@publishvue/chessground/premove.js

lichess.org chess ui

import * as util from './util';
function diff(a, b) {
    return Math.abs(a - b);
}
function pawn(color) {
    return (x1, y1, x2, y2) => diff(x1, x2) < 2 &&
        (color === 'white'
            ? // allow 2 squares from first two ranks, for horde
                y2 === y1 + 1 || (y1 <= 1 && y2 === y1 + 2 && x1 === x2)
            : y2 === y1 - 1 || (y1 >= 6 && y2 === y1 - 2 && x1 === x2));
}
export const knight = (x1, y1, x2, y2) => {
    const xd = diff(x1, x2);
    const yd = diff(y1, y2);
    return (xd === 1 && yd === 2) || (xd === 2 && yd === 1);
};
const bishop = (x1, y1, x2, y2) => {
    return diff(x1, x2) === diff(y1, y2);
};
const rook = (x1, y1, x2, y2) => {
    return x1 === x2 || y1 === y2;
};
export const queen = (x1, y1, x2, y2) => {
    return bishop(x1, y1, x2, y2) || rook(x1, y1, x2, y2);
};
function king(color, rookFiles, canCastle) {
    return (x1, y1, x2, y2) => (diff(x1, x2) < 2 && diff(y1, y2) < 2) ||
        (canCastle &&
            y1 === y2 &&
            y1 === (color === 'white' ? 0 : 7) &&
            ((x1 === 4 && ((x2 === 2 && rookFiles.includes(0)) || (x2 === 6 && rookFiles.includes(7)))) ||
                rookFiles.includes(x2)));
}
function rookFilesOf(pieces, color) {
    const backrank = color === 'white' ? '1' : '8';
    const files = [];
    for (const [key, piece] of pieces) {
        if (key[1] === backrank && piece.color === color && piece.role === 'rook') {
            files.push(util.key2pos(key)[0]);
        }
    }
    return files;
}
export function premove(pieces, key, canCastle) {
    const piece = pieces.get(key);
    if (!piece)
        return [];
    const pos = util.key2pos(key), r = piece.role, mobility = r === 'pawn'
        ? pawn(piece.color)
        : r === 'knight'
            ? knight
            : r === 'bishop'
                ? bishop
                : r === 'rook'
                    ? rook
                    : r === 'queen'
                        ? queen
                        : king(piece.color, rookFilesOf(pieces, piece.color), canCastle);
    return util.allPos
        .filter(pos2 => (pos[0] !== pos2[0] || pos[1] !== pos2[1]) && mobility(pos[0], pos[1], pos2[0], pos2[1]))
        .map(util.pos2key);
}
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