/* Service worker — the piece that makes this installable as a real app.
 *
 * Deliberately minimal, and deliberately network-first for everything.
 * Caching the shell aggressively is the usual PWA advice, but here it would
 * mean shipping a stale UI against a changed API and calling it offline
 * support — this app cannot do anything useful without the network anyway,
 * since grading is a live API call. So the cache exists only as a fallback
 * for the app shell when the connection drops, and never for /api/.
 */

// Substituted server-side to the path this app is mounted under (e.g.
// "/cards"), or left empty when served from the domain root — see
// app.py's _static_templated. Every absolute reference below has to go
// through this, since a service worker has no page URL of its own to
// resolve relative paths against.
const BASE = '__BASE__';

const CACHE = 'card-grader-v1';
const SHELL = [
  `${BASE}/`,
  `${BASE}/static/app.js`,
  `${BASE}/static/style.css`,
  `${BASE}/static/icon.svg`,
  `${BASE}/static/manifest.json`,
];

self.addEventListener('install', (event) => {
  event.waitUntil(
    caches.open(CACHE).then((cache) => cache.addAll(SHELL)).then(() => self.skipWaiting())
  );
});

self.addEventListener('activate', (event) => {
  event.waitUntil(
    caches.keys()
      .then((keys) => Promise.all(
        keys.filter((k) => k !== CACHE).map((k) => caches.delete(k))))
      .then(() => self.clients.claim())
  );
});

self.addEventListener('fetch', (event) => {
  const { request } = event;
  if (request.method !== 'GET') return;

  const url = new URL(request.url);
  // Never cache the API. A stale grade or a stale settings blob would be
  // worse than an honest failure.
  if (url.pathname.startsWith(`${BASE}/api/`)) return;

  event.respondWith(
    fetch(request)
      .then((response) => {
        if (response && response.ok && url.origin === self.location.origin) {
          const copy = response.clone();
          caches.open(CACHE).then((cache) => cache.put(request, copy));
        }
        return response;
      })
      .catch(() => caches.match(request).then((hit) => hit || caches.match(`${BASE}/`)))
  );
});