xchess/lib/move-disambiguator.js

Chess Engine

export const DISAMBIGUATION_NONE = 0;
export const DISAMBIGUATION_FILE = 1;
export const DISAMBIGUATION_RANK = 2;
export const DISAMBIGUATION_FULL = 3;

const DisambiguationMap = new WeakMap();

export function GetMoveDisambiguation(move){
	return DisambiguationMap.get(move);
}

export function SetMoveDisambiguation(move, level){
	DisambiguationMap.set(move, level)
}

export function ComputeDisambiguationLevels(moves){
	const group = GroupMoves(moves);
	for(const [key, moves] of group){
		if(moves.length > 1)
			ComputeLocalDisambiguation(moves);
		else for(const move of moves)
			SetMoveDisambiguation(move, DISAMBIGUATION_NONE);
	}
}

function ComputeLocalDisambiguation(moves){
	// Index Moves
	const group = new Map();
	for(const move of moves){
		const {file, rank} = move.from;
		const fileMoves = group.get(file);
		if(fileMoves)
			fileMoves.push(move);
		else
			group.set(file, [move]);
		const rankMoves = group.get(rank);
		if(rankMoves)
			rankMoves.push(move);
		else
			group.set(rank, [move]);
	}
	// Compute Levels
	for(const move of moves){
		const {file, rank} = move.from;
		const fileMoves = group.get(file);
		const rankMoves = group.get(rank);
		if(fileMoves.length > 1){
			if(rankMoves.length > 1)
				SetMoveDisambiguation(move, DISAMBIGUATION_FULL);
			else
				SetMoveDisambiguation(move, DISAMBIGUATION_RANK);
		} else SetMoveDisambiguation(move, DISAMBIGUATION_FILE);
	}
}

function MoveGroupKey({target, to}){
	return `${target.char}${to}`;
}

function GroupMoves(moves){
	const group = new Map();
	for(const move of moves){
		const key = MoveGroupKey(move);
		const submoves = group.get(key);
		if(submoves)
			submoves.push(move);
		else
			group.set(key, [move]);
	}
	return group;
}