Init

src/service-worker.ts

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+/// <reference types="@sveltejs/kit" />
+/// <reference no-default-lib="true"/>
+/// <reference lib="esnext" />
+/// <reference lib="webworker" />
+
+// Offline-first: the app shell and static assets are cached on install.
+// GitHub API calls are never cached (sync needs live data).
+
+import { build, files, version } from '$service-worker';
+
+const sw = self as unknown as ServiceWorkerGlobalScope;
+const CACHE = `papure-${version}`;
+const ASSETS = [...build, ...files, '/'];
+
+sw.addEventListener('install', (event) => {
+	event.waitUntil(
+		caches
+			.open(CACHE)
+			.then((c) => c.addAll(ASSETS))
+			.then(() => sw.skipWaiting())
+	);
+});
+
+sw.addEventListener('activate', (event) => {
+	event.waitUntil(
+		caches
+			.keys()
+			.then((keys) => Promise.all(keys.filter((k) => k !== CACHE).map((k) => caches.delete(k))))
+			.then(() => sw.clients.claim())
+	);
+});
+
+sw.addEventListener('fetch', (event) => {
+	const req = event.request;
+	if (req.method !== 'GET') return;
+	const url = new URL(req.url);
+	if (url.origin !== sw.location.origin) return;
+
+	// Navigations: network first, fall back to the cached shell (SPA).
+	if (req.mode === 'navigate') {
+		event.respondWith(
+			fetch(req).catch(async () => (await caches.match('/')) ?? Response.error())
+		);
+		return;
+	}
+
+	// Assets: cache first (they're versioned or fixed).
+	event.respondWith(
+		caches.match(req).then(
+			(hit) =>
+				hit ??
+				fetch(req).then((res) => {
+					if (res.ok && ASSETS.includes(url.pathname)) {
+						const copy = res.clone();
+						void caches.open(CACHE).then((c) => c.put(req, copy));
+					}
+					return res;
+				})
+		)
+	);
+});