SocialPub/PrivaPub/Domain/Timelines/Fanout.cs

using MongoDB.Driver;
using MongoDB.Entities;

using PrivaPub.Domain.Social;
using PrivaPub.Models.Group;
using PrivaPub.Models.Post;
using PrivaPub.Models.Social;
using PrivaPub.StaticServices;

using GroupEntity = PrivaPub.Models.Group.Group;

namespace PrivaPub.Domain.Timelines
{
	public interface IFanout
	{
		Task Distribute(Post post, CancellationToken token);
	}

	public class Fanout : IFanout
	{
		readonly DbEntities _dbEntities;

		public Fanout(DbEntities dbEntities)
		{
			_dbEntities = dbEntities;
		}

		public async Task Distribute(Post post, CancellationToken token)
		{
			var recipients = new HashSet<string>(StringComparer.Ordinal);
			if (!post.IsFederatedCopy && !string.IsNullOrEmpty(post.GroupUserId))
				recipients.Add(post.GroupUserId);

			switch (post.Visibility)
			{
				case PostVisibility.Public or PostVisibility.Unlisted or PostVisibility.FollowersOnly:
					var followers = post.IsFederatedCopy
						? await _dbEntities.Followings.Match(f => f.TargetActorURI == post.ActorURI && f.State == FollowState.Accepted).ExecuteAsync(token)
						: await _dbEntities.Followings.Match(f => f.TargetAccountId == post.GroupUserId && f.TargetIsLocal && f.State == FollowState.Accepted).ExecuteAsync(token);
					foreach (var following in followers)
						if (await Shows(following, post, token))
							recipients.Add(following.AvatarId);
					if (!string.IsNullOrEmpty(post.AudienceURI))
						foreach (var member in await _dbEntities.Followings.Match(f => f.TargetActorURI == post.AudienceURI && f.State == FollowState.Accepted).ExecuteAsync(token))
							recipients.Add(member.AvatarId);
					// a public post (not a boost, not a reply) comes to those following one of its hashtags, as on Mastodon
					if (post.Visibility == PostVisibility.Public && post.Tags.Count > 0 && string.IsNullOrEmpty(post.ReblogOfPostId)
						&& string.IsNullOrEmpty(post.InReplyToURI) && string.IsNullOrEmpty(post.AnsweringToPostId))
					{
						var tags = post.Tags.ToList();
						foreach (var followed in await DB.Default.Find<FollowedTag>().Match(t => tags.Contains(t.Name)).ExecuteAsync(token))
							recipients.Add(followed.AvatarId);
					}
					break;
				case PostVisibility.Direct when !string.IsNullOrEmpty(post.ConversationId):
					var conversation = await _dbEntities.DmGroups.MatchID(post.ConversationId).ExecuteFirstAsync(token);
					foreach (var member in conversation?.Members.Where(m => !m.IsForeign) ?? Enumerable.Empty<GroupMember>())
						recipients.Add(member.AvatarId);
					break;
				case PostVisibility.Circle when !string.IsNullOrEmpty(post.GroupId):
					var circle = await DB.Default.Find<GroupEntity>().MatchID(post.GroupId).ExecuteFirstAsync(token);
					foreach (var member in circle?.Members.Where(m => !m.IsForeign) ?? Enumerable.Empty<GroupMember>())
						recipients.Add(member.AvatarId);
					break;
			}

			recipients.ExceptWith(await Relationships.Hidden.RecipientsHiding(recipients, post.ActorURI, token));
			foreach (var avatarId in recipients)
			{
				try
				{
					await DB.Default.SaveAsync(new TimelineEntry
					{
						AvatarId = avatarId,
						PostId = post.ID,
						AuthorAccountId = post.AuthorAccountId ?? post.GroupUserId,
						ReblogOfPostId = post.ReblogOfPostId
					}, token);
				}
				catch (MongoWriteException ex) when (ex.WriteError?.Category == ServerErrorCategory.DuplicateKey)
				{
				}
			}

			if (string.IsNullOrEmpty(post.ReblogOfPostId))
				foreach (var mention in post.Mentions.Where(m => m.IsLocal && !string.IsNullOrEmpty(m.AccountId)))
					await Notifications.Add(mention.AccountId, NotificationType.Mention, post.AuthorAccountId ?? post.GroupUserId, post.ActorURI, post.ID, token);
			if (Streams.Anyone)
				await Stream(post, recipients, token);
		}

