Starkt typade hubbar

// INotificationClient.cs
public interface INotificationClient
{
    Task ReceiveMessage(string user, string message);
    Task OrderShipped(int orderId, string trackingNumber);
    Task UserJoined(string username);
    Task UserLeft(string username);
    Task SystemAlert(string message);
}

public class ChatHub : Hub<INotificationClient>
{
    public async Task SendMessage(string message)
    {
        var user = Context.User!.Identity!.Name ?? "Anonymous";

        // Compile-time safety — no magic strings!
        await Clients.All.ReceiveMessage(user, message);
        await Clients.Others.UserJoined(user); // IntelliSense works
    }
}

public async Task NotifyOrderShipped(int orderId, string customerId)
{
    await Clients.User(customerId)
                 .OrderShipped(orderId, "TRK-12345");

    await Clients.Group("admins")
                 .SystemAlert($"Order {orderId} shipped to {customerId}");

    await Clients.Caller.ReceiveMessage("System", "Notification sent");
}

public class ShipmentService
{
    private readonly IHubContext<ChatHub, INotificationClient> _hub;

    public ShipmentService(
        IHubContext<ChatHub, INotificationClient> hub) => _hub = hub;

    public async Task ProcessShipmentAsync(int orderId, string customerId)
    {
        // Fully typed — no magic strings
        await _hub.Clients.User(customerId)
                  .OrderShipped(orderId, "TRK-99999");
    }
}

// CORRECT
public interface IMyClient
{
    Task ReceiveMessage(string msg);         // OK
    Task UpdateProgress(int percent);        // OK
    Task<string> GetUserInput();            // NOT SUPPORTED
}
// Return types other than Task are not supported in hub client interfaces
// For request-response patterns, use client-callable hub methods instead

public class RoomHub : Hub<IRoomClient>
{
    public async Task JoinRoom(string room)
    {
        await Groups.AddToGroupAsync(Context.ConnectionId, room);
        await Clients.Group(room).UserJoined(Context.User!.Identity!.Name!);
    }

    public async Task BroadcastToRoom(string room, string message)
    {
        var user = Context.User!.Identity!.Name!;
        await Clients.Group(room).ReceiveMessage(user, message);
    }
}

// NSubstitute test
var mockClients = Substitute.For<IHubCallerClients<INotificationClient>>();
var mockAllClients = Substitute.For<INotificationClient>();
mockClients.All.Returns(mockAllClients);

var hub = new ChatHub { Clients = mockClients };
await hub.SendMessage("Hello!");

await mockAllClients.Received(1).ReceiveMessage("System", "Hello!");

// Three separate hubs
app.MapHub<ChatHub>("/hubs/chat");
app.MapHub<NotificationHub>("/hubs/notifications");
app.MapHub<DashboardHub>("/hubs/dashboard");

// Each with its own client interface:
// Hub<IChatClient>, Hub<INotificationClient>, Hub<IDashboardClient>

public interface IOrderClient
{
    Task OrderUpdated(OrderStatusDto status);
}

public record OrderStatusDto(
    int OrderId,
    string Status,
    decimal Total,
    DateTime UpdatedAt);

// Usage in hub:
await Clients.User(customerId).OrderUpdated(
    new OrderStatusDto(order.Id, order.Status.ToString(),
                       order.Total, DateTime.UtcNow));