fix: extract service worker setup to Svelte app initialization

lib/frontend/sw-boot.js

@@ -0,0 +1,40 @@
+import { swStatusStore } from './stores'
+
+export default () => {
+  if (!window.navigator || !window.navigator.serviceWorker) {
+    return
+  }
+
+  const { serviceWorker } = window.navigator
+
+  serviceWorker.register('sw.js', {
+    scope: './',
+  }).then((registration) => {
+    swStatusStore.set(`Service worker registered with scope ${registration.scope}`)
+    setTimeout(() => {
+      swStatusStore.set(null)
+    }, 4500)
+
+    registration.addEventListener('updatefound', () => {
+      console.info('Service worker will be updated...')
+      const newWorker = registration.installing
+
+      newWorker.addEventListener('statechange', () => {
+        if (newWorker.state === 'installed') {
+          newWorker.postMessage({ action: 'skipWaiting' })
+        }
+      })
+    })
+  }).catch((err) => {
+    swStatusStore.set(`Service worker error: ${err.toString()}`)
+  })
+
+  let refreshing
+  serviceWorker.addEventListener('controllerchange', () => {
+    if (refreshing) {
+      return
+    }
+    window.location.reload()
+    refreshing = true
+  })
+}