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;

		public AnnounceHandler(DbEntities dbEntities, ILocalActorService localActors, IRemotePosts remotePosts, IFanout fanout)
		{
			_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")
				return;
			var objectUri = Id(inner);
			var announceId = Id(activity);
			if (objectUri == default || announceId == default)
				return;
			if (await _dbEntities.Posts.Match(p => p.ObjectURI == announceId).ExecuteAnyAsync(token))
				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)
				return;
			if (original == default && !isLocal)
				original = await _remotePosts.StoreContext(objectUri, 0, token);
			if (original == default || original.Visibility is not (PostVisibility.Public or PostVisibility.Unlisted))
				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.At(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)
				return;
			try
			{
				await DB.Default.SaveAsync(reblog, token);
			}
			catch (MongoWriteException ex) when (ex.WriteError?.Category == ServerErrorCategory.DuplicateKey)
			{
				return;
			}

			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);
		}

		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>()
		};
	}
}