using System;
using System.IO;
using System.IO.Compression;
using System.Threading;
using System.Threading.Tasks;

namespace GZipComressionTestApp
{
    class Program
    {
        static void Main(string[] args)
        {
            var task = Task.Run(() => CompressFile("SkypeSetup.exe", "SkypeSetup.exe.gz"));
            task.Wait();

            Console.ReadKey();
        }

        public static async Task CompressFile(string inputFile, string outPutFile)
        {
            using (var fileStream = new FileStream(inputFile, FileMode.Open, FileAccess.Read))
            {
                var chunk = new byte[200];

                var bytesToRead = (int) fileStream.Length;
                var bytesRead = 0;

                while (bytesToRead > 0)
                {
                    var numberOfReadBytes = await fileStream.ReadAsync(chunk, bytesRead, bytesToRead);
                    // не понимаю как запустить задачу CompressChunk

                    if(numberOfReadBytes == 0)
                        break;

                    bytesRead += numberOfReadBytes;
                    bytesToRead -= numberOfReadBytes;

                }
            }
        }

        private static async Task CompressChunk(byte[] chunk, string outPutFile)
        {
            using (var memoryStream = new MemoryStream(chunk))
            {
                await CompressChunk(memoryStream, outPutFile);
            }
        }

        private static async Task CompressChunk(Stream memoryStream, string outPutFile)
        {
            using (var fileStream = File.Create(outPutFile))
            using (var gzipStream = new GZipStream(fileStream, CompressionMode.Compress))
            {
                await memoryStream.CopyToAsync(gzipStream);
                gzipStream.Close();
            }
        }

    }
}