using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Text;
using System.Drawing.Drawing2D;
using System.Drawing;
using System.IO;
using System.Drawing.Imaging;

public partial class ValidateCode : System.Web.UI.Page
{
    private string code;
    private const int ImageHeigth = 22;             //验证码图片的高度
    private const double ImageLengthBase = 12.5;    //验证码图片中每个字符的宽度
    private const int ImageLineNumber = 25;         //噪音线的数量
    private const int ImagePointNumber = 100;       //噪点的数量
    private int length;
    public static string VALIDATECODEKEY;       //此处用来保存验证码到Session的Key的名称

    //静态构造函数初始化验证码在Session中的Key名称
    static ValidateCode()
    {
        VALIDATECODEKEY = "VALIDATECODEKEY";
    }

    //设置验证码的长度和内容
    public ValidateCode()
    {
        this.length = 4;
        this.code = string.Empty;
    }

    /// <summary>
    /// 产生随机的验证码并加入Session
    /// </summary>
    /// <param name="length">验证码长度</param>
    /// <returns></returns>
    public string CreateCode(int length)
    {
        if (length <= 0)
        {
            return string.Empty;
        }
        Random random = new Random();
        StringBuilder builder = new StringBuilder();
        //产生随机的验证码并拼接起来
        for (int i = 0; i < length; i++)
        {
            builder.Append(random.Next(0, 10));
        }
        this.code = builder.ToString();
        this.Session[VALIDATECODEKEY] = this.code;
        return this.code;
    }

    /// <summary>
    /// 根据长度产生验证码
    /// 并将验证码画成图片
    /// </summary>
    /// <param name="length">验证码长度</param>
    public void CreateValidateImage(int length) 
    {
        this.code = this.CreateCode(length);
        this.CreateValidateImage(this.code);
    }
    /// <summary>
    /// 根据产生的验证码生成图片
    /// </summary>
    /// <param name="code">验证码</param>
    public void CreateValidateImage(string code) 
    {
        if (!string.IsNullOrEmpty(code))
        {
            this.Session[VALIDATECODEKEY] = code;
            //初始化位图Bitmap对象，指定图片对象的大小(宽,高)
            Bitmap image = new Bitmap((int)Math.Ceiling((double)(code.Length * ImageLengthBase)), ImageHeigth);
            //初始化一块画布
            Graphics graphics = Graphics.FromImage(image);
            Random random = new Random();
            try
            {
                int num5;
                graphics.Clear(Color.White);
                //绘制噪音线
                for (num5 = 0; num5 < ImageLineNumber; num5++)
                {
                    int num = random.Next(image.Width);
                    int num3 = random.Next(image.Height);
                    int num2 = random.Next(image.Width);
                    int num4 = random.Next(image.Height);
                    graphics.DrawLine(new Pen(Color.Silver), num, num3, num2, num4);
                }
                //验证码字体样式
                Font font = new Font("Tahoma", 12, FontStyle.Italic | FontStyle.Bold);
                LinearGradientBrush brush = new LinearGradientBrush(new Rectangle(0, 0, image.Width, image.Height), Color.Blue, Color.DarkRed, 1.2f, true);
                //绘制验证码到画布
                graphics.DrawString(code, font, brush, (float)2, (float)2);
                //绘制噪点
                for (num5 = 0; num5 < ImagePointNumber; num5++)
                {
                    int x = random.Next(image.Width);
                    int y = random.Next(image.Height);
                    image.SetPixel(x, y, Color.FromArgb(random.Next()));
                }
                graphics.DrawRectangle(new Pen(Color.Silver), 0, 0, image.Width - 1, image.Height - 1);
                MemoryStream stream = new MemoryStream();
                //保存图片
                image.Save(stream, ImageFormat.Gif);
                base.Response.ClearContent();
                base.Response.ContentType = "image/Gif";
                base.Response.BinaryWrite(stream.ToArray());
            }
            finally
            {
                graphics.Dispose();
                image.Dispose();
            }
        }
    }
    protected override void OnLoad(EventArgs e) 
    {
        this.CreateValidateImage(this.length);
    }

    // Properties
    public string Code
    {
        get
        {
            return this.Code;
        }
    }
    public int Length
    {
        get
        {
            return this.length;
        }
        set
        {
            this.length = value;
        }
    }
}