# Copyright 2023 Mattia Giambirtone & All Contributors # # Licensed under the Apache License, Version 2.0 (the "License"); # you may not use this file except in compliance with the License. # You may obtain a copy of the License at # # http://www.apache.org/licenses/LICENSE-2.0 # # Unless required by applicable law or agreed to in writing, software # distributed under the License is distributed on an "AS IS" BASIS, # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. # See the License for the specific language governing permissions and # limitations under the License. import ../util/matrix export matrix import std/strutils import std/strformat import std/sequtils type PieceColor* = enum ## A piece color enumeration None = 0'i8, White, Black PieceKind* = enum ## A chess piece enumeration Empty = 0'i8, # No piece Bishop = 'b', King = 'k' Knight = 'n', Pawn = 'p', Queen = 'q', Rook = 'r', Piece* = object ## A chess piece color*: PieceColor kind*: PieceKind MoveFlag* = enum ## An enumeration of move flags Default = 0'i8, # No flag EnPassant, # Move is a capture with en passant Capture, # Move is a capture DoublePush, # Move is a double pawn push # Castling metadata CastleLong, CastleShort, # Pawn promotion metadata PromoteToQueen, PromoteToRook, PromoteToBishop, PromoteToKnight # Useful type aliases Location* = tuple[row, col: int8] Attacked = seq[tuple[source, target, direction: Location]] Pieces = tuple[king: Location, queens: seq[Location], rooks: seq[Location], bishops: seq[Location], knights: seq[Location], pawns: seq[Location]] CountData = tuple[nodes: uint64, captures: uint64, castles: uint64, checks: uint64, promotions: uint64, enPassant: uint64, checkmates: uint64] Move* = object ## A chess move startSquare*: Location targetSquare*: Location flag*: MoveFlag Position* = ref object ## A chess position move: Move # Did the rooks on either side/the king move? castlingAvailable: tuple[white, black: tuple[queen, king: bool]] # Number of half-moves that were performed # to reach this position starting from the # root of the tree plyFromRoot: int16 # Number of half moves since # last piece capture or pawn movement. # Used for the 50-move rule halfMoveClock: int8 # Full move counter. Increments # every 2 ply fullMoveCount: int16 # En passant target square (see https://en.wikipedia.org/wiki/En_passant) enPassantSquare*: Move # Locations of all pieces pieces: tuple[white: Pieces, black: Pieces] # Potential attacking moves for black and white attacked: tuple[white: Attacked, black: Attacked] pinned: tuple[white: Attacked, black: Attacked] # The original piece captured to reach this position (may be empty) captured: Piece # The piece that moved to reach this position (needed to undo moves) moved: Piece # Active color turn: PieceColor CacheEntry[T] = ref object valid: bool data: T Cache = object canCastle: tuple[white, black: CacheEntry[tuple[queen, king: bool]]] inCheck: tuple[white, black: CacheEntry[bool]] ChessBoard* = ref object ## A chess board object grid: Matrix[Piece] position: Position # List of reached positions positions: seq[Position] # Cached results of expensive # functions in the current position cache: Cache # Initialized only once, copied every time var empty: seq[Piece] = @[] for _ in countup(0, 63): empty.add(Piece(kind: Empty, color: None)) func emptyPiece*: Piece {.inline.} = Piece(kind: Empty, color: None) func emptyLocation*: Location {.inline.} = (-1 , -1) func opposite*(c: PieceColor): PieceColor {.inline.} = (if c == White: Black else: White) proc algebraicToLocation*(s: string): Location {.inline.} proc makeMove*(self: ChessBoard, move: Move): Move {.discardable.} func emptyMove*: Move {.inline.} = Move(startSquare: emptyLocation(), targetSquare: emptyLocation()) func `+`*(a, b: Location): Location = (a.row + b.row, a.col + b.col) func `-`*(a: Location): Location = (-a.row, -a.col) func `-`*(a, b: Location): Location = (a.row - b.row, a.col - b.col) func isValid*(a: Location): bool {.inline.} = a.row in 0..7 and a.col in 0..7 proc generateMoves(self: ChessBoard, location: Location): seq[Move] proc getAttackers*(self: ChessBoard, loc: Location, color: PieceColor): seq[Location] proc getAttackFor*(self: ChessBoard, source, target: Location): tuple[source, target, direction: Location] proc isAttacked*(self: ChessBoard, loc: Location, color: PieceColor = None): bool proc undoMove*(self: ChessBoard, move: Move) proc isLegal(self: ChessBoard, move: Move): bool {.inline.} proc doMove(self: ChessBoard, move: Move) proc pretty*(self: ChessBoard): string proc spawnPiece(self: ChessBoard, location: Location, piece: Piece) proc updateAttackedSquares(self: ChessBoard) proc getPinnedDirections(self: ChessBoard, loc: Location): seq[Location] proc getAttacks*(self: ChessBoard, loc: Location): Attacked proc getSlidingAttacks(self: ChessBoard, loc: Location): tuple[attacks: Attacked, pins: Attacked] func invalidateCache(self: ChessBoard) {.inline.} proc extend[T](self: var seq[T], other: openarray[T]) {.inline.} = for x in other: self.add(x) # Due to our board layout, directions of movement are reversed for white/black so # we need these helpers to avoid going mad with integer tuples and minus signs # everywhere func topLeftDiagonal(color: PieceColor): Location {.inline.} = (if color == White: (-1, -1) else: (1, 1)) func topRightDiagonal(color: PieceColor): Location {.inline.} = (if color == White: (-1, 1) else: (1, -1)) func bottomLeftDiagonal(color: PieceColor): Location {.inline.} = (if color == White: (1, -1) else: (-1, 1)) func bottomRightDiagonal(color: PieceColor): Location {.inline.} = (if color == White: (1, 1) else: (-1, -1)) func leftSide(color: PieceColor): Location {.inline.} = (if color == White: (0, -1) else: (0, 1)) func rightSide(color: PieceColor): Location {.inline.} = (if color == White: (0, 1) else: (0, -1)) func topSide(color: PieceColor): Location {.inline.} = (if color == White: (-1, 0) else: (1, 0)) func bottomSide(color: PieceColor): Location {.inline.} = (if color == White: (1, 0) else: (-1, 0)) func forward(color: PieceColor): Location {.inline.} = (if color == White: (-1, 0) else: (1, 0)) func doublePush(color: PieceColor): Location {.inline.} = (if color == White: (-2, 0) else: (2, 0)) func longCastleKing: Location {.inline.} = (0, -2) func shortCastleKing: Location {.inline.} = (0, 2) func longCastleRook: Location {.inline.} = (0, 3) func shortCastleRook: Location {.inline.