source: ChapterX.Application/Auth/RegisterHandler.cs@ dc383dd

using ChapterX.Domain.Repositories;
using MediatR;

namespace ChapterX.Application.Auth
{
    public class RegisterHandler : IRequestHandler<RegisterRequest, RegisterResponse>
    {
        private readonly IUserRepository _userRepository;
        private readonly IWriterRepository _writerRepository;

        public RegisterHandler(IUserRepository userRepository, IWriterRepository writerRepository)
        {
            _userRepository = userRepository;
            _writerRepository = writerRepository;
        }

        public async Task<RegisterResponse> Handle(RegisterRequest request, CancellationToken cancellationToken)
        {
            var existing = await _userRepository.GetByEmailAsync(request.Email, cancellationToken);
            if (existing != null)
                throw new InvalidOperationException("Email already in use.");

            var user = new Domain.Entities.User
            {
                Username = request.Username,
                Email = request.Email,
                Name = request.Name,
                Surname = request.Surname,
                Password = BCrypt.Net.BCrypt.HashPassword(request.Password),
                CreatedAt = DateTime.UtcNow,
                UpdatedAt = DateTime.UtcNow
            };

            await _userRepository.AddAsync(user, cancellationToken);

            var writer = new Domain.Entities.Writer { Id = user.Id };
            await _writerRepository.AddAsync(writer, cancellationToken);

            return new RegisterResponse(user.Id, user.Username, user.Email);
        }
    }
}