Add service worker for offline compatibility

Makefile

@@ -8,7 +8,7 @@ build:
 
 dist: build
 	mkdir -p $(BUILD)/build
-	cp -r $(SRC)/*.html $(SRC)/term.js src/examples $(BUILD)
+	cp -r $(SRC)/*.html $(SRC)/term.js src/examples $(SRC)/sw.js $(BUILD)
 	cp $(SRC)/build/firmware.js $(SRC)/build/simulator.js $(SRC)/build/firmware.wasm  $(BUILD)/build/
 
 watch: dist

src/simulator.ts

@@ -15,6 +15,22 @@ declare global {
   }
 }
 
+function initServiceWorker() {
+  if ("serviceWorker" in navigator) {
+    window.addEventListener("load", () => {
+      navigator.serviceWorker.register("sw.js").then(
+        function (_registration) {
+          console.log("Simulator ServiceWorker registration successful");
+        },
+        function (err) {
+          console.log("Simulator ServiceWorker registration failed: ", err);
+        }
+      );
+    });
+  }
+}
+
+initServiceWorker();
 const fs = new FileSystem();
 const board = createBoard(new Notifications(window.parent), fs);
 window.addEventListener("message", createMessageListener(board));

src/sw.js

@@ -0,0 +1,68 @@
+function initSimulatorServiceWorker() {
+  const simUrls = ["simulator.html", "build/simulator.js", "build/firmware.js"];
+  let didInstall = false;
+  const cacheName = "simulator";
+
+  self.addEventListener("install", function (ev) {
+    didInstall = true;
+    console.log("Installing service worker...");
+    ev.waitUntil(
+      caches
+        .open(cacheName)
+        .then(function (cache) {
+          console.log("Opened cache");
+          return cache.addAll(simUrls);
+        })
+        .then(function () {
+          return self.skipWaiting();
+        })
+    );
+  });
+
+  self.addEventListener("activate", function (ev) {
+    console.log("Activating service worker...");
+    ev.waitUntil(
+      caches
+        .keys()
+        .then(function (_cacheNames) {
+          // Delete old versions in cache here.
+        })
+        .then(function () {
+          if (didInstall) {
+            // Only notify clients for the first activation
+            didInstall = false;
+            // Necessary?
+            return notifyAllClientsAsync();
+          }
+          return Promise.resolve();
+        })
+    );
+  });
+
+  self.addEventListener("fetch", function (ev) {
+    ev.respondWith(
+      caches.match(ev.request).then(function (response) {
+        return response || fetch(ev.request);
+      })
+    );
+  });
+
+  function notifyAllClientsAsync() {
+    var scope = self;
+    return scope.clients
+      .claim()
+      .then(function () {
+        return scope.clients.matchAll();
+      })
+      .then(function (clients) {
+        clients.forEach(function (client) {
+          return client.postMessage({
+            type: "serviceworker",
+            state: "activated",
+          });
+        });
+      });
+  }
+}
+
+initSimulatorServiceWorker();