Flesh out websockets a little more

src/api.ts

@@ -5,14 +5,37 @@ const wsServer = new WebSocketServer({ port: 8080 });
 
 const wsConnections: WebSocket[] = [];
 
+let updateTimer: NodeJS.Timer | null = null;
+
+// If any clients are connected, send an update every 250 ms.
+const setOrClearInterval = () => {
+  if (wsConnections.length && !updateTimer) {
+    updateTimer = setInterval(() => {
+      wsConnections.forEach((wsSocket) => {
+        wsSocket.send("something");
+      });
+    }, 250);
+  } else if (!wsConnections.length && updateTimer) {
+    clearInterval(updateTimer);
+    updateTimer = null;
+  } else {
+    log.warn("unexpected state in setOrClearInterval");
+  }
+};
+
 wsServer.on("connection", (wsSocket) => {
   wsConnections.push(wsSocket);
+  setOrClearInterval();
 
   wsSocket.on("error", log.error);
 
+  wsSocket.on("close", () => {
+    const index = wsConnections.indexOf(wsSocket);
+    if (index > -1) wsConnections.splice(index, 1);
+    setOrClearInterval();
+  });
+
   wsSocket.on("message", (data) => {
     log.warn(`Received message ${data} on read-only socket`);
   });
-
-  wsSocket.send("something");
 });