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

using MongoDB.Driver;
using MongoDB.Entities;

using PrivaPub.Domain.Social;
using PrivaPub.Domain.Timelines;
using PrivaPub.Federation.Actors;
using PrivaPub.Federation.Objects;
using PrivaPub.Infrastructure.Ids;
using PrivaPub.Models.Post;
using PrivaPub.Models.Social;
using PrivaPub.Models.User;
using PrivaPub.StaticServices;

using System.Globalization;
using System.Text.Json.Nodes;

using static PrivaPub.Federation.Objects.ActivityJson;

using PostEntity = PrivaPub.Models.Post.Post;

namespace PrivaPub.Federation.Inbox.Handlers
{
	public class AnnounceHandler : IActivityHandler
	{
		readonly DbEntities _dbEntities;
		readonly ILocalActorService _localActors;
		readonly IRemotePosts _remotePosts;
		readonly IFanout _fanout;
		readonly IRemoteActorService _remoteActors;

		public AnnounceHandler(DbEntities dbEntities, ILocalActorService localActors, IRemotePosts remotePosts, IFanout fanout, IRemoteActorService remoteActors)
		{
			_remoteActors = remoteActors;
			_dbEntities = dbEntities;
			_localActors = localActors;
			_remotePosts = remotePosts;
			_fanout = fanout;
		}

		public string Type => "Announce";

		public async Task Handle(JsonNode activity, ForeignAvatar actor, CancellationToken token)
		{
			var inner = activity["object"];
			if (inner is JsonObject && Value(inner, "type") is "Create" or "Update" or "Delete" or "Like" or "Dislike" or "Undo" or "Add" or "Remove" or "Block")
			{
				await GroupActivity(inner, actor, token);
				return;
			}
			var objectUri = Id(inner);
			var announceId = Id(activity);
			if (objectUri == default || announceId == default)
			{
				Arrival.Drop("unparseable");
				return;
			}
			if (await _dbEntities.Posts.Match(p => p.ObjectURI == announceId).ExecuteAnyAsync(token))
			{
				Arrival.Drop("duplicate");
				return;
			}

			var isLocal = objectUri.StartsWith(_localActors.BaseAddress + "/", StringComparison.OrdinalIgnoreCase);
			var original = await _dbEntities.Posts.Match(p => p.ObjectURI == objectUri && !p.DeletedAt.HasValue && p.ReblogOfPostId == null).ExecuteFirstAsync(token);
			var followed = await _dbEntities.Followings.Match(f => f.TargetActorURI == actor.ActorURI && f.State == FollowState.Accepted).ExecuteAnyAsync(token);
			if (original is not { IsFederatedCopy: false } && !followed)
			{
				Arrival.Drop("not-followed");
				return;
			}
			if (original == default && !isLocal)
				original = await _remotePosts.StoreContext(objectUri, 0, token);
			if (original == default)
			{
				Arrival.Drop("fetch-failed");
				return;
			}
			Arrival.About(original.ObjectType ?? "Note", original.Visibility, original.CreationDate);
			if (original.Visibility is not (PostVisibility.Public or PostVisibility.Unlisted))
			{
				Arrival.Drop("not-public");
				return;
			}

			var to = Strings(activity["to"]);
			var cc = Strings(activity["cc"]);
			var published = DateTimeOffset.TryParse(Value(activity, "published"), CultureInfo.InvariantCulture, DateTimeStyles.AssumeUniversal, out var at)
				? at.UtcDateTime
				: DateTime.UtcNow;
			var reblog = new PostEntity
			{
				ID = PrivacyIds.Arrived(published),
				ObjectURI = announceId,
				ActivityURI = announceId,
				ActorURI = actor.ActorURI,
				AuthorAccountId = actor.ID,
				ReblogOfPostId = original.ID,
				Visibility = Addressing.Classify(to, cc, actor.FollowersURL),
				To = to,
				Cc = cc,
				IsFederatedCopy = true,
				CreationDate = published,
				UpdateDate = published
			};
			if (reblog.Visibility == PostVisibility.Direct)
			{
				Arrival.Drop("not-public");
				return;
			}
			try
			{
				await DB.Default.SaveAsync(reblog, token);
			}
			catch (MongoWriteException ex) when (ex.WriteError?.Category == ServerErrorCategory.DuplicateKey)
			{
				Arrival.Drop("duplicate");
				return;
			}
			Arrival.Accept("stored");
			Arrival.About(local: original.IsFederatedCopy ? default : await _localActors.FindById(Models.Federation.LocalActorKind.Person, original.GroupUserId, token));

