using System;
using System.Drawing;
using System.Drawing.Imaging;
using System.IO;
using System.Threading.Tasks;

namespace Znyc.Admin.Commons.VerificationCode
{
    /// <summary>
    /// 验证码实现
    /// </summary>
    public class Captcha
    {
        private const string Letters = "1,2,3,4,5,6,7,8,9,A,B,C,D,E,F,G,H,J,K,L,M,N,P,Q,R,S,T,U,V,W,X,Y,Z";

        /// <summary>
        /// 生成验证码图片
        /// </summary>
        /// <param name="captchaCode">验证码</param>
        /// <param name="width">图形宽度，默认为验证码长度x25</param>
        /// <param name="height">图形高度，默认30px</param>
        /// <returns></returns>
        public async Task<CaptchaResult> GenerateCaptchaImageAsync(string captchaCode, int width = 0, int height = 30)
        {
            //验证码颜色集合
            Color[] c =
            {
                Color.Black, Color.Red, Color.DarkBlue, Color.Green, Color.Orange, Color.Brown, Color.DarkCyan,
                Color.Purple
            };

            //验证码字体集合
            string[] fonts = { "Verdana", "Microsoft Sans Serif", "Comic Sans MS", "Arial" };

            //定义图像的大小，生成图像的实例
            Bitmap image = new Bitmap(width == 0 ? captchaCode.Length * 25 : width, height);

            Graphics g = Graphics.FromImage(image);

            //背景设为白色
            g.Clear(Color.White);

            Random random = new Random();
            // 画图片的背景噪音线
            for (int i = 0; i < 100; i++)
            {
                int x = random.Next(image.Width);
                int y = random.Next(image.Height);
                g.DrawRectangle(new Pen(Color.LightGray, 0), x, y, 1, 1);
            }

            //验证码绘制在g中
            for (int i = 0; i < captchaCode.Length; i++)
            {
                //随机颜色索引值
                int cindex = random.Next(c.Length);

                //随机字体索引值
                int findex = random.Next(fonts.Length);

                //字体
                Font f = new Font(fonts[findex], 15, FontStyle.Bold);

                //颜色
                Brush b = new SolidBrush(c[cindex]);

                int ii = 4;
                if ((i + 1) % 2 == 0)
                {
                    ii = 2;
                }

                //绘制一个验证字符
                g.DrawString(captchaCode.Substring(i, 1), f, b, 17 + i * 17, ii);
            }

            //画图片的前景噪音点
            for (int i = 0; i < 100; i++)
            {
                int x = random.Next(image.Width);
                int x1 = random.Next(image.Width);
                int y = random.Next(image.Height);
                int y1 = random.Next(image.Height);
                if (i % 11 == 0)
                {
                    g.DrawLine(new Pen(Color.Silver), x, y, x1, y1);
                }

                image.SetPixel(x, y, Color.FromArgb(random.Next()));
            }

            //画图片的边框线
            //g.DrawRectangle(new Pen(Color.Silver), 0, 0, image.Width - 1, image.Height - 1);
            MemoryStream ms = new MemoryStream();
            image.Save(ms, ImageFormat.Png);

            g.Dispose();
            image.Dispose();

            return await Task.FromResult(new CaptchaResult
            {
                CaptchaCode = captchaCode,
                CaptchaMemoryStream = ms,
                Timestamp = DateTime.Now
            });
        }

        /// <summary>
        /// 生成随机验证码字符
        /// </summary>
        /// <param name="codeLength">验证码位数</param>
        /// <returns></returns>
        public async Task<string> GenerateRandomCaptchaAsync(int codeLength = 4)
        {
            string[] array = Letters.Split(new[] { ',' });

            Random random = new Random();

            int temp = -1;

            string captcheCode = string.Empty;

            for (int i = 0; i < codeLength; i++)
            {
                if (temp != -1)
                {
                    random = new Random(i * temp * unchecked((int)DateTime.Now.Ticks));
                }

                int index = random.Next(array.Length);

                if (temp != -1 && temp == index)
                {
                    return await GenerateRandomCaptchaAsync(codeLength);
                }

                temp = index;

                captcheCode += array[index];
            }

            return await Task.FromResult(captcheCode);
        }
    }
}