export function levenshtein(a, b) {
	const m = a.length, n = b.length;
	if (!m) return n;
	if (!n) return m;
	const dp = Array.from({length: m + 1}, (_, i) => [i, ...Array(n).fill(0)]);
	for (let j = 0; j <= n; j++) dp[0][j] = j;
	for (let i = 1; i <= m; i++) {
		for (let j = 1; j <= n; j++) {
			dp[i][j] = a[i - 1] === b[j - 1]
				? dp[i - 1][j - 1]
				: 1 + Math.min(dp[i - 1][j - 1], dp[i - 1][j], dp[i][j - 1]);
		}
	}
	return dp[m][n];
}

/** Normalized similarity in [0,1]: 1 - editDistance / maxLength. */
export function similarity(a, b) {
	a = a.toLowerCase(); b = b.toLowerCase();
	return 1 - levenshtein(a, b) / Math.max(a.length, b.length, 1);
}

/**
 * Scores `text` against a single lowercased `term`. Substring containment always wins.
 * Otherwise, only rescues genuine typos: requires the same leading letter and a tight
 * absolute edit-distance cap, so unrelated words can't win purely on coincidental
 * letter overlap (e.g. "Viennese" vs "diannes").
 */
function scoreAgainst(text, term) {
	if (text.includes(term)) return 1 - (text.length - term.length) / text.length * 0.3;
	if (!text.length || !term.length || text[0] !== term[0]) return 0;
	const dist = levenshtein(text, term);
	const maxAllowed = Math.max(1, Math.ceil(term.length * 0.34));
	if (dist > maxAllowed) return 0;
	return 1 - dist / Math.max(text.length, term.length);
}

/** Compares `target` against one or more search terms; returns avg/max/per-term similarity. */
export function fuzzyMatch(target, ...terms) {
	if (!terms.length) throw new Error('Requires at least 1 term to compare');
	const lowerTarget = String(target).toLowerCase();
	const words = lowerTarget.split(/\W+/).filter(Boolean);

	const similarities = terms.map(term => {
		const t = term.toLowerCase();
		return Math.max(scoreAgainst(lowerTarget, t), ...words.map(w => scoreAgainst(w, t)));
	});

	return {
		avg: similarities.reduce((acc, s) => acc + s, 0) / similarities.length,
		max: Math.max(...similarities),
		similarities,
	};
}

/** Derives a readable pseudo-title from a URL's last path segment, e.g. ".../diannes-southwest-salad/" -> "Diannes Southwest Salad". */
export function titleFromUrl(url) {
	const slug = String(url).replace(/\/$/, '').split('/').pop() || url;
	const clean = slug.replace(/\.(zim|meta4|html?|md)$/i, '').replace(/[-_.]+/g, ' ');
	return clean.replace(/\b\w/g, c => c.toUpperCase());
}