feat(trainer): add GitHub activity heatmap, 4-option quiz mode, active typing, and duplicate checks

app/static/sw.js

@@ -0,0 +1,101 @@
+// Service Worker for Notes English PWA (Stage 2)
+// Strategy: Cache-first for static assets, Network-first for API calls.
+
+const CACHE_NAME = 'notes-v2.0';
+const OFFLINE_URL = '/';
+
+const PRECACHE_URLS = [
+  '/',
+  '/static/css/style.css',
+  '/static/js/app.js',
+  '/manifest.json',
+];
+
+// -----------------------------------------------------------------------
+// Install: pre-cache core assets
+// -----------------------------------------------------------------------
+self.addEventListener('install', (event) => {
+  event.waitUntil(
+    caches.open(CACHE_NAME).then((cache) => {
+      return cache.addAll(PRECACHE_URLS);
+    }).then(() => self.skipWaiting())
+  );
+});
+
+// -----------------------------------------------------------------------
+// Activate: delete old caches
+// -----------------------------------------------------------------------
+self.addEventListener('activate', (event) => {
+  event.waitUntil(
+    caches.keys().then((keys) => {
+      return Promise.all(
+        keys
+          .filter((key) => key !== CACHE_NAME)
+          .map((key) => caches.delete(key))
+      );
+    }).then(() => self.clients.claim())
+  );
+});
+
+// -----------------------------------------------------------------------
+// Fetch: strategy based on request type
+// -----------------------------------------------------------------------
+self.addEventListener('fetch', (event) => {
+  const { request } = event;
+  const url = new URL(request.url);
+
+  // Skip cross-origin requests
+  if (url.origin !== location.origin) return;
+
+  // API calls → Network-first (never serve API from cache)
+  if (url.pathname.startsWith('/api/')) {
+    event.respondWith(
+      fetch(request).catch(() => {
+        return new Response(
+          JSON.stringify({ error: 'Offline. Please check your connection.' }),
+          { status: 503, headers: { 'Content-Type': 'application/json' } }
+        );
+      })
+    );
+    return;
+  }
+
+  // Static assets (CSS, JS, icons) → Cache-first
+  if (
+    url.pathname.startsWith('/static/') ||
+    url.pathname === '/manifest.json' ||
+    url.pathname === '/sw.js'
+  ) {
+    event.respondWith(
+      caches.match(request).then((cached) => {
+        return cached || fetch(request).then((response) => {
+          if (response.ok) {
+            const clone = response.clone();
+            caches.open(CACHE_NAME).then((cache) => cache.put(request, clone));
+          }
+          return response;
+        });
+      })
+    );
+    return;
+  }
+
+  // HTML navigation (SPA root) → Network-first with offline fallback
+  event.respondWith(
+    fetch(request)
+      .then((response) => {
+        if (response.ok) {
+          const clone = response.clone();
+          caches.open(CACHE_NAME).then((cache) => cache.put(request, clone));
+        }
+        return response;
+      })
+      .catch(() => {
+        return caches.match(OFFLINE_URL).then((cached) => {
+          return cached || new Response('<h1>Offline</h1><p>Please check your connection.</p>', {
+            headers: { 'Content-Type': 'text/html' },
+          });
+        });
+      })
+  );
+});