/** Adding a locale: add the code here and add one catalog file. Nothing else. */
export const SUPPORTED_LOCALES = ['es', 'en'] as const;

export type Locale = (typeof SUPPORTED_LOCALES)[number];

export const DEFAULT_LOCALE: Locale = 'es';

export function isLocale(value: unknown): value is Locale {
  return typeof value === 'string' && (SUPPORTED_LOCALES as readonly string[]).includes(value);
}

/**
 * Picks a locale from an `Accept-Language` header. Used by the API only as the
 * last fallback: a stored `profiles.locale` always wins when the user is known.
 */
export function localeFromAcceptLanguage(header: string | null | undefined): Locale {
  if (!header) return DEFAULT_LOCALE;
  const ranked = header
    .split(',')
    .map((part) => {
      const [tag = '', ...rest] = part.trim().split(';');
      const q = rest.find((p) => p.trim().startsWith('q='))?.split('=')[1];
      return { tag: tag.trim().toLowerCase(), q: q ? Number(q) : 1 };
    })
    .filter((entry) => entry.tag.length > 0 && Number.isFinite(entry.q))
    .sort((a, b) => b.q - a.q);

  for (const { tag } of ranked) {
    const base = tag.split('-')[0];
    if (isLocale(base)) return base;
  }
  return DEFAULT_LOCALE;
}