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

/// <summary>
/// CancelKey の受付。
///
/// <code><![CDATA[
/// using (var ck = CancelKey.Create())
/// {
///     ck.Token
/// }
/// ]]></code>
/// </summary>
public static class CancelKey
{
    /// <summary>
    /// <see cref="Console.CancelKeyPress/> の受付開始。
    /// </summary>
    /// <returns></returns>
    public static CancelKeyRegistration Create() => new CancelKeyRegistration(new CancellationTokenSource());

    /// <summary>
    /// <see cref="Console.CancelKeyPress"/> の購読解除用の disposable。
    /// </summary>
    public struct CancelKeyRegistration : IDisposable
    {
        private CancellationTokenSource _cts;
        private ConsoleCancelEventHandler _handler;

        internal CancelKeyRegistration(CancellationTokenSource cts)
        {
            _cts = cts;

            var handler = cts.ToCancelEventHandler();
            _handler = handler;

            Console.CancelKeyPress += handler;
        }

        /// <summary>
        /// <see cref="Console.CancelKeyPress"/> が発生したときにキャンセルされる<see cref="CancellationToken"/>。
        /// </summary>
        public CancellationToken Token => _cts.Token;

        public void Dispose()
        {
            // Ctrl + C された後にここを通るとデッドロックしてる感じある。
            Console.CancelKeyPress -= _handler;
            _cts.Dispose();
        }
    }

    /// <summary>
    /// <see cref="CancellationTokenSource.Cancel"/>を<see cref="ConsoleCancelEventHandler"/>でラップする。
    /// </summary>
    /// <param name="cts"></param>
    /// <returns></returns>
    private static ConsoleCancelEventHandler ToCancelEventHandler(this CancellationTokenSource cts) => cts.Cancel;
    private static void Cancel(this CancellationTokenSource cts, object sender, ConsoleCancelEventArgs e) => cts.Cancel();
}


class Program
{
    static async Task Main()
    {
        using (var ck = CancelKey.Create())
        {
            ck.Token.Register(() => Console.WriteLine("cancelled"));

            while (!ck.Token.IsCancellationRequested)
            {
                Console.WriteLine(".");
                await Task.Delay(100, ck.Token);
            }
            Console.WriteLine("a");
        }
    }
}