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

using MongoDB.Entities;

using PrivaPub.Federation.Actors;
using PrivaPub.Models.Federation;
using PrivaPub.Models.Social;
using PrivaPub.Models.User;
using PrivaPub.StaticServices;

using System.Text.Json.Nodes;

using static PrivaPub.Federation.Inbox.ForeignMembers;
using static PrivaPub.Federation.Objects.ActivityJson;

using PostEntity = PrivaPub.Models.Post.Post;

namespace PrivaPub.Federation.Inbox.Handlers
{
	public class UndoHandler : IActivityHandler
	{
		readonly DbEntities _dbEntities;
		readonly ILocalActorService _localActors;

		public UndoHandler(DbEntities dbEntities, ILocalActorService localActors)
		{
			_dbEntities = dbEntities;
			_localActors = localActors;
		}

		public string Type => "Undo";

		public async Task Handle(JsonNode activity, ForeignAvatar actor, CancellationToken token)
		{
			var inner = activity["object"];
			var innerType = inner is JsonObject ? Value(inner, "type") : default;
			var innerId = Id(inner);

			if (innerType is null or "Follow")
				await UndoFollow(inner, innerId, actor, token);
			if (innerType is null or "Like")
				await UndoLike(inner, innerId, actor, token);
			if (innerType is null or "Announce")
				await UndoAnnounce(innerId, actor, token);
			if (innerType is null or "Dislike")
				await UndoDislike(inner, innerId, actor, token);
		}

		async Task UndoDislike(JsonNode inner, string innerId, ForeignAvatar actor, CancellationToken token)
		{
			var downvote = innerId == default
				? default
				: await DB.Default.Find<Downvote>().Match(d => d.ActivityURI == innerId && d.ActorURI == actor.ActorURI).ExecuteFirstAsync(token);
			if (downvote == default && inner is JsonObject && Id(inner["object"]) is { } objectUri)
			{
				var post = await _dbEntities.Posts.Match(p => p.ObjectURI == objectUri).ExecuteFirstAsync(token);
				downvote = post == default
					? default
					: await DB.Default.Find<Downvote>().Match(d => d.PostId == post.ID && d.ActorURI == actor.ActorURI).ExecuteFirstAsync(token);
			}
			if (downvote == default)
				return;
			await DB.Default.DeleteAsync<Downvote>(downvote.ID);
			await DB.Default.Update<PostEntity>().MatchID(downvote.PostId).Modify(b => b.Inc(p => p.DownvotesCount, -1)).ExecuteAsync(token);
		}

		async Task UndoFollow(JsonNode inner, string innerId, ForeignAvatar actor, CancellationToken token)
		{
			var followers = await _dbEntities.Followers.Match(f => f.ActorURI == actor.ActorURI).ExecuteAsync(token);
			var targetUri = inner is JsonObject ? Id(inner["object"]) : default;
			var target = targetUri == default ? default : await _localActors.FindByUri(targetUri, token);
			foreach (var follower in followers)
			{
				var matchesActivity = innerId != default && follower.FollowActivityURI == innerId;
				var matchesTarget = target != default && target.Id == follower.LocalActorId && target.Kind == follower.LocalActorKind;
				if (!matchesActivity && !matchesTarget)
					continue;

				await DB.Default.DeleteAsync<Follower>(follower.ID);
				if (follower.LocalActorKind == LocalActorKind.Group)
					await RemoveForeignMember(follower.LocalActorId, actor.ActorURI, token);
			}
		}

		async Task UndoLike(JsonNode inner, string innerId, ForeignAvatar actor, CancellationToken token)
		{
			var favourite = innerId == default
				? default
				: await _dbEntities.Favourites.Match(f => f.ActivityURI == innerId && f.ActorURI == actor.ActorURI).ExecuteFirstAsync(token);
			if (favourite == default && inner is JsonObject && Id(inner["object"]) is { } objectUri)
			{
				var post = await _dbEntities.Posts.Match(p => p.ObjectURI == objectUri).ExecuteFirstAsync(token);
				favourite = post == default
					? default
					: await _dbEntities.Favourites.Match(f => f.PostId == post.ID && f.ActorURI == actor.ActorURI).ExecuteFirstAsync(token);
			}
			if (favourite == default)
				return;
			await DB.Default.DeleteAsync<Favourite>(favourite.ID);
			await DB.Default.Update<PostEntity>().MatchID(favourite.PostId).Modify(b => b.Inc(p => p.FavouritesCount, -1)).ExecuteAsync(token);
		}

		async Task UndoAnnounce(string innerId, ForeignAvatar actor, CancellationToken token)
		{
			if (innerId == default)
				return;
			var reblog = await _dbEntities.Posts
				.Match(p => p.ObjectURI == innerId && p.ActorURI == actor.ActorURI && p.ReblogOfPostId != null)
				.ExecuteFirstAsync(token);
			if (reblog == default)
				return;
			await DB.Default.DeleteAsync<PostEntity>(reblog.ID);
			await DB.Default.DeleteAsync<TimelineEntry>(e => e.PostId == reblog.ID);
			await DB.Default.Update<PostEntity>().MatchID(reblog.ReblogOfPostId).Modify(b => b.Inc(p => p.ReblogsCount, -1)).ExecuteAsync(token);
		}
	}
}