SocialPub/PrivaPub/Federation/Inbox/Handlers/DislikeHandler.cs

using MongoDB.Driver;
using MongoDB.Entities;

using PrivaPub.Domain.Privacy;
using PrivaPub.Models.Social;
using PrivaPub.Models.User;
using PrivaPub.StaticServices;

using System.Text.Json.Nodes;

using static PrivaPub.Federation.Objects.ActivityJson;

using PostEntity = PrivaPub.Models.Post.Post;

namespace PrivaPub.Federation.Inbox.Handlers
{
	public class DislikeHandler : IActivityHandler
	{
		readonly DbEntities _dbEntities;

		public DislikeHandler(DbEntities dbEntities)
		{
			_dbEntities = dbEntities;
		}

		public string Type => "Dislike";

		public async Task Handle(JsonNode activity, ForeignAvatar actor, CancellationToken token)
		{
			var objectUri = Id(activity["object"]);
			var post = objectUri == default
				? default
				: await _dbEntities.Posts.Match(p => p.ObjectURI == objectUri && !p.DeletedAt.HasValue && p.ReblogOfPostId == null).ExecuteFirstAsync(token);
			if (post == default || !await VisibilityPolicy.RemoteCanSee(post, actor, token))
			{
				Arrival.Drop(post == default ? "unknown-object" : "not-visible");
				return;
			}
			Arrival.About(post.ObjectType ?? "Note", post.Visibility, post.CreationDate);

			try
			{
				await DB.Default.SaveAsync(new Downvote { AccountId = actor.ID, ActorURI = actor.ActorURI, PostId = post.ID, ActivityURI = Id(activity) }, token);
			}
			catch (MongoWriteException ex) when (ex.WriteError?.Category == ServerErrorCategory.DuplicateKey)
			{
				Arrival.Drop("duplicate");
				return;
			}
			Arrival.Accept("stored");
			await DB.Default.Update<PostEntity>().MatchID(post.ID).Modify(b => b.Inc(p => p.DownvotesCount, 1)).ExecuteAsync(token);
			// a vote replaces the other one: Lemmy turns an upvote into a downvote with this Dislike alone
			if (await DB.Default.Find<Favourite>().Match(f => f.PostId == post.ID && f.ActorURI == actor.ActorURI).ExecuteFirstAsync(token) is { } liked
				&& (await DB.Default.DeleteAsync<Favourite>(liked.ID)).DeletedCount > 0)
				await DB.Default.Update<PostEntity>().MatchID(post.ID).Modify(b => b.Inc(p => p.FavouritesCount, -1)).ExecuteAsync(token);
		}
	}
}