/**
 * Service worker (docs/07 §11). Built to dist/sw.js by vite.config.ts, which fills in VERSION with a build id,
 * so every deploy with changed files installs a new worker.
 * - Page loads: network first, never cached (index.html is always fresh online); offline → /offline.html.
 * - /assets/* (hashed, immutable): cache first, at most MAX_ASSETS entries.
 * - /api, /ws, /healthz, /internal and other origins: not touched at all.
 */
const VERSION = '__BUILD__';
const SHELL = `bg-shell-${VERSION}`;
const ASSETS = 'bg-assets-v1'; // hashed files never change, so they survive deploys
const OFFLINE_URL = '/offline.html';
const MAX_ASSETS = 200;
const BYPASS = /^\/(api|ws|healthz|internal)(\/|$)/;

self.addEventListener('install', (event) => {
  event.waitUntil(
    caches
      .open(SHELL)
      .then((cache) => cache.add(new Request(OFFLINE_URL, { cache: 'reload' })))
      .then(() => self.skipWaiting()),
  );
});

self.addEventListener('activate', (event) => {
  event.waitUntil(
    (async () => {
      for (const key of await caches.keys()) {
        if (key.startsWith('bg-') && key !== SHELL && key !== ASSETS) await caches.delete(key);
      }
      await self.clients.claim();
    })(),
  );
});

self.addEventListener('fetch', (event) => {
  const req = event.request;
  if (req.method !== 'GET') return;
  const url = new URL(req.url);
  if (url.origin !== self.location.origin || BYPASS.test(url.pathname)) return;
  if (req.mode === 'navigate') event.respondWith(page(req));
  else if (url.pathname.startsWith('/assets/')) event.respondWith(asset(event, req));
});

async function page(req) {
  try {
    return await fetch(req);
  } catch {
    const offline = await caches.match(OFFLINE_URL, { cacheName: SHELL });
    return offline ?? new Response('인터넷 연결이 없어요.', { status: 503, headers: { 'Content-Type': 'text/plain; charset=utf-8' } });
  }
}

async function asset(event, req) {
  const cache = await caches.open(ASSETS);
  const hit = await cache.match(req);
  if (hit) return hit;
  const res = await fetch(req);
  // A missing file falls back to index.html on the server; never keep that (or partial/error responses).
  if (res.status === 200 && !(res.headers.get('Content-Type') ?? '').startsWith('text/html')) {
    event.waitUntil(cache.put(req, res.clone()).then(() => trim(cache)));
  }
  return res;
}

async function trim(cache) {
  const keys = await cache.keys();
  for (const key of keys.slice(0, Math.max(0, keys.length - MAX_ASSETS))) await cache.delete(key);
}