SocialPub/PrivaPub/Federation/Rendering/ActivityPubRenderer.cs

using Markdig;

using PrivaPub.Models.Federation;

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

using PostEntity = PrivaPub.Models.Post.Post;
using PrivaPub.Federation.Actors;

namespace PrivaPub.Federation.Rendering
{
	public static class ActivityPubRenderer
	{
		public const string ActivityStreams = "https://www.w3.org/ns/activitystreams";
		public const string Public = "https://www.w3.org/ns/activitystreams#Public";

		static readonly MarkdownPipeline Pipeline = new MarkdownPipelineBuilder().DisableHtml().Build();

		public static string Html(string markdown) =>
			string.IsNullOrEmpty(markdown) ? string.Empty : Markdown.ToHtml(markdown, Pipeline).Trim();

		public static string Timestamp(DateTime value) =>
			DateTime.SpecifyKind(value, DateTimeKind.Utc).ToString("yyyy-MM-ddTHH:mm:ssZ", CultureInfo.InvariantCulture);

		public static JsonObject Actor(LocalActor actor)
		{
			var document = new JsonObject
			{
				["@context"] = new JsonArray(ActivityStreams, "https://w3id.org/security/v1"),
				["id"] = actor.Uri,
				["type"] = actor.Kind switch
				{
					LocalActorKind.Group => "Group",
					LocalActorKind.Application => "Application",
					_ => "Person"
				},
				["preferredUsername"] = actor.UserName,
				["name"] = actor.Name,
				["summary"] = Html(actor.Summary),
				["url"] = actor.Uri,
				["inbox"] = actor.Inbox,
				["outbox"] = actor.Outbox,
				["followers"] = actor.Followers,
				["following"] = actor.Following,
				["published"] = Timestamp(actor.Published),
				["manuallyApprovesFollowers"] = actor.ManuallyApprovesFollowers,
				["discoverable"] = actor.Discoverable,
				["endpoints"] = new JsonObject { ["sharedInbox"] = actor.SharedInbox },
				["publicKey"] = new JsonObject
				{
					["id"] = actor.KeyId,
					["owner"] = actor.Uri,
					["publicKeyPem"] = Keys.ToSubjectPublicKeyInfoPem(actor.PublicKeyPem)
				}
			};
			if (!string.IsNullOrEmpty(actor.PictureURL))
				document["icon"] = new JsonObject { ["type"] = "Image", ["url"] = actor.PictureURL };
			if (!string.IsNullOrEmpty(actor.ThumbnailURL))
				document["image"] = new JsonObject { ["type"] = "Image", ["url"] = actor.ThumbnailURL };
			return document;
		}

		public static JsonObject Note(PostEntity post, LocalActor author, LocalActor group, string inReplyTo)
		{
			var to = new JsonArray(Public);
			var cc = new JsonArray(author.Followers);
			if (group != default)
				cc.Add(group.Uri);

			var note = NoteBody(author.PostUri(post.ID), author, post.Title, post.Text, post.HasContentWarning,
				post.CreationDate, to, cc, inReplyTo);
			if (group != default)
				note["audience"] = group.Uri;
			return note;
		}

		public static JsonObject DirectNote(PostEntity post, LocalActor author, IReadOnlyList<(string Uri, string Handle)> recipients,
			string context)
		{
			var note = NoteBody(author.PostUri(post.ID), author, post.Title, post.Text, post.HasContentWarning,
				post.CreationDate, new JsonArray(recipients.Select(r => (JsonNode)r.Uri).ToArray()), new JsonArray(), default);
			note["tag"] = new JsonArray(recipients.Select(r => (JsonNode)new JsonObject
			{
				["type"] = "Mention",
				["href"] = r.Uri,
				["name"] = "@" + r.Handle
			}).ToArray());
			note["content"] = string.Join(" ", recipients.Select(r => $"<span class=\"h-card\"><a href=\"{r.Uri}\" class=\"u-url mention\">@{r.Handle}</a></span>"))
				+ " " + note["content"]!.GetValue<string>();
			if (!string.IsNullOrEmpty(context))
				note["context"] = context;
			return note;
		}

		static JsonObject NoteBody(string id, LocalActor author, string title, string text, bool sensitive,
			DateTime published, JsonArray to, JsonArray cc, string inReplyTo)
		{
			var note = new JsonObject
			{
				["id"] = id,
				["type"] = "Note",
				["attributedTo"] = author.Uri,
				["content"] = Html(text),
				["published"] = Timestamp(published),
				["url"] = id,
				["to"] = to,
				["cc"] = cc,
				["sensitive"] = sensitive
			};
			if (sensitive && !string.IsNullOrEmpty(title))
				note["summary"] = title;
			else if (!string.IsNullOrEmpty(title))
				note["name"] = title;
			if (!string.IsNullOrEmpty(inReplyTo))
				note["inReplyTo"] = inReplyTo;
			return note;
		}

		public static JsonObject Create(LocalActor actor, JsonObject note, string activityId) => new()
		{
			["@context"] = ActivityStreams,
			["id"] = actor.ActivityUri(activityId),
			["type"] = "Create",
			["actor"] = actor.Uri,
			["published"] = note["published"]?.DeepClone(),
			["to"] = note["to"]?.DeepClone(),
			["cc"] = note["cc"]?.DeepClone(),
			["object"] = note
		};

		public static JsonObject Announce(LocalActor group, string objectUri, string activityId) => new()
		{
			["@context"] = ActivityStreams,
			["id"] = group.ActivityUri(activityId),
			["type"] = "Announce",
			["actor"] = group.Uri,
			["published"] = Timestamp(DateTime.UtcNow),
			["to"] = new JsonArray(Public),
			["cc"] = new JsonArray(group.Followers),
			["object"] = objectUri
		};

		public static JsonObject Delete(LocalActor actor, string objectUri, string activityId, JsonArray to, JsonArray cc) => new()
		{
			["@context"] = ActivityStreams,
			["id"] = actor.ActivityUri(activityId),
			["type"] = "Delete",
			["actor"] = actor.Uri,
			["to"] = to,
			["cc"] = cc,
			["object"] = new JsonObject { ["id"] = objectUri, ["type"] = "Tombstone" }
		};

		public static JsonObject Accept(LocalActor actor, JsonNode follow, string activityId) => new()
		{
			["@context"] = ActivityStreams,
			["id"] = actor.ActivityUri(activityId),
			["type"] = "Accept",
			["actor"] = actor.Uri,
			["object"] = follow.DeepClone()
		};

		public static JsonObject OrderedCollection(string id, int totalItems, IEnumerable<JsonNode> items)
		{
			var collection = new JsonObject
			{
				["@context"] = ActivityStreams,
				["id"] = id,
				["type"] = "OrderedCollection",
				["totalItems"] = totalItems
			};
			if (items != default)
				collection["orderedItems"] = new JsonArray(items.ToArray());
			return collection;
		}
	}
}