Add a serviceworker (#234)

* Add a serviceworker

* rename + fix random extra character

* Fixing worker typings

* Fixing types properly this time.

* Once of those rare cases where this matters.

* Naming the things.

* Move registration to the app (so we can use snackbar later)

* Moving SW plugin later so it picks up things like HTML

* MVP service worker

* Two stage-service worker

* Fix prerendering by conditionally awaiting Custom Elements polyfill.

* Fix icon 404's

* add doc comment to autoswplugin

* Fix type

src/components/compress/index.tsx

@@ -1,4 +1,5 @@
 import { h, Component } from 'preact';
+import { get, set } from 'idb-keyval';
 
 import { bind, Fileish } from '../../lib/initial-util';
 import { blobToImg, drawableToImageData, blobToText } from '../../lib/util';
@@ -155,6 +156,12 @@ async function processSvg(blob: Blob): Promise<HTMLImageElement> {
   return blobToImg(new Blob([newSource], { type: 'image/svg+xml' }));
 }
 
+async function getOldestServiceWorker() {
+  const reg = await navigator.serviceWorker.getRegistration();
+  if (!reg) return null;
+  return reg.active || reg.waiting || reg.installing;
+}
+
 // These are only used in the mobile view
 const resultTitles = ['Top', 'Bottom'];
 // These are only used in the desktop view
@@ -195,6 +202,17 @@ export default class Compress extends Component<Props, State> {
     super(props);
     this.widthQuery.addListener(this.onMobileWidthChange);
     this.updateFile(props.file);
+
+    // If this is the first time the user has interacted with the app, tell the service worker to
+    // cache all the codecs.
+    get<boolean | undefined>('user-interacted')
+      .then(async (userInteracted: boolean | undefined) => {
+        if (userInteracted) return;
+        set('user-interacted', true);
+        const serviceWorker = await getOldestServiceWorker();
+        if (!serviceWorker) return; // Service worker not installing yet.
+        serviceWorker.postMessage('cache-all');
+      });
   }
 
   @bind