		// the post to the streams it belongs in: the homes it reached (but not where an exclusive list keeps its author
		// apart), the lists of those homes that hold its author, and the public feeds and hashtags when it is public
		static async Task Stream(Post post, IReadOnlyCollection<string> recipients, CancellationToken token)
		{
			var update = new Streams.Event("update", post.ID);
			var author = post.AuthorAccountId ?? post.GroupUserId;
			var listening = recipients.Where(Streams.Listening).ToList();
			if (listening.Count > 0)
			{
				var memberships = await DB.Default.Find<PersonaListMember>().Match(m => listening.Contains(m.AvatarId) && m.AccountId == author).ExecuteAsync(token);
				var listIds = memberships.Select(m => m.ListId).Distinct().ToList();
				var exclusive = listIds.Count == 0
					? new HashSet<string>()
					: (await DB.Default.Find<PersonaList>().Match(l => listIds.Contains(l.ID) && l.Exclusive).ExecuteAsync(token)).Select(l => l.ID).ToHashSet();
				foreach (var avatarId in listening)
				{
					var lists = memberships.Where(m => m.AvatarId == avatarId).Select(m => m.ListId).ToList();
					if (!lists.Any(exclusive.Contains))
						Streams.ToPersona(avatarId, new Streams.Key(Streams.User), update);
					foreach (var listId in lists)
						Streams.ToPersona(avatarId, new Streams.Key(Streams.List, listId), update);
				}
			}
			if (post.Visibility != PostVisibility.Public || !string.IsNullOrEmpty(post.ReblogOfPostId) || !Privacy.VisibilityPolicy.Shown(post))
				return;
			var local = !post.IsFederatedCopy;
			if (!post.IsLocalOnly)
				Streams.ToAll(new Streams.Key(Streams.Public), update);
			Streams.ToAll(new Streams.Key(local ? Streams.PublicLocal : Streams.PublicRemote), update);
			foreach (var tag in post.Tags.Distinct())
			{
				if (!post.IsLocalOnly)
					Streams.ToAll(new Streams.Key(Streams.Hashtag, tag), update);
				if (local)
					Streams.ToAll(new Streams.Key(Streams.HashtagLocal, tag), update);
			}
		}

		// a post's deletion, told before its home entries go: to the homes holding it or a boost of it (the boost's id
		// there), to its author's own connections, and to the public feeds and hashtags when it was public. Nobody else
		// hears of it, not even its id.
		public static async Task Deleting(Post post, CancellationToken token)
		{
			if (!Streams.Anyone || post == default)
				return;
			var entries = await DB.Default.Find<TimelineEntry>().Match(e => e.PostId == post.ID || e.ReblogOfPostId == post.ID).ExecuteAsync(token);
			foreach (var entry in entries.Where(e => Streams.Listening(e.AvatarId)))
				Streams.ToPersonaEverywhere(entry.AvatarId, new Streams.Event("delete", entry.PostId));
			var author = post.AuthorAccountId ?? post.GroupUserId;
			if (!post.IsFederatedCopy && !string.IsNullOrEmpty(author))
				Streams.ToPersonaEverywhere(author, new Streams.Event("delete", post.ID));
			if (post.Visibility != PostVisibility.Public || !string.IsNullOrEmpty(post.ReblogOfPostId))
				return;
			var gone = new Streams.Event("delete", post.ID);
			var local = !post.IsFederatedCopy;
			Streams.ToAll(new Streams.Key(Streams.Public), gone);
			Streams.ToAll(new Streams.Key(local ? Streams.PublicLocal : Streams.PublicRemote), gone);
			foreach (var tag in post.Tags.Distinct())
			{
				Streams.ToAll(new Streams.Key(Streams.Hashtag, tag), gone);
				if (local)
					Streams.ToAll(new Streams.Key(Streams.HashtagLocal, tag), gone);
			}
		}

		// an edit to the homes holding the post and, when it is public, to the public feeds (status.update)
		public static async Task Edited(Post post, CancellationToken token)
		{
			if (!Streams.Anyone)
				return;
			var update = new Streams.Event("status.update", post.ID);
			var homes = (await DB.Default.Find<TimelineEntry>().Match(e => e.PostId == post.ID).ExecuteAsync(token)).Select(e => e.AvatarId).Distinct();
			foreach (var avatarId in homes.Where(Streams.Listening))
				Streams.ToPersona(avatarId, new Streams.Key(Streams.User), update);
			if (post.Visibility == PostVisibility.Public && Privacy.VisibilityPolicy.Shown(post))
			{
				if (!post.IsLocalOnly)
					Streams.ToAll(new Streams.Key(Streams.Public), update);
				Streams.ToAll(new Streams.Key(post.IsFederatedCopy ? Streams.PublicRemote : Streams.PublicLocal), update);
			}
		}

		async Task<bool> Shows(Following following, Post post, CancellationToken token)
		{
			if (!string.IsNullOrEmpty(post.ReblogOfPostId))
				return following.ShowReblogs;
			var repliedTo = post.InReplyToAccountId;
			var author = post.AuthorAccountId ?? post.GroupUserId;
			if (string.IsNullOrEmpty(post.InReplyToURI) || repliedTo == author || repliedTo == following.AvatarId)
				return true;
			if (string.IsNullOrEmpty(repliedTo))
				return false;
			return await _dbEntities.Followings
				.Match(f => f.AvatarId == following.AvatarId && f.TargetAccountId == repliedTo && f.State == FollowState.Accepted)
				.ExecuteAnyAsync(token);
		}
	}
}