/**
 * Where an uploaded image is fetched from.
 *
 * Image paths are stored in the database as site-relative — `/uploads/<id>.jpg`
 * — and that is deliberate: a stored value outlives any hostname it might be
 * baked with, and rewriting them would be a migration to undo the day the host
 * changes. So the origin is joined on here instead, from a value the server
 * sends at runtime (#103).
 *
 * Empty base means the app's own origin, which is the default and is what local
 * development has — there is no second hostname on a laptop. Point it at one in
 * production and user-supplied files stop sharing an origin with the
 * application.
 *
 * The base is cached in a module variable rather than threaded through context,
 * because it is a deployment constant: one value, fetched once, never changing
 * while the tab is open. Anything rendered before the fetch resolves gets the
 * relative path, which still works — the app's origin goes on serving these
 * files, hardened, and the separate host points at the same directory. It
 * simply misses the isolation for that first paint.
 */

let base = '';

/**
 * Called once, from the config the app already fetches at startup. Trailing
 * slashes are trimmed on the server, and again here, so that a base configured
 * either way joins cleanly with a path that always begins with one.
 */
export function setUploadsBase(value: string | undefined | null): void {
  // Trimmed with a loop rather than a `/+$/` regex, which backtracks.
  let trimmed = value ?? '';
  while (trimmed.endsWith('/')) trimmed = trimmed.slice(0, -1);
  base = trimmed;
}

export function uploadUrl(storedPath: string): string {
  // Absolute already, or empty. Either way there is nothing to join: returning
  // it untouched means a value that was somehow stored absolute keeps working
  // rather than being mangled into a nonsense URL.
  if (!base || !storedPath.startsWith('/')) return storedPath;
  return `${base}${storedPath}`;
}