Show waiting players during practice

server.js

@@ -76,6 +76,15 @@ const server = http.createServer((request, response) => {
     return;
   }
 
+  if (requestUrl.pathname === "/lobby") {
+    response.writeHead(200, {
+      "Cache-Control": "no-store",
+      "Content-Type": "application/json; charset=utf-8",
+    });
+    response.end(request.method === "HEAD" ? undefined : JSON.stringify(lobbyStatus()));
+    return;
+  }
+
   const staticName = staticFiles.get(requestUrl.pathname);
   if (!staticName) {
     response.writeHead(404);
@@ -257,6 +266,13 @@ function pairClients(xClient, oClient) {
   send(oClient, { type: "paired", player: "O", roomId });
 }
 
+function lobbyStatus() {
+  return {
+    activeGames: rooms.size,
+    waitingPlayers: waitingClientId && clients.has(waitingClientId) ? 1 : 0,
+  };
+}
+
 function handleSocketData(client, buffer) {
   if (!clients.has(client.id)) {
     return;