} = (0, -2) func kingSideRook(color: PieceColor): Location {.inline.} = (if color == White: (7, 7) else: (0, 7)) func queenSideRook(color: PieceColor): Location {.inline.} = (if color == White: (7, 0) else: (0, 0)) func bottomLeftKnightMove(color: PieceColor, long: bool = true): Location {.inline.} = if color == White: if long: return (2, -1) else: return (1, -2) elif color == Black: if long: return (-2, 1) else: return (1, -2) func bottomRightKnightMove(color: PieceColor, long: bool = true): Location {.inline.} = if color == White: if long: return (2, 1) else: return (1, 2) elif color == Black: if long: return (-2, -1) else: return (-1, -2) func topLeftKnightMove(color: PieceColor, long: bool = true): Location {.inline.} = if color == White: if long: return (-2, -1) else: return (-1, -2) elif color == Black: if long: return (2, 1) else: return (1, 2) func topRightKnightMove(color: PieceColor, long: bool = true): Location {.inline.} = if color == White: if long: return (-2, 1) else: return (-1, 2) elif color == Black: if long: return (2, -1) else: return (-1, 2) func getActiveColor*(self: ChessBoard): PieceColor {.inline.} = ## Returns the currently active color ## (turn of who has to move) return self.position.turn func getEnPassantTarget*(self: ChessBoard): Location {.inline.} = ## Returns the current en passant target square return self.position.enPassantSquare.targetSquare func getMoveCount*(self: ChessBoard): int {.inline.} = ## Returns the number of full moves that ## have been played return self.position.fullMoveCount func getHalfMoveCount*(self: ChessBoard): int {.inline.} = ## Returns the current number of half-moves ## since the last irreversible move return self.position.halfMoveClock func getStartRow(piece: Piece): int {.inline.} = ## Retrieves the starting row of ## the given piece inside our 8x8 ## grid case piece.color: of None: return -1 of White: case piece.kind: of Pawn: return 6 else: return 7 of Black: case piece.kind: of Pawn: return 1 else: return 0 func getLastRow(color: PieceColor): int {.inline.} = ## Retrieves the location of the last ## row relative to the given color case color: of White: return 0 of Black: return 7 else: return -1 proc newChessboard: ChessBoard = ## Returns a new, empty chessboard new(result) # Turns our flat sequence into an 8x8 grid result.grid = newMatrixFromSeq[Piece](empty, (8, 8)) result.cache = Cache(canCastle: (white: CacheEntry[tuple[queen, king: bool]](), black: CacheEntry[tuple[queen, king: bool]]()), inCheck: (white: CacheEntry[bool](), black: CacheEntry[bool]())) result.position = Position(attacked: (@[], @[]), enPassantSquare: emptyMove(), move: emptyMove(), turn: White, fullMoveCount: 1, pieces: (white: (king: emptyLocation(), queens: @[], rooks: @[], bishops: @[], knights: @[], pawns: @[]), black: (king: emptyLocation(), queens: @[], rooks: @[], bishops: @[], knights: @[], pawns: @[]))) proc newChessboardFromFEN*(state: string): ChessBoard = ## Initializes a chessboard with the ## state encoded by the given FEN string result = newChessboard() var # Current location in the grid row: int8 = 0 column: int8 = 0 # Current section in the FEN string section = 0 # Current index into the FEN string index = 0 # Temporary variable to store the piece piece: Piece # See https://en.wikipedia.org/wiki/Forsyth%E2%80%93Edwards_Notation while index <= state.high(): var c = state[index] if c == ' ': # Next section inc(section) inc(index) continue case section: of 0: # Piece placement data case c.toLowerAscii(): # Piece of 'r', 'n', 'b', 'q', 'k', 'p': # We know for a fact these values are in our # enumeration, so all is good {.push.} {.warning[HoleEnumConv]:off.} piece = Piece(kind: PieceKind(c.toLowerAscii()), color: if c.isUpperAscii(): White else: Black) {.pop.} case piece.color: of Black: case piece.kind: of Pawn: result.position.pieces.black.pawns.add((row, column)) of Bishop: result.position.pieces.black.bishops.add((row, column)) of Knight: result.position.pieces.black.knights.add((row, column)) of Rook: result.position.pieces.black.rooks.add((row, column)) of Queen: result.position.pieces.black.queens.add((row, column)) of King: result.position.pieces.black.king = (row, column) else: discard of White: case piece.kind: of Pawn: result.position.pieces.white.pawns.add((row, column)) of Bishop: result.position.pieces.white.bishops.add((row, column)) of Knight: result.position.pieces.white.knights.add((row, column)) of Rook: result.position.pieces.white.rooks.add((row, column)) of Queen: result.position.pieces.white.queens.add((row, column)) of King: result.position.pieces.white.king = (row, column) else: discard else: discard result.grid[row, column] = piece inc(column) of '/': # Next row inc(row) column = 0 of '0'..'9': # Skip x columns let x = int(uint8(c) - uint8('0')) if x > 8: raise newException(ValueError, "invalid skip value (> 8) in FEN string") column += int8(x) else: raise newException(ValueError, "invalid piece identifier in FEN string") of 1: # Active color case c: of 'w': result.position.turn = White of 'b': result.position.turn = Black else: raise newException(ValueError, "invalid active color identifier in FEN string") of 2: # Castling availability case c: of '-': # Neither side can castle anywhere: do nothing, # as the castling metadata is set to this state # by default discard of 'K': result.position.castlingAvailable.white.king = true of 'Q': result.position.castlingAvailable.white.queen = true of 'k': result.position.castlingAvailable.black.king = true of 'q': result.position.castlingAvailable.black.queen = true else: raise newException(ValueError, "invalid castling availability in FEN string") of 3: # En passant target square case c: of '-': # Field is already uninitialized to the correct state discard else: result.position.enPassantSquare.targetSquare = state[index..index+1].algebraicToLocation() # Square metadata is 2 bytes long inc(index) of 4: # Halfmove clock var s = "" while not state[index].isSpaceAscii(): s.add(state[index]) inc(index) # Backtrack so the space is seen by the # next iteration of the loop dec(index) result.position.halfMoveClock = parseInt(s).int8 of 5: # Fullmove number var s = "" while index <= state.high(): s.add(state[index]) inc(index) result.position.fullMoveCount = parseInt(s).int8 else: raise newException(ValueError, "too many fields in FEN string") inc(index) result.updateAttackedSquares() proc newDefaultChessboard*: ChessBoard {.inline.