using System;

using System.Threading.Tasks;

using System.Reactive.Linq;

public class Program

{

    public static async Task Main()

    {

        Console.WriteLine("Hello World");

        //Console.WriteLine(await TestApi());

        var observable = Observable.Interval(TimeSpan.FromMilliseconds(100))

            .SelectMany(_ => Observable.FromAsync(() => TestApi()))

            //.Concat()

            .DistinctUntilChanged()

            .SelectMany(_ => Observable.FromAsync(() => GetApi()))

            //.Concat()

            .Scan((-1, (bool?)null),

                  (prev, cur) =>

                  {

                      Console.WriteLine("*");

                      return (cur, prev.Item1 == -1 ? null : cur == prev.Item1);

                  })

            ;

        var subscription = observable.Subscribe(xs => Console.WriteLine(xs));

        await Task.Delay(5000);

        subscription.Dispose();

        await Task.Delay(2000);

    }

    public static Task<string> TestApi()

    {

        return Task.Run(() =>

        {

            return DateTime.Now.Second.ToString();

        });

    }

    public static Task<int> GetApi()

    {

        return Task.Run(() =>

        {

            return (DateTime.Now.Second / 5);

        });

    }

}