misskey/packages/sw/src/scripts/lang.ts

/*
 * Language manager for SW
 */
import { get, set } from 'idb-keyval';
import { I18n, type Locale } from '@/scripts/i18n';

class SwLang {
	public cacheName = `mk-cache-${_VERSION_}`;

	public lang: Promise<string> = get('lang').then(async prelang => {
		if (!prelang) return 'en-US';
		return prelang;
	});

	public setLang(newLang: string): Promise<I18n<Locale>> {
		this.lang = Promise.resolve(newLang);
		set('lang', newLang);
		return this.fetchLocale();
	}

	public i18n: Promise<I18n> | null = null;

	public fetchLocale(): Promise<I18n<Locale>> {
		return (this.i18n = this._fetch());
	}

	private async _fetch(): Promise<I18n<Locale>> {
		// Service Workerは何度も起動しそのたびにlocaleを読み込むので、CacheStorageを使う
		const localeUrl = `/assets/locales/${await this.lang}.${_VERSION_}.json`;
		let localeRes = await caches.match(localeUrl);

		// _DEV_がtrueの場合は常に最新化
		if (!localeRes || _DEV_) {
			localeRes = await fetch(localeUrl);
			const clone = localeRes.clone();
			if (!clone.clone().ok) throw new Error('locale fetching error');

			caches.open(this.cacheName).then(cache => cache.put(localeUrl, clone));
		}

		return new I18n<Locale>(await localeRes.json());
	}
}

export const swLang = new SwLang();