/** Text-to-speech through the browser's built-in voices; no audio files or services. */

const supported = () => typeof window !== 'undefined' && 'speechSynthesis' in window;

function voices(): Promise<SpeechSynthesisVoice[]> {
	if (!supported()) return Promise.resolve([]);
	const now = speechSynthesis.getVoices();
	if (now.length) return Promise.resolve(now);
	return new Promise((resolve) => {
		const done = () => resolve(speechSynthesis.getVoices());
		speechSynthesis.addEventListener('voiceschanged', done, { once: true });
		setTimeout(done, 1500);
	});
}

const matches = (voice: SpeechSynthesisVoice, lang: string) =>
	voice.lang.replace('_', '-').toLowerCase().startsWith(lang.slice(0, 2).toLowerCase());

function best(list: SpeechSynthesisVoice[], lang: string) {
	const candidates = list.filter((v) => matches(v, lang));
	return (
		candidates.find(
			(v) => v.lang.replace('_', '-').toLowerCase() === lang.toLowerCase() && !v.localService
		) ??
		candidates.find((v) => v.lang.replace('_', '-').toLowerCase() === lang.toLowerCase()) ??
		candidates[0]
	);
}

export async function hasVoice(lang: string): Promise<boolean> {
	return !!best(await voices(), lang);
}

export async function speak(text: string, lang: string, rate = 0.9) {
	if (!supported()) return;
	const voice = best(await voices(), lang);
	speechSynthesis.cancel();
	const utterance = new SpeechSynthesisUtterance(text);
	utterance.lang = lang;
	utterance.rate = rate;
	if (voice) utterance.voice = voice;
	speechSynthesis.speak(utterance);
}