SocialPub/PrivaPub/Federation/Outbox/OutboxPublisher.cs

using MongoDB.Entities;

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

using System.Text.Json.Nodes;

using PostEntity = PrivaPub.Models.Post.Post;

namespace PrivaPub.Federation.Outbox
{
	public interface IOutboxPublisher
	{
		Task<IReadOnlyList<string>> Audience(LocalActor author, PostEntity post, CancellationToken token);
		Task Publish(LocalActor author, PostEntity post, JsonObject activity, CancellationToken token);
		Task PublishUpdate(LocalActor author, PostEntity post, string reason, CancellationToken token);
		Task PublishProfile(LocalActor actor, CancellationToken token);
		Task PublishFeatured(string personaId, PostEntity post, bool featured, CancellationToken token);
	}

	public class OutboxPublisher : IOutboxPublisher
	{
		readonly DbEntities _dbEntities;
		readonly ILocalActorService _localActors;
		readonly IDeliveryService _delivery;

		public OutboxPublisher(DbEntities dbEntities, ILocalActorService localActors, IDeliveryService delivery)
		{
			_dbEntities = dbEntities;
			_localActors = localActors;
			_delivery = delivery;
		}

		public async Task<IReadOnlyList<string>> Audience(LocalActor author, PostEntity post, CancellationToken token)
		{
			if (post.Visibility == PostVisibility.LocalGeo || post.IsLocalOnly)
				return Array.Empty<string>();
			if (post.Visibility == PostVisibility.Circle)
				return await CircleMembers(post.GroupId, token);

			var inboxes = new List<string>();
			if (post.Visibility is PostVisibility.Public or PostVisibility.Unlisted or PostVisibility.FollowersOnly)
				inboxes.AddRange(await _delivery.FollowerInboxes(author, token));

			//nothing is addressed to an account that blocked the author (it would refuse it, and Mastodon counts on that)
			var blockers = (await DB.Default.Find<BlockedBy>().Match(b => b.AvatarId == author.Id).ExecuteAsync(token))
				.Select(b => b.ActorURI).ToHashSet(StringComparer.Ordinal);
			var addressed = post.Mentions.Where(m => !m.IsLocal).Select(m => m.ActorURI)
				.Concat(post.Visibility == PostVisibility.Direct ? post.To.Concat(post.Cc) : Enumerable.Empty<string>())
				.Where(uri => !uri.StartsWith(author.BaseAddress + "/", StringComparison.OrdinalIgnoreCase) && !blockers.Contains(uri))
				.Distinct(StringComparer.Ordinal)
				.ToList();
			foreach (var uri in addressed)
			{
				var actor = await _dbEntities.ForeignAvatars.Match(a => a.ActorURI == uri).ExecuteFirstAsync(token);
				if (Preferred(actor) is { } inbox)
					inboxes.Add(inbox);
			}

			if (post.Visibility != PostVisibility.Direct && !string.IsNullOrEmpty(post.InReplyToAccountId))
			{
				var parentAuthor = await _dbEntities.ForeignAvatars.MatchID(post.InReplyToAccountId).ExecuteFirstAsync(token);
				if (Preferred(parentAuthor) is { } inbox && !blockers.Contains(parentAuthor.ActorURI))
					inboxes.Add(inbox);
			}

			if (post.Visibility is PostVisibility.Public or PostVisibility.Unlisted && !string.IsNullOrEmpty(post.QuotedPostId))
			{
				var quoted = await _dbEntities.Posts.MatchID(post.QuotedPostId).ExecuteFirstAsync(token);
				var quotedAuthor = quoted is { IsFederatedCopy: true }
					? await _dbEntities.ForeignAvatars.Match(a => a.ActorURI == quoted.ActorURI).ExecuteFirstAsync(token)
					: default;
				if (Preferred(quotedAuthor) is { } inbox)
					inboxes.Add(inbox);
			}

			return inboxes.Where(i => !string.IsNullOrEmpty(i)).Distinct(StringComparer.Ordinal).ToList();
		}

		// a server's shared inbox when it has one, as Mastodon delivers: one delivery a server, whoever on it is named, and
		// none of the races a server runs into when the same activity reaches two of its inboxes at once (BookWyrm kept
		// two copies of a post that named a follower)
		static string Preferred(ForeignAvatar actor) =>
			actor == default ? default : !string.IsNullOrEmpty(actor.SharedInboxURL) ? actor.SharedInboxURL : actor.InboxURL is { Length: > 0 } inbox ? inbox : default;

		async Task<IReadOnlyList<string>> CircleMembers(string groupId, CancellationToken token) =>
			(await CircleRecipients(groupId, token)).Select(r => r.InboxURL).Distinct(StringComparer.Ordinal).ToList();

