CellularManagement/src/CellularManagement.Infrastructure/Services/Security/CaptchaService.cs

using CellularManagement.Domain.Services;
using SkiaSharp;

namespace CellularManagement.Infrastructure.Services.Security;

public class CaptchaService : ICaptchaService
{
    private readonly Random _random = new();
    private readonly string[] _fonts = { "Arial", "Verdana", "Times New Roman", "Tahoma" };
    private readonly SKColor[] _colors = {
        SKColors.Black, SKColors.Red, SKColors.Blue, SKColors.Green, SKColors.Purple, SKColors.Orange
    };

    public (string Code, byte[] ImageBytes) GenerateCaptcha(int length = 4)
    {
        string code = GenerateRandomCode(length);
        int width = Math.Max(120, 10 + length * 25);
        int height = 40;

        using var bitmap = new SKBitmap(width, height);
        using var canvas = new SKCanvas(bitmap);
        canvas.Clear(SKColors.White);

        // 干扰线
        for (int i = 0; i < 5; i++)
        {
            using var paint = new SKPaint
            {
                Color = _colors[_random.Next(_colors.Length)],
                StrokeWidth = 1
            };
            canvas.DrawLine(
                _random.Next(width), _random.Next(height),
                _random.Next(width), _random.Next(height),
                paint
            );
        }

        // 干扰点
        for (int i = 0; i < 100; i++)
        {
            using var paint = new SKPaint
            {
                Color = _colors[_random.Next(_colors.Length)],
                StrokeWidth = 1
            };
            canvas.DrawPoint(_random.Next(width), _random.Next(height), paint);
        }

        // 绘制验证码字符
        for (int i = 0; i < code.Length; i++)
        {
            using var paint = new SKPaint
            {
                Color = _colors[_random.Next(_colors.Length)],
                TextSize = 24,
                IsAntialias = true,
                Typeface = SKTypeface.FromFamilyName(_fonts[_random.Next(_fonts.Length)], SKFontStyle.Bold)
            };
            float x = 10 + i * 25;
            float y = 30 + _random.Next(-5, 5);
            canvas.DrawText(code[i].ToString(), x, y, paint);
        }

        using var ms = new MemoryStream();
        using var image = SKImage.FromBitmap(bitmap);
        image.Encode(SKEncodedImageFormat.Png, 100).SaveTo(ms);

        return (code, ms.ToArray());
    }

    private string GenerateRandomCode(int length)
    {
        const string chars = "2345678ABCDEFGHJKLMNPQRSTUVWXYZ";
        return new string(Enumerable.Repeat(chars, length)
            .Select(s => s[_random.Next(s.Length)]).ToArray());
    }
}