TelegramBotFramework/TelegramBotBase/Base/Async.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;

namespace TelegramBotBase.Base;

public static class Async
{
    public delegate Task AsyncEventHandler<in TEventArgs>(object sender, TEventArgs e) where TEventArgs : EventArgs;

    public static IEnumerable<AsyncEventHandler<TEventArgs>> GetHandlers<TEventArgs>(
        this AsyncEventHandler<TEventArgs> handler)
        where TEventArgs : EventArgs
    {
        return handler.GetInvocationList().Cast<AsyncEventHandler<TEventArgs>>();
    }

    public static Task InvokeAllAsync<TEventArgs>(this AsyncEventHandler<TEventArgs> handler, object sender,
                                                  TEventArgs e)
        where TEventArgs : EventArgs
    {
        return Task.WhenAll(
            handler.GetHandlers()
                   .Select(handleAsync => handleAsync(sender, e)));
    }
}