import { useEffect } from 'react';
import { getFallbackSession, subscribeSessionChanges } from '../state/sessions';

/**
 * #69 — `useSessionSync` (the full cross-tab session sync, with in-place token
 * rotation handling) is mounted only inside the authenticated `ClientRoot`
 * shell, so a tab parked on the login/register/OIDC-callback pages never
 * learns that another tab just signed in. Left alone, that tab keeps showing
 * the login form and, if submitted, starts a second device/session for the
 * same account.
 *
 * This is a deliberately lighter watcher for the unauthenticated routes: it
 * only cares about a session APPEARING where there was none before (a fresh
 * login completed in another tab) and reloads so this tab picks up the
 * authenticated shell instead. It does not need `useSessionSync`'s
 * rotation/relogin handling since there is no running client here to keep in
 * sync — do not import/duplicate that logic, just reload.
 */
export function useSessionAppeared(): void {
  useEffect(() => {
    // If we already have a session, there's nothing to watch for here — the
    // authenticated shell's own useSessionSync takes over once mounted.
    if (getFallbackSession()) return undefined;

    const unsubscribe = subscribeSessionChanges((session) => {
      if (session) {
        window.location.reload();
      }
    });

    return unsubscribe;
  }, []);
}