/** Lowercase, strip punctuation and diacritics-insensitive comparison helpers for answers. */

const PUNCTUATION = /[.,!?¿¡;:"“”„‘’'`()[\]{}…~·-]/g;

export function normalize(value: string): string {
	return value
		.normalize('NFC')
		.toLowerCase()
		.replace(/[’‘`]/g, "'")
		.replace(PUNCTUATION, ' ')
		.replace(/\s+/g, ' ')
		.trim();
}

export function stripDiacritics(value: string): string {
	// Only Latin marks: decomposing Hangul would break Korean answers.
	return value.replace(/[À-ɏ]/g, (c) => c.normalize('NFD').replace(/[̀-ͯ]/g, ''));
}

export function distance(a: string, b: string): number {
	const row = Array.from({ length: b.length + 1 }, (_, i) => i);
	for (let i = 1; i <= a.length; i++) {
		let previous = row[0];
		row[0] = i;
		for (let j = 1; j <= b.length; j++) {
			const current = row[j];
			row[j] = Math.min(row[j] + 1, row[j - 1] + 1, previous + (a[i - 1] === b[j - 1] ? 0 : 1));
			previous = current;
		}
	}
	return row[b.length];
}

export type Verdict = 'correct' | 'accent' | 'typo' | 'wrong';

/** Compare a typed answer with every accepted answer, forgiving accents and one-letter typos. */
export function grade(input: string, accepted: string[]): { verdict: Verdict; match: string } {
	const given = normalize(input);
	let best: { verdict: Verdict; match: string } = { verdict: 'wrong', match: accepted[0] };
	if (!given) return best;
	for (const answer of accepted) {
		const expected = normalize(answer);
		if (given === expected) return { verdict: 'correct', match: answer };
		if (stripDiacritics(given) === stripDiacritics(expected))
			best = { verdict: 'accent', match: answer };
		else if (
			best.verdict === 'wrong' &&
			[...expected].length >= 5 &&
			distance(stripDiacritics(given), stripDiacritics(expected)) === 1
		)
			best = { verdict: 'typo', match: answer };
	}
	return best;
}

/** Split a sentence into word tiles, keeping punctuation attached to the word. */
export function tiles(sentence: string): string[] {
	return sentence.split(/\s+/).filter(Boolean);
}

export function sameTiles(a: string[], b: string[]): boolean {
	return normalize(a.join(' ')) === normalize(b.join(' '));
}

/** Key for telling multiple-choice options apart; unlike `normalize` it keeps apostrophes (its / it's). */
export const optionKey = (value: string) =>
	value.normalize('NFC').trim().toLowerCase().replace(/\s+/g, ' ');