using System;

using System.Collections;

using System.Collections.Generic;

using System.Linq;

using System.Threading.Tasks;

​

namespace task_or_not_task

{

    // fake types

    using STREAM = Int32;

    using PNG = Int32;

​

    public static class Program

    {

        public static void Main(string[] args)

        {

            streams

                .Load()

                .Resize()

                .Upload()

                .printReport()

                .ToArray();

        }

​

        public static IEnumerable<STREAM> Load(this IEnumerable<STREAM> ix)

        {

            foreach (var s in streams)

            {

                randomWait();

                $"stream {s} loaded ..".localLog();

                yield return s;

            }

        }

        public static IEnumerable<PNG> Resize(this IEnumerable<STREAM> streams)

        {

            foreach (var s in streams)

            {

                randomWait();

                $"image {s} resized ..".localLog();

                yield return (PNG)s;

            }

        }

        public static IEnumerable<string> Upload(this IEnumerable<PNG> previews)

        {

            foreach (var p in previews)

            {

                randomWait();

                $"image {p} resized ..".localLog();

                yield return getUrl(p);

            }

        }

        public static IEnumerable<string> printReport(this IEnumerable<string> urls)

        {

            foreach (var u in urls)

            {

                u.localLog();

                yield return u;

            }

        }

​

        public static void randomWait()

        {

            var rand = new Random(DateTime.UtcNow.Millisecond);

            Task.Delay(rand.Next(100, 400)).Wait();

        }

        public static void localLog(this string s) => Console.WriteLine(s);

        public static string getUrl(this int previewNmae)

            => $@"uploaded file - URL: {dstUrl}\{previewNmae}.{dstExt}";

        public const string dstUrl = @"https:\\my-site.com";

        public const string dstExt = "png";

        public const int initialIndex = 0;

        public static STREAM[] streams = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };

    }

}

​