xchess/lib/move-parser.js

Chess Engine

export {ParseMove, ParseCastling, ParseICCF, ParseAlgebraic}

import {Square} from './square.js'
import {File} from './file.js'
import {Rank} from './rank.js'
import {INVALID_MOVE_STRING} from './errors.js'

const IccfPromotion = [, 'queen', 'rook', 'bishop', 'knight'];
const AlgebraicPromotion = new Map();

AlgebraicPromotion.set('Q', 'queen');
AlgebraicPromotion.set('R', 'rook');
AlgebraicPromotion.set('B', 'bishop');
AlgebraicPromotion.set('N', 'knight');

const KC = /^[0O]-[0O]$/i;
const QC = /^[0O]-[0O]-[0O]$/i;
const ICCF = /^([1-8][1-8])([1-8][1-8])([1-4])?$/;
const ALGEBRAIC = /^((?<Sign>[♔-♟])|(?<Char>[QKRBNP]))?(?<FromFile>[a-h])?(?<FromRank>[1-8])?(-|\s+|(?<Capture>x))?(?<To>[a-h][1-8])([/=]?(?<Promotion>[QRBNqrbn]))?/;

function AlgebraicToPromotion(value){
	return AlgebraicPromotion.get(value.toUpperCase());
}

function ParseMove(value){
	const MoveCond = ParseCastling(value) ?? ParseICCF(value) ?? ParseAlgebraic(value);
	if(MoveCond) return MoveCond;
	throw INVALID_MOVE_STRING(value);
}

function ParseCastling(value){
	if(KC.test(value))
		return {kc: true};
	if(QC.test(value))
		return {qc: true};
	return null;
}

function ParseICCF(value){
	const iccf = ICCF.exec(value);
	if(iccf){
		const [, From, To, Promotion] = iccf;
		const from = Square.from(From);
		const to = Square.from(To);
		const result = {from, to};
		if(Promotion)
			result.promotion = IccfPromotion[+ Promotion];
		return result;
	}	return null;
}

function ParseAlgebraic(value){
	const config = ALGEBRAIC.exec(value);
	if(config){
		const {Sign, Char, FromFile, FromRank, Capture, To, Promotion} = config.groups;
		const result = {to: Square.from(To)};
		if(FromFile && FromRank)
			result.from = Square.from(FromFile + FromRank);
		else if(FromFile)
			result.file = File.from(FromFile);
		else if(FromRank)
			result.rank = Rank.from(FromRank);
		if(Sign)
			result.sign = Sign;
		else if(Char)
			result.char = Char;
		else if(!result.from)
			result.char = 'P';
		if(Capture)
			result.capture = true;
		if(Promotion)
			result.promotion = AlgebraicToPromotion(Promotion);
		return result;
	}	return null;
}