SocialPub/PrivaPub/Federation/Actors/ActorDocument.cs

using System.Globalization;
using System.Text.Json;
using System.Text.Json.Nodes;

using PrivaPub.Federation.Objects;
using PrivaPub.Models.Post;

namespace PrivaPub.Federation.Actors
{
	public sealed record ActorKey(string Id, string Pem);

	public sealed class ActorDocument
	{
		static readonly string[] ActorTypes = { "Person", "Service", "Application", "Group", "Organization", "Feed" };

		public string Id { get; init; }
		public string Type { get; init; }
		public string PreferredUsername { get; init; }
		public string Name { get; init; }
		public string Summary { get; init; }
		public string Url { get; init; }
		public string Inbox { get; init; }
		public string Outbox { get; init; }
		public string Followers { get; init; }
		public string Following { get; init; }
		public string Featured { get; init; }
		public string Wall { get; init; }
		public string WebFinger { get; init; }//FEP-2c59: its handle, user@domain, where the domain is not its host's
		public string SharedInbox { get; init; }
		public string Icon { get; init; }
		public bool Discoverable { get; init; } = true;
		public bool Indexable { get; init; }
		public bool Locked { get; init; }
		public bool Memorial { get; init; }
		public string Header { get; init; }
		public string IconDescription { get; init; }
		public string HeaderDescription { get; init; }
		public string MovedTo { get; init; }
		public string Moderators { get; init; }
		public List<PostFlair> Flairs { get; init; } = new();
		public List<string> SearchableBy { get; init; }
		public List<string> AlsoKnownAs { get; init; } = new();//the accounts it says it also is (a Move's target names the moved one)
		public DateTime? Published { get; init; }
		public List<CustomEmoji> Emojis { get; init; } = new();
		public Dictionary<string, string> Fields { get; init; } = new();
		public IReadOnlyList<ActorKey> Keys { get; init; } = Array.Empty<ActorKey>();
		public List<Models.User.AssertionKey> AssertionKeys { get; init; } = new();
		public List<string> Features { get; init; } = new();

		public ActorKey Key(string keyId) => Keys.FirstOrDefault(k => k.Id == keyId);

		// a property of URIs: one, an array of them, or objects carrying an id
		static List<string> Uris(JsonElement value) => (value.ValueKind == JsonValueKind.Array ? value.EnumerateArray().ToList() : new List<JsonElement> { value })
			.Select(v => v.ValueKind == JsonValueKind.String ? v.GetString() : RemoteActorService.Text(v, "id"))
			.Where(v => Uri.TryCreate(v, UriKind.Absolute, out var uri) && uri.Scheme is "https" or "http")
			.Distinct(StringComparer.Ordinal)
			.Take(20)
			.ToList();

		public static ActorDocument Parse(JsonElement root)
		{
			if (root.ValueKind != JsonValueKind.Object)
				return default;
			var id = RemoteActorService.Text(root, "id");
			var type = RemoteActorService.Text(root, "type");
			if (Origin.Of(id) == default || !ActorTypes.Contains(type))
				return default;

			var inbox = RemoteActorService.Text(root, "inbox");
			return new ActorDocument
			{
				Id = id,
				Type = type,
				Features = ActorFeatures.Detect(root),
				PreferredUsername = RemoteActorService.Text(root, "preferredUsername"),
				Name = RemoteActorService.Text(root, "name"),
				// (Lemmy's feed keeps its text in `description`)
				Summary = RemoteActorService.Text(root, "summary") ?? (type == "Feed" ? RemoteActorService.Text(root, "description") : default),
				Url = RemoteActorService.Text(root, "url") ?? id,
				Inbox = Origin.Same(inbox, id) ? inbox : default,
				Outbox = RemoteActorService.Text(root, "outbox"),
				Followers = RemoteActorService.Text(root, "followers"),
				Following = RemoteActorService.Text(root, "following"),
				Featured = RemoteActorService.Text(root, "featured"),
				Wall = RemoteActorService.Text(root, "wall") ?? RemoteActorService.Text(root, "sm:wall"),
				WebFinger = RemoteActorService.Text(root, "webfinger")?.Replace("acct:", "", StringComparison.OrdinalIgnoreCase).TrimStart('@'),
				SharedInbox = root.TryGetProperty("endpoints", out var endpoints) ? RemoteActorService.Text(endpoints, "sharedInbox") : default,
				Icon = root.TryGetProperty("icon", out var icon) ? RemoteActorService.Text(icon, "url") : default,
				Discoverable = !root.TryGetProperty("discoverable", out var discoverable) || discoverable.ValueKind != JsonValueKind.False,
				Keys = ParseKeys(root, id),
				AssertionKeys = ParseAssertionKeys(root, id),
				Indexable = Flag(root, "indexable"),
				Locked = Flag(root, "manuallyApprovesFollowers"),
				Memorial = Flag(root, "memorial"),
				Header = root.TryGetProperty("image", out var image) ? ObjectShapes.Image(JsonNode.Parse(image.GetRawText())) : default,
				IconDescription = root.TryGetProperty("icon", out var described) ? Alt(described) : default,
				HeaderDescription = root.TryGetProperty("image", out var headerImage) ? Alt(headerImage) : default,
				MovedTo = RemoteActorService.Text(root, "movedTo"),
				Flairs = type != "Group" ? new() : ObjectShapes.Flairs(root.TryGetProperty("tag", out var labels) ? JsonNode.Parse(labels.GetRawText()) : default,
					root.TryGetProperty("lemmy:tagsForPosts", out var older) ? JsonNode.Parse(older.GetRawText()) : default),
				SearchableBy = root.TryGetProperty("searchableBy", out var searchable) ? ObjectShapes.SearchableBy(JsonNode.Parse(searchable.GetRawText())) : default,
				Moderators = type == "Group" ? RemoteActorService.Text(root, "attributedTo") ?? RemoteActorService.Text(root, "moderators") : default,
				AlsoKnownAs = root.TryGetProperty("alsoKnownAs", out var aliases) ? Uris(aliases) : new(),
				Published = DateTimeOffset.TryParse(RemoteActorService.Text(root, "published"), CultureInfo.InvariantCulture, DateTimeStyles.AssumeUniversal, out var published)
					? published.UtcDateTime
					: default(DateTime?),
				Emojis = root.TryGetProperty("tag", out var tags) ? ObjectShapes.Emojis(JsonNode.Parse(tags.GetRawText())) : new(),
				Fields = root.TryGetProperty("attachment", out var attachment) ? ParseFields(JsonNode.Parse(attachment.GetRawText())) : new()
			};
		}

