using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Drawing;
using System.Web.UI.WebControls;
using System.Drawing.Imaging;
using System.Web.SessionState;

namespace Bowin.Common
{
    public class VerificationCodeModule : IHttpModule, IRequiresSessionState
    {

        public void Dispose()
        { }

        public void Init(HttpApplication context)
        {
            context.PreRequestHandlerExecute += new EventHandler(context_PreRequestHandlerExecute);

        }
        void context_PreRequestHandlerExecute(object sender, EventArgs e)
        {
            HttpApplication context = (HttpApplication)sender;
            string str = context.Request.Url.ToString();
            if (str.Contains("verificationCode.png"))
            {
                //context.Response.Cache.SetNoStore();
                this._random = new Random();
                this._code = GetRandomCode();
                context.Session["code"] = this._code;
                this.SetPageNoCache(context);
                this.OnPaint(context);
                context.Response.End();
            }
            else
            { return; }
        }

        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;

        /**/
        /**/
        /**/
        /// <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); 
        }

        /**/
        /**/
        /**/
        /// <summary> 
        /// 设置页面不被缓存 
        /// </summary> 
        private void SetPageNoCache(HttpApplication context)
        {
            context.Response.Buffer = true;
            context.Response.ExpiresAbsolute = System.DateTime.Now.AddSeconds(-1);
            context.Response.Expires = 0;
            context.Response.CacheControl = "no-cache";
            context.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];
        }
        /**/
        /**/
        /**/
        /// <summary> 
        /// 绘画事件 
        /// </summary> 
        private void OnPaint(HttpApplication context)
        {
            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(context.Response.OutputStream, ImageFormat.Gif);
                context.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]));
            }
        }

    }
}