P6: emoji reactions in and out

- Incoming reactions in all three shapes: Misskey and Sharkey Likes carrying an emoji (`content` or
  `_misskey_reaction`), Pleroma, Akkoma and Iceshrimp.NET EmojiReacts, and their Undo. Unicode reactions are one
  grapheme; custom ones need their Emoji tag and keep its image; `:name@host:` is read as `name`. A Like whose
  content is a heart stays a favourite.
- Reactions are kept per account and emoji on our posts and on remote ones we hold, and the author of a local post
  gets a `pleroma:emoji_reaction` notification with the emoji.
- Personas react through Pleroma's API (PUT/DELETE /api/v1/pleroma/statuses/:id/reactions/:emoji, GET for the list),
  which sends an EmojiReact (or its Undo) to the post's author.
- Statuses carry `emoji_reactions` (read by Phanpy) and `pleroma.emoji_reactions`, with counts and whether the viewer
  reacted.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_012CzABvBkbcFqoHdmi8b9WB

PrivaPub/Domain/Social/Notifications.cs

@@ -8,7 +8,7 @@ namespace PrivaPub.Domain.Social
 	public static class Notifications
 	{
 		public static async Task Add(string avatarId, NotificationType type, string fromAccountId, string fromActorUri, string postId,
-			CancellationToken token)
+			CancellationToken token, string emoji = default, string emojiUrl = default)
 		{
 			if (string.IsNullOrEmpty(avatarId) || avatarId == fromAccountId && type != NotificationType.Poll)
 				return;
@@ -23,7 +23,9 @@ namespace PrivaPub.Domain.Social
 					FromAccountId = fromAccountId,
 					FromActorURI = fromActorUri,
 					PostId = postId,
-					DedupeKey = $"{type}|{avatarId}|{fromActorUri}|{postId}"
+					Emoji = emoji,
+					EmojiURL = emojiUrl,
+					DedupeKey = emoji == default ? $"{type}|{avatarId}|{fromActorUri}|{postId}" : $"{type}|{avatarId}|{fromActorUri}|{postId}|{emoji}"
 				}, token);
 			}
 			catch (MongoWriteException ex) when (ex.WriteError?.Category == ServerErrorCategory.DuplicateKey)