		const int MaxFields = 16;

		static bool Flag(JsonElement root, string property) =>
			root.TryGetProperty(property, out var value) && value.ValueKind == JsonValueKind.True;

		static string Alt(JsonElement image) =>
			image.ValueKind == JsonValueKind.Object ? ObjectShapes.Text(RemoteActorService.Text(image, "name") ?? RemoteActorService.Text(image, "summary"), 1500) : default;

		static Dictionary<string, string> ParseFields(JsonNode attachment)
		{
			var fields = new Dictionary<string, string>();
			foreach (var field in ObjectShapes.Objects(attachment).Where(a => ActivityJson.Value(a, "type") is "PropertyValue" or "Note"))
			{
				var name = ObjectShapes.Text(ActivityJson.Value(field, "name"), 255);
				var value = ActivityJson.Value(field, "value") ?? ActivityJson.Value(field, "content");
				if (name == default || value == default || fields.ContainsKey(name))
					continue;
				fields[name] = ContentSanitizer.Html(value.Length <= 2048 ? value : value[..2048]);
				if (fields.Count == MaxFields)
					break;
			}
			return fields;
		}

		const int MaxAssertionKeys = 5;

		// its Ed25519 keys (FEP-521a) its document holds, as Mastodon reads them: Multikeys it controls, under its own id
		static List<Models.User.AssertionKey> ParseAssertionKeys(JsonElement root, string actorId)
		{
			var keys = new List<Models.User.AssertionKey>();
			if (!root.TryGetProperty("assertionMethod", out var methods))
				return keys;
			var candidates = methods.ValueKind switch
			{
				JsonValueKind.Object => new[] { methods },
				JsonValueKind.Array => methods.EnumerateArray().Where(k => k.ValueKind == JsonValueKind.Object).ToArray(),
				_ => Array.Empty<JsonElement>()
			};
			foreach (var key in candidates.Take(MaxAssertionKeys))
			{
				var keyId = RemoteActorService.Text(key, "id");
				var publicKey = Signing.IntegrityProofs.FromMultikey(RemoteActorService.Text(key, "publicKeyMultibase"));
				if (RemoteActorService.Text(key, "type") != "Multikey" || RemoteActorService.Text(key, "controller") != actorId
					|| keyId == default || !keyId.StartsWith(actorId + "#", StringComparison.Ordinal) || publicKey == default)
					continue;
				keys.Add(new Models.User.AssertionKey { Id = keyId, PublicKey = Convert.ToBase64String(publicKey) });
			}
			return keys;
		}

		static List<ActorKey> ParseKeys(JsonElement root, string actorId)
		{
			var keys = new List<ActorKey>();
			if (!root.TryGetProperty("publicKey", out var publicKey))
				return keys;
			var candidates = publicKey.ValueKind switch
			{
				JsonValueKind.Object => new[] { publicKey },
				JsonValueKind.Array => publicKey.EnumerateArray().Where(k => k.ValueKind == JsonValueKind.Object).ToArray(),
				_ => Array.Empty<JsonElement>()
			};
			foreach (var key in candidates)
			{
				var keyId = RemoteActorService.Text(key, "id");
				var owner = RemoteActorService.Text(key, "owner");
				var pem = RemoteActorService.Text(key, "publicKeyPem");
				if (string.IsNullOrEmpty(pem) || owner != actorId || !Origin.Same(keyId, actorId))
					continue;
				keys.Add(new ActorKey(keyId, pem));
			}
			return keys;
		}
	}
}