using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.IO;
using System.Linq;
using System.Net;
using System.Threading;
using System.Threading.Tasks;

namespace Masuit.Tools.Core.Net
{
    public delegate void FileMergeProgressChangedEventHandler(object sender, int e);
    public class MultiThreadDownloader
    {
        #region Variables
        public event EventHandler TotalProgressChanged;
        public event FileMergeProgressChangedEventHandler FileMergeProgressChanged;
        private readonly AsyncOperation _aop;
        #endregion

        #region DownloadManager
        public MultiThreadDownloader(string sourceUrl, string tempDir, string savePath, int numOfParts)
        {
            _url = sourceUrl;
            NumberOfParts = numOfParts;
            TempFileDirectory = tempDir;
            PartialDownloaderList = new List<PartialDownloader>();
            _aop = AsyncOperationManager.CreateOperation(null);
            FilePath = savePath;
        }
        public MultiThreadDownloader(string sourceUrl, string savePath, int numOfParts) : this(sourceUrl, null, savePath, numOfParts)
        {
            TempFileDirectory = Environment.GetEnvironmentVariable("temp");
        }
        public MultiThreadDownloader(string sourceUrl, int numOfParts) : this(sourceUrl, null, numOfParts)
        {
        }
        #endregion

        #region Events

        private void temp_DownloadPartCompleted(object sender, EventArgs e)
        {
            WaitOrResumeAll(PartialDownloaderList, true);

            if (TotalBytesReceived == Size)
            {
                UpdateProgress();
                MergeParts();
                return;
            }

            OrderByRemaining(PartialDownloaderList);

            int rem = PartialDownloaderList[0].RemainingBytes;
            if (rem < 50 * 1024)
            {
                WaitOrResumeAll(PartialDownloaderList, false);
                return;
            }

            int from = PartialDownloaderList[0].CurrentPosition + rem / 2;
            int to = PartialDownloaderList[0].To;
            if (from > to)
            {
                WaitOrResumeAll(PartialDownloaderList, false);
                return;
            }
            PartialDownloaderList[0].To = from - 1;

            WaitOrResumeAll(PartialDownloaderList, false);

            PartialDownloader temp = new PartialDownloader(_url, TempFileDirectory, Guid.NewGuid().ToString(), from, to, true);
            temp.DownloadPartCompleted += temp_DownloadPartCompleted;
            temp.DownloadPartProgressChanged += temp_DownloadPartProgressChanged;
            PartialDownloaderList.Add(temp);
            temp.Start();
        }

        void temp_DownloadPartProgressChanged(object sender, EventArgs e)
        {
            UpdateProgress();
        }

        void UpdateProgress()
        {
            int pr = (int)(TotalBytesReceived * 1d / Size * 100);
            if (TotalProgress != pr)
            {
                TotalProgress = pr;
                if (TotalProgressChanged != null)
                {
                    _aop.Post(state => TotalProgressChanged(this, EventArgs.Empty), null);
                }
            }
        }
        #endregion

        #region Helpers
        void CreateFirstPartitions()
        {
            Size = GetContentLength(_url, ref _rangeAllowed, ref _url);
            int maximumPart = (int)(Size / (25 * 1024));
            maximumPart = maximumPart == 0 ? 1 : maximumPart;
            if (!_rangeAllowed)
                NumberOfParts = 1;
            else if (NumberOfParts > maximumPart)
                NumberOfParts = maximumPart;

            for (int i = 0; i < NumberOfParts; i++)
            {
                PartialDownloader temp = CreateNewPd(i, NumberOfParts, Size);
                temp.DownloadPartProgressChanged += temp_DownloadPartProgressChanged;
                temp.DownloadPartCompleted += temp_DownloadPartCompleted;
                PartialDownloaderList.Add(temp);
                temp.Start();
            }
        }
        void MergeParts()
        {
            List<PartialDownloader> mergeOrderedList = SortPDsByFrom(PartialDownloaderList);
            using (var fs = new FileStream(FilePath, FileMode.Create, FileAccess.ReadWrite))
            {
                long totalBytesWritten = 0;
                int mergeProgress = 0;
                foreach (var item in mergeOrderedList)
                {
                    using (FileStream pds = new FileStream(item.FullPath, FileMode.Open, FileAccess.Read))
                    {
                        byte[] buffer = new byte[4096];
                        int read;
                        while ((read = pds.Read(buffer, 0, buffer.Length)) > 0)
                        {
                            fs.Write(buffer, 0, read);
                            totalBytesWritten += read;
                            int temp = (int)(totalBytesWritten * 1d / Size * 100);
                            if (temp != mergeProgress && FileMergeProgressChanged != null)
                            {
                                mergeProgress = temp;
                                _aop.Post(state => FileMergeProgressChanged(this, temp), null);
                            }
                        }
                    }
                    File.Delete(item.FullPath);
                }
            }
        }
        PartialDownloader CreateNewPd(int order, int parts, long contentLength)
        {
            int division = (int)contentLength / parts;
            int remaining = (int)contentLength % parts;
            int start = division * order;
            int end = start + division - 1;
            end += (order == parts - 1) ? remaining : 0;
            return new PartialDownloader(_url, TempFileDirectory, Guid.NewGuid().ToString(), start, end, true);
        }
        public static void WaitOrResumeAll(List<PartialDownloader> list, bool wait)
        {
            foreach (PartialDownloader item in list)
            {
                if (wait)
                    item.Wait();
                else
                    item.ResumeAfterWait();
            }
        }


