import type { Chess } from 'chess.js';
import { gameResult, verifyPgnExtends } from '$lib/game-logic';
import type { GameResult, ResultReason } from '$lib/types';

/**
 * Verify an opponent's claimed result against the game we actually have.
 * Returns null when the claim cannot be trusted, in which case the caller must
 * not write it: believing one persists a result into our own repo.
 */
export function verifyOpponentResult(
	opponentRecord: Record<string, unknown>,
	opponentColor: 'white' | 'black',
	current: Chess
): { result: GameResult; resultReason: ResultReason } | null {
	const pgn = opponentRecord.pgn as string | undefined;
	if (pgn) {
		// A fabricated game that does not continue ours proves nothing.
		const verified = verifyPgnExtends(current, pgn);
		if (!verified.ok) return null;
		const outcome = gameResult(verified.chess);
		if (outcome) return { result: outcome.result, resultReason: outcome.reason };
	}

	// Resignation leaves no trace on the board, so it is only credible when the
	// opponent is the one giving up.
	const reason = opponentRecord.resultReason as ResultReason | undefined;
	const result = opponentRecord.result as GameResult | undefined;
	if (reason === 'resignation' && result) {
		const opponentLost =
			(opponentColor === 'white' && result === '0-1') ||
			(opponentColor === 'black' && result === '1-0');
		if (opponentLost) return { result, resultReason: reason };
	}

	return null;
}