feat: Initial prototype

sw.js

@@ -0,0 +1,48 @@
+// Bump VERSION whenever a shell file changes. New versions wait for approval.
+const VERSION = 'v6';
+const BASE = self.registration.scope;
+const PREFIX = `ascii-pwa-${encodeURIComponent(BASE)}-`;
+const CACHE = `${PREFIX}${VERSION}`;
+const SHELL = [
+    './', './index.html', './style.css', './appearance.js', './app.js',
+    './renderer.js', './bitmap.js', './font-catalog.js', './vendor/figlet.js',
+    './translations.js', './pwa.js', './manifest.webmanifest',
+    './fonts/IBMPlexMono-Regular.subset.woff2',
+    './fonts/IBMPlexMono-Bold.subset.woff2',
+    './icons/ascii.svg', './icons/icon-192.png', './icons/icon-512.png',
+    './icons/apple-touch-icon.png', './icons/maskable.svg',
+    './icons/maskable-192.png', './icons/maskable-512.png',
+].map(path => new URL(path, BASE).href);
+const HOME = new URL('./', BASE).href;
+const ROUTES = new Set([new URL(HOME).pathname, new URL('./index.html', BASE).pathname]);
+
+self.addEventListener('install', event => {
+    event.waitUntil(caches.open(CACHE).then(cache => cache.addAll(SHELL)));
+});
+self.addEventListener('message', event => {
+    if (event.data === 'ACTIVATE_UPDATE') self.skipWaiting();
+});
+self.addEventListener('activate', event => {
+    event.waitUntil((async () => {
+        const names = await caches.keys();
+        await Promise.all(names.filter(name => name.startsWith(PREFIX) && name !== CACHE)
+            .map(name => caches.delete(name)));
+        await self.clients.claim();
+    })());
+});
+self.addEventListener('fetch', event => {
+    const {request} = event;
+    const url = new URL(request.url);
+    if (request.method !== 'GET' || url.origin !== self.location.origin) return;
+    if (request.mode === 'navigate') {
+        if (!ROUTES.has(url.pathname)) return;
+        event.respondWith(caches.open(CACHE).then(async cache =>
+            (await cache.match(HOME)) || fetch(request)));
+    } else {
+        url.search = '';
+        url.hash = '';
+        if (!SHELL.includes(url.href)) return;
+        event.respondWith(caches.open(CACHE).then(async cache =>
+            (await cache.match(url.href)) || fetch(request)));
+    }
+});