Signalr

// Define the client interface
public interface IChatClient
{
    Task ReceiveMessage(string user, string message);
    Task UserJoined(string user);
    Task UserLeft(string user);
}

// Implement the strongly-typed hub
public class ChatHub : Hub<IChatClient>
{
    public async Task SendMessage(string user, string message)
    {
        // Compiler checks client method calls
        await Clients.All.ReceiveMessage(user, message);
    }

    public override async Task OnConnectedAsync()
    {
        await Clients.Others.UserJoined(Context.User?.Identity?.Name ?? "Anonymous");
        await base.OnConnectedAsync();
    }

    public override async Task OnDisconnectedAsync(Exception? exception)
    {
        await Clients.Others.UserLeft(Context.User?.Identity?.Name ?? "Anonymous");
        await base.OnDisconnectedAsync(exception);
    }
}

public class NotificationHub : Hub<INotificationClient>
{
    public async Task JoinGroup(string groupName)
    {
        await Groups.AddToGroupAsync(Context.ConnectionId, groupName);
        await Clients.Group(groupName).UserJoined(Context.User?.Identity?.Name);
    }

    public async Task LeaveGroup(string groupName)
    {
        await Groups.RemoveFromGroupAsync(Context.ConnectionId, groupName);
    }

    public async Task SendToGroup(string groupName, string message)
    {
        await Clients.Group(groupName).ReceiveNotification(message);
    }
}

// Use custom objects to avoid breaking changes
public class SendMessageRequest
{
    public string Message { get; set; } = string.Empty;
    public string? Recipient { get; set; }  // Added later without breaking clients
    public int? Priority { get; set; }       // Added later without breaking clients
}

public class ChatHub : Hub<IChatClient>
{
    public async Task SendMessage(SendMessageRequest request)
    {
        // Handle both old and new clients
        if (request.Recipient != null)
        {
            await Clients.User(request.Recipient).ReceiveMessage(request.Message);
        }
        else
        {
            await Clients.All.ReceiveMessage(request.Message);
        }
    }
}

const connection = new signalR.HubConnectionBuilder()
    .withUrl("/chatHub")
    .withAutomaticReconnect([0, 2000, 5000, 10000, 30000]) // Retry delays
    .configureLogging(signalR.LogLevel.Information)
    .build();

// Handle reconnection events
connection.onreconnecting(error => {
    console.log("Reconnecting...", error);
    updateUIForReconnecting();
});

connection.onreconnected(connectionId => {
    console.log("Reconnected with ID:", connectionId);
    // Rejoin groups - reconnection does not restore group membership
    rejoinGroups();
    updateUIForConnected();
});

connection.onclose(error => {
    console.log("Connection closed", error);
    updateUIForDisconnected();
});

async function start() {
    try {
        await connection.start();
        console.log("SignalR Connected");
    } catch (err) {
        console.log(err);
        setTimeout(start, 5000);
    }
}

start();

var connection = new HubConnectionBuilder()
    .WithUrl("https://localhost:5001/chatHub", options =>
    {
        options.AccessTokenProvider = () => Task.FromResult(GetAccessToken());
    })
    .WithAutomaticReconnect()
    .Build();

connection.Reconnecting += error =>
{
    _logger.LogWarning("Connection lost. Reconnecting: {Error}", error?.Message);
    return Task.CompletedTask;
};

connection.Reconnected += connectionId =>
{
    _logger.LogInformation("Reconnected with ID: {ConnectionId}", connectionId);
    // Rejoin groups after reconnection
    return RejoinGroupsAsync();
};

connection.Closed += async error =>
{
    _logger.LogError("Connection closed: {Error}", error?.Message);
    await Task.Delay(Random.Shared.Next(0, 5) * 1000);
    await connection.StartAsync();
};

await connection.StartAsync();

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddSignalR(options =>
{
    options.EnableDetailedErrors = builder.Environment.IsDevelopment();
    options.MaximumReceiveMessageSize = 64 * 1024; // 64 KB
    options.StreamBufferCapacity = 10;
    options.KeepAliveInterval = TimeSpan.FromSeconds(15);
    options.ClientTimeoutInterval = TimeSpan.FromSeconds(30);
})
.AddMessagePackProtocol(); // Binary protocol for performance

builder.Services.AddAuthentication(JwtBearerDefaults.AuthenticationScheme)
    .AddJwtBearer(options =>
    {
        options.Events = new JwtBearerEvents
        {
            OnMessageReceived = context =>
            {
                // Read token from query string for WebSocket connections
                var accessToken = context.Request.Query["access_token"];
                var path = context.HttpContext.Request.Path;
                if (!string.IsNullOrEmpty(accessToken) && path.StartsWithSegments("/hubs"))
                {
                    context.Token = accessToken;
                }
                return Task.CompletedTask;
            }
        };
    });

var app = builder.Build();

app.UseAuthentication();
app.UseAuthorization();

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

public class NotificationService
{
    private readonly IHubContext<NotificationHub, INotificationClient> _hubContext;

    public NotificationService(IHubContext<NotificationHub, INotificationClient> hubContext)
    {
        _hubContext = hubContext;
    }

    public async Task NotifyAllAsync(string message)
    {
        await _hubContext.Clients.All.ReceiveNotification(message);
    }

    public async Task NotifyUserAsync(string userId, string message)
    {
        await _hubContext.Clients.User(userId).ReceiveNotification(message);
    }

    public async Task NotifyGroupAsync(string groupName, string message)
    {
        await _hubContext.Clients.Group(groupName).ReceiveNotification(message);
    }
}

builder.Services.AddSignalR()
    .AddStackExchangeRedis(connectionString, options =>
    {
        options.Configuration.ChannelPrefix = RedisChannel.Literal("MyApp");
    });