SocialPub/PrivaPub/Federation/Actors/RemoteActorService.cs

using MongoDB.Entities;

using PrivaPub.Models.User;
using PrivaPub.StaticServices;

using System.Text.Json;

using Microsoft.Extensions.Caching.Memory;

using PrivaPub.Federation.Objects;
using PrivaPub.Federation.Signing;
using PrivaPub.Infrastructure.Http;

namespace PrivaPub.Federation.Actors
{
	public interface IRemoteActorService
	{
		Task<FetchedJson> FetchObject(string uri, CancellationToken token);
		Task<ForeignAvatar> GetActor(string actorUri, bool refresh, CancellationToken token);
		Task<ForeignAvatar> GetActorByKeyId(string keyId, bool refresh, CancellationToken token);
		Task<string> ResolveHandle(string handle, CancellationToken token);
	}

	public class RemoteActorService : IRemoteActorService
	{
		public const string ActivityJson = "application/activity+json";
		const string Accept = "application/activity+json, application/ld+json; profile=\"https://www.w3.org/ns/activitystreams\"";
		static readonly TimeSpan CacheLifetime = TimeSpan.FromDays(1);
		static readonly TimeSpan RefetchInterval = TimeSpan.FromMinutes(5);

		readonly IFederationHttp _http;
		readonly ILocalActorService _localActors;
		readonly IMemoryCache _cache;
		readonly DbEntities _dbEntities;

		public RemoteActorService(IFederationHttp http, ILocalActorService localActors, IMemoryCache cache, DbEntities dbEntities)
		{
			_http = http;
			_localActors = localActors;
			_cache = cache;
			_dbEntities = dbEntities;
		}

		public async Task<FetchedJson> FetchObject(string uri, CancellationToken token)
		{
			var signer = await _localActors.GetInstanceActor(token);
			var fetched = await Get(uri, signer, token);
			if (fetched == default)
				return default;

			var id = Text(fetched.Root, "id");
			if (Origin.IsDocumentAt(id, fetched.FinalUri))
				return fetched;

			var finalUri = fetched.FinalUri;
			fetched.Dispose();
			if (!Origin.Same(id, finalUri.AbsoluteUri))
				return default;

			var named = await Get(id, signer, token);
			if (named != default && Origin.IsDocumentAt(Text(named.Root, "id"), named.FinalUri))
				return named;
			named?.Dispose();
			return default;
		}

		public async Task<ForeignAvatar> GetActor(string actorUri, bool refresh, CancellationToken token)
		{
			if (string.IsNullOrEmpty(actorUri))
				return default;
			actorUri = StripFragment(actorUri);

			var cached = await _dbEntities.ForeignAvatars.Match(a => a.ActorURI == actorUri).ExecuteFirstAsync(token);
			if (cached != default && !refresh && DateTime.UtcNow - cached.UpdatedAt < CacheLifetime)
				return cached;
			if (!MayFetch(actorUri))
				return cached;

			using var fetched = await FetchObject(actorUri, token);
			var actor = fetched == default ? default : ActorDocument.Parse(fetched.Root);
			if (actor == default)
				return cached;

			var key = cached == default ? default : actor.Key(cached.PublicKeyId);
			return await Upsert(actor, key ?? actor.Keys.FirstOrDefault(), token);
		}

		public async Task<ForeignAvatar> GetActorByKeyId(string keyId, bool refresh, CancellationToken token)
		{
			if (Origin.Of(keyId) == default)
				return default;

			var cached = await _dbEntities.ForeignAvatars.Match(a => a.PublicKeyId == keyId).ExecuteFirstAsync(token);
			if (cached != default && !string.IsNullOrEmpty(cached.PublicKey) && !refresh)
				return cached;
			if (!MayFetch(keyId))
				return cached;

			using var fetched = await FetchObject(StripFragment(keyId), token);
			if (fetched == default)
				return cached;

