using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace TemuKJD.BLL.Tools
{
    public class DownloadBLL
    {
        public static string downloadFile(string url, string fileName, Control ctrl)
        {
            if (ctrl == null)
                ctrl = new Control();

            //string StrFileName = "d:\\wgscd.zip"; //根据实际情况设置 
            //string StrUrl = "https://files.cnblogs.com/files/wgscd/xxx.zip"; //根据实际情况设置
            string StrFileName = fileName;
            string StrUrl = url;
            //打开上次下载的文件或新建文件 
            long lStartPos = 0;
            System.IO.FileStream fs;
            if (System.IO.File.Exists(StrFileName))//另外如果文件已经下载完毕，就不需要再断点续传了，不然请求的range 会不合法会抛出异常。
            {
                fs = System.IO.File.OpenWrite(StrFileName);
                lStartPos = fs.Length;
                fs.Seek(lStartPos, System.IO.SeekOrigin.Current); //移动文件流中的当前指针 
            }
            else
            {
                fs = new System.IO.FileStream(StrFileName, System.IO.FileMode.Create);
                lStartPos = 0;
            }
            //打开网络连接 
            try
            {
                System.Net.HttpWebRequest request = (System.Net.HttpWebRequest)System.Net.HttpWebRequest.Create(StrUrl);
                if (lStartPos > 0)
                {
                    request.AddRange((int)lStartPos); // 设置Range值
                }
                System.Net.WebResponse response = request.GetResponse();
                //向服务器请求，获得服务器回应数据流 
                System.IO.Stream ns = response.GetResponseStream();
                long totalSize = response.ContentLength;
                long hasDownSize = 0;
                byte[] nbytes = new byte[512];//521,2048 etc
                int nReadSize = 0;
                nReadSize = ns.Read(nbytes, 0, nbytes.Length);
                while (nReadSize > 0)
                {
                    fs.Write(nbytes, 0, nReadSize);
                    nReadSize = ns.Read(nbytes, 0, 512);
                    hasDownSize += nReadSize;
                    ctrl.Invoke(new Action(() =>
                    {
                        //ctrl.Text = "" + hasDownSize + "/" + totalSize + "   (" + (((double)hasDownSize * 100 / totalSize).ToString("0.00")) + "%)"; // 显示下载百分比
                        ctrl.Text = "正在下载模块 " + ((double)(hasDownSize + lStartPos) * 100 / (totalSize + lStartPos)).ToString("0.00") + "%"; // 显示下载百分比
                    }));
                    //Application.DoEvents();
                }
                fs.Close();
                ns.Close();
                ctrl.Invoke(new Action(() =>
                {
                    ctrl.Text = "模块下载完成 " + ((double)(hasDownSize + lStartPos) * 100 / (totalSize + lStartPos)).ToString("0.00") + "%"; // 显示下载百分比
                }));
                return "下载完成";
            }
            catch (Exception ex)
            {
                fs.Close();
                return "下载过程中出现错误:" + ex.ToString();
            }
        }
    }
}