        private static void BubbleSort(List<PartialDownloader> list)
        {
            bool switched = true;
            while (switched)
            {
                switched = false;
                for (int i = 0; i < list.Count - 1; i++)
                {
                    if (list[i].RemainingBytes < list[i + 1].RemainingBytes)
                    {
                        PartialDownloader temp = list[i];
                        list[i] = list[i + 1];
                        list[i + 1] = temp;
                        switched = true;
                    }
                }
            }
        }
        //Sorts the downloader by From property to merge the parts
        public static List<PartialDownloader> SortPDsByFrom(List<PartialDownloader> list)
        {
            return list.OrderBy(x => x.From).ToList();
        }
        public static void OrderByRemaining(List<PartialDownloader> list)
        {
            BubbleSort(list);
        }

        public static long GetContentLength(string url, ref bool rangeAllowed, ref string redirectedUrl)
        {
            HttpWebRequest req = WebRequest.Create(url) as HttpWebRequest;
            req.UserAgent = "Mozilla/4.0 (compatible; MSIE 11.0; Windows NT 6.2; .NET CLR 1.0.3705;)";
            req.ServicePoint.ConnectionLimit = 4;
            HttpWebResponse resp = req.GetResponse() as HttpWebResponse;
            redirectedUrl = resp.ResponseUri.OriginalString;
            long ctl = resp.ContentLength;
            rangeAllowed = resp.Headers.AllKeys.Select((v, i) => new { HeaderName = v, HeaderValue = resp.Headers[i] }).Any(k => k.HeaderName.ToLower().Contains("range") && k.HeaderValue.ToLower().Contains("byte"));
            resp.Close();
            req.Abort();
            return ctl;
        }
        #endregion

        #region Public Methods
        public void Pause()
        {
            foreach (var t in PartialDownloaderList)
            {
                if (!t.Completed)
                    t.Stop();
            }

            //Setting a Thread.Sleep ensures all downloads are stopped and exit from loop.
            Thread.Sleep(200);
        }
        public void Start()
        {
            Task th = new Task(CreateFirstPartitions);
            th.Start();
        }

        public void Resume()
        {
            int count = PartialDownloaderList.Count;
            for (int i = 0; i < count; i++)
            {
                if (PartialDownloaderList[i].Stopped)
                {
                    int from = PartialDownloaderList[i].CurrentPosition + 1;
                    int to = PartialDownloaderList[i].To;
                    if (from > to) continue;
                    PartialDownloader temp = new PartialDownloader(_url, TempFileDirectory, Guid.NewGuid().ToString(), from, to, _rangeAllowed);

                    temp.DownloadPartProgressChanged += temp_DownloadPartProgressChanged;
                    temp.DownloadPartCompleted += temp_DownloadPartCompleted;
                    PartialDownloaderList.Add(temp);
                    PartialDownloaderList[i].To = PartialDownloaderList[i].CurrentPosition;
                    temp.Start();
                }
            }
        }
        #endregion

        #region Property Variables

        private string _url;
        private bool _rangeAllowed;

        #endregion

        #region Properties
        public bool RangeAllowed
        {
            get => _rangeAllowed;
            set => _rangeAllowed = value;
        }
        public string TempFileDirectory { get; set; }

        public string Url
        {
            get => _url;
            set => _url = value;
        }

        public int NumberOfParts { get; set; }

        public long TotalBytesReceived => PartialDownloaderList.Where(t => t != null).Sum(t => t.TotalBytesRead);

        public int TotalProgress { get; private set; }

        public long Size { get; private set; }

        public int TotalSpeedInBytes => PartialDownloaderList.Sum(t => t.SpeedInBytes);
        public List<PartialDownloader> PartialDownloaderList { get; }

        public string FilePath { get; set; }

        #endregion

    }
}