using Microsoft.AspNetCore.SignalR.Client;

namespace ConsoleApp4;

internal static class Program
{
    static HubConnection hubConnection = null!;

    static void Main()
    {
        hubConnection = new HubConnectionBuilder().WithUrl("...").Build();
    }

    static void Register(IClient client)
    {
        // \/ Remove type argument here \/
        hubConnection.RegisterClient<IClient>(client);
    }
}

[AttributeUsage(AttributeTargets.Method)]
internal class HubServerProxyAttribute : Attribute
{
}

[AttributeUsage(AttributeTargets.Method)]
internal class HubClientProxyAttribute : Attribute
{
}

internal static partial class MyCustomExtensions
{
    [HubClientProxy]
    public static partial IDisposable RegisterClient<T>(this HubConnection connection, T provider);

    [HubServerProxy]
    public static partial T GetServerProxy<T>(this HubConnection connection);
}

public interface IServerHub
{
    Task SendMessage(string message);
}

public interface IClient
{
    Task ReceiveMessage(string message);
}

public class Client : IClient
{
    public Task ReceiveMessage(string message) => Task.CompletedTask;
}