			var actor = ActorDocument.Parse(fetched.Root);
			if (actor == default)
			{
				var owner = Text(fetched.Root, "owner");
				if (Text(fetched.Root, "id") != keyId || !Origin.Same(owner, keyId))
					return default;
				using var ownerDocument = await FetchObject(owner, token);
				actor = ownerDocument == default ? default : ActorDocument.Parse(ownerDocument.Root);
			}

			var key = actor?.Key(keyId);
			if (key == default)
				return default;
			return await Upsert(actor, key, token);
		}

		public async Task<string> ResolveHandle(string handle, CancellationToken token)
		{
			var parts = handle?.TrimStart('@').Split('@');
			if (parts is not { Length: 2 } || string.IsNullOrEmpty(parts[0]) || string.IsNullOrEmpty(parts[1]))
				return default;

			var url = $"https://{parts[1]}/.well-known/webfinger?resource={Uri.EscapeDataString($"acct:{parts[0]}@{parts[1]}")}";
			using var fetched = await _http.GetJson(url, "application/jrd+json, application/json", sign: default, token);
			if (fetched == default)
				return default;
			var document = fetched.Document;
			if (!document.RootElement.TryGetProperty("links", out var links) || links.ValueKind != JsonValueKind.Array)
				return default;

			foreach (var link in links.EnumerateArray())
			{
				var type = Text(link, "type") ?? string.Empty;
				if (Text(link, "rel") == "self" && (type.Contains("activity+json") || type.Contains("ld+json")))
					return Text(link, "href");
			}
			return default;
		}

		async Task<FetchedJson> Get(string uri, LocalActor signer, CancellationToken token) =>
			await _http.GetJson(uri, Accept, request => HttpSignatures.Sign(request, signer, body: null), token);

		bool MayFetch(string uri)
		{
			var key = "remote-actor:fetched:" + uri;
			if (_cache.TryGetValue(key, out _))
				return false;
			_cache.Set(key, true, RefetchInterval);
			return true;
		}

		static async Task<ForeignAvatar> Upsert(ActorDocument actor, ActorKey key, CancellationToken token)
		{
			var now = DateTime.UtcNow;
			return await DB.Default.UpdateAndGet<ForeignAvatar>()
				.Match(a => a.ActorURI == actor.Id)
				.Modify(a => a.UserName, actor.PreferredUsername)
				.Modify(a => a.Name, actor.Name)
				.Modify(a => a.Biography, ContentSanitizer.Html(actor.Summary))
				.Modify(a => a.Url, actor.Url)
				.Modify(a => a.Domain, new Uri(actor.Id).Authority)
				.Modify(a => a.InboxURL, actor.Inbox)
				.Modify(a => a.OutboxURL, actor.Outbox)
				.Modify(a => a.SharedInboxURL, actor.SharedInbox)
				.Modify(a => a.PictureURL, actor.Icon)
				.Modify(a => a.IsDiscoverable, actor.Discoverable)
				.Modify(a => a.AvatarType, Enum.TryParse<AvatarType>(actor.Type, out var type) ? type : AvatarType.Person)
				.Modify(a => a.PublicKeyId, key?.Id)
				.Modify(a => a.PublicKey, key?.Pem)
				.Modify(a => a.UpdatedAt, now)
				.Modify(b => b.SetOnInsert(a => a.CreatedAt, now))
				.Option(o => o.IsUpsert = true)
				.ExecuteAsync(token);
		}

		public static string StripFragment(string uri)
		{
			var hash = uri.IndexOf('#');
			return hash < 0 ? uri : uri[..hash];
		}

		public static string Text(JsonElement element, string property)
		{
			if (element.ValueKind != JsonValueKind.Object || !element.TryGetProperty(property, out var value))
				return default;
			return value.ValueKind switch
			{
				JsonValueKind.String => value.GetString(),
				JsonValueKind.Object => Text(value, "id") ?? Text(value, "href"),
				JsonValueKind.Array => value.EnumerateArray().Select(v => v.ValueKind == JsonValueKind.String ? v.GetString() : Text(v, "id")).FirstOrDefault(v => v != null),
				_ => default
			};
		}
	}
}