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fen.go
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fen.go
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package chess
import (
"fmt"
"strconv"
"strings"
)
var charToPieceMap = map[rune]Piece{
'p': BlackPawn,
'P': WhitePawn,
'q': BlackQueen,
'Q': WhiteQueen,
'k': BlackKing,
'K': WhiteKing,
'r': BlackRook,
'R': WhiteRook,
'b': BlackBishop,
'B': WhiteBishop,
'n': BlackKnight,
'N': WhiteKnight,
}
var pieceToCharMap = map[Piece]rune{
BlackPawn: 'p',
WhitePawn: 'P',
BlackQueen: 'q',
WhiteQueen: 'Q',
BlackKing: 'k',
WhiteKing: 'K',
BlackRook: 'r',
WhiteRook: 'R',
BlackBishop: 'b',
WhiteBishop: 'B',
BlackKnight: 'n',
WhiteKnight: 'N',
}
var charToDigitMap = map[rune]int{
'1': 1,
'2': 2,
'3': 3,
'4': 4,
'5': 5,
'6': 6,
'7': 7,
'8': 8,
}
var digits = "012345678"
func parseBoard(s string) (Board, error) {
pieces := make(map[Square]Piece)
rank, file := 7, 0
for _, r := range s {
if r == '/' {
rank--
file = 0
} else if piece, ok := charToPieceMap[r]; ok {
square := getSquare(File(file), Rank(rank))
pieces[square] = piece
file++
} else if n, ok := charToDigitMap[r]; ok {
file += n
} else {
return nil, fmt.Errorf("failed to parse symbol: %c", r)
}
}
return pieces, nil
}
// ParseFEN - parses Position from FEN format (https://en.wikipedia.org/wiki/Forsyth%E2%80%93Edwards_Notation)
func ParseFEN(fen string) (*Position, error) {
segments := strings.Split(fen, " ")
if len(segments) != 6 {
return nil, fmt.Errorf("expected 6 segemnts, got %d", len(segments))
}
board, err := parseBoard(segments[0])
if err != nil {
return nil, err
}
castleRights := parseCastleRights(segments[2])
epSquare, ok := strToSquareMap[segments[3]]
if !ok {
return nil, fmt.Errorf("fail to parse '%s' as an en-passant square", segments[3])
}
position := &Position{board: board, activeColor: White, epSquare: epSquare, castleRight: castleRights}
if segments[1] == "b" {
position.activeColor = Black
}
halfMoveClock, err := strconv.Atoi(segments[4])
if err != nil {
return nil, fmt.Errorf("fail to parse halfmoves: %v", err)
}
position.halfMoveClock = uint8(halfMoveClock)
fullMovesNumber, err := strconv.Atoi(segments[5])
if err != nil {
return nil, fmt.Errorf("fail to parse full moves number: %v", err)
}
position.movesCount = uint8(fullMovesNumber)
return position, nil
}
func GenerateFEN(position *Position) string {
s := ""
// board
for r := 7; r >= 0; r-- {
n := 0
for f := 0; f < numOfSquaresInRow; f++ {
piece := position.board[getSquare(File(f), Rank(r))]
if piece == NoPiece {
n++
} else {
if n > 0 {
s += string(digits[n])
}
s += string(pieceToCharMap[piece])
n = 0
}
}
if n > 0 {
s += string(digits[n])
}
if r > 0 {
s += "/"
}
}
epSquare := "-"
if position.epSquare != NoSquare {
epSquare = position.epSquare.String()
}
return fmt.Sprintf("%s %s %s %s %d %d", s, position.activeColor, position.castleRight, epSquare,
position.halfMoveClock, position.movesCount)
}