SocialPub/PrivaPub/Domain/Moderation/Restrictions.cs

using MongoDB.Driver;
using MongoDB.Entities;

using PrivaPub.Domain.Privacy;
using PrivaPub.Models.User;

namespace PrivaPub.Domain.Moderation
{
	// Who the staff's moderation holds back right now, in memory (completion program R6), for the places that decide one
	// item at a time and must not ask the database each time: a token's persona, a delivery's signer and inbox, a post
	// shown or not, a stream. The posts of a suspended or silenced account carry their own flags (Post.AuthorSuspended,
	// AuthorLimited) for queries; a banned login's personas never do, since flagging all of them at once would pair them
	// in stored data, so they are suspended here alone (Counted.HeldBackPersonas).
	//
	// Read at start, again after every act that changes it (AccountModeration, a ban, a removal) and when five minutes old;
	// a process that never loaded it (the CLI) starts with nobody held back and loads it on first use.
	public static class Restrictions
	{
		static readonly TimeSpan Staleness = TimeSpan.FromMinutes(5);

		public sealed class Set
		{
			public static readonly Set Empty = new(new HashSet<string>(), new HashSet<string>(), new HashSet<string>(), new HashSet<string>());

			public Set(IReadOnlySet<string> suspendedPersonas, IReadOnlySet<string> silencedPersonas, IReadOnlySet<string> suspendedActors,
				IReadOnlySet<string> suspendedInboxes)
			{
				SuspendedPersonas = suspendedPersonas;
				SilencedPersonas = silencedPersonas;
				SuspendedActors = suspendedActors;
				SuspendedInboxes = suspendedInboxes;
			}

			// suspended themselves, or held back with their login (banned or deleted)
			public IReadOnlySet<string> SuspendedPersonas { get; }
			public IReadOnlySet<string> SilencedPersonas { get; }
			// accounts elsewhere the staff suspended: their actors' ids, and their own inboxes (never a shared one, which
			// serves the rest of their server)
			public IReadOnlySet<string> SuspendedActors { get; }
			public IReadOnlySet<string> SuspendedInboxes { get; }
		}

		static volatile Set _current = Set.Empty;
		static DateTime _loadedAt = DateTime.MinValue;
		static int _reloading;

		public static Set Current
		{
			get
			{
				RefreshIfStale();
				return _current;
			}
		}

		public static bool IsSuspended(string personaId) => !string.IsNullOrEmpty(personaId) && Current.SuspendedPersonas.Contains(personaId);

		public static bool IsSilenced(string personaId) => !string.IsNullOrEmpty(personaId) && Current.SilencedPersonas.Contains(personaId);

		public static bool IsSuspendedActor(string actorUri) => !string.IsNullOrEmpty(actorUri) && Current.SuspendedActors.Contains(actorUri);

		public static bool IsSuspendedInbox(string inbox) => !string.IsNullOrEmpty(inbox) && Current.SuspendedInboxes.Contains(inbox);

		public static async Task Reload(CancellationToken token = default)
		{
			var suspended = (await Counted.HeldBackPersonas(token)).ToHashSet(StringComparer.Ordinal);
			var silenced = (await DB.Default.Find<Avatar>().Match(a => a.SilencedAt != null && a.DeletionAt == null)
				.Project(a => a.Include(x => x.ID)).ExecuteAsync(token)).Select(a => a.ID).ToHashSet(StringComparer.Ordinal);
			var actors = await DB.Default.Find<ForeignAvatar>().Match(f => f.SuspendedAt != null)
				.Project(f => f.Include(x => x.ActorURI).Include(x => x.InboxURL).Include(x => x.SharedInboxURL)).ExecuteAsync(token);
			// a single-user server's actor may name its server's shared inbox as its own: that one still serves the others there
			var inboxes = actors.Where(a => !string.IsNullOrEmpty(a.InboxURL) && a.InboxURL != a.SharedInboxURL)
				.Select(a => a.InboxURL).ToHashSet(StringComparer.Ordinal);
			if (inboxes.Count > 0)
			{
				var candidates = inboxes.ToList();
				var shared = await DB.Default.Find<ForeignAvatar>().Match(f => candidates.Contains(f.SharedInboxURL))
					.Project(f => f.Include(x => x.SharedInboxURL)).ExecuteAsync(token);
				inboxes.ExceptWith(shared.Select(f => f.SharedInboxURL));
			}
			_current = new Set(suspended, silenced,
				actors.Select(a => a.ActorURI).Where(u => !string.IsNullOrEmpty(u)).ToHashSet(StringComparer.Ordinal),
				inboxes);
			_loadedAt = DateTime.UtcNow;
		}

		// what a reload says, without waiting for it where waiting is not possible
		public static void ReloadSoon() => _loadedAt = DateTime.MinValue;

		static void RefreshIfStale()
		{
			if (DateTime.UtcNow - _loadedAt < Staleness || Interlocked.Exchange(ref _reloading, 1) == 1)
				return;
			_ = Task.Run(async () =>
			{
				try
				{
					await Reload(CancellationToken.None);
				}
				catch (Exception ex)
				{
					Serilog.Log.ForContext(typeof(Restrictions)).Warning(ex, "The moderation's restrictions could not be reloaded");
				}
				finally
				{
					Interlocked.Exchange(ref _reloading, 0);
				}
			});
		}
	}
}