} = ## Initializes a chessboard with the ## starting position return newChessboardFromFEN("rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1") proc countPieces*(self: ChessBoard, kind: PieceKind, color: PieceColor): int = ## Returns the number of pieces with ## the given color and type in the given ## position case color: of White: case kind: of Pawn: return self.position.pieces.white.pawns.len() of Bishop: return self.position.pieces.white.bishops.len() of Knight: return self.position.pieces.white.knights.len() of Rook: return self.position.pieces.white.rooks.len() of Queen: return self.position.pieces.white.queens.len() of King: # There shall be only one, forever return 1 else: raise newException(ValueError, "invalid piece type") of Black: case kind: of Pawn: return self.position.pieces.black.pawns.len() of Bishop: return self.position.pieces.black.bishops.len() of Knight: return self.position.pieces.black.knights.len() of Rook: return self.position.pieces.black.rooks.len() of Queen: return self.position.pieces.black.queens.len() of King: # In perpetuity return 1 else: raise newException(ValueError, "invalid piece type") of None: raise newException(ValueError, "invalid piece color") func countPieces*(self: ChessBoard, piece: Piece): int {.inline.} = ## Returns the number of pieces on the board that ## are of the same type and color as the given piece return self.countPieces(piece.kind, piece.color) func rankToColumn(rank: int): int8 {.inline.} = ## Converts a chess rank (1-indexed) ## into a 0-indexed column value for our ## board. This converter is necessary because ## chess positions are indexed differently with ## respect to our internal representation const indeces: array[8, int8] = [7, 6, 5, 4, 3, 2, 1, 0] return indeces[rank - 1] func rowToRank(row: int): int {.inline.} = ## Converts a row into our grid into ## a chess rank const indeces = [8, 7, 6, 5, 4, 3, 2, 1] return indeces[row] proc algebraicToLocation*(s: string): Location = ## Converts a square location from algebraic ## notation to its corresponding row and column ## in the chess grid (0 indexed) if len(s) != 2: raise newException(ValueError, "algebraic position must be of length 2") var s = s.toLowerAscii() if s[0] notin 'a'..'h': raise newException(ValueError, &"algebraic position has invalid first character ('{s[0]}')") if s[1] notin '1'..'8': raise newException(ValueError, &"algebraic position has invalid second character ('{s[1]}')") let rank = int8(uint8(s[0]) - uint8('a')) # Convert the file character to a number let file = rankToColumn(int8(uint8(s[1]) - uint8('0'))) return (file, rank) func locationToAlgebraic*(loc: Location): string {.inline.} = ## Converts a location from our internal row, column ## notation to a square in algebraic notation return &"{char(uint8(loc.col) + uint8('a'))}{rowToRank(loc.row)}" func getPiece*(self: ChessBoard, loc: Location): Piece {.inline.} = ## Gets the piece at the given location return self.grid[loc.row, loc.col] func getPiece*(self: ChessBoard, square: string): Piece {.inline.} = ## Gets the piece on the given square ## in algebraic notation return self.getPiece(square.algebraicToLocation()) func isPromotion*(move: Move): bool {.inline.} = ## Returns whrther the given move is a ## pawn promotion or not return move.flag in [PromoteToBishop, PromoteToKnight, PromoteToRook, PromoteToQueen] 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 var color = color if color == None: color = self.getActiveColor() case color: of White: if self.cache.inCheck.white.valid: return self.cache.inCheck.white.data result = self.isAttacked(self.position.pieces.white.king, Black) of Black: if self.cache.inCheck.black.valid: return self.cache.inCheck.black.data result = self.isAttacked(self.position.pieces.black.king, White) else: # Unreachable discard case color: of White: self.cache.inCheck.white.valid = true self.cache.inCheck.white.data = result of Black: self.cache.inCheck.black.valid = true self.cache.inCheck.black.data = result else: # Unreachable discard proc canCastle*(self: ChessBoard, color: PieceColor = None): tuple[queen, king: bool] {.inline.} = ## Returns the sides on which castling is allowed ## for the given color. If the color is None, the ## currently active color is used var color = color if color == None: color = self.getActiveColor() # If the rooks or king have been moved, castling # rights have been lost case color: of White: if self.cache.canCastle.white.valid: return self.cache.canCastle.white.data result.king = self.position.castlingAvailable.white.king result.queen = self.position.castlingAvailable.white.queen of Black: if self.cache.canCastle.black.valid: return self.cache.canCastle.black.data result.king = self.position.castlingAvailable.black.king result.queen = self.position.castlingAvailable.black.queen of None: # Unreachable discard if result.king or result.queen: var loc: Location queenSide: Location kingSide: Location if self.inCheck(color): # King can not castle out of check return (false, false) # If the path between the king and rook on a given side is blocked or any of the # squares where the king would travel to are attacked by the opponent, # then castling is (temporarily) prohibited on that side case color: of White: loc = self.position.pieces.white.king queenSide = color.leftSide() kingSide = color.rightSide() of Black: loc = self.position.pieces.black.king queenSide = color.rightSide() kingSide = color.leftSide() of None: # Unreachable discard if result.king: # Short castle var location = loc otherPiece: Piece while true: location = location + kingSide if not location.isValid(): break otherPiece = self.grid[location.row, location.col] if otherPiece.color == None: continue if otherPiece.color == color.opposite() or otherPiece.kind != Rook or self.isAttacked(location, color.opposite()): result.king = false break if location == color.kingSideRook(): result.king = self.grid[location.row, location.col].kind == Rook break if result.queen: # Long castle var location = loc otherPiece: Piece while true: location = location + queenSide if not location.isValid(): break otherPiece = self.grid[location.row, location.col] if otherPiece.color == None: continue if otherPiece.color == color.opposite() or otherPiece.kind != Rook or self.isAttacked(location, color.opposite()): result.queen = false break if location == color.queenSideRook(): result.queen = self.grid[location.row, location.col].kind == Rook break case color: of White: self.cache.canCastle.white.data = result self.cache.canCastle.white.valid = true of Black: self.cache.canCastle.black.data = result self.cache.canCastle.white.valid = true else: discard proc getCheckResolutions(self: ChessBoard, color: PieceColor): seq[Location] = ## Returns the squares that need to be covered to ## resolve the current check (includes capturing ## the checking piece). In case of double check, an ## empty list is returned (as the king must move) var king: Location case color: of White: king = self.position.pieces.white.king of Black: king = self.position.pieces.black.king else: return @[] let attackers: seq[Location] = self.getAttackers(king, color.opposite()) if attackers.len() > 1: # Double checks require to move the king return @[] let attacker = attackers[0] attackerPiece = self.grid[attacker.row, attacker.col] attack = self.getAttackFor(attacker, king) # Capturing the piece resolves the check result.add(attacker) # Blocking the attack is also a viable strategy # (unless the check is from a knight or a pawn, # in which case either the king has to move or # that piece has to be captured) if attackerPiece.kind notin [Knight, Pawn]: var location = attacker while location != king: location = location + attack.direction if not location.isValid(): break result.add(location) proc generatePawnMoves(self: ChessBoard, location: Location): seq[Move] = ## Generates the possible moves for the pawn in the given ## location var piece = self.grid[location.row, location.col] locations: seq[Location] = @[] flags: seq[MoveFlag] = @[] doAssert piece.kind == Pawn, &"generatePawnMoves called on a {piece.kind}" # Pawns can move forward one square let forward = (piece.color.forward() + location) # Only if the square is empty though if forward.isValid() and self.grid[forward.row, forward.col].color == None: locations.add(forward) flags.add(Default) # If the pawn is on its first rank, it can push two squares if location.row == piece.getStartRow(): let double = location + piece.color.doublePush() # Check that both squares are empty if double.isValid() and self.grid[forward.row, forward.col].color == None and self.grid[double.row, double.col].color == None: locations.add(double) flags.add(DoublePush) # They can also move on either diagonal one # square, but only to capture or for en passant for diagonal in [location + piece.color.topRightDiagonal(), location + piece.color.topLeftDiagonal()]: if diagonal.isValid(): if diagonal == self.position.enPassantSquare.targetSquare: locations.add(diagonal) flags.add(EnPassant) elif self.grid[diagonal.row, diagonal.col].color == piece.color.opposite() and self.grid[diagonal.row, diagonal.col].kind != King: locations.add(diagonal) flags.add(Capture) var newLocation: Location newFlags: seq[MoveFlag] newLocations: seq[Location] # Check for pins let pins = self.getPinnedDirections(location) for pin in pins: newLocation = location + pin let loc = locations.find(newLocation) if loc != -1: # Pin direction is legal for this piece newLocations.add(newLocation) newFlags.add(flags[loc]) if pins.len() > 0: locations = newLocations flags = newFlags let checked = self.inCheck() let resolutions = if not checked: @[] else: self.getCheckResolutions(piece.color) var targetPiece: Piece for (target, flag) in zip(locations, flags): if checked and target notin resolutions: continue targetPiece = self.grid[target.row, target.col] if target.row == piece.color.getLastRow(): # Pawn reached the other side of the board: generate all potential piece promotions for promotionType in [PromoteToKnight, PromoteToBishop, PromoteToRook, PromoteToQueen]: result.add(Move(startSquare: location, targetSquare: target, flag: promotionType)) continue result.add(Move(startSquare: location, targetSquare: target, flag: flag)) proc generateSlidingMoves(self: ChessBoard, location: Location): seq[Move] = ## Generates moves for the sliding piece in the given location let 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.color.topLeftDiagonal()) directions.add(piece.color.topRightDiagonal()) directions.add(piece.color.bottomLeftDiagonal()) directions.add(piece.color.bottomRightDiagonal()) if piece.kind in [Queen, Rook]: directions.add(piece.color.topSide()) directions.add(piece.color.bottomSide()) directions.add(piece.color.rightSide()) directions.add(piece.color.leftSide()) let pinned = self.getPinnedDirections(location) if pinned.len() > 0: directions = pinned let checked = self.inCheck() let resolutions = if not checked: @[] else: self.getCheckResolutions(piece.color) 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 checked and square notin resolutions: continue if otherPiece.color == piece.color.opposite: # Target square contains an enemy piece: capture # it and stop going any further if otherPiece.kind != King: # Can't capture the king result.add(Move(startSquare: location, targetSquare: square, flag: Capture)) break # Target square is empty result.add(Move(startSquare: location, targetSquare: square)) 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.color.topLeftDiagonal(), piece.color.topRightDiagonal(), piece.color.bottomRightDiagonal(), piece.color.bottomLeftDiagonal(), piece.color.topSide(), piece.color.bottomSide(), piece.color.leftSide(), piece.color.rightSide()] # Castling let canCastle = self.canCastle(piece.color) if canCastle.queen: directions.add(longCastleKing()) if canCastle.king: directions.add(shortCastleKing()) var flag = Default for direction in directions: # Step in this direction once let square: Location = location + direction # End of board reached if not square.isValid(): continue if self.isAttacked(square, piece.color.opposite()): continue if direction == longCastleKing(): flag = CastleLong elif direction == shortCastleKing(): flag = CastleShort else: flag = Default let otherPiece = self.grid[square.row, square.col] if otherPiece.color == self.getActiveColor.opposite(): flag = Capture # A friendly piece is in the way, move onto the next direction if otherPiece.color == piece.color: continue # Target square is empty or contains an enemy piece: # All good for us! result.add(Move(startSquare: location, targetSquare: square, flag: flag)) 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.color.bottomLeftKnightMove(), piece.color.bottomRightKnightMove(), piece.color.topLeftKnightMove(), piece.color.topRightKnightMove(), piece.color.bottomLeftKnightMove(long=false), piece.color.bottomRightKnightMove(long=false), piece.color.topLeftKnightMove(long=false), piece.color.topRightKnightMove(long=false)] let