SocialPub/PrivaPub/Domain/Statuses/InteractionApprovals.cs

using MongoDB.Entities;

using PrivaPub.Federation.Actors;
using PrivaPub.Federation.Objects;
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.Domain.Statuses
{
	public enum InteractionKind
	{
		Reply,
		Like,
		Announce
	}

	// GoToSocial's interaction policies (canReply, canLike, canAnnounce): who may answer, like or boost a post at once, who
	// must ask its author first, and who may not. Asked, the author answers Accept with an authorization (`result`), which
	// the interaction then carries for everyone else (replyAuthorization, likeAuthorization, announceAuthorization), or
	// Reject. Our own posts state no such policy: anyone may.
	public interface IInteractionApprovals
	{
		Task<QuotePermission> Judge(PostEntity target, LocalActor actor, InteractionKind kind, CancellationToken token);
		Task Ask(LocalActor actor, PostEntity target, InteractionKind kind, JsonObject interaction, string localId, CancellationToken token);
		Task<bool> Answered(JsonNode answer, ForeignAvatar actor, bool accepted, CancellationToken token);
		Task<bool> MayReply(NoteDocument reply, ForeignAvatar replier, PostEntity parent, CancellationToken token);
	}

	public class InteractionApprovals : IInteractionApprovals
	{
		readonly DbEntities _dbEntities;
		readonly IRemoteActorService _remoteActors;
		readonly ILocalActorService _localActors;
		readonly IDeliveryService _delivery;
		readonly IOutboxPublisher _outbox;

		public InteractionApprovals(DbEntities dbEntities, IRemoteActorService remoteActors, ILocalActorService localActors, IDeliveryService delivery,
			IOutboxPublisher outbox)
		{
			_dbEntities = dbEntities;
			_remoteActors = remoteActors;
			_localActors = localActors;
			_delivery = delivery;
			_outbox = outbox;
		}

		static string Prefix(InteractionKind kind) => kind switch
		{
			InteractionKind.Reply => "reply-request-",
			InteractionKind.Like => "like-request-",
			_ => "announce-request-"
		};

		static InteractionRule Rule(PostEntity post, InteractionKind kind) => kind switch
		{
			InteractionKind.Reply => post.ReplyPolicy,
			InteractionKind.Like => post.LikePolicy,
			_ => post.AnnouncePolicy
		};

		public async Task<QuotePermission> Judge(PostEntity target, LocalActor actor, InteractionKind kind, CancellationToken token)
		{
			if (!target.IsFederatedCopy || Rule(target, kind) is not { } rule)
				return QuotePermission.Granted;
			if (await Includes(rule.Automatic, target, actor, token))
				return QuotePermission.Granted;
			return await Includes(rule.Manual, target, actor, token) ? QuotePermission.AskFirst : QuotePermission.Denied;
		}

		// whether a policy's list names the persona: anyone, the persona itself, the author's followers when it follows the
		// author, the accounts the author follows when the author follows it
		async Task<bool> Includes(List<string> who, PostEntity target, LocalActor actor, CancellationToken token)
		{
			if (who.Count == 0)
				return false;
			if (who.Any(Addressing.IsPublic) || who.Contains(actor.Uri))
				return true;
			var author = await _dbEntities.ForeignAvatars.Match(f => f.ActorURI == target.ActorURI).ExecuteFirstAsync(token);
			if (author == default)
				return false;
			if (!string.IsNullOrEmpty(author.FollowersURL) && who.Contains(author.FollowersURL)
				&& await _dbEntities.Followings.Match(f => f.AvatarId == actor.Id && f.TargetActorURI == author.ActorURI && f.State == FollowState.Accepted)
					.ExecuteAnyAsync(token))
				return true;
			return !string.IsNullOrEmpty(author.FollowingURL) && who.Contains(author.FollowingURL)
				&& await _dbEntities.Followers.Match(f => f.LocalActorId == actor.Id && f.ActorURI == author.ActorURI && f.IsAccepted).ExecuteAnyAsync(token);
		}

