import {
  DEFAULT_LOCALE,
  detectBrowserLocale,
  initI18n,
  isSupportedLocale,
  type SupportedLocale,
} from '@chat-app/shared/i18n';

const LOCAL_STORAGE_KEY = 'chatapp.locale';

export function getCachedLocale(): SupportedLocale | null {
  try {
    const raw = window.localStorage.getItem(LOCAL_STORAGE_KEY);
    return isSupportedLocale(raw) ? raw : null;
  } catch {
    return null;
  }
}

export function cacheLocale(locale: SupportedLocale): void {
  try {
    window.localStorage.setItem(LOCAL_STORAGE_KEY, locale);
  } catch {
    // Ignore (private mode, quota, etc.). Profile row remains source of truth.
  }
}

// Precedence for the very first paint (before we know the user):
//   1. cached choice from a previous session
//   2. navigator language(s)
//   3. DEFAULT_LOCALE (en)
export function resolveInitialLocale(): SupportedLocale {
  return (
    getCachedLocale() ??
    detectBrowserLocale(typeof navigator !== 'undefined' ? navigator.languages : undefined) ??
    DEFAULT_LOCALE
  );
}

export function bootstrapI18n(): void {
  const initialLocale = resolveInitialLocale();
  initI18n({
    initialLocale,
    onLanguageChanged: (locale) => cacheLocale(locale),
  });
}