using FluentValidation;
using MediatR;

namespace MyNewProjectName.Application.Behaviors;

/// <summary>
/// Validation behavior for MediatR pipeline
/// </summary>
public class ValidationBehavior<TRequest, TResponse> : IPipelineBehavior<TRequest, TResponse>
    where TRequest : notnull
{
    private readonly IEnumerable<IValidator<TRequest>> _validators;

    public ValidationBehavior(IEnumerable<IValidator<TRequest>> validators)
    {
        _validators = validators;
    }

    public async Task<TResponse> Handle(TRequest request, RequestHandlerDelegate<TResponse> next, CancellationToken cancellationToken)
    {
        if (!_validators.Any())
        {
            return await next();
        }

        var context = new ValidationContext<TRequest>(request);

        var validationResults = await Task.WhenAll(
            _validators.Select(v => v.ValidateAsync(context, cancellationToken)));

        var failures = validationResults
            .Where(r => r.Errors.Any())
            .SelectMany(r => r.Errors)
            .ToList();

        if (failures.Any())
        {
            var errors = failures
                .GroupBy(e => e.PropertyName, e => e.ErrorMessage)
                .ToDictionary(g => g.Key, g => g.ToArray());

            throw new MyNewProjectName.Domain.Exceptions.ValidationException(errors);
        }

        return await next();
    }
}