@lichess-org/chessground/src/premove.ts

lichess.org chess ui

import * as util from './util.js';
import * as cg from './types.js';
import { HeadlessState } from './state.js';
import { Mobility, MobilityContext } from './types.js';

const pawn: Mobility = (ctx: MobilityContext) =>
  util.diff(ctx.orig.pos[0], ctx.dest.pos[0]) <= 1 &&
  (util.diff(ctx.orig.pos[0], ctx.dest.pos[0]) === 1
    ? ctx.dest.pos[1] === ctx.orig.pos[1] + (ctx.color === 'white' ? 1 : -1)
    : util.pawnDirAdvance(...ctx.orig.pos, ...ctx.dest.pos, ctx.color === 'white'));

const knight: Mobility = (ctx: MobilityContext) => util.knightDir(...ctx.orig.pos, ...ctx.dest.pos);

const bishop: Mobility = (ctx: MobilityContext) => util.bishopDir(...ctx.orig.pos, ...ctx.dest.pos);

const rook: Mobility = (ctx: MobilityContext) => util.rookDir(...ctx.orig.pos, ...ctx.dest.pos);

const queen: Mobility = (ctx: MobilityContext) => bishop(ctx) || rook(ctx);

const king: Mobility = (ctx: MobilityContext) =>
  util.kingDirNonCastling(...ctx.orig.pos, ...ctx.dest.pos) ||
  (ctx.orig.pos[1] === ctx.dest.pos[1] &&
    ctx.orig.pos[1] === (ctx.color === 'white' ? 0 : 7) &&
    ((ctx.orig.pos[0] === 4 &&
      ((ctx.dest.pos[0] === 2 && ctx.rookFilesFriendlies.includes(0)) ||
        (ctx.dest.pos[0] === 6 && ctx.rookFilesFriendlies.includes(7)))) ||
      ctx.rookFilesFriendlies.includes(ctx.dest.pos[0])));

const mobilityByRole = { pawn, knight, bishop, rook, queen, king };

export function premove(state: HeadlessState, key: cg.Key): cg.Key[] {
  const pieces = state.pieces;
  const piece = pieces.get(key);
  if (!piece || piece.color === state.turnColor) return [];
  const color = piece.color,
    friendlies = new Map([...pieces].filter(([_, p]) => p.color === color)),
    enemies = new Map([...pieces].filter(([_, p]) => p.color === util.opposite(color))),
    orig = { key, pos: util.key2pos(key) },
    mobility: Mobility = (ctx: MobilityContext) =>
      mobilityByRole[piece.role](ctx) && state.premovable.additionalPremoveRequirements(ctx),
    partialCtx = {
      orig,
      role: piece.role,
      allPieces: pieces,
      friendlies: friendlies,
      enemies: enemies,
      color: color,
      rookFilesFriendlies: Array.from(pieces)
        .filter(
          ([k, p]) => k[1] === (color === 'white' ? '1' : '8') && p.color === color && p.role === 'rook',
        )
        .map(([k]) => util.key2pos(k)[0]),
      lastMove: state.lastMove,
    };
  // todo - remove more properties from MobilityContext that aren't used in this file, and adjust as needed in lila.
  return util.allPosAndKey.filter(dest => mobility({ ...partialCtx, dest })).map(pk => pk.key);
}