using System;

using System.Threading;

using System.Threading.Tasks;

​

public class Program

{

    public static void Main()

    {

        var timer = new CountDownTimer();

        var progress = new CountDownPercentage(e =>

        {

            var remainingTime = e.RemainingTime;

            var percentage = e.ProgressPercentage;

            Console.WriteLine("{0}, {1}%", remainingTime, percentage);

        }

​

        );

        timer.Wait(4, progress).Wait();

        Console.WriteLine("Hello World. Times up");

    }

}

​

public class CountDownPercentage : IProgress<CountdownReport>

{

    private Action<CountdownReport> handler;

    public CountDownPercentage(Action<CountdownReport> handler)

    {

        this.handler = handler;

    }

​

    public void Report(CountdownReport value)

    {

        if (handler != null)

        {

            handler(value);

        }

    }

}

​

public class CountDownTimer

{

    TimeSpan delay = TimeSpan.FromSeconds(1);

    public Task Wait(int seconds, IProgress<CountdownReport> progress = null)

    {

        return Wait(seconds, CancellationToken.None, progress);

    }

​

    public async Task Wait(int seconds, CancellationToken cancellationToken = default (CancellationToken), IProgress<CountdownReport> progress = null)

    {

        var total = TimeSpan.FromSeconds(seconds);

        var current = total.TotalSeconds;

        while (current > 0)

        {

            reportProgress(progress, total, current);

            try

            {

                //simulate wait

                await Task.Delay(delay, cancellationToken);

            }

            catch (TaskCanceledException e)

            {

                current = 0;

            }

​

            current--;

        }

​

        if (current > -1)

        {

            reportProgress(progress, total, current);

        }

    }

​

    private void reportProgress(IProgress<CountdownReport> progress, TimeSpan total, double current)

    {

        if (progress != null)

        {

            var percentageRemaining = (int)((current / total.TotalSeconds) * 100);

            var progressPercentage = 100 - percentageRemaining;

            var timeRemaining = TimeSpan.FromSeconds(current);

            var report = new CountdownReport{InitialTime = total, RemainingTime = timeRemaining, ProgressPercentage = progressPercentage, RemainingPercentage = percentageRemaining};

            //report progress

            progress.Report(report);

        }

    }

}

​

public class CountdownReport

{

    public TimeSpan InitialTime

    {

        get;

        set;

    }

​

    public int ProgressPercentage

    {

        get;

        set;

    }

​

    public int RemainingPercentage

    {

        get;

        set;

    }

​

    public TimeSpan RemainingTime

    {

        get;

        set;

    }

}