type NavigateFn = (to: string, opts?: { replace?: boolean }) => void;

let navigateFn: NavigateFn | null = null;

/** Register (or clear) the router's navigate fn. Called by NavigationBridge. */
export function setNavigate(fn: NavigateFn | null): void {
  navigateFn = fn;
}

/** Soft-redirect to login on a 401, preserving SPA state and the return path.
 *  Falls back to a hard navigation when no router navigate is registered yet
 *  (e.g. a 401 during the very first load). No-op when already on /login. */
export function redirectToLogin(): void {
  const { pathname, search } = window.location;
  if (pathname === "/login") return;
  const from = encodeURIComponent(pathname + search);
  const target = `/login?reason=expired&from=${from}`;
  if (navigateFn) {
    navigateFn(target, { replace: true });
  } else {
    window.location.assign(target);
  }
}