feat: Initial prototype

pwa.js

@@ -0,0 +1,51 @@
+export function setupPWA({failed}) {
+    const install = document.getElementById('install');
+    const guide = document.getElementById('install-guide');
+    const update = document.getElementById('update');
+    const standalone = () => window.matchMedia('(display-mode: standalone)').matches || navigator.standalone;
+    let prompt;
+    guide.hidden = !!standalone();
+    window.addEventListener('beforeinstallprompt', event => {
+        event.preventDefault();
+        prompt = event;
+        install.hidden = false;
+        guide.hidden = true;
+    });
+    install.addEventListener('click', async () => {
+        if (!prompt) return;
+        const pending = prompt;
+        prompt = undefined;
+        install.hidden = true;
+        try {
+            await pending.prompt();
+            await pending.userChoice;
+        } catch {
+            // Keep manual installation guidance available if the prompt fails.
+        } finally {
+            guide.hidden = !!standalone();
+        }
+    });
+    window.addEventListener('appinstalled', () => {
+        prompt = undefined;
+        install.hidden = true;
+        guide.hidden = true;
+    });
+    if (!('serviceWorker' in navigator)) return;
+    let controlled = !!navigator.serviceWorker.controller;
+    navigator.serviceWorker.addEventListener('controllerchange', () => {
+        if (controlled) window.location.reload();
+        controlled = true;
+    });
+    navigator.serviceWorker.register('./sw.js', {scope: './', type: 'module', updateViaCache: 'none'})
+        .then(registration => {
+            const showUpdate = () => { update.hidden = !registration.waiting; };
+            showUpdate();
+            registration.addEventListener('updatefound', () => {
+                const worker = registration.installing;
+                if (worker) worker.addEventListener('statechange', showUpdate);
+            });
+            update.addEventListener('click', () => {
+                if (registration.waiting) registration.waiting.postMessage('ACTIVATE_UPDATE');
+            });
+        }).catch(failed);
+}