			await DB.Default.Update<PostEntity>().MatchID(original.ID).Modify(b => b.Inc(p => p.ReblogsCount, 1)).ExecuteAsync(token);
			if (!original.IsFederatedCopy)
				await Notifications.Add(original.GroupUserId, NotificationType.Reblog, actor.ID, actor.ActorURI, original.ID, token);
			await _fanout.Distribute(reblog, token);
		}

		async Task GroupActivity(JsonNode inner, ForeignAvatar group, CancellationToken token)
		{
			Arrival.About(Value(inner, "type"));
			if (group.AvatarType != AvatarType.Group
				|| !await _dbEntities.Followings.Match(f => f.TargetActorURI == group.ActorURI && f.State == FollowState.Accepted).ExecuteAnyAsync(token))
			{
				Arrival.Drop("not-followed");
				return;
			}
			var objectUri = Id(inner["object"]);
			switch (Value(inner, "type"))
			{
				case "Create" when objectUri != default:
					if (await _dbEntities.Posts.Match(p => p.ObjectURI == objectUri).ExecuteAnyAsync(token))
					{
						Arrival.Drop("duplicate");
						return;
					}
					var post = await _remotePosts.StoreContext(objectUri, 0, token);
					if (post == default)
					{
						Arrival.Drop("fetch-failed");
						return;
					}
					Arrival.Accept("stored");
					Arrival.About(visibility: post.Visibility);
					await DB.Default.Update<PostEntity>().MatchID(post.ID).Modify(p => p.AudienceURI, group.ActorURI).ExecuteAsync(token);
					post.AudienceURI = group.ActorURI;
					await _fanout.Distribute(post, token);
					break;
				case "Update" when objectUri != default:
					var stored = await _dbEntities.Posts.Match(p => p.ObjectURI == objectUri && p.AudienceURI == group.ActorURI && !p.DeletedAt.HasValue)
						.ExecuteFirstAsync(token);
					if (stored == default)
					{
						Arrival.Drop("unknown-object");
						return;
					}
					Arrival.About(visibility: stored.Visibility, created: stored.CreationDate);
					using (var fetched = await _remoteActors.FetchObject(objectUri, token))
					{
						var note = fetched == default ? default : NoteParser.Parse(System.Text.Json.Nodes.JsonNode.Parse(fetched.Root.GetRawText()));
						if (note == default || note.AttributedTo != stored.ActorURI)
						{
							Arrival.Drop(note == default ? "fetch-failed" : "misattributed");
							return;
						}
						Arrival.Accept("edit");
						stored.Revisions.Add(new PostRevision
						{
							Title = stored.Title,
							SpoilerText = stored.SpoilerText,
							ContentHtml = stored.ContentHtml,
							HasContentWarning = stored.HasContentWarning,
							EditedAt = stored.EditedAt ?? stored.CreationDate
						});
						stored.Title = note.Title;
						stored.SpoilerText = note.SpoilerText;
						stored.HasContentWarning = note.Sensitive;
						stored.Text = note.ContentHtml;
						stored.ContentHtml = note.ContentHtml;
						stored.Tags = note.Tags.ToList();
						stored.Media = note.Attachments.ToList();
						stored.EditedAt = note.Updated ?? DateTime.UtcNow;
						await DB.Default.SaveAsync(stored, token);
					}
					break;
				case "Delete" when objectUri != default:
					var deleted = await _dbEntities.Posts.Match(p => p.ObjectURI == objectUri && p.AudienceURI == group.ActorURI).ExecuteFirstAsync(token);
					if (deleted == default)
					{
						Arrival.Drop("unknown-object");
						return;
					}
					Arrival.About(visibility: deleted.Visibility, created: deleted.CreationDate);
					using (var check = await _remoteActors.FetchObject(objectUri, token))
						if (check != default && Value(System.Text.Json.Nodes.JsonNode.Parse(check.Root.GetRawText()), "type") != "Tombstone")
						{
							Arrival.Drop("not-deleted");
							return;
						}
					Arrival.Accept("removed");
					await DB.Default.DeleteAsync<PostEntity>(deleted.ID);
					await DB.Default.DeleteAsync<TimelineEntry>(e => e.PostId == deleted.ID);
					break;
				default:
					Arrival.Drop("unsupported");
					break;
			}
		}

		static List<string> Strings(JsonNode node) => node switch
		{
			JsonArray array => array.Select(Id).Where(id => id != default).ToList(),
			JsonNode single when Id(single) is { } id => new List<string> { id },
			_ => new List<string>()
		};
	}
}