feat(pwa): implement dynamic manifest.webmanifest and service worker for multi-tenant support

src/service-worker.js

@@ -0,0 +1,77 @@
+/// <reference types="@sveltejs/kit" />
+import { build, files, version } from '$service-worker';
+
+// Create a unique cache name for this deployment
+const CACHE = `cache-${version}`;
+
+const ASSETS = [
+	...build, // the app itself
+	...files  // everything in `static`
+];
+
+self.addEventListener('install', (event) => {
+	// Create a new cache and add all files to it
+	async function addFilesToCache() {
+		const cache = await caches.open(CACHE);
+		await cache.addAll(ASSETS);
+	}
+
+	event.waitUntil(addFilesToCache());
+});
+
+self.addEventListener('activate', (event) => {
+	// Delete old caches
+	async function deleteOldCaches() {
+		for (const key of await caches.keys()) {
+			if (key !== CACHE) await caches.delete(key);
+		}
+	}
+
+	event.waitUntil(deleteOldCaches());
+});
+
+self.addEventListener('fetch', (event) => {
+	// ignore POST requests etc
+	if (event.request.method !== 'GET') return;
+
+	async function respond() {
+		const url = new URL(event.request.url);
+		const cache = await caches.open(CACHE);
+
+		// `build`/`files` can always be served from the cache
+		if (ASSETS.includes(url.pathname)) {
+			const response = await cache.match(url.pathname);
+
+			if (response) {
+				return response;
+			}
+		}
+
+		// for everything else, try the network first, but fallback to the cache if we're offline
+		try {
+			const response = await fetch(event.request);
+
+			// if we're offline, fetch can return a value that is not a response
+			// instead of throwing - check it is a real response
+			if (response instanceof Response) {
+				if (response.status === 200) {
+					cache.put(event.request, response.clone());
+				}
+				return response;
+			}
+			throw new Error('invalid response');
+		} catch (err) {
+			const response = await cache.match(event.request);
+
+			if (response) {
+				return response;
+			}
+
+			// if there is no match, the throw will propagate to the browser, which
+			// will show its default offline page.
+			throw err;
+		}
+	}
+
+	event.respondWith(respond());
+});