
|
|
|
self.position = newPos
|
|
inc(self.positionIndex)
|
|
|
|
|
|
proc spawnPiece(self: ChessBoard, location: Location, piece: Piece) =
|
|
## Internal helper to "spawn" a given piece at the given
|
|
## location. Note that this will overwrite whatever piece
|
|
## was previously located there: use with caution. Does
|
|
## not automatically update the attacked square metadata
|
|
## or other positional information
|
|
doAssert piece.kind != King, "spawnPiece: cannot spawn a king"
|
|
case piece.color:
|
|
of White:
|
|
case piece.kind:
|
|
of Pawn:
|
|
self.position.pieces.white.pawns.add(location)
|
|
of Knight:
|
|
self.position.pieces.white.knights.add(location)
|
|
of Bishop:
|
|
self.position.pieces.white.bishops.add(location)
|
|
of Rook:
|
|
self.position.pieces.white.rooks.add(location)
|
|
of Queen:
|
|
self.position.pieces.white.queens.add(location)
|
|
else:
|
|
discard
|
|
of Black:
|
|
case piece.kind:
|
|
of Pawn:
|
|
self.position.pieces.black.pawns.add(location)
|
|
of Knight:
|
|
self.position.pieces.black.knights.add(location)
|
|
of Bishop:
|
|
self.position.pieces.black.bishops.add(location)
|
|
of Rook:
|
|
self.position.pieces.black.rooks.add(location)
|
|
of Queen:
|
|
self.position.pieces.black.queens.add(location)
|
|
else:
|
|
discard
|
|
else:
|
|
# Unreachable
|
|
discard
|
|
self.grid[location.row, location.col] = piece
|
|
|
|
|
|
proc undoLastMove*(self: ChessBoard): Move {.discardable.} =
|
|
## Undoes the last move, restoring any captured pieces,
|
|
## as well castling and en passant status. If there are
|
|
## no moves to undo, this is a no-op. Returns the move
|
|
## that was performed (which may be an empty move)
|
|
result = emptyMove()
|
|
if self.positions.len() == 0:
|
|
return
|
|
let positionIndex = max(0, self.positionIndex - 1)
|
|
if positionIndex in 0..self.positions.high():
|
|
self.positionIndex = positionIndex
|
|
self.position = self.positions[positionIndex]
|
|
let
|
|
currentMove = self.position.move
|
|
oppositeMove = Move(piece: currentMove.piece, targetSquare: currentMove.startSquare, startSquare: currentMove.targetSquare)
|
|
self.spawnPiece(currentMove.startSquare, currentMove.piece)
|
|
if self.position.captured != emptyPiece():
|
|
self.spawnPiece(self.position.move.targetSquare, self.position.captured)
|
|
self.updateAttackedSquares()
|
|
self.updatePositions(oppositeMove)
|
|
return self.position.move
|
|
|
|
|
|
|
|
proc checkMove(self: ChessBoard, move: Move): bool =
|
|
## Internal function called by makeMove to check a move for legality
|
|
# Start square doesn't contain a piece (and it isn't the en passant square)
|
|
# or it is of the wrong color for which turn it is to move
|
|
if move.piece.kind == Empty or move.piece.color != self.getActiveColor():
|
|
return false
|
|
var destination = self.grid[move.targetSquare.row, move.targetSquare.col]
|
|
# Destination square is occupied by a piece of the same color as the piece
|
|
# being moved: illegal!
|
|
if destination.kind != Empty and destination.color == self.getActiveColor():
|
|
return false
|
|
if move notin self.generateMoves(move.startSquare):
|
|
# Piece cannot arrive to destination (blocked,
|
|
# pinned, or otherwise invalid move)
|
|
return false
|
|
self.doMove(move)
|
|
defer: self.undoLastMove()
|
|
# Move would reveal an attack
|
|
# on our king: not allowed
|
|
if self.inCheck(move.piece.color):
|
|
return false
|
|
# All checks have passed: move is legal
|
|
result = true
|
|
|
|
|
|
proc makeMove*(self: ChessBoard, move: Move): Move {.discardable.} =
|
|
## Like the other makeMove(), but with a Move object
|
|
result = move
|
|
if not self.checkMove(move):
|
|
return emptyMove()
|
|
self.doMove(result)
|
|
|
|
|
|
|
|
proc makeMove*(self: ChessBoard, startSquare, targetSquare: string): Move {.discardable.} =