		// asks the author, with the interaction as the request's instrument; it goes to no one else until the author agrees
		public async Task Ask(LocalActor actor, PostEntity target, InteractionKind kind, JsonObject interaction, string localId, CancellationToken token)
		{
			var author = await _dbEntities.ForeignAvatars.Match(f => f.ActorURI == target.ActorURI).ExecuteFirstAsync(token);
			if (string.IsNullOrEmpty(author?.InboxURL))
				return;
			var instrument = (JsonObject)interaction.DeepClone();
			instrument.Remove("@context");
			await _delivery.Enqueue(actor, new[] { author.InboxURL }, new JsonObject
			{
				["@context"] = ActivityPubRenderer.Context(),
				["id"] = actor.ActivityUri(Prefix(kind) + localId),
				["type"] = kind switch { InteractionKind.Reply => "ReplyRequest", InteractionKind.Like => "LikeRequest", _ => "AnnounceRequest" },
				["actor"] = actor.Uri,
				["to"] = target.ActorURI,
				["object"] = target.ObjectURI,
				["instrument"] = instrument
			}, token);
		}

		// an author's answer to one of our requests (the request, or the interaction itself when it was sent unasked)
		public async Task<bool> Answered(JsonNode answer, ForeignAvatar actor, bool accepted, CancellationToken token)
		{
			var answered = answer["object"];
			var answeredId = Id(answered);
			if (answeredId == default)
				return false;
			var (kind, localId) = Request(answeredId);
			if (localId == default && answered is JsonObject request && Value(request, "type") is "ReplyRequest" or "LikeRequest" or "AnnounceRequest")
				answeredId = Id(request["instrument"]);
			if (localId == default && answeredId != default)
				(kind, localId) = await Interaction(answeredId, token);
			if (localId == default)
				return false;

			if (kind == InteractionKind.Like)
			{
				var like = await DB.Default.Find<Favourite>().OneAsync(localId, token);
				var liked = like == default ? default : await _dbEntities.Posts.MatchID(like.PostId).ExecuteFirstAsync(token);
				if (like is not { Approval: ApprovalState.Pending } || liked?.ActorURI != actor.ActorURI)
					return true;
				if (!accepted)
				{
					await DB.Default.DeleteAsync<Favourite>(like.ID);
					await DB.Default.Update<PostEntity>().MatchID(liked.ID).Modify(b => b.Inc(p => p.FavouritesCount, -1)).ExecuteAsync(token);
					return true;
				}
				var stamp = Id(answer["result"]);
				if (stamp == default || !await Verified(stamp, like.ActivityURI, liked, token))
					return true;
				await DB.Default.Update<Favourite>().MatchID(like.ID).Modify(f => f.Approval, ApprovalState.Accepted).Modify(f => f.ApprovalURI, stamp)
					.ExecuteAsync(token);
				var liker = await _localActors.FindById(Models.Federation.LocalActorKind.Person, like.AccountId, token);
				if (liker != default && !string.IsNullOrEmpty(actor.InboxURL))
					await _delivery.Enqueue(liker, new[] { actor.InboxURL }, new JsonObject
					{
						["@context"] = ActivityPubRenderer.Context(),
						["id"] = like.ActivityURI,
						["type"] = "Like",
						["actor"] = liker.Uri,
						["object"] = liked.ObjectURI,
						["likeAuthorization"] = stamp
					}, token);
				return true;
			}

			var post = await _dbEntities.Posts.Match(p => p.ID == localId && !p.IsFederatedCopy && !p.DeletedAt.HasValue).ExecuteFirstAsync(token);
			var target = post == default ? default : await _dbEntities.Posts.MatchID(kind == InteractionKind.Reply ? post.AnsweringToPostId : post.ReblogOfPostId)
				.ExecuteFirstAsync(token);
			if (post is not { Approval: ApprovalState.Pending } || target?.ActorURI != actor.ActorURI)
				return true;
			var author = await _localActors.FindById(Models.Federation.LocalActorKind.Person, post.GroupUserId, token);
			if (author == default)
				return true;
			if (!accepted)
			{
				await DB.Default.Update<PostEntity>().MatchID(post.ID).Modify(p => p.Approval, ApprovalState.Rejected).ExecuteAsync(token);
				if (kind == InteractionKind.Announce)
					await DB.Default.Update<PostEntity>().MatchID(target.ID).Modify(b => b.Inc(p => p.ReblogsCount, -1)).ExecuteAsync(token);
				return true;
			}
			var authorization = Id(answer["result"]);
			var interactionUri = kind == InteractionKind.Reply ? post.ObjectURI : post.ActivityURI;
			if (authorization == default || !await Verified(authorization, interactionUri, target, token))
				return true;
			post.Approval = ApprovalState.Accepted;
			post.ApprovalURI = authorization;
			await DB.Default.Update<PostEntity>().MatchID(post.ID).Modify(p => p.Approval, ApprovalState.Accepted).Modify(p => p.ApprovalURI, authorization)
				.ExecuteAsync(token);
			// now it goes where it was meant to, carrying the authorization
			if (kind == InteractionKind.Reply)
			{
				var create = ActivityPubRenderer.Create(author, ActivityPubRenderer.Note(post, author, default, post.InReplyToURI), $"create-{post.ID}");
				await _outbox.Publish(author, post, create, token);
				return true;
			}
			var announce = new JsonObject
			{
				["@context"] = ActivityPubRenderer.Context(),
				["id"] = post.ActivityURI,
				["type"] = "Announce",
				["actor"] = author.Uri,
				["published"] = ActivityPubRenderer.Timestamp(post.CreationDate),
				["to"] = new JsonArray(post.To.Select(t => (JsonNode)t).ToArray()),
				["cc"] = new JsonArray(post.Cc.Select(c => (JsonNode)c).ToArray()),
				["object"] = target.ObjectURI,
				["announceAuthorization"] = authorization
			};
			await _delivery.EnqueueToFollowers(author, announce, token, string.IsNullOrEmpty(actor.InboxURL) ? default : new[] { actor.InboxURL });
			return true;
		}

