hn-dotnet/Application/VoteForComment/VoteForCommentCommandHandler.cs

using System.Threading;
using System.Threading.Tasks;
using HN.Domain;
using MediatR;

namespace HN.Application
{
  public sealed class VoteForCommentCommandHandler : IRequestHandler<VoteForCommentCommand>
  {
    private readonly ICommentRepository _commentRepository;
    private readonly IExecutingUserProvider _executingUserProvider;

    public VoteForCommentCommandHandler(ICommentRepository commentRepository, IExecutingUserProvider executingUserProvider)
    {
      _commentRepository = commentRepository;
      _executingUserProvider = executingUserProvider;
    }

    public async Task<Unit> Handle(VoteForCommentCommand request, CancellationToken cancellationToken)
    {
      var comment = await _commentRepository.GetByIdAsync(request.CommentId);
      var userId = _executingUserProvider.GetCurrentUserId();

      switch (request.Type)
      {
        case VoteType.Up:
          comment.Upvote(userId);
          break;
        case VoteType.Down:
          comment.Downvote(userId);
          break;
      }

      await _commentRepository.UpdateAsync(comment);

      return Unit.Value;
    }
  }
}