using FluentValidation;
using MediatR;

namespace TakeoutSaaS.Application.App.Common.Behaviors;

/// <summary>
/// MediatR 请求验证行为，统一触发 FluentValidation。
/// </summary>
/// <typeparam name="TRequest">请求类型。</typeparam>
/// <typeparam name="TResponse">响应类型。</typeparam>
public sealed class ValidationBehavior<TRequest, TResponse>(IEnumerable<IValidator<TRequest>> validators) : IPipelineBehavior<TRequest, TResponse>
    where TRequest : notnull, IRequest<TResponse>
{
    private readonly IEnumerable<IValidator<TRequest>> _validators = validators;

    /// <summary>
    /// 执行验证并在通过时继续后续处理。
    /// </summary>
    public async Task<TResponse> Handle(TRequest request, RequestHandlerDelegate<TResponse> next, CancellationToken cancellationToken)
    {
        if (_validators.Any())
        {
            var context = new ValidationContext<TRequest>(request);
            var validationResults = await Task.WhenAll(_validators.Select(v => v.ValidateAsync(context, cancellationToken)));
            var failures = validationResults.SelectMany(r => r.Errors).Where(f => f is not null).ToList();

            if (failures.Count > 0)
            {
                throw new ValidationException(failures);
            }
        }

        return await next();
    }
}