hn-dotnet/Application/VoteForLink/VoteForLinkCommandHandler.cs

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

namespace HN.Application
{
  public sealed class VoteForLinkCommandHandler : IRequestHandler<VoteForLinkCommand>
  {
    private readonly ILinkRepository _linkRepository;
    private readonly IExecutingUserProvider _executingUserProvider;

    public VoteForLinkCommandHandler(ILinkRepository linkRepository, IExecutingUserProvider executingUserProvider)
    {
      _linkRepository = linkRepository;
      _executingUserProvider = executingUserProvider;
    }

    public async Task<Unit> Handle(VoteForLinkCommand request, CancellationToken cancellationToken)
    {
      var link = await _linkRepository.GetByIdAsync(request.LinkId);
      var userId = _executingUserProvider.GetCurrentUserId();

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

      await _linkRepository.UpdateAsync(link);

      return Unit.Value;
    }
  }
}