feat: service worker cache static app resources, and all entry points (#18043)

* feat: service worker cache static app resources, and all entry points

* review comments

* review

* lint

* minor tweaks

* review comments

* optimize disabled cache

---------

Co-authored-by: Alex <alex.tran1502@gmail.com>

web/src/service-worker/cache.ts

@@ -0,0 +1,106 @@
+import { build, files, version } from '$service-worker';
+
+const useCache = true;
+const CACHE = `cache-${version}`;
+
+export const APP_RESOURCES = [
+  ...build, // the app itself
+  ...files, // everything in `static`
+];
+
+export const isURL = (request: URL | RequestInfo): request is URL => (request as URL).href !== undefined;
+export const isRequest = (request: RequestInfo): request is Request => (request as Request).url !== undefined;
+
+export async function deleteOldCaches() {
+  for (const key of await caches.keys()) {
+    if (key !== CACHE) {
+      await caches.delete(key);
+    }
+  }
+}
+
+export async function addFilesToCache() {
+  const cache = await caches.open(CACHE);
+  await cache.addAll(APP_RESOURCES);
+}
+
+const pendingLoads = new Map<string, AbortController>();
+
+export async function cancelLoad(urlString: string) {
+  const pending = pendingLoads.get(urlString);
+  if (pending) {
+    pending.abort();
+    pendingLoads.delete(urlString);
+  }
+}
+
+export async function getCachedOrFetch(request: URL | Request | string, cancelable: boolean = false) {
+  const cached = await checkCache(request);
+  if (cached.response) {
+    return cached.response;
+  }
+
+  try {
+    if (!cancelable) {
+      const response = await fetch(request);
+      checkResponse(response);
+      return response;
+    }
+
+    return await fetchWithCancellation(request, cached.cache);
+  } catch {
+    return new Response(undefined, {
+      status: 499,
+      statusText: 'Request canceled: Instructions unclear, accidentally interrupted myself',
+    });
+  }
+}
+
+async function fetchWithCancellation(request: URL | Request | string, cache: Cache) {
+  const cacheKey = getCacheKey(request);
+  const cancelToken = new AbortController();
+
+  try {
+    pendingLoads.set(cacheKey, cancelToken);
+    const response = await fetch(request, {
+      signal: cancelToken.signal,
+    });
+
+    checkResponse(response);
+    setCached(response, cache, cacheKey);
+    return response;
+  } finally {
+    pendingLoads.delete(cacheKey);
+  }
+}
+
+async function checkCache(url: URL | Request | string) {
+  if (!useCache) {
+    return;
+  }
+  const cache = await caches.open(CACHE);
+  const response = await cache.match(url);
+  return { cache, response };
+}
+
+async function setCached(response: Response, cache: Cache, cacheKey: URL | Request | string) {
+  if (response.status === 200) {
+    cache.put(cacheKey, response.clone());
+  }
+}
+
+function checkResponse(response: Response) {
+  if (!(response instanceof Response)) {
+    throw new TypeError('invalid response from fetch');
+  }
+}
+
+function getCacheKey(request: URL | Request | string) {
+  if (isURL(request)) {
+    return request.toString();
+  } else if (isRequest(request)) {
+    return request.url;
+  } else {
+    return request;
+  }
+}