SignalR Real-Time Communication

// Hub definition
[Authorize]
public class ChatHub : Hub {
    public async Task SendMessage(string message) {
        var user = Context.User?.Identity?.Name ?? "Anonymous";
        // Broadcast to ALL connected clients
        await Clients.All.SendAsync("ReceiveMessage", user, message);
    }

    public async Task JoinRoom(string roomName) {
        await Groups.AddToGroupAsync(Context.ConnectionId, roomName);
        await Clients.Group(roomName).SendAsync("UserJoined", Context.User?.Identity?.Name);
    }

    public async Task SendToRoom(string roomName, string message) {
        // Only send to users in this group
        await Clients.Group(roomName).SendAsync("ReceiveMessage", 
            Context.User?.Identity?.Name, message);
    }

    public override async Task OnConnectedAsync() {
        await Clients.Others.SendAsync("UserConnected", Context.ConnectionId);
        await base.OnConnectedAsync();
    }

    public override async Task OnDisconnectedAsync(Exception? ex) {
        await Clients.Others.SendAsync("UserDisconnected", Context.ConnectionId);
        await base.OnDisconnectedAsync(ex);
    }
}

// Program.cs
builder.Services.AddSignalR()
    .AddStackExchangeRedis("localhost:6379");  // Scale-out across servers

app.MapHub<ChatHub>("/hubs/chat");

// JavaScript client (npm install @microsoft/signalr)
// const connection = new signalR.HubConnectionBuilder()
//     .withUrl("/hubs/chat", { accessTokenFactory: () => getJwtToken() })
//     .withAutomaticReconnect()
//     .build();
// await connection.start();
// connection.on("ReceiveMessage", (user, msg) => displayMessage(user, msg));
// await connection.invoke("SendMessage", "Hello everyone!");