|
|
## Makes a move on the board from the chosen start square to
|
|
## the chosen target square, ensuring it is legal (turns are
|
|
## taken into account!). This function returns a Move object: if the move
|
|
## is legal and has been performed, the fields will be populated properly.
|
|
## For efficiency purposes, no exceptions are raised if the move is
|
|
## illegal, but the move's piece kind will be Empty (its color will be None
|
|
## too) and the locations will both be set to the tuple (-1, -1)
|
|
var
|
|
startLocation = startSquare.algebraicToPosition()
|
|
targetLocation = targetSquare.algebraicToPosition()
|
|
result = Move(startSquare: startLocation, targetSquare: targetLocation, piece: self.grid[startLocation.row, startLocation.col])
|
|
return self.makeMove(result)
|
|
|
|
|
|
proc makeMove*(self: ChessBoard, startSquare, targetSquare: Location): Move {.discardable.} =
|
|
## Like the other makeMove(), but with two locations
|
|
result = Move(startSquare: startSquare, targetSquare: targetSquare, piece: self.grid[startSquare.row, startSquare.col])
|
|
return self.makeMove(result)
|
|
|
|
|
|
|
|
|
|
proc `$`*(self: ChessBoard): string =
|
|
result &= "- - - - - - - -"
|
|
for i, row in self.grid:
|
|
result &= "\n"
|
|
for piece in row:
|
|
if piece.kind == Empty:
|
|
result &= "x "
|
|
continue
|
|
if piece.color == White:
|
|
result &= &"{char(piece.kind).toUpperAscii()} "
|
|
else:
|
|
result &= &"{char(piece.kind)} "
|
|
result &= &"{rankToColumn(i + 1) + 1}"
|
|
result &= "\n- - - - - - - -"
|
|
result &= "\na b c d e f g h"
|
|
|
|
|
|
proc pretty*(self: ChessBoard): string =
|
|
## Returns a colorized version of the
|
|
## board for easier visualization
|
|
result &= "- - - - - - - -"
|
|
|
|
for i, row in self.grid:
|
|
result &= "\n"
|
|
for j, piece in row:
|
|
if piece.kind == Empty:
|
|
result &= "\x1b[36;1mx"
|
|
# Avoids the color overflowing
|
|
# onto the numbers
|
|
if j < 7:
|
|
result &= " \x1b[0m"
|
|
else:
|
|
result &= "\x1b[0m "
|
|
continue
|
|
if piece.color == White:
|
|
result &= &"\x1b[37;1m{char(piece.kind).toUpperAscii()}\x1b[0m "
|
|
else:
|
|
result &= &"\x1b[30;1m{char(piece.kind)} "
|
|
result &= &"\x1b[33;1m{rankToColumn(i + 1) + 1}\x1b[0m"
|
|
|
|
result &= "\n- - - - - - - -"
|
|
result &= "\n\x1b[31;1ma b c d e f g h"
|
|
result &= "\x1b[0m"
|
|
|
|
|
|
when isMainModule:
|
|
proc testPiece(piece: Piece, kind: PieceKind, color: PieceColor) =
|
|
doAssert piece.kind == kind and piece.color == color, &"expected piece of kind {kind} and color {color}, got {piece.kind} / {piece.color} instead"
|
|
|
|
proc testPieceCount(board: ChessBoard, kind: PieceKind, color: PieceColor, count: int) =
|
|
let pieces = board.countPieces(kind, color)
|
|
doAssert pieces == count, &"expected {count} pieces of kind {kind} and color {color}, got {pieces} instead"
|
|
|
|
echo "Running tests"
|
|
var b = newDefaultChessboard()
|
|
# Ensure correct number of pieces
|
|
testPieceCount(b, Pawn, White, 8)
|
|
testPieceCount(b, Pawn, Black, 8)
|
|
testPieceCount(b, Knight, White, 2)
|
|
testPieceCount(b, Knight, Black, 2)
|
|
testPieceCount(b, Bishop, White, 2)
|
|
testPieceCount(b, Bishop, Black, 2)
|
|
testPieceCount(b, Rook, White, 2)
|
|
testPieceCount(b, Rook, Black, 2)
|
|
testPieceCount(b, Queen, White, 1)
|
|
testPieceCount(b, Queen, Black, 1)
|
|
testPieceCount(b, King, White, 1)
|
|
testPieceCount(b, King, Black, 1)
|
|
|
|
|
|
# Ensure pieces are in the correct location
|
|
|
|
# Pawns
|
|
for loc in ["a2", "b2", "c2", "d2", "e2", "f2", "g2", "h2"]:
|
|
testPiece(b.getPiece(loc), Pawn, White)
|
|
for loc in ["a7", "b7", "c7", "d7", "e7", "f7", "g7", "h7"]:
|
|
testPiece(b.getPiece(loc), Pawn, Black)
|
|
# Rooks
|
|
testPiece(b.getPiece("a1"), Rook, White)
|
|
testPiece(b.getPiece("h1"), Rook, White)
|
|
testPiece(b.getPiece("a8"), Rook, Black)
|
|
testPiece(b.getPiece("h8"), Rook, Black)
|
|
# Knights
|
|
testPiece(b.getPiece("b1"), Knight, White)
|
|
testPiece(b.getPiece("g1"), Knight, White)
|
|
testPiece(b.getPiece("b8"), Knight, Black)
|
|
testPiece(b.getPiece("g8"), Knight, Black)
|
|
# Bishops
|
|
testPiece(b.getPiece("c1"), Bishop, White)
|
|
testPiece(b.getPiece("f1"), Bishop, White)
|
|
testPiece(b.getPiece("c8"), Bishop, Black)
|
|
testPiece(b.getPiece("f8"), Bishop, Black)
|
|
# Kings
|
|
testPiece(b.getPiece("e1"), King, White)
|
|
testPiece(b.getPiece("e8"), King, Black)
|
|
# Queens
|
|
testPiece(b.getPiece("d1"), Queen, White)
|
|
testPiece(b.getPiece("d8"), Queen, Black)
|
|
echo "All tests were successful" |