1 files changed, 131 insertions, 0 deletions
diff --git a/src/content/sw.js b/src/content/sw.js
new file mode 100644
index 0000000..9e17707
--- /dev/null
+++ b/src/content/sw.js
@@ -0,0 +1,131 @@
+const CACHE_NAME = "static-shared-assets";
+
+const FALLBACK_PATHS = {
+	img: "/fallback-image-FIXME.svg",
+	data: {
+		static: "/fallback-data-FIXME.json",
+	},
+};
+
+const leafValues = tree =>
+	Object.values(tree).map(x =>
+		typeof x !== "object"
+			? x
+			: leafValues(x)
+	);
+
+const collectLeaves = tree =>
+	leafValues(tree).flat(Infinity);
+
+const DEFAULT_INSTALL_PATHS = [
+	"/",
+	"index.html",
+	"style.css",
+	"img/favicon.svg",
+	"papo.js",
+].concat(collectLeaves(FALLBACK_PATHS));
+
+const mkInstallHandler = ({ self, caches }) => event => {
+	self.skipWaiting();
+	event.waitUntil(
+		caches.open(CACHE_NAME).then(
+			cache => cache.addAll(DEFAULT_INSTALL_PATHS),
+		),
+	);
+};
+
+const store = async (caches, request, response) => {
+	const cache = await caches.open(CACHE_NAME);
+	await cache.put(request, response);
+};
+
+const getPrefixIn = (paths, segments) => {
+	if (paths === undefined) {
+		return null;
+	}
+
+	if (segments.length === 0) {
+		return null;
+	}
+
+	if (typeof paths === "string") {
+		return paths;
+	}
+
+	return getPrefixIn(paths[segments[0]], segments.slice(1));
+};
+
+const maybeFallback = async (caches, request, paths = FALLBACK_PATHS) => {
+	const url          = new URL(request.url)
+	const segments     = url.pathname.split("/").filter(s => !!s)
+	const fallbackPath = getPrefixIn(paths, segments);
+	if (fallbackPath) {
+		return await caches.match(fallbackPath);
+	}
+
+	return null;
+}
+
+const fromCache = async (caches, fetch, { request, preloadResponse }) => {
+	const cachedResponse = await caches.match(request);
+	if (cachedResponse) {
+		fetch(request).then(async freshResponse =>
+			store(caches, request, freshResponse));
+		return cachedResponse;
+	}
+
+	const preloadedResponse = await preloadResponse;
+	if (preloadedResponse) {
+		store(caches, request, preloadeResponse.clone());
+		return preloadedResponse;
+	}
+
+	try {
+		// FIXME: do integration test with real lack of internet.
+		const fetchedResponse = await fetch(request);
+		store(caches, request, fetchedResponse.clone());
+		return fetchedResponse;
+	} catch (e) {
+		const fallbackResponse = await maybeFallback(caches, request);
+		if (fallbackResponse) {
+			return fallbackResponse;
+		}
+
+		throw e;
+	}
+};
+
+const mkFetchHandler = ({ caches }) => (event, mkfetch = () => fetch) => {
+	if (event.request.method !== "GET") {
+		return;
+	}
+
+	event.respondWith(fromCache(caches, mkfetch(), event));
+};
+
+const mkActivateHandler = ({ self, clients }) => event =>
+	event.waitUntil(Promise.all([
+		clients.claim(),
+		self.registration.navigationPreload?.enable(),
+	]));
+
+const registerListeners = env => {
+	env.self.addEventListener("install",   mkInstallHandler(env));
+	env.self.addEventListener("activate", mkActivateHandler(env));
+	env.self.addEventListener("fetch",       mkFetchHandler(env));
+};
+
+const main = ({
+	self,
+	caches,
+	clients,
+	out = console.log,
+	err = console.warn,
+} = {}) =>
+	registerListeners({
+		self,
+		caches,
+		clients,
+		out,
+		err,
+	});