feat(#20): Make the site a PWA

src/app.html

@@ -4,6 +4,20 @@
 		<meta charset="utf-8" />
 		<link rel="icon" href="%sveltekit.assets%/favicon.png" />
 		<meta name="viewport" content="width=device-width, initial-scale=1" />
+		<link rel="manifest" href="/site.webmanifest" />
+		<meta name="theme-color" content="#f00000" />
+		<meta
+			name="description"
+			content="A free and open source web app to track completion of a living Pokédex, which works offline."
+		/>
+		<meta property="og:title" content="Living Dex Tracker - A free Pokédex completion tool" />
+		<meta property="og:url" content="https://pokedex.jcreek.co.uk" />
+		<meta
+			property="og:description"
+			content="A free and open source web app to track completion of a living Pokédex, which works offline."
+		/>
+		<link rel="canonical" href="https://pokedex.jcreek.co.uk" />
+		<link rel="apple-touch-icon" href="%sveltekit.assets%/apple-touch-icon.png" />
 		%sveltekit.head%
 		<link rel="stylesheet" href="%sveltekit.assets%/output.css" />
 	</head>

src/service-worker.js

@@ -0,0 +1,80 @@
+/// <reference types="@sveltejs/kit" />
+import { build, files, version } from '$service-worker';
+
+// Create a unique cache name for this deployment
+const CACHE = `cache-${version}`;
+
+const ASSETS = [
+	...build, // the app itself
+	...files // everything in `static`
+];
+
+self.addEventListener('install', (event) => {
+	// Create a new cache and add all files to it
+	async function addFilesToCache() {
+		const cache = await caches.open(CACHE);
+		await cache.addAll(ASSETS);
+	}
+
+	event.waitUntil(addFilesToCache());
+});
+
+self.addEventListener('activate', (event) => {
+	// Remove previous cached data from disk
+	async function deleteOldCaches() {
+		for (const key of await caches.keys()) {
+			if (key !== CACHE) await caches.delete(key);
+		}
+	}
+
+	event.waitUntil(deleteOldCaches());
+});
+
+self.addEventListener('fetch', (event) => {
+	// ignore POST requests etc
+	if (event.request.method !== 'GET') return;
+
+	async function respond() {
+		const url = new URL(event.request.url);
+		const cache = await caches.open(CACHE);
+
+		// `build`/`files` can always be served from the cache
+		if (ASSETS.includes(url.pathname)) {
+			const response = await cache.match(url.pathname);
+
+			if (response) {
+				return response;
+			}
+		}
+
+		// for everything else, try the network first, but
+		// fall back to the cache if we're offline
+		try {
+			const response = await fetch(event.request);
+
+			// if we're offline, fetch can return a value that is not a Response
+			// instead of throwing - and we can't pass this non-Response to respondWith
+			if (!(response instanceof Response)) {
+				throw new Error('invalid response from fetch');
+			}
+
+			if (response.status === 200) {
+				cache.put(event.request, response.clone());
+			}
+
+			return response;
+		} catch (err) {
+			const response = await cache.match(event.request);
+
+			if (response) {
+				return response;
+			}
+
+			// if there's no cache, then just error out
+			// as there is nothing we can do to respond to this request
+			throw err;
+		}
+	}
+
+	event.respondWith(respond());
+});

static/site.webmanifest

@@ -0,0 +1,22 @@
+{
+	"name": "Living Dex Tracker",
+	"short_name": "Living Dex Tracker",
+	"description": "A tool to enable you to track your progress in completing the living Pokédex in Pokémon games.",
+	"icons": [
+		{
+			"src": "/android-chrome-192x192.png",
+			"sizes": "192x192",
+			"type": "image/png"
+		},
+		{
+			"src": "/android-chrome-512x512.png",
+			"sizes": "512x512",
+			"type": "image/png",
+			"purpose": "any maskable"
+		}
+	],
+	"start_url": "/",
+	"theme_color": "#f00000",
+	"background_color": "#f0f0f0",
+	"display": "standalone"
+}