using System;
using System.Net;
using System.Threading;
using System.Threading.Tasks;

namespace ConsoleApp3
{
    class Program
    {
        static void Main(string[] args)
        {
            CancellationTokenSource cts = new CancellationTokenSource();

            Call(cts.Token);

            for (int i = 0; i < 1000; i++)
            {
                Thread.Sleep(20);
                if (i == 30)
                    cts.Cancel();
                Console.WriteLine($"Do something else({i})");
            }

            Console.ReadLine();
        }

        static async void Call(CancellationToken cancellationToken)
        {
            try
            {
                Downloader downloader = new Downloader();
                string res = await downloader.DownloadAsync("https://pokeapi.co/api/v2/pokemon/1/", cancellationToken);
                Console.WriteLine($"RESPONCE: {res}");
            }
            catch (OperationCanceledException)
            {
                Console.WriteLine($"ERROR");
            }
        }
    }


    class Downloader
    {
        public Task<string> DownloadAsync(string url, CancellationToken cancellationToken)
        {
            TaskCompletionSource<string> tcs = new TaskCompletionSource<string>();

            using (var client = new WebClient())
            {
                Uri Uri = new Uri(url);
                cancellationToken.Register(() => client.CancelAsync());
                client.DownloadStringCompleted += (object sender, DownloadStringCompletedEventArgs e) =>
                {
                    if (e.Cancelled)
                    {
                        try
                        {
                            cancellationToken.ThrowIfCancellationRequested();
                        }
                        catch (Exception ex)
                        {
                            Console.WriteLine(ex.Message + "xui" + e.Error.Message);
                            tcs.SetCanceled();
                            return;
                        }
                    }
                    //if (e.Error != null)
                    //{
                    //    Console.WriteLine("Can't set result" + e.Error.Message);
                    //    return;
                    //}
                    tcs.SetResult(e.Result);
                };

                client.DownloadStringAsync(Uri, cancellationToken);
            }

            return tcs.Task;
        }
    }
}