iot/projects/Infrastructure/Web/Mvc/CaptchaHelper.cs

using Microsoft.AspNetCore.Hosting;
using System;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Drawing.Imaging;
using System.Drawing.Text;
using System.Globalization;
using System.IO;
using System.Security.Cryptography;

namespace Infrastructure.Web.Mvc
{
    public class CaptchaHelper : IDisposable
    {
        private readonly PrivateFontCollection _collection;

        public CaptchaHelper(IWebHostEnvironment env)
        {
            if (env is null)
            {
                throw new ArgumentNullException(nameof(env));
            }

            _collection = new PrivateFontCollection();
            _collection.AddFontFile(Path.Combine(env.WebRootPath, "fonts", "arial.ttf"));
        }

        public byte[] GetCaptcha(string code, int width = 80, int height = 30)
        {
            return GetImage(code, width, height);
        }

        private static Color GetColor()
        {
            var colors = new Color[] {
                Color.DodgerBlue,
                Color.SteelBlue,
                Color.LimeGreen,
                Color.LightSeaGreen,
                Color.DarkGoldenrod,
                Color.Chocolate,
                Color.IndianRed,
                Color.Cyan
            };
            return colors[GetRandom(0, 7)];
        }

        private byte[] GetImage(string value, int width, int height)
        {
            using var image = DrawImage(value, width, height);
            using var stream = new MemoryStream();
            image.Save(stream, ImageFormat.Jpeg);
            return stream.ToArray();
        }

        private Bitmap DrawImage(string value, int width, int height)
        {
            var size = new Size(80, 30);
            var image = new Bitmap(size.Width, size.Height);
            var g = Graphics.FromImage(image);

            g.Clear(Color.FloralWhite);
            using (var pen = new Pen(Color.Lavender))
            {
                g.DrawRectangle(pen, 0, 0, width, height);
            }
            DrawBeziers(g, width, height);
            var top = 0; var left = 0;
            var index = 0;
            DrawChar(value[index++], g, left, top, width, height);
            left += width / 4;
            DrawChar(value[index++], g, left, top, width, height);
            left += width / 4;
            DrawChar(value[index++], g, left, top, width, height);
            left += width / 4;
            DrawChar(value[index++], g, left, top, width, height);

            return image;
        }

        private static void DrawBeziers(Graphics g, int width, int height)
        {
            for (int i = 0; i < width * height / 100; i++)
            {
                using var pen = new Pen(GetColor(), 0);
                var x = GetRandom(0, width);
                var y = GetRandom(0, height);
                if (GetRandom() > 4)
                {
                    g.DrawEllipse(pen, x, y, GetRandom(), GetRandom());
                }
                else
                {
                    g.DrawBezier(pen, x, y, x + 5, y + 5, x + 10, y + 10, x + 20, y + 20);
                }
            }
        }

        private void DrawChar(char ch, Graphics g, int left, int top, int width, int height)
        {
            var fontSize = 16;
            fontSize += GetRandom(-5, 5);
            var value = ch.ToString(CultureInfo.CurrentCulture);
            using var font = new Font(_collection.Families[0], fontSize);
            var point = new Point(left, top);
            var size = new Size(width, height);
            using var brush = new LinearGradientBrush(new Rectangle(point, size), GetColor(), GetColor(), new Random(DateTime.Now.Millisecond).Next(0, 359));
            g.DrawString(value, font, brush, point);
        }

        private static int GetRandom(int min = 0, int max = 9)
        {
            var random = new byte[1];
            using (var rg = RandomNumberGenerator.Create())
            {
                rg.GetBytes(random);
            }
            return new Random(Convert.ToInt32(random[0])).Next(min, max);
        }

        protected virtual void Dispose(bool disposing)
        {
            if (disposing)
            {
                this._collection.Dispose();
            }
        }

        public void Dispose()
        {
            Dispose(true);
            GC.SuppressFinalize(this);
        }

        ~CaptchaHelper()
        {
            Dispose(false);
        }
    }
}