using System;
using System.Drawing;
using System.Drawing.Imaging;
using System.IO;

public class CaptchaService
{
    private string generatedCaptchaCode;

    // 生成验证码图像并返回Base64字符串
    public (string captchaImage, string captchaCode) GenerateCaptcha()
    {
        generatedCaptchaCode = GenerateRandomCode(5); // 生成5位随机字符
        Bitmap bitmap = new Bitmap(100, 40);

        using (Graphics g = Graphics.FromImage(bitmap))
        {
            g.Clear(Color.White);
            using (Font font = new Font("Arial", 20))
            {
                g.DrawString(generatedCaptchaCode, font, Brushes.Black, 10, 10);
            }
        }

        using (MemoryStream ms = new MemoryStream())
        {
            bitmap.Save(ms, ImageFormat.Png);
            string base64Image = Convert.ToBase64String(ms.ToArray());
            return (base64Image, generatedCaptchaCode);
        }
    }

    // 验证用户输入的验证码
    public bool ValidateCaptcha(string userInput)
    {
        return userInput.Equals(generatedCaptchaCode, StringComparison.OrdinalIgnoreCase);
    }

    // 生成随机字符
    private string GenerateRandomCode(int length)
    {
        const string chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
        Random random = new Random();
        return new string(Enumerable.Repeat(chars, length)
            .Select(s => s[random.Next(s.Length)]).ToArray());
    }
}