add WebSocket support for real-time status updates

data/websocket.js

@@ -0,0 +1,37 @@
+const gateway = `ws://${window.location.hostname}/ws`;
+let ws;
+
+let callbacks = {};
+
+export function initWebSocket() {
+    if (ws) return;
+
+    ws = new WebSocket(gateway);
+
+    ws.onopen = () => {
+        console.info("WebSocket connection opened");
+    };
+
+    ws.onclose = (event) => {
+        console.info("WebSocket connection closed, reason:", event.reason);
+        ws = null;
+    };
+
+    ws.onerror = (event) => {
+        console.warn("WebSocket encountered error, closing socket.", event);
+        ws.close();
+        ws = null;
+    };
+
+    ws.onmessage = (event) => {
+        const message = JSON.parse(event.data);
+        console.log("received websocket data", message);
+        if (message.type in callbacks) {
+            callbacks[message.type](message.data);
+        }
+    };
+}
+
+export function registerCallback(type, callback) {
+    callbacks[type] = callback;
+}