import { resolveLocale, type Locale } from '@wellformed/shared';

/**
 * The language a request's browser asks for.
 *
 * Inside a workspace the workspace's own locale answers, and this is never
 * consulted. It matters at the edges, where there is no workspace to ask: the
 * language a brand-new workspace opens in, and the language of mail sent to
 * someone who is locked out and has no session at all.
 *
 * The q-weights are ignored: browsers already send the list in preference
 * order, and parsing weights buys nothing but a place for a malformed header
 * to matter. An absent or unreadable header falls through to English.
 */
export function localeFromHeader(header: string | undefined): Locale {
  if (!header) return resolveLocale([]);
  const tags = header
    .split(',')
    .map((part) => part.split(';')[0]?.trim() ?? '')
    .filter(Boolean);
  return resolveLocale(tags);
}