Add lightweight offline web game for tablets

web/sw.js

@@ -0,0 +1,31 @@
+const VERSION = 'pawplay-web-1.0.0';
+const ROOT = new URL('./', self.location.href).href;
+const SHELL = new URL('index.html', ROOT).href;
+const ASSETS = ['index.html', 'game.js?v=1.0.0', 'style.css?v=1.0.0', 'manifest.webmanifest', 'icon.svg', 'apple-touch-icon.png', 'icon-512.png'].map(path => new URL(path, ROOT).href);
+self.addEventListener('install', event => {
+  event.waitUntil((async () => {
+    const cache = await caches.open(VERSION);
+    try { await cache.addAll(ASSETS); }
+    catch (error) { await caches.delete(VERSION); throw error; }
+  })());
+});
+// A new version waits until existing game windows close, keeping one complete
+// shell/version per session. Never force-activate over an in-progress game.
+self.addEventListener('activate', event => {
+  event.waitUntil((async () => {
+    for (const key of await caches.keys()) {
+      if (key.startsWith('pawplay-web-') && key !== VERSION) await caches.delete(key);
+    }
+    await self.clients.claim();
+  })());
+});
+self.addEventListener('fetch', event => {
+  if (event.request.method !== 'GET') return;
+  const url = new URL(event.request.url);
+  if (!url.href.startsWith(ROOT)) return;
+  if (event.request.mode === 'navigate') {
+    event.respondWith((async () => (await (await caches.open(VERSION)).match(SHELL)) || fetch(event.request))());
+  } else if (ASSETS.includes(url.href)) {
+    event.respondWith((async () => (await (await caches.open(VERSION)).match(event.request)) || fetch(event.request))());
+  }
+});