chess-polyglot/lib/polyglot.js

chess-polyglot is node module to grab moves from Polyglot-formatted opening-book bin files

const poly = require('../build/Release/chess-polyglot.node');
const Chess = require('chess.js').Chess;

class Polyglot
{
  hash(fen) {
    const pieceTypes = {
      bp: 0, wp: 1,
      bn: 2, wn: 3,
      bb: 4, wb: 5,
      br: 6, wr: 7,
      bq: 8, wq: 9,
      bk: 10, wk: 11
    };
    const files = "abcdefgh";

    const game = new Chess(fen);
    const result = game.validate_fen(fen);
    if (!result.valid) {
      throw result.error;
    }
    // piece offsets
    const pieceOffsets = [];
    for (var file = 0; file < 8; file++) {
      for (var rank = 1; rank <= 8; rank++) {
        const piece = game.get(files[file] + rank);
        if (piece) {
          pieceOffsets.push(64 * pieceTypes[piece.color + piece.type] + 8 * (rank - 1) + file);
        }
      }
    }
    // castling offsets
    const castlingOffsets = [];
    const fenTokens = game.fen().split(' ');
    const castlingField = fenTokens[2];
    if (castlingField.indexOf('K') != -1) {
      castlingOffsets.push(0);
    }
    if (castlingField.indexOf('Q') != -1) {
      castlingOffsets.push(1);
    }
    if (castlingField.indexOf('k') != -1) {
      castlingOffsets.push(2);
    }
    if (castlingField.indexOf('q') != -1) {
      castlingOffsets.push(3);
    }
    // enpassant offsets
    var epOffset = -1;
    var fenEpSquare = fenTokens[3];
    if (fenEpSquare !== '-') {
      fenEpSquare = fenEpSquare[0] + (game.turn() === 'w' ? '5' : '4');
      const epSquareIndex = files.indexOf(fenEpSquare[0]);
      if (epSquareIndex > 0) {
        var leftPiece = game.get(files[epSquareIndex - 1] + fenEpSquare[1]);
        if (leftPiece && leftPiece.type === 'p' &&
          leftPiece.color === game.turn()) {
          epOffset = epSquareIndex;
        }
      }
      if (epSquareIndex < 7) {
        var rightPiece = game.get(files[epSquareIndex + 1] + fenEpSquare[1]);
        if (rightPiece && rightPiece.type === 'p' &&
          rightPiece.color === game.turn()) {
          epOffset = epSquareIndex;
        }
      }
    }
    // white turn
    const isWhitesTurn = game.turn() === 'w';

    return poly.hash(pieceOffsets, castlingOffsets, epOffset, isWhitesTurn);
  }

  find(fen, bookFile, bestMove) {
    var game = new Chess(fen);
    var key = this.hash(fen);
    return poly.find(key, bookFile, bestMove);
  }
}

module.exports = Polyglot;