// STEM Copilot — Service Worker (PWA installability + safe caching)
//
// Caching strategy:
//   • API calls (/chat, /auth, …)      → never touched, always network.
//   • Navigations + app code (HTML/JS/  → NETWORK-FIRST. This is critical: a
//     CSS)                                cache-first shell used to serve a stale
//                                         index.html / app.js after every deploy,
//                                         which forced users to hard-refresh
//                                         (Ctrl+Shift+R) and could surface an old,
//                                         un-gated build of the app. Network-first
//                                         means everyone always gets the live code.
//   • Other static assets (images,      → cache-first (fine to be stale).
//     fonts)
const CACHE_NAME = 'stemcopilot-v3';
const ASSET_URLS = [
  '/assets/bot.png',
  '/assets/stem_black.png',
  '/assets/stembotix.png',
];

self.addEventListener('install', (e) => {
  e.waitUntil(caches.open(CACHE_NAME).then((cache) => cache.addAll(ASSET_URLS)));
  self.skipWaiting();
});

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

function _isApi(url) {
  return ['/chat', '/auth', '/threads', '/history', '/user', '/export',
          '/health', '/feedback', '/notes', '/upload-doc', '/rename', '/thread']
    .some((p) => url.includes(p));
}

// HTML navigations and the core app code must always come fresh from the network.
function _isAppCode(req, url) {
  return req.mode === 'navigate'
      || url.endsWith('/')
      || url.includes('/static/app.js')
      || url.includes('/static/style.css')
      || url.includes('/static/index.html');
}

self.addEventListener('fetch', (e) => {
  const url = e.request.url;
  if (_isApi(url)) return; // straight to network, no SW involvement

  if (_isAppCode(e.request, url)) {
    // Network-first: fetch live, fall back to cache only when offline.
    e.respondWith(
      fetch(e.request)
        .then((resp) => {
          const copy = resp.clone();
          caches.open(CACHE_NAME).then((c) => c.put(e.request, copy)).catch(() => {});
          return resp;
        })
        .catch(() => caches.match(e.request))
    );
    return;
  }

  // Everything else (images, fonts): cache-first.
  e.respondWith(caches.match(e.request).then((cached) => cached || fetch(e.request)));
});