libchess/pkg/board/board.go

package board

import (
	"fmt"
	"strconv"
	"strings"
)

// CastleRights is a helper for maintaining castling rights.
type CastleRights struct {
	WhiteKingSide  bool
	WhiteQueenSide bool
	BlackKingSide  bool
	BlackQueenSide bool
}

// NewCastleRights returns an initialized CastleRights from the given string.
func NewCastleRights(s string) (*CastleRights, error) {
	cr := &CastleRights{}
	for _, c := range s {
		switch c {
		case 'K':
			cr.WhiteKingSide = true
		case 'Q':
			cr.WhiteQueenSide = true
		case 'k':
			cr.BlackKingSide = true
		case 'q':
			cr.BlackQueenSide = true
		default:
			return nil, fmt.Errorf("invalid castle-rights: %s", s)
		}
	}
	return cr, nil
}

func (cr CastleRights) String() string {
	var out string
	if cr.WhiteKingSide {
		out += WhiteKing.String()
	}
	if cr.WhiteQueenSide {
		out += WhiteQueen.String()
	}
	if cr.BlackKingSide {
		out += BlackKing.String()
	}
	if cr.BlackQueenSide {
		out += BlackQueen.String()
	}
	return out
}

// Board represents a chess board.
type Board struct {
	// White
	WhiteKing   Bitboard
	WhiteQueen  Bitboard
	WhiteBishop Bitboard
	WhiteKnight Bitboard
	WhiteRook   Bitboard
	WhitePawn   Bitboard
	// Black
	BlackKing   Bitboard
	BlackQueen  Bitboard
	BlackBishop Bitboard
	BlackKnight Bitboard
	BlackRook   Bitboard
	BlackPawn   Bitboard
	// Convenience
	WhitePieces Bitboard
	BlackPieces Bitboard
	FreeSquares Bitboard

	Turn         Color
	CastleRights CastleRights
	EnPassent    *Square
	HalfMove     uint64
	FullMove     uint64
}

// NewBoard returns an initialized *Board.
func NewBoard(pieces map[Square]Piece, turn Color, cr CastleRights, ep *Square, halfMove, fullMove uint64) (*Board, error) {
	board := new(Board)
	board.WhiteKing = NewBitboard(nil)
	board.WhiteQueen = NewBitboard(nil)
	board.WhiteBishop = NewBitboard(nil)
	board.WhiteKnight = NewBitboard(nil)
	board.WhiteRook = NewBitboard(nil)
	board.WhitePawn = NewBitboard(nil)
	board.BlackKing = NewBitboard(nil)
	board.BlackQueen = NewBitboard(nil)
	board.BlackBishop = NewBitboard(nil)
	board.BlackKnight = NewBitboard(nil)
	board.BlackRook = NewBitboard(nil)
	board.BlackPawn = NewBitboard(nil)
	board.Turn = turn
	board.CastleRights = cr
	board.EnPassent = ep
	board.HalfMove = halfMove
	board.FullMove = fullMove
	for square, piece := range pieces {
		switch piece {
		case WhiteKing:
			board.WhiteKing = board.WhiteKing | NewBitboard(map[Square]bool{square: true})
		case WhiteQueen:
			board.WhiteQueen = board.WhiteQueen | NewBitboard(map[Square]bool{square: true})
		case WhiteBishop:
			board.WhiteBishop = board.WhiteBishop | NewBitboard(map[Square]bool{square: true})
		case WhiteKnight:
			board.WhiteKnight = board.WhiteKnight | NewBitboard(map[Square]bool{square: true})
		case WhiteRook:
			board.WhiteRook = board.WhiteRook | NewBitboard(map[Square]bool{square: true})
		case WhitePawn:
			board.WhitePawn = board.WhitePawn | NewBitboard(map[Square]bool{square: true})
		case BlackKing:
			board.BlackKing = board.BlackKing | NewBitboard(map[Square]bool{square: true})
		case BlackQueen:
			board.BlackQueen = board.BlackQueen | NewBitboard(map[Square]bool{square: true})
		case BlackBishop:
			board.BlackBishop = board.BlackBishop | NewBitboard(map[Square]bool{square: true})
		case BlackKnight:
			board.BlackKnight = board.BlackKnight | NewBitboard(map[Square]bool{square: true})
		case BlackRook:
			board.BlackRook = board.BlackRook | NewBitboard(map[Square]bool{square: true})
		case BlackPawn:
			board.BlackPawn = board.BlackPawn | NewBitboard(map[Square]bool{square: true})
		default:
			panic("invalid piece")
		}
	}
	board.UpdateConvenienceBitboards()
	return board, nil
}

