chessgroundx/fen.js

Extended lichess.org Chess UI

import { pos2key, invRanks, roleOf, letterOf, changeNumber } from './util.js';
import * as cg from './types.js';
export const initial = 'rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR';
export function read(fen, bd) {
    const piecesPart = fen.split(' ')[0];
    const bracketIdx = piecesPart.indexOf('[');
    let boardPart;
    let pocketPart;
    if (bracketIdx > -1) {
        boardPart = piecesPart.slice(0, bracketIdx);
        pocketPart = piecesPart.slice(bracketIdx + 1, piecesPart.indexOf(']'));
    }
    else {
        const ranks = piecesPart.split('/');
        boardPart = ranks.slice(0, bd.height).join('/');
        // Handle "pocket after an extra slash" format
        pocketPart = ranks.length > bd.height ? ranks[bd.height] : undefined;
    }
    return {
        pieces: readBoard(boardPart),
        pockets: readPockets(pocketPart),
    };
}
function readBoard(fen) {
    if (fen === 'start')
        fen = initial;
    const pieces = new Map();
    let row = fen.split('/').length - 1;
    let col = 0;
    let promoted = false;
    let mirror = false;
    let num = 0;
    for (const c of fen) {
        switch (c) {
            case ' ':
            case '[':
                return pieces;
            case '/':
                --row;
                if (row < 0)
                    return pieces;
                col = 0;
                num = 0;
                break;
            case '+':
                promoted = true;
                break;
            case '|':
                mirror = true;
                break;
            case '~': {
                const piece = pieces.get(pos2key([col - 1, row]));
                if (piece)
                    piece.promoted = true;
                break;
            }
            default: {
                const nb = c.charCodeAt(0);
                if (48 <= nb && nb < 58) {
                    num = 10 * num + nb - 48;
                }
                else {
                    col += num;
                    num = 0;
                    const letter = c.toLowerCase();
                    const piece = {
                        role: roleOf(letter),
                        color: (c === letter ? 'black' : 'white'),
                    };
                    if (promoted) {
                        piece.role = ('p' + piece.role);
                        piece.promoted = true;
                        promoted = false;
                    }
                    if (mirror) {
                        piece.mirror = true;
                        mirror = false;
                    }
                    pieces.set(pos2key([col, row]), piece);
                    ++col;
                }
            }
        }
    }
    return pieces;
}
function readPockets(pocketStr) {
    if (pocketStr !== undefined) {
        const whitePocket = new Map();
        const blackPocket = new Map();
        for (const p of pocketStr) {
            const role = roleOf(p);
            if (/[A-Z]/.test(p))
                changeNumber(whitePocket, role, 1);
            else if (/[a-z]/.test(p))
                changeNumber(blackPocket, role, 1);
        }
        return {
            white: whitePocket,
            black: blackPocket,
        };
    }
    else {
        return undefined;
    }
}
export function write(boardState, bd) {
    return writeBoard(boardState.pieces, bd) + writePockets(boardState.pockets);
}
export function writeBoard(pieces, bd) {
    return invRanks
        .slice(-bd.height)
        .map(y => cg.files
        .slice(0, bd.width)
        .map(x => {
        const piece = pieces.get((x + y));
        if (piece) {
            let p = letterOf(piece.role, piece.color === 'white');
            if (piece.promoted && p.charAt(0) !== '+')
                p += '~';
            if (piece.mirror)
                p = '|' + p;
            return p;
        }
        else
            return '1';
    })
        .join(''))
        .join('/')
        .replace(/1{2,}/g, s => s.length.toString());
}
function writePockets(pockets) {
    if (pockets)
        return '[' + writePocket(pockets.white, true) + writePocket(pockets.black, false) + ']';
    else
        return '';
}
function writePocket(pocket, asWhite) {
    const letters = [];
    for (const [r, n] of pocket.entries())
        letters.push(letterOf(r, asWhite).repeat(n));
    return letters.join('');
}
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