SocialPub/PrivaPub/Federation/Actors/Walls.cs

using MongoDB.Entities;

using PrivaPub.Domain.Social;
using PrivaPub.Domain.Timelines;
using PrivaPub.Federation.Inbox;
using PrivaPub.Federation.Outbox;
using PrivaPub.Federation.Rendering;
using PrivaPub.Models.Post;
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.Actors
{
	public interface IWalls
	{
		Task<LocalActor> OwnerOf(string wallUri, CancellationToken token);
		Task<bool> MayWrite(LocalActor owner, ForeignAvatar author, CancellationToken token);
		Task Hosted(PostEntity post, LocalActor owner, CancellationToken token);
		Task Receive(JsonNode activity, ForeignAvatar owner, bool add, CancellationToken token);
		Task<bool> Remove(LocalActor owner, PostEntity post, CancellationToken token);
	}

	// Walls (FEP-400e, Smithereen's; owner decision 2026-10-06). A persona's actor names its wall (`…/graffiti`), on which
	// the accounts following it may write: their public post, sent with the wall as its `target`, is hosted here, shown to
	// the persona and its followers, and told to its followers' servers with Add{Note}. The persona may take it off again
	// (Remove, which Smithereen takes for a deletion, as it is on its walls). Another server's account that tells its
	// followers here of a post on its wall (Add) has it shown to them as on its wall.
	public class Walls : IWalls
	{
		public const string Path = "graffiti";

		readonly DbEntities _dbEntities;
		readonly ILocalActorService _localActors;
		readonly IRemotePosts _remotePosts;
		readonly IDeliveryService _delivery;
		readonly IFanout _fanout;

		public Walls(DbEntities dbEntities, ILocalActorService localActors, IRemotePosts remotePosts, IDeliveryService delivery, IFanout fanout)
		{
			_dbEntities = dbEntities;
			_localActors = localActors;
			_remotePosts = remotePosts;
			_delivery = delivery;
			_fanout = fanout;
		}

		public async Task<LocalActor> OwnerOf(string wallUri, CancellationToken token)
		{
			if (string.IsNullOrEmpty(wallUri) || !wallUri.EndsWith("/" + Path, StringComparison.Ordinal))
				return default;
			var owner = await _localActors.FindByUri(wallUri[..^(Path.Length + 1)], token);
			return owner is { HasWall: true } && owner.Wall == wallUri ? owner : default;
		}

		// its followers, as the actor says to Smithereen (wallPosting), unless the persona hides them
		public async Task<bool> MayWrite(LocalActor owner, ForeignAvatar author, CancellationToken token) =>
			await _dbEntities.Followers.Match(f => f.LocalActorId == owner.Id && f.LocalActorKind == owner.Kind && f.ActorURI == author.ActorURI && f.IsAccepted)
				.ExecuteAnyAsync(token)
			&& !(await Domain.Relationships.Hidden.RecipientsHiding(new[] { owner.Id }, author.ActorURI, token)).Contains(owner.Id);

		public async Task Hosted(PostEntity post, LocalActor owner, CancellationToken token)
		{
			await Notifications.Add(owner.Id, NotificationType.Mention, post.AuthorAccountId, post.ActorURI, post.ID, token);
			var add = new JsonObject
			{
				["@context"] = ActivityPubRenderer.Context(),
				["id"] = owner.ActivityUri($"wall-{post.ID}"),
				["type"] = "Add",
				["actor"] = owner.Uri,
				["object"] = post.ObjectURI,
				["target"] = new JsonObject { ["type"] = "OrderedCollection", ["id"] = owner.Wall, ["attributedTo"] = owner.Uri },
				["to"] = new JsonArray(ActivityPubRenderer.Public, owner.Followers, post.ActorURI)
			};
			await _delivery.EnqueueToFollowers(owner, add, token, await AuthorInbox(post, token));
		}

		public async Task Receive(JsonNode activity, ForeignAvatar owner, bool add, CancellationToken token)
		{
			var objectUri = Id(activity["object"]);
			if (objectUri == default)
			{
				Arrival.Drop("unparseable");
				return;
			}
			if (!add)
			{
				var walled = await _dbEntities.Posts.Match(p => p.ObjectURI == objectUri && p.WallOwnerURI == owner.ActorURI).ExecuteFirstAsync(token);
				if (walled == default)
				{
					Arrival.Drop("unknown-object");
					return;
				}
				await RemoteDeletes.Remove(walled, objectUri, token);
				Arrival.Accept("unwalled");
				return;
			}

			var post = await _dbEntities.Posts.Match(p => p.ObjectURI == objectUri && !p.DeletedAt.HasValue).ExecuteFirstAsync(token)
				?? await _remotePosts.StoreContext(objectUri, 0, token);
			if (post is not { IsFederatedCopy: true, ReblogOfPostId: null, Visibility: PostVisibility.Public or PostVisibility.Unlisted } || !string.IsNullOrEmpty(post.InReplyToURI))
			{
				Arrival.Drop("unknown-object");
				return;
			}
			Arrival.About(post.ObjectType ?? "Note", post.Visibility, post.CreationDate);
			if (post.WallOwnerURI == owner.ActorURI)
			{
				Arrival.Drop("duplicate");
				return;
			}
			post.WallURI = owner.WallURL;
			post.WallOwnerURI = owner.ActorURI;
			post.WallOwnerAccountId = owner.ID;
			await DB.Default.Update<PostEntity>().MatchID(post.ID)
				.Modify(p => p.WallURI, post.WallURI)
				.Modify(p => p.WallOwnerURI, post.WallOwnerURI)
				.Modify(p => p.WallOwnerAccountId, post.WallOwnerAccountId)
				.ExecuteAsync(token);
			await _fanout.Distribute(post, token);
			Arrival.Accept("walled");
		}

		public async Task<bool> Remove(LocalActor owner, PostEntity post, CancellationToken token)
		{
			if (post == default || !owner.HasWall || post.WallURI != owner.Wall)
				return false;
			var remove = new JsonObject
			{
				["@context"] = ActivityPubRenderer.Context(),
				["id"] = owner.ActivityUri($"unwall-{post.ID}"),
				["type"] = "Remove",
				["actor"] = owner.Uri,
				["object"] = post.ObjectURI,
				// (a plain id: Smithereen refuses a Remove whose target is an object)
				["target"] = owner.Wall,
				["to"] = new JsonArray(ActivityPubRenderer.Public, owner.Followers, post.ActorURI)
			};
			await _delivery.EnqueueToFollowers(owner, remove, token, await AuthorInbox(post, token));
			await RemoteDeletes.Remove(post, post.ObjectURI, token);
			return true;
		}

		async Task<IEnumerable<string>> AuthorInbox(PostEntity post, CancellationToken token)
		{
			var author = await _dbEntities.ForeignAvatars.Match(a => a.ActorURI == post.ActorURI).ExecuteFirstAsync(token);
			var inbox = string.IsNullOrEmpty(author?.SharedInboxURL) ? author?.InboxURL : author.SharedInboxURL;
			return inbox == default ? Array.Empty<string>() : new[] { inbox };
		}
	}
}