// UpdateConvenienceBitboards updates the convenience bitboards.
func (b *Board) UpdateConvenienceBitboards() {
	b.WhitePieces = b.WhiteKing | b.WhiteQueen | b.WhiteBishop | b.WhiteKnight | b.WhiteRook | b.WhitePawn
	b.BlackPieces = b.BlackKing | b.BlackQueen | b.BlackBishop | b.BlackKnight | b.BlackRook | b.BlackPawn
	b.FreeSquares = ^(b.WhitePieces | b.BlackPieces)
}

// IsOccupied returns true if the given field is occupied.
func (b Board) IsOccupied(sq Square) bool {
	return sq.Bitboard()&b.FreeSquares == 0
}

// Piece returns the piece on the given field.
func (b Board) Piece(sq Square) Piece {
	contains := func(bb Bitboard, sq Square) bool {
		for _, square := range bb.Squares() {
			if square == sq {
				return true
			}
		}
		return false
	}
	if contains(b.WhiteKing, sq) {
		return WhiteKing
	}
	if contains(b.WhiteQueen, sq) {
		return WhiteQueen
	}
	if contains(b.WhiteBishop, sq) {
		return WhiteBishop
	}
	if contains(b.WhiteKnight, sq) {
		return WhiteKnight
	}
	if contains(b.WhiteRook, sq) {
		return WhiteRook
	}
	if contains(b.WhitePawn, sq) {
		return WhitePawn
	}
	if contains(b.BlackKing, sq) {
		return BlackKing
	}
	if contains(b.BlackQueen, sq) {
		return BlackQueen
	}
	if contains(b.BlackBishop, sq) {
		return BlackBishop
	}
	if contains(b.BlackKnight, sq) {
		return BlackKnight
	}
	if contains(b.BlackRook, sq) {
		return BlackRook
	}
	if contains(b.BlackPawn, sq) {
		return BlackPawn
	}
	return NoPiece
}

func (b Board) String() string {
	fen := ""
	for r := 7; r >= 0; r-- {
		for f := 0; f < 8; f++ {
			sq := NewSquare(File(f), Rank(r))
			p := b.Piece(sq)
			if p != NoPiece {
				fen += p.String()
			} else {
				fen += "1"
			}
		}
		if r != 0 {
			fen += "/"
		}
	}
	for i := 8; i > 1; i-- {
		repeatStr := strings.Repeat("1", i)
		countStr := strconv.Itoa(i)
		fen = strings.Replace(fen, repeatStr, countStr, -1)
	}
	ep := "-"
	if b.EnPassent != nil {
		ep = b.EnPassent.String()
	}
	fen += fmt.Sprintf(
		" %s %s %s %d %d",
		b.Turn,
		b.CastleRights,
		ep,
		b.HalfMove,
		b.FullMove,
	)
	return fen
}

// Draw prints an ASCII art of this board to STDOUT.
func (b Board) Draw() string {
	s := "\n  A B C D E F G H\n"
	for r := 7; r >= 0; r-- {
		s += Rank(r).String()
		s += " "
		for f := 0; f < 8; f++ {
			p := b.Piece(NewSquare(File(f), Rank(r)))
			if p == NoPiece {
				s += "."
			} else {
				s += p.Rune()
			}
			s += " "
		}
		s += "\n"
	}
	return s
}

// UpdatePiece moves the a piece on the board from the given src to dest square.
func (b *Board) UpdatePiece(src, dest Square) error {
	if !b.IsOccupied(src) {
		return fmt.Errorf("can not move piece on vacant square: %s", src)
	}
	if b.IsOccupied(dest) {
		return fmt.Errorf("can not move to occupied square: %s", dest)
	}
	switch b.Piece(src) {
	case WhiteKing:
		b.WhiteKing.Flip(src)
		b.WhiteKing.Flip(dest)
	case WhiteQueen:
		b.WhiteQueen.Flip(src)
		b.WhiteQueen.Flip(dest)
	case WhiteRook:
		b.WhiteRook.Flip(src)
		b.WhiteRook.Flip(dest)
	case WhiteBishop:
		b.WhiteBishop.Flip(src)
		b.WhiteBishop.Flip(dest)
	case WhiteKnight:
		b.WhiteKnight.Flip(src)
		b.WhiteKnight.Flip(dest)
	case WhitePawn:
		b.WhitePawn.Flip(src)
		b.WhitePawn.Flip(dest)
	case BlackKing:
		b.BlackKing.Flip(src)
		b.BlackKing.Flip(dest)
	case BlackQueen:
		b.BlackQueen.Flip(src)
		b.BlackQueen.Flip(dest)
	case BlackRook:
		b.BlackRook.Flip(src)
		b.BlackRook.Flip(dest)
	case BlackBishop:
		b.BlackBishop.Flip(src)
		b.BlackBishop.Flip(dest)
	case BlackKnight:
		b.BlackKnight.Flip(src)
		b.BlackKnight.Flip(dest)
	case BlackPawn:
		b.BlackPawn.Flip(src)
		b.BlackPawn.Flip(dest)
	default:
		panic("")
	}
	b.UpdateConvenienceBitboards()
	return nil
}