// https://gist.github.com/adactio/3717b7da007a9363ddf21f584aae34af

// HTML files: try the network first, then the cache.
// Other files: try the cache first, then the network.
// Both: cache a fresh version if possible.
// (beware: the cache will grow and grow; there's no cleanup)

const cacheName = "appname-files";

addEventListener("fetch", fetchEvent => {
  const request = fetchEvent.request;
  if (request.method !== "GET") return;
  fetchEvent.respondWith(async () => {
    const fetchPromise = fetch(request);
    fetchEvent.waitUntil(async () => {
      const responseFromFetch = await fetchPromise;
      const responseCopy = responseFromFetch.clone();
      const myCache = await caches.open(cacheName);
      return myCache.put(request, responseCopy);
    }());
    if (request.headers.get("Accept").includes("text/html")) {
      try { return await fetchPromise; }
      catch(error) { return caches.match(request); }
    } else {
      const responseFromCache = await caches.match(request);
      return responseFromCache || fetchPromise;
    }
  }());
});