using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Text;

#region histroy
///程式代號：OpenFile
///程式名稱：檔案下載
///程式說明：        
///xx.YYYY/MM/DD    VER     AUTHOR       COMMENTS(說明修改的內容)  
///01.2012/05/10    1.0     Ethan        CREATE 
#endregion

namespace OT.Web
{
    public partial class OpenFile : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            // 在這裡放置使用者程式碼以初始化網頁
            Response.Expires = 0;
            FnOpenFile();
        }

        private void FnOpenFile()
        {
            try
            {
                //防止在IE中直接開啟本程式操作檔案
                if (Request["U"] == null && Session["U"] == null)
                {
                    WriteMsg("非法登入，不可操作檔案！");
                }
                //重定向後開啟檔案
                else if (Session["U"] != null)
                {
                    string strFileName = Session["U"].ToString();
                    Session.Remove("U");//及時釋放Session
                    this.ReadFile(strFileName);
                }
                //遠端呼叫本程式時帶入參數檔案名稱U，為防止User看到U的內容，進行一次重定向
                else if (Request["U"] != null)
                {
                    string strFileName = Request.QueryString["U"].ToString();
                    strFileName = FnHidToFileName(strFileName).Replace("\\", "/");
                    //Session["U"] = strFileName;//用Session記錄U做重定向動作
                    //Session["FileName"] = Request.QueryString["FileName"].ToString();
                    //Response.Redirect(@"OpenFile.aspx", false);

                    this.ReadFile(strFileName);
                }
            }
            catch (Exception ex)
            {
                Session.Remove("U");//及時釋放Session
                this.WriteMsg("開啟檔案出錯，請重新試一次！");
            }
        }

        /// <summary>
        /// 將用於URL中傳參的Base64碼轉為String，轉換前將Base64碼中用*和@替換的＋和/還原
        /// </summary>
        /// <param name="strFrom"></param>
        /// <returns></returns>
        public string FnHidToFileName(string strFrom)
        {
            string strTo = strFrom.Replace("*", "+").Replace("@", "/").Replace("!", "=");
            strTo = FnBase64ToString(strTo);
            return strTo;
        }
        /// <summary>
        /// 將Base64碼轉為String
        /// </summary>
        /// <param name="strFrom"></param>
        /// <returns></returns>
        public string FnBase64ToString(string strFrom)
        {
            byte[] byTo = Convert.FromBase64String(strFrom);
            string strTo = System.Text.Encoding.Default.GetString(byTo);
            return strTo;
        }
        /// <summary>
        /// 開啟檔案
        /// </summary>
        /// <param name="strFileName"></param>
        private void ReadFile(string strFileName)
        {
            string strDownFileName = UTF_FileName(Request.QueryString["FileName"].ToString());
            strDownFileName = HttpUtility.UrlEncode(strDownFileName, System.Text.Encoding.UTF8); //解決中文問題
            Response.ContentType = "application/octet-stream";
            Response.AddHeader("Content-Disposition"
                , String.Format("attachment; filename=\"{0}\";", strDownFileName));
            //Response.Write("**" + fileName);
            Response.WriteFile(UTF_FileName(strFileName));
            try
            {
                Response.End(); //如果提前結束會出現異常。
            }
            catch (Exception ex) { return; }
        }

        private static string UTF_FileName(string filename)
        {
            return HttpUtility.UrlDecode(filename);
            //return HttpUtility.UrlEncode(filename, System.Text.Encoding.UTF8);
        }
        /// <summary>
        /// Alert訊息並關閉畫面
        /// </summary>
        /// <param name="Msg">alert出來的訊息內容</param>
        private void WriteMsg(string Msg)
        {
            StringBuilder sbScript = new StringBuilder();
            sbScript.Append("<script language='javascript'>");
            sbScript.Append("ShowArtAlert('" + Msg + "');");
            sbScript.Append("window.opener=null;window.open('','_self');window.close();");
            sbScript.Append("</script>");
            this.ClientScript.RegisterStartupScript(GetType(), "close", sbScript.ToString());
        }

    }
}