pinned = self.getPinnedDirections(location) if pinned.len() > 0: # Knight is pinned: can't move! return @[] let checked = self.inCheck() let resolutions = if not checked: @[] else: self.getCheckResolutions(piece.color) 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 or the opponent king is is in the way if otherPiece.color == piece.color or otherPiece.kind == King: continue if checked and square notin resolutions: continue if otherPiece.color != None: # Target square contains an enemy piece: capture # it result.add(Move(startSquare: location, targetSquare: square, flag: Capture)) else: # Target square is empty result.add(Move(startSquare: location, targetSquare: square)) 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 generateAllMoves*(self: ChessBoard): seq[Move] = ## Returns the list of all possible legal moves ## in the current position for i, row in self.grid: for j, piece in row: if self.grid[i, j].color == self.getActiveColor(): for move in self.generateMoves((int8(i), int8(j))): result.add(move) proc isAttacked*(self: ChessBoard, loc: Location, color: PieceColor = None): bool = ## Returns whether the given location is attacked ## by the given color var color = color if color == None: color = self.getActiveColor().opposite() case color: of Black: for attack in self.position.attacked.black: if attack.target == loc: return true of White: for attack in self.position.attacked.white: if attack.target == loc: return true of None: discard proc getAttackers*(self: ChessBoard, loc: Location, color: PieceColor): seq[Location] = ## Returns all the attackers of the given color ## for the given square case color: of Black: for attack in self.position.attacked.black: if attack.target == loc: result.add(attack.source) of White: for attack in self.position.attacked.white: if attack.target == loc: result.add(attack.source) of None: discard proc getAttacks*(self: ChessBoard, loc: Location): Attacked = ## Returns all the squares attacked by the piece in the given ## location let piece = self.grid[loc.row, loc.col] case piece.color: of Black: for attack in self.position.attacked.black: if attack.source == loc: result.add(attack) of White: for attack in self.position.attacked.white: if attack.source == loc: result.add(attack) of None: discard proc getAttackFor*(self: ChessBoard, source, target: Location): tuple[source, target, direction: Location] = ## Returns the first attacks of the piece in the given ## source location that also attacks the target location let piece = self.grid[source.row, source.col] case piece.color: of Black: for attack in self.position.attacked.black: if attack.target == target and attack.source == source: return attack of White: for attack in self.position.attacked.white: if attack.target == target and attack.source == source: return attack of None: discard proc isAttacked*(self: ChessBoard, square: string): bool = ## Returns whether the given square is attacked ## by the current return self.isAttacked(square.algebraicToLocation()) func addAttack(self: ChessBoard, attack: tuple[source, target, direction: Location], color: PieceColor) {.inline.} = if attack.source.isValid() and attack.target.isValid(): case color: of White: self.position.attacked.white.add(attack) of Black: self.position.attacked.black.add(attack) else: discard proc getPinnedDirections(self: ChessBoard, loc: Location): seq[Location] = let piece = self.grid[loc.row, loc.col] case piece.color: of None: discard of White: for pin in self.position.pinned.black: if pin.target == loc: result.add(pin.direction) of Black: for pin in self.position.pinned.white: if pin.target == loc: result.add(pin.direction) proc updatePawnAttacks(self: ChessBoard) = ## Internal helper of updateAttackedSquares for loc in self.position.pieces.white.pawns: # Pawns are special in how they capture (i.e. the # squares they can move to do not match the squares # they can capture on. Sneaky fucks) self.addAttack((loc, loc + White.topRightDiagonal(), White.topRightDiagonal()), White) self.addAttack((loc, loc + White.topLeftDiagonal(), White.topRightDiagonal()), White) # We do the same thing for black for loc in self.position.pieces.black.pawns: self.addAttack((loc, loc + Black.topRightDiagonal(), Black.topRightDiagonal()), Black) self.addAttack((loc, loc + Black.topLeftDiagonal(), Black.topRightDiagonal()), Black) proc updateKingAttacks(self: ChessBoard) = ## Internal helper of updateAttackedSquares var king = self.position.pieces.white.king self.addAttack((king, king + White.topRightDiagonal(), White.topRightDiagonal()), White) self.addAttack((king, king + White.topLeftDiagonal(), White.topLeftDiagonal()), White) self.addAttack((king, king + White.bottomLeftDiagonal(), White.bottomLeftDiagonal()), White) self.addAttack((king, king + White.bottomRightDiagonal(), White.bottomRightDiagonal()), White) king = self.position.pieces.black.king self.addAttack((king, king + Black.topRightDiagonal(), Black.topRightDiagonal()), Black) self.addAttack((king, king + Black.topLeftDiagonal(), Black.topLeftDiagonal()), Black) self.addAttack((king, king + Black.bottomLeftDiagonal(), Black.bottomLeftDiagonal()), Black) self.addAttack((king, king + Black.bottomRightDiagonal(), Black.bottomRightDiagonal()), Black) proc updateKnightAttacks(self: ChessBoard) = ## Internal helper of updateAttackedSquares for loc in self.position.pieces.white.knights: self.addAttack((loc, loc + White.topLeftKnightMove(), White.topLeftKnightMove()), White) self.addAttack((loc, loc + White.topRightKnightMove(), White.topRightKnightMove()), White) self.addAttack((loc, loc + White.bottomLeftKnightMove(), White.bottomLeftKnightMove()), White) self.addAttack((loc, loc + White.bottomRightKnightMove(), White.bottomRightKnightMove()), White) self.addAttack((loc, loc + White.topLeftKnightMove(long=false), White.topLeftKnightMove(long=false)), White) self.addAttack((loc, loc + White.topRightKnightMove(long=false), White.topRightKnightMove(long=false)), White) self.addAttack((loc, loc + White.bottomLeftKnightMove(long=false), White.bottomLeftKnightMove(long=false)), White) self.addAttack((loc, loc + White.bottomRightKnightMove(long=false), White.bottomRightKnightMove(long=false)), White) for loc in self.position.pieces.black.knights: self.addAttack((loc, loc + Black.topLeftKnightMove(), Black.topLeftKnightMove()), Black) self.addAttack((loc, loc + Black.topRightKnightMove(), Black.topRightKnightMove()), Black) self.addAttack((loc, loc + Black.bottomLeftKnightMove(), Black.bottomLeftKnightMove()), Black) self.addAttack((loc, loc + Black.bottomRightKnightMove(), Black.bottomRightKnightMove()), Black) self.addAttack((loc, loc + Black.topLeftKnightMove(long=false), Black.topLeftKnightMove(long=false)), Black) self.addAttack((loc, loc + Black.topRightKnightMove(long=false), Black.topRightKnightMove(long=false)), Black) self.addAttack((loc, loc + Black.bottomLeftKnightMove(long=false), Black.bottomLeftKnightMove(long=false)), Black) self.addAttack((loc, loc + Black.bottomRightKnightMove(long=false), Black.bottomRightKnightMove(long=false)), Black) proc getSlidingAttacks(self: ChessBoard, loc: Location): tuple[attacks: Attacked, pins: Attacked] = ## Internal helper of updateSlidingAttacks var directions: seq[Location] = @[] let piece = self.grid[loc.row, loc.col] if piece.kind in [Bishop, Queen]: directions.add(piece.color.topLeftDiagonal()) directions.add(piece.color.topRightDiagonal()) directions.add(piece.color.bottomLeftDiagonal()) directions.add(piece.color.bottomRightDiagonal()) if piece.kind in [Queen, Rook]: directions.add(piece.color.topSide()) directions.add(piece.color.bottomSide()) directions.add(piece.color.rightSide()) directions.add(piece.color.leftSide()) for direction in directions: var square = loc otherPiece: Piece # Slide in this direction as long as it's possible while true: square = square + direction # End of board reached if not square.isValid(): break otherPiece = self.grid[square.row, square.col] # Target square is attacked (even if a friendly piece # is present, because in this case we're defending # it) result.attacks.add((loc, square, direction)) # Empty square, keep going if otherPiece.color == None: continue if otherPiece.color == piece.color.opposite and otherPiece.kind != King: # We found an enemy piece that is not # the enemy king. We don't break out # immediately because we first want # to check if we've pinned a piece var otherSquare: Location = square behindPiece: Piece while true: otherSquare = otherSquare + direction if not otherSquare.isValid(): break behindPiece = self.grid[otherSquare.row, otherSquare.col] if behindPiece.color == None: continue if behindPiece.color == piece.color.opposite and behindPiece.kind == King: # The enemy king is behind this enemy piece: pin it in # this direction relative to them (that's why we have the # minus sign: up for us is down for them and vice versa) result.pins.add((loc, square, -direction)) else: break break proc updateSlidingAttacks(self: ChessBoard) = ## Internal helper of updateAttackedSquares var data: tuple[attacks: Attacked, pins: Attacked] for loc in self.position.pieces.white.bishops: data = self.getSlidingAttacks(loc) self.position.attacked.white.extend(data.attacks) self.position.pinned.white.extend(data.pins) for loc in self.position.pieces.white.rooks: data = self.getSlidingAttacks(loc) self.position.attacked.white.extend(data.attacks) self.position.pinned.white.extend(data.pins) for loc in self.position.pieces.white.queens: data = self.getSlidingAttacks(loc) self.position.attacked.white.extend(data.attacks) self.position.pinned.white.extend(data.pins) for loc in self.position.pieces.black.bishops: data = self.getSlidingAttacks(loc) self.position.attacked.black.extend(data.attacks) self.position.pinned.black.extend(data.pins) for loc in self.position.pieces.black.rooks: data = self.getSlidingAttacks(loc) self.position.attacked.black.extend(data.attacks) self.position.pinned.black.extend(data.pins) for loc in self.position.pieces.black.queens: data = self.getSlidingAttacks(loc) self.position.attacked.black.extend(data.attacks) self.position.pinned.black.extend(data.pins) proc updateAttackedSquares(self: ChessBoard) = ## Updates internal metadata about which squares ## are attacked self.position.attacked.white.setLen(0) self.position.attacked.black.setLen(0) # Pawns self.updatePawnAttacks() # Sliding pieces self.updateSlidingAttacks() # Knights self.updateKnightAttacks() # Kings self.updateKingAttacks() # Invalidate the cache whenever updates to the # metadata are made self.invalidateCache() proc removePiece(self: ChessBoard, location: Location, attack: bool = true) = ## 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.black.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 if attack: self.updateAttackedSquares() proc movePiece(self: ChessBoard, move: Move, attack: bool = true) = ## Internal helper to move a piece. If attack ## is set to false, then this function does ## not update attacked squares metadata, just ## positional info and the grid itself let piece = self.grid[move.startSquare.row, move.startSquare.col] case piece.color: of White: case 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: self.position.pieces.white.queens.delete(self.position.pieces.white.queens.find(move.startSquare)) self.position.pieces.white.queens.add(move.targetSquare) of King: self.position.pieces.white.king = move.targetSquare else: discard of Black: case 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] = piece if attack: self.updateAttackedSquares() else: # Just to be sure self.invalidateCache() proc movePiece(self: ChessBoard, startSquare, targetSquare: Location, attack: bool = true) = ## Like the other movePiece(), but with two locations self.movePiece(Move(startSquare: startSquare, targetSquare: targetSquare), attack) proc updateLocations(self: ChessBoard, move: Move) = ## Internal helper to update the position of ## the pieces on the board after a move if move.flag == Capture: self.position.captured = self.grid[move.targetSquare.row, move.targetSquare.col] self.removePiece(move.targetSquare, attack=false) # Update the positional metadata of the moving piece self.movePiece(move) func invalidateCache(self: ChessBoard) {.inline.