		async Task<IReadOnlyList<ForeignAvatar>> CircleRecipients(string groupId, CancellationToken token)
		{
			var circle = string.IsNullOrEmpty(groupId) ? default : await _dbEntities.Groups.MatchID(groupId).ExecuteFirstAsync(token);
			if (circle == default)
				return Array.Empty<ForeignAvatar>();
			var remote = circle.Members.Where(m => m.IsForeign).Select(m => m.AvatarId).ToList();
			if (remote.Count == 0)
				return Array.Empty<ForeignAvatar>();
			return (await _dbEntities.ForeignAvatars.Match(a => remote.Contains(a.ActorURI)).ExecuteAsync(token))
				.Where(a => !string.IsNullOrEmpty(a.InboxURL))
				.ToList();
		}

		public async Task Publish(LocalActor author, PostEntity post, JsonObject activity, CancellationToken token)
		{
			if (post.Visibility == PostVisibility.Circle)
			{
				foreach (var member in await CircleRecipients(post.GroupId, token))
					await _delivery.Enqueue(author, new[] { member.InboxURL }, Naming(activity, new[] { member }), token);
				return;
			}
			var inboxes = await Audience(author, post, token);
			if (inboxes.Count > 0)
				await _delivery.Enqueue(author, inboxes, activity, token);
		}

		// a persona pins its post or unpins it: Add or Remove on its featured collection (/trophies, which serves the same
		// pins), told to the post's audience as Mastodon tells it
		public async Task PublishFeatured(string personaId, PostEntity post, bool featured, CancellationToken token)
		{
			var author = await _localActors.FindById(LocalActorKind.Person, personaId, token);
			if (author is not { IsFederated: true } || post.IsLocalOnly)
				return;
			await Publish(author, post, new JsonObject
			{
				["@context"] = ActivityPubRenderer.Context(),
				["id"] = author.ActivityUri($"{(featured ? "feature" : "unfeature")}-{post.ID}-{DateTime.UtcNow.Ticks}"),
				["type"] = featured ? "Add" : "Remove",
				["actor"] = author.Uri,
				["object"] = author.PostUri(post.ID),
				["target"] = author.Featured,
				["to"] = new JsonArray(Objects.Addressing.Public),
				["cc"] = new JsonArray(author.Followers)
			}, token);
		}

		public async Task PublishUpdate(LocalActor author, PostEntity post, string reason, CancellationToken token)
		{
			var group = string.IsNullOrEmpty(post.GroupId) ? default : await _localActors.FindById(LocalActorKind.Group, post.GroupId, token);
			await Publish(author, post, ActivityPubRenderer.UpdateOf(post, author, group, reason), token);
		}

		// Mastodon keeps a post only when it names one of its own accounts, and GoToSocial shows a post that is neither
		// public nor for followers only to the accounts it mentions; a circle post names only the circle. So each member's
		// copy, or a member's refetch, also names that member in cc and mentions them, silently, in its tags (owner decision
		// 2026-10-04): it tells each member nothing but that they are in the circle.
		public static JsonObject Naming(JsonObject activityOrObject, IEnumerable<ForeignAvatar> members)
		{
			var named = members.ToList();
			var copy = (JsonObject)activityOrObject.DeepClone();
			if (copy["object"] is JsonObject inner)
			{
				Name(copy, named, mention: false);
				if (inner.ContainsKey("to"))
					Name(inner, named, mention: true);
			}
			else
				Name(copy, named, mention: copy.ContainsKey("attributedTo"));
			return copy;
		}

		static void Name(JsonObject node, IReadOnlyList<ForeignAvatar> members, bool mention)
		{
			var cc = node["cc"] as JsonArray ?? new JsonArray();
			var tags = node["tag"] as JsonArray ?? new JsonArray();
			foreach (var member in members)
			{
				if (!cc.Any(c => c?.GetValue<string>() == member.ActorURI))
					cc.Add(member.ActorURI);
				if (mention && !tags.Any(t => t?["href"]?.GetValue<string>() == member.ActorURI))
					tags.Add(new JsonObject { ["type"] = "Mention", ["href"] = member.ActorURI, ["name"] = Handle(member) });
			}
			node["cc"] = cc;
			if (mention)
				node["tag"] = tags;
		}

		static string Handle(ForeignAvatar member) =>
			string.IsNullOrEmpty(member.UserName) ? member.ActorURI : $"@{member.UserName}@{new Uri(member.ActorURI).Authority}";

		public async Task PublishProfile(LocalActor actor, CancellationToken token)
		{
			var document = ActivityPubRenderer.Actor(actor);
			document.Remove("@context");
			var update = new JsonObject
			{
				["@context"] = ActivityPubRenderer.Context(),
				["id"] = actor.ActivityUri($"update-profile-{DateTimeOffset.UtcNow.ToUnixTimeMilliseconds()}"),
				["type"] = "Update",
				["actor"] = actor.Uri,
				["to"] = new JsonArray(ActivityPubRenderer.Public),
				["cc"] = new JsonArray(actor.Followers),
				["object"] = document
			};
			await _delivery.EnqueueToFollowers(actor, update, token);
		}
	}
}