CellularManagement/src/CellularManagement.Application/Features/Auth/Commands/GenerateCaptcha/GenerateCaptchaCommandHandler.cs

using MediatR;
using CellularManagement.Domain.Services;
using CellularManagement.Application.Common;
using System.Text;
using CellularManagement.Domain.Common;
using Microsoft.Extensions.Caching.Memory;

namespace CellularManagement.Application.Features.Auth.Commands.GenerateCaptcha;

public class GenerateCaptchaCommandHandler : IRequestHandler<GenerateCaptchaCommand, OperationResult<GenerateCaptchaResponse>>
{
    private readonly ICaptchaService _captchaService;
    private readonly ICacheService _cacheService;
    private const string RATE_LIMIT_KEY_PREFIX = "captcha_rate_limit:";
    private const int MAX_REQUESTS_PER_MINUTE = 30;

    public GenerateCaptchaCommandHandler(
        ICaptchaService captchaService,
        ICacheService cacheService)
    {
        _captchaService = captchaService;
        _cacheService = cacheService;
    }

    public async Task<OperationResult<GenerateCaptchaResponse>> Handle(
        GenerateCaptchaCommand request,
        CancellationToken cancellationToken)
    {
        try
        {
            // 获取客户端IP或标识
            var clientId = request.ClientId ?? "anonymous";
            var rateLimitKey = $"{RATE_LIMIT_KEY_PREFIX}{clientId}";

            // 检查请求频率
            var requestCount = _cacheService.Get<int>(rateLimitKey);
            if (requestCount >= MAX_REQUESTS_PER_MINUTE)
            {
                var remainingTime = _cacheService.Get<DateTime>($"{rateLimitKey}:expiry");
                var seconds = remainingTime != default 
                    ? (int)(remainingTime - DateTime.UtcNow).TotalSeconds 
                    : 60;
                
                return OperationResult<GenerateCaptchaResponse>.CreateFailure(
                    $"请求过于频繁，请{seconds}秒后再试");
            }

            // 更新请求计数
            var rateLimitOptions = new MemoryCacheEntryOptions()
                .SetAbsoluteExpiration(TimeSpan.FromMinutes(1));
            _cacheService.Set(rateLimitKey, requestCount + 1, rateLimitOptions);
            _cacheService.Set($"{rateLimitKey}:expiry", DateTime.UtcNow.AddMinutes(1), rateLimitOptions);

            // 生成验证码
            var (code, imageBytes) = _captchaService.GenerateCaptcha(request.Length);

            // 生成唯一ID
            var captchaId = Guid.NewGuid().ToString();

            // 将验证码存入缓存，设置5分钟过期
            var cacheOptions = new MemoryCacheEntryOptions()
                .SetAbsoluteExpiration(TimeSpan.FromMinutes(5));
            _cacheService.Set($"captcha:{captchaId}", code, cacheOptions);

            // 将图片转换为Base64
            var base64Image = Convert.ToBase64String(imageBytes);

            return await Task.FromResult(OperationResult<GenerateCaptchaResponse>.CreateSuccess(new GenerateCaptchaResponse
            {
                CaptchaId = captchaId,
                ImageBase64 = base64Image
            }));
        }
        catch (Exception ex)
        {
            return await Task.FromResult(OperationResult<GenerateCaptchaResponse>.CreateFailure("生成验证码失败"));
        }
    }
}