} = ## Invalidates the internal caches self.cache.canCastle.white.valid = false self.cache.canCastle.black.valid = false self.cache.inCheck.white.valid = false self.cache.inCheck.black.valid = false 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 # Record the final move in the position self.position.move = move let piece = self.grid[move.startSquare.row, move.startSquare.col] self.position.moved = piece # Needed to detect draw by the 50 move rule var halfMoveClock = self.position.halfMoveClock fullMoveCount = self.position.fullMoveCount castlingAvailable = self.position.castlingAvailable if piece.kind == Pawn or move.flag == Capture: self.position.halfMoveClock = 0 else: inc(halfMoveClock) if piece.color == Black: inc(fullMoveCount) # Castling check: have the rooks moved? if piece.kind == Rook: case piece.color: of White: if move.startSquare.row == piece.getStartRow(): if move.startSquare.col == 0: # Queen side castlingAvailable.white.queen = false elif move.startSquare.col == 7: # King side castlingAvailable.white.king = false of Black: if move.startSquare.row == piece.getStartRow(): if move.startSquare.col == 0: # Queen side castlingAvailable.black.queen = false elif move.startSquare.col == 7: # King side castlingAvailable.black.king = false else: discard # Has a rook been captured? if move.flag == Capture: let piece = self.grid[move.targetSquare.row, move.targetSquare.col] if piece.kind == Rook: case piece.color: of White: if move.targetSquare == piece.color.queenSideRook(): # Queen side castlingAvailable.white.queen = false elif move.targetSquare == piece.color.kingSideRook(): # King side castlingAvailable.white.king = false of Black: if move.targetSquare == piece.color.queenSideRook(): # Queen side castlingAvailable.black.queen = false elif move.targetSquare == piece.color.kingSideRook(): # King side castlingAvailable.black.king = false else: # Unreachable discard # Has the king moved? if piece.kind == King or move.flag in [CastleLong, CastleShort]: # Revoke all castling rights for the moving king case piece.color: of White: castlingAvailable.white.king = false castlingAvailable.white.queen = false of Black: castlingAvailable.black.king = false castlingAvailable.black.queen = false else: discard let previous = self.position # Record final position for future reference self.positions.add(previous) # Create new position self.position = Position(plyFromRoot: self.position.plyFromRoot + 1, halfMoveClock: halfMoveClock, fullMoveCount: fullMoveCount, captured: emptyPiece(), turn: self.getActiveColor().opposite, castlingAvailable: castlingAvailable, # Updated at the next call to doMove() move: emptyMove(), pieces: previous.pieces, ) if move.isPromotion(): # Move is a pawn promotion: get rid of the pawn # and spawn a new piece self.removePiece(move.startSquare) case move.flag: of PromoteToBishop: self.spawnPiece(move.targetSquare, Piece(kind: Bishop, color: piece.color)) of PromoteToKnight: self.spawnPiece(move.targetSquare, Piece(kind: Knight, color: piece.color)) of PromoteToRook: self.spawnPiece(move.targetSquare, Piece(kind: Rook, color: piece.color)) of PromoteToQueen: self.spawnPiece(move.targetSquare, Piece(kind: Queen, color: piece.color)) else: discard if move.flag in [CastleShort, CastleLong]: # Move the rook onto the # correct file var location: Location target: Location if move.flag == CastleShort: location = piece.color.kingSideRook() target = shortCastleRook() else: location = piece.color.queenSideRook() target = longCastleRook() let rook = self.grid[location.row, location.col] let move = Move(startSquare: location, targetSquare: location + target, flag: move.flag) self.movePiece(move, attack=false) if move.flag == EnPassant: self.removePiece(move.targetSquare + piece.color.bottomSide()) # Update position and attack metadata self.updateLocations(move) # Check for double pawn push if move.flag == DoublePush: self.position.enPassantSquare = Move(startSquare: (move.startSquare.row, move.startSquare.col), targetSquare: move.targetSquare + piece.color.bottomSide()) else: self.position.enPassantSquare = emptyMove() 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 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) of King: self.position.pieces.white.king = 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) of King: self.position.pieces.black.king = location else: discard else: # Unreachable discard self.grid[location.row, location.col] = piece proc resetBoard*(self: ChessBoard) = ## Resets the internal grid representation ## according to the positional data stored ## in the chessboard. Warning: this can be ## expensive, especially in critical paths ## or tight loops self.grid = newMatrixFromSeq[Piece](empty, (8, 8)) for loc in self.position.pieces.white.pawns: self.grid[loc.row, loc.col] = Piece(color: White, kind: Pawn) for loc in self.position.pieces.black.pawns: self.grid[loc.row, loc.col] = Piece(color: Black, kind: Pawn) for loc in self.position.pieces.white.bishops: self.grid[loc.row, loc.col] = Piece(color: White, kind: Bishop) for loc in self.position.pieces.black.bishops: self.grid[loc.row, loc.col] = Piece(color: Black, kind: Bishop) for loc in self.position.pieces.white.knights: self.grid[loc.row, loc.col] = Piece(color: White, kind: Knight) for loc in self.position.pieces.black.knights: self.grid[loc.row, loc.col] = Piece(color: Black, kind: Knight) for loc in self.position.pieces.white.rooks: self.grid[loc.row, loc.col] = Piece(color: White, kind: Rook) for loc in self.position.pieces.black.rooks: self.grid[loc.row, loc.col] = Piece(color: Black, kind: Rook) for loc in self.position.pieces.white.queens: self.grid[loc.row, loc.col] = Piece(color: White, kind: Queen) for loc in self.position.pieces.black.queens: self.grid[loc.row, loc.col] = Piece(color: Black, kind: Queen) self.grid[self.position.pieces.white.king.row, self.position.pieces.white.king.col] = Piece(color: White, kind: King) self.grid[self.position.pieces.black.king.row, self.position.pieces.black.king.col] = Piece(color: Black, kind: King) proc undoMove*(self: ChessBoard, move: Move) = ## Undoes the given move if self.positions.len() == 0: return self.invalidateCache() let previous = self.position var position = self.positions[^1] while position.move != move: discard self.positions.pop() position = self.positions[^1] self.position = position self.grid[move.startSquare.row, move.startSquare.col] = self.position.moved if move.flag == Capture: self.grid[move.targetSquare.row, move.targetSquare.col] = previous.captured else: self.grid[move.targetSquare.row, move.targetSquare.col] = emptyPiece() # Reset the location of the rook in the # grid (it's already correct in the piece # list) if move.flag == CastleLong: let rookOld = move.targetSquare + (if self.getActiveColor() == White: self.getActiveColor().rightSide() else: self.getActiveColor().leftSide()) rookNew = self.getActiveColor().queenSideRook() self.grid[rookNew.row, rookNew.col] = self.grid[rookOld.row, rookOld.col] self.grid[rookOld.row, rookOld.col] = emptyPiece() if move.flag == CastleShort: let rookOld = move.targetSquare + (if self.getActiveColor() == White: self.getActiveColor().leftSide() else:self.getActiveColor().rightSide()) rookNew = self.getActiveColor().kingSideRook() self.grid[rookNew.row, rookNew.col] = self.grid[rookOld.row, rookOld.col] self.grid[rookOld.row, rookOld.col] = emptyPiece() if move.flag == EnPassant: let target = self.getEnPassantTarget() + self.getActiveColor().topSide() self.grid[target.row, target.col] = Piece(kind: Pawn, color: self.getActiveColor().opposite()) proc isLegal(self: ChessBoard, move: Move): bool {.inline.