using System;

using System.Diagnostics;

using System.Linq;

using System.Threading.Tasks;

using Console = System.Console;

public class Program

{

    static (int, int)[] delays = new (int, int)[]

    {

        (1, 200), (2, 500), (3, 300), (4, 400), (5, 300)

    };

    static Random rnd = new Random(DateTime.Now.Millisecond);

    public static void Main()

    {

        ParallelForEach();

        Console.WriteLine("");

        ParallelForAll();

        Console.WriteLine("");

        TaskWaitAllLinq();

        Console.WriteLine("");

        TaskWaitAll();

    }

    private static void ParallelForEach()

    {

        Console.WriteLine("Parallel.ForEach()");

        var now = DateTime.Now;

        var watch = Stopwatch.StartNew();

        Parallel.ForEach(delays, ((int I, int Pause) args) => DoWork(now, args.I, args.Pause).Wait());

        watch.Stop();

        Console.WriteLine($"Works took {watch.ElapsedMilliseconds}ms");

    }

    private static void ParallelForAll()

    {

        Console.WriteLine("Parallel.ForAll()");

        var now = DateTime.Now;

        var watch = Stopwatch.StartNew();

        delays.AsParallel().ForAll(((int I, int Pause) args) => DoWork(now, args.I, args.Pause).Wait());

        watch.Stop();

        Console.WriteLine($"Works took {watch.ElapsedMilliseconds}ms");

    }

    private static void TaskWaitAllLinq()

    {

        Console.WriteLine("Task.WaitAll() with Linq");

        var now = DateTime.Now;

        var watch = Stopwatch.StartNew();

        Task.WaitAll(delays.Select(((int I, int Pause) args) => DoWork(now, args.I, args.Pause)).ToArray());

        watch.Stop();

        Console.WriteLine($"Works took {watch.ElapsedMilliseconds}ms");

    }

    private static void TaskWaitAll()

    {

        Console.WriteLine("Task.WaitAll()");

        var now = DateTime.Now;

        var watch = Stopwatch.StartNew();

        var tasks = new Task[delays.Length];

        foreach ((int I, int Pause) args in delays)

        {

            tasks[args.I - 1] = DoWork(now, args.I, args.Pause);

        }

        Task.WaitAll(tasks);

        watch.Stop();

        Console.WriteLine($"Works took {watch.ElapsedMilliseconds}ms");

    }

    private static async Task DoWork(DateTime startOn, int i, int pause)

    {

        var watch = Stopwatch.StartNew();

        Console.WriteLine($"Work #{i} starts after {(DateTime.Now - startOn).TotalMilliseconds:F0}ms and waits for {pause}ms");

        while (watch.ElapsedMilliseconds < pause)

        {

            var diff = pause - watch.ElapsedMilliseconds;

            var wait = diff < 50 ? diff : Math.Round((pause - watch.ElapsedMilliseconds) / 2.0);

            await Task.Delay((int)wait);

            Console.WriteLine($"  #{i}: work in progress...");

            for (var j = rnd.Next() % 1_000; 0 < j; j--);

        }

        watch.Stop();

        Console.WriteLine($"Work #{i} ends after {watch.ElapsedMilliseconds}ms");

    }

}