using System;
using System.Collections;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Web;
using System.Web.SessionState;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.HtmlControls;
using System.Drawing.Imaging;
using System.Drawing.Text;

namespace UrlWrite
{
 /**//// <summary>
 /// 页面验证码程序
 /// 使用：在页面中加入HTML代码 <img src="/blog/VerifyCode.aspx">
 /// </summary>
 public class VerifyCode : System.Web.UI.Page
 {

  #region Private Members
   static string[] FontItems  = new string[] {   "Arial",
                "Helvetica",
                "Geneva",
                "sans-serif",
                "Verdana"
               };

  static Brush[] BrushItems = new Brush[] {     Brushes.OliveDrab,
             Brushes.ForestGreen,
             Brushes.DarkCyan,
             Brushes.LightSlateGray,
             Brushes.RoyalBlue,
             Brushes.SlateBlue,
             Brushes.DarkViolet,
             Brushes.MediumVioletRed,
             Brushes.IndianRed,
             Brushes.Firebrick,
             Brushes.Chocolate,
             Brushes.Peru,
             Brushes.Goldenrod
            };

  static string[] BrushName = new string[] {    "OliveDrab",
              "ForestGreen",
              "DarkCyan",
              "LightSlateGray",
              "RoyalBlue",
              "SlateBlue",
              "DarkViolet",
              "MediumVioletRed",
              "IndianRed",
              "Firebrick",
              "Chocolate",
              "Peru",
              "Goldenrod"
             };

  private static Color BackColor    =  Color.White;
  private static Pen   BorderColor  =  Pens.DarkGray;
  private static int   Width        =  52;
  private static int   Height       =  21;

  private Random _random;
  private string _code;
  private int    _brushNameIndex;
  #endregion // end of Private Members

  #region Web Form Designer generated code
          override protected void OnInit(EventArgs e)
          {
           //
           // CODEGEN: This call is required by the ASP.NET Web Form Designer.
           //
           InitializeComponent();
           base.OnInit(e);
          }
       
  /**//// <summary>
  /// Required method for Designer support - do not modify
  /// the contents of this method with the code editor.
  /// </summary>
  private void InitializeComponent()
  {   
   this.Load += new System.EventHandler(this.Page_Load);

  }
  #endregion

  #region PageLoad Event
   public void Page_Load(object sender, System.EventArgs e)
   {
    //
    // TODO : initialize
    //
    this._random = new Random();
    this._code = GetRandomCode();

    //
    // TODO : use Session["code"] save the VerifyCode
    //
    Session["code"] = this._code;

    //
    // TODO : output Image
    //
    this.SetPageNoCache();
    this.OnPaint();
   }
  #endregion // end of PageLoad Event

  #region Helper Methods
   /**//// <summary>
   /// 设置页面不被缓存
   /// </summary>
   private void SetPageNoCache()
   {
    Response.Buffer = true;
    Response.ExpiresAbsolute = System.DateTime.Now.AddSeconds(-1);
    Response.Expires = 0;
    Response.CacheControl = "no-cache";
    Response.AppendHeader("Pragma","No-Cache");
   }

  /**//// <summary>
  /// 取得一个 4 位的随机码
  /// </summary>
  /// <returns></returns>
  private string GetRandomCode()
  {
   return Guid.NewGuid().ToString().Substring(0, 4);
  }

  /**//// <summary>
  /// 随机取一个字体
  /// </summary>
  /// <returns></returns>
  private Font GetFont()
  {
   int fontIndex = _random.Next(0, FontItems.Length);
   FontStyle fontStyle = GetFontStyle(_random.Next(0, 2));
   return new Font(FontItems[fontIndex], 12, fontStyle);
  }

  /**//// <summary>
  /// 取一个字体的样式
  /// </summary>
  /// <param name="index"></param>
  /// <returns></returns>
  private FontStyle GetFontStyle(int index)
  {
   switch (index)
   {
    case 0:
     return FontStyle.Bold;
    case 1:
     return FontStyle.Italic;
    default:
     return FontStyle.Regular;
   }
  }

  /**//// <summary>
  /// 随机取一个笔刷
  /// </summary>
  /// <returns></returns>
  private Brush GetBrush()
  {
   int brushIndex = _random.Next(0, BrushItems.Length);
   _brushNameIndex = brushIndex;
   return BrushItems[brushIndex];
  }
  #endregion // end of Helper Methods

  #region Paint Methods
   /**//// <summary>
   /// 绘画事件
   /// </summary>
   private void OnPaint()
   {
    Bitmap objBitmap = null;
    Graphics g = null;

    try
    {
     objBitmap = new Bitmap(Width, Height);
     g = Graphics.FromImage(objBitmap);

     Paint_Background(g);
     Paint_Text(g);
     Paint_TextStain(objBitmap);
     Paint_Border(g);

     objBitmap.Save(Response.OutputStream, ImageFormat.Gif);
     Response.ContentType = "image/gif";
    }
    catch {}
    finally
    {
     if (null != objBitmap)
      objBitmap.Dispose();
     if (null != g)
      g.Dispose();
    }
   }

  /**//// <summary>
  /// 绘画背景颜色
  /// </summary>
  /// <param name="g"></param>
  private void Paint_Background(Graphics g)
  {
   g.Clear(BackColor);
  }

  /**//// <summary>
  /// 绘画边框
  /// </summary>
  /// <param name="g"></param>
  private void Paint_Border(Graphics g)
  {
   g.DrawRectangle(BorderColor, 0, 0, Width - 1, Height - 1);
  }

  /**//// <summary>
  /// 绘画文字
  /// </summary>
  /// <param name="g"></param>
  private void Paint_Text(Graphics g)
  {
   g.DrawString(_code, GetFont(), GetBrush(), 3, 1);
  }

  /**//// <summary>
  /// 绘画文字噪音点
  /// </summary>
  /// <param name="g"></param>
  private void Paint_TextStain(Bitmap b)
  {
   for (int n=0; n<30; n++)
   {
    int x = _random.Next(Width);
    int y = _random.Next(Height);
    b.SetPixel(x, y, Color.FromName(BrushName[_brushNameIndex]));
   }
  }
  #endregion // end of Paint Methods

 } // end of class

} // end of namespace