} = ## Returns whether the given move is legal return move in self.generateMoves(move.startSquare) proc makeMove*(self: ChessBoard, move: Move): Move {.discardable.} = ## Makes a move on the board result = move self.position.move = move if not self.isLegal(move): return emptyMove() self.doMove(move) result = self.position.move 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 toChar*(piece: Piece): char = if piece.color == White: return char(piece.kind).toUpperAscii() return char(piece.kind) 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" proc toFEN*(self: ChessBoard): string = ## Returns a FEN string of the current ## position in the chessboard var skip: int # Piece placement data for i, row in self.grid: skip = 0 for j, piece in row: if piece.kind == Empty: inc(skip) elif skip > 0: result &= &"{skip}{piece.toChar()}" skip = 0 else: result &= piece.toChar() if skip > 0: result &= $skip if i < 7: result &= "/" result &= " " # Active color result &= (if self.getActiveColor() == White: "w" else: "b") result &= " " # Castling availability let castleWhite = self.position.castlingAvailable.white let castleBlack = self.position.castlingAvailable.black if not (castleBlack.king or castleBlack.queen or castleWhite.king or castleWhite.queen): result &= "-" else: if castleWhite.king: result &= "K" if castleWhite.queen: result &= "Q" if castleBlack.king: result &= "k" if castleBlack.queen: result &= "q" result &= " " # En passant target if self.getEnPassantTarget() == emptyLocation(): result &= "-" else: result &= self.getEnPassantTarget().locationToAlgebraic() result &= " " # Halfmove clock result &= $self.getHalfMoveCount() result &= " " # Fullmove number result &= $self.getMoveCount() proc perftBulkCount*(self: ChessBoard, ply: int, verbose: bool = false, divide: bool = false): int = ## Version of perft that implements bulk-counting. ## Only the total number of nodes reached after the ## given number of ply is returned let moves = self.generateAllMoves() if ply == 1: return len(moves) for move in moves: if verbose: let canCastle = self.canCastle(self.getActiveColor()) echo &"Ply: {self.position.plyFromRoot}" echo &"Move: {move.startSquare.locationToAlgebraic()}{move.targetSquare.locationToAlgebraic()}, from ({move.startSquare.row}, {move.startSquare.col}) to ({move.targetSquare.row}, {move.targetSquare.col})" echo &"Turn: {self.getActiveColor()}" echo &"Piece: {self.grid[move.startSquare.row, move.startSquare.col].kind}" echo &"Flag: {move.flag}" echo &"In check: {(if self.inCheck(self.getActiveColor()): \"yes\" else: \"no\")}" echo &"Can castle:\n - King side: {(if canCastle.king: \"yes\" else: \"no\")}\n - Queen side: {(if canCastle.queen: \"yes\" else: \"no\")}" echo &"Before: {self.toFEN()}\n" echo self.pretty() self.doMove(move) if verbose: echo &"Now: {self.toFEN()}\n" echo self.pretty() try: discard readLine(stdin) except IOError: discard except EOFError: discard let next = self.perftBulkCount(ply - 1, verbose) result += next if divide: echo &"{move.startSquare.locationToAlgebraic()}{move.targetSquare.locationToAlgebraic()}: {next}" if verbose: echo "" self.undoMove(move) proc perft*(self: ChessBoard, ply: int, verbose: bool = false, divide: bool = false): CountData = ## Counts (and debugs) the number of legal positions reached after ## the given number of ply var verbose = verbose if ply == 0: result = (1, 0, 0, 0, 0, 0, 0) else: let moves = self.generateAllMoves() if len(moves) == 0: inc(result.checkmates) for move in moves: if verbose: let canCastle = self.canCastle(self.getActiveColor()) echo &"Ply: {self.position.plyFromRoot}" echo &"Move: {move.startSquare.locationToAlgebraic()}{move.targetSquare.locationToAlgebraic()}, from ({move.startSquare.row}, {move.startSquare.col}) to ({move.targetSquare.row}, {move.targetSquare.col})" echo &"Turn: {self.getActiveColor()}" echo &"Piece: {self.grid[move.startSquare.row, move.startSquare.col].kind}" echo &"Flag: {move.flag}" echo &"In check: {(if self.inCheck(): \"yes\" else: \"no\")}" echo &"Can castle:\n - King side: {(if canCastle.king: \"yes\" else: \"no\")}\n - Queen side: {(if canCastle.queen: \"yes\" else: \"no\")}" echo &"Position before move: {self.toFEN()}" stdout.write("En Passant target: ") if self.getEnPassantTarget() != emptyLocation(): echo self.getEnPassantTarget().locationToAlgebraic() else: echo "None" echo "\n", self.pretty() self.doMove(move) case move.flag: of Capture: inc(result.captures) of CastleShort, CastleLong: inc(result.castles) of PromoteToBishop, PromoteToKnight, PromoteToQueen, PromoteToRook: inc(result.promotions) of EnPassant: inc(result.enPassant) else: discard if self.inCheck(): # Opponent king is in check inc(result.checks) if verbose: let canCastle = self.canCastle(self.getActiveColor()) echo "\n" echo &"Opponent in check: {(if self.inCheck(): \"yes\" else: \"no\")}" echo &"Opponent can castle:\n - King side: {(if canCastle.king: \"yes\" else: \"no\")}\n - Queen side: {(if canCastle.queen: \"yes\" else: \"no\")}" echo &"Position after move: {self.toFEN()}" echo "\n", self.pretty() stdout.write(">>> ") try: discard readLine(stdin) except IOError: discard except EOFError: discard let next = self.perft(ply - 1, verbose) if divide: echo &"{move.startSquare.locationToAlgebraic()}{move.targetSquare.locationToAlgebraic()}: {next.nodes}" if verbose: echo "" result.nodes += next.nodes result.captures += next.captures result.checks += next.checks result.promotions += next.promotions result.castles += next.castles result.enPassant += next.enPassant result.checkmates += next.checkmates self.undoMove(move) 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) when compileOption("profiler"): import nimprof b = newChessboardFromFEN("8/2p5/3p4/KP5r/1R3p1k/8/4P1P1/8 w - - ") #echo b.perftBulkCount(4, divide=true) echo b.perft(2, verbose=false, divide=true) echo "All tests were successful"