SocialPub/PrivaPub/Federation/Inbox/Communities.cs

using MongoDB.Entities;

using PrivaPub.Federation.Actors;
using PrivaPub.Federation.Objects;
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.Inbox
{
	public static class Communities
	{
		// the remote community a post was made in: its own audience, or the first one its thread names on the way up (a
		// comment fetched for its thread, or delivered to a persona, may name none)
		public static async Task<string> Of(PostEntity post, DbEntities dbEntities, CancellationToken token)
		{
			for (var depth = 0; post != default && depth < RemotePosts.MaxDepth; depth++)
			{
				if (!string.IsNullOrEmpty(post.AudienceURI))
					return post.AudienceURI;
				post = string.IsNullOrEmpty(post.AnsweringToPostId) ? default : await dbEntities.Posts.MatchID(post.AnsweringToPostId).ExecuteFirstAsync(token);
			}
			return default;
		}

		// whether an account may act for a community's moderators: anyone on the community's own server (its admins and
		// moderators, as Lemmy's verify_mod_or_admin_action allows), or an account its moderators collection lists
		public static async Task<bool> Moderates(ForeignAvatar community, string actorUri, IRemoteActorService remoteActors, CancellationToken token)
		{
			if (actorUri == default || community == default)
				return false;
			if (Origin.Same(actorUri, community.ActorURI))
				return true;
			if (string.IsNullOrEmpty(community.ModeratorsURL))
				return false;
			using var fetched = await remoteActors.FetchObject(community.ModeratorsURL, token);
			if (fetched == default)
				return false;
			var collection = JsonNode.Parse(fetched.Root.GetRawText());
			var items = collection?["orderedItems"] ?? collection?["items"] ?? collection?["first"]?["orderedItems"] ?? collection?["first"]?["items"];
			return items is JsonArray listed && listed.Any(item => Id(item) == actorUri);
		}
	}
}