		(InteractionKind Kind, string LocalId) Request(string requestId)
		{
			if (requestId == default || !requestId.StartsWith(_localActors.BaseAddress + "/", StringComparison.OrdinalIgnoreCase))
				return default;
			foreach (var kind in new[] { InteractionKind.Reply, InteractionKind.Like, InteractionKind.Announce })
			{
				var marker = requestId.LastIndexOf("/grunts/" + Prefix(kind), StringComparison.Ordinal);
				if (marker >= 0)
					return (kind, requestId[(marker + "/grunts/".Length + Prefix(kind).Length)..]);
			}
			return default;
		}

		// an interaction of ours named by its own id, as an answer to one sent unasked names it
		async Task<(InteractionKind Kind, string LocalId)> Interaction(string uri, CancellationToken token)
		{
			if (!uri.StartsWith(_localActors.BaseAddress + "/", StringComparison.OrdinalIgnoreCase))
				return default;
			if (await DB.Default.Find<Favourite>().Match(f => f.ActivityURI == uri).ExecuteFirstAsync(token) is { } like)
				return (InteractionKind.Like, like.ID);
			if (await _dbEntities.Posts.Match(p => (p.ObjectURI == uri || p.ActivityURI == uri) && !p.IsFederatedCopy).ExecuteFirstAsync(token) is { } post)
				return (post.ReblogOfPostId != default ? InteractionKind.Announce : InteractionKind.Reply, post.ID);
			return default;
		}

		// an authorization is the target author's own document: on its server, naming the interaction and the post
		async Task<bool> Verified(string authorization, string interactionUri, PostEntity target, CancellationToken token)
		{
			if (!Origin.Same(authorization, target.ActorURI))
				return false;
			using var fetched = await _remoteActors.FetchObject(authorization, token);
			if (fetched == default)
				return false;
			var stamp = JsonNode.Parse(fetched.Root.GetRawText());
			return Value(stamp, "type") is "ReplyAuthorization" or "LikeAuthorization" or "AnnounceAuthorization" or "LikeApproval" or "ReplyApproval"
				or "AnnounceApproval"
				&& Id(stamp["interactingObject"]) == interactionUri && Id(stamp["interactionTarget"]) == target.ObjectURI
				&& Id(stamp["attributedTo"]) == target.ActorURI;
		}

		// as a third party: a reply its parent's policy does not let in at once carries the parent author's authorization
		public async Task<bool> MayReply(NoteDocument reply, ForeignAvatar replier, PostEntity parent, CancellationToken token)
		{
			if (parent is not { IsFederatedCopy: true, ReplyPolicy: { } rule } || replier.ActorURI == parent.ActorURI)
				return true;
			// anyone, the replier itself, or a collection (followers, following) whose members we cannot list from here
			var author = await _dbEntities.ForeignAvatars.Match(f => f.ActorURI == parent.ActorURI).ExecuteFirstAsync(token);
			if (rule.Automatic.Any(Addressing.IsPublic) || rule.Automatic.Contains(replier.ActorURI)
				|| author != default && (rule.Automatic.Contains(author.FollowersURL) || rule.Automatic.Contains(author.FollowingURL)))
				return true;
			return reply.ReplyAuthorization != default && await Verified(reply.ReplyAuthorization, reply.Id, parent, token);
		}
	}
}