PrivaPub/Domain/Social/Reactions.cs

@@ -0,0 +1,179 @@
+using MongoDB.Driver;
+using MongoDB.Entities;
+
+using PrivaPub.Federation.Actors;
+using PrivaPub.Federation.Inbox.Handlers;
+using PrivaPub.Federation.Objects;
+using PrivaPub.Federation.Outbox;
+using PrivaPub.Federation.Rendering;
+using PrivaPub.Models.Social;
+using PrivaPub.Models.User;
+using PrivaPub.StaticServices;
+
+using System.Globalization;
+using System.Text.Json.Nodes;
+
+using PostEntity = PrivaPub.Models.Post.Post;
+
+namespace PrivaPub.Domain.Social
+{
+	public interface IReactions
+	{
+		Task Receive(PostEntity post, ForeignAvatar actor, string content, JsonNode tags, string activityId, CancellationToken token);
+		Task<bool> Withdraw(ForeignAvatar actor, string activityId, string objectUri, string content, CancellationToken token);
+		Task<bool> React(LocalActor me, PostEntity post, string emoji, CancellationToken token);
+		Task<bool> Unreact(LocalActor me, PostEntity post, string emoji, CancellationToken token);
+	}
+
+	public class Reactions : IReactions
+	{
+		static readonly string[] Hearts = { "❤", "❤️", "♥", "♥️" };
+
+		readonly DbEntities _dbEntities;
+		readonly IDeliveryService _delivery;
+
+		public Reactions(DbEntities dbEntities, IDeliveryService delivery)
+		{
+			_dbEntities = dbEntities;
+			_delivery = delivery;
+		}
+
+		public static bool IsHeart(string content) => content == default || Hearts.Contains(content.Trim());
+
+		public async Task Receive(PostEntity post, ForeignAvatar actor, string content, JsonNode tags, string activityId, CancellationToken token)
+		{
+			if (!LikeHandler.MaySee(post, actor) || Normalise(content, ObjectShapes.Emojis(tags)) is not { } emoji)
+				return;
+			try
+			{
+				await DB.Default.SaveAsync(new Reaction
+				{
+					PostId = post.ID, AccountId = actor.ID, ActorURI = actor.ActorURI, Emoji = emoji.Name, EmojiURL = emoji.Url, ActivityURI = activityId
+				}, token);
+			}
+			catch (MongoWriteException ex) when (ex.WriteError?.Category == ServerErrorCategory.DuplicateKey)
+			{
+				return;
+			}
+			if (!post.IsFederatedCopy)
+				await Notifications.Add(post.GroupUserId, NotificationType.Reaction, actor.ID, actor.ActorURI, post.ID, token, emoji.Name, emoji.Url);
+		}
+
+		public async Task<bool> Withdraw(ForeignAvatar actor, string activityId, string objectUri, string content, CancellationToken token)
+		{
+			var reaction = activityId == default
+				? default
+				: await DB.Default.Find<Reaction>().Match(r => r.ActivityURI == activityId && r.ActorURI == actor.ActorURI).ExecuteFirstAsync(token);
+			if (reaction == default && objectUri != default && Normalise(content, new()) is { } emoji)
+			{
+				var post = await _dbEntities.Posts.Match(p => p.ObjectURI == objectUri).ExecuteFirstAsync(token);
+				reaction = post == default
+					? default
+					: await DB.Default.Find<Reaction>().Match(r => r.PostId == post.ID && r.ActorURI == actor.ActorURI && r.Emoji == emoji.Name).ExecuteFirstAsync(token);
+			}
+			if (reaction == default)
+				return false;
+			await DB.Default.DeleteAsync<Reaction>(reaction.ID);
+			return true;
+		}
+
+		public async Task<bool> React(LocalActor me, PostEntity post, string emoji, CancellationToken token)
+		{
+			var known = post.Emojis.Select(e => (e.Shortcode, e.URL))
+				.Concat((await DB.Default.Find<Reaction>().Match(r => r.PostId == post.ID && r.EmojiURL != null).ExecuteAsync(token)).Select(r => (r.Emoji, r.EmojiURL)))
+				.Select(e => new Models.Post.CustomEmoji { Shortcode = e.Item1, URL = e.Item2 })
+				.ToList();
+			if (Normalise(emoji, known) is not { } picked)
+				return false;
+			var reaction = new Reaction
+			{
+				PostId = post.ID, AccountId = me.Id, ActorURI = me.Uri, IsLocal = true, Emoji = picked.Name, EmojiURL = picked.Url,
+				ActivityURI = me.ActivityUri($"react-{post.ID}-{Guid.NewGuid():N}")
+			};
+			try
+			{
+				await DB.Default.SaveAsync(reaction, token);
+			}
+			catch (MongoWriteException ex) when (ex.WriteError?.Category == ServerErrorCategory.DuplicateKey)
+			{
+				return true;
+			}
+			if (!post.IsFederatedCopy)
+				await Notifications.Add(post.GroupUserId, NotificationType.Reaction, me.Id, me.Uri, post.ID, token, picked.Name, picked.Url);
+			else
+				await Tell(me, post, Activity(me, post, reaction), token);
+			return true;
+		}
+
+		public async Task<bool> Unreact(LocalActor me, PostEntity post, string emoji, CancellationToken token)
+		{
+			var name = Normalise(emoji, post.Emojis.ToList(), requireKnownCustom: false)?.Name;
+			var reaction = name == default
+				? default
+				: await DB.Default.Find<Reaction>().Match(r => r.PostId == post.ID && r.ActorURI == me.Uri && r.Emoji == name).ExecuteFirstAsync(token);
+			if (reaction == default)
+				return false;
+			await DB.Default.DeleteAsync<Reaction>(reaction.ID);
+			if (post.IsFederatedCopy)
+				await Tell(me, post, new JsonObject
+				{
+					["@context"] = ActivityPubRenderer.Context(),
+					["id"] = me.ActivityUri($"undo-{reaction.ID}"),
+					["type"] = "Undo",
+					["actor"] = me.Uri,
+					["object"] = Activity(me, post, reaction)
+				}, token);
+			return true;
+		}
+
+		static JsonObject Activity(LocalActor me, PostEntity post, Reaction reaction)
+		{
+			var react = new JsonObject
+			{
+				["@context"] = ActivityPubRenderer.Context(),
+				["id"] = reaction.ActivityURI,
+				["type"] = "EmojiReact",
+				["actor"] = me.Uri,
+				["object"] = post.ObjectURI,
+				["to"] = new JsonArray(post.ActorURI),
+				["content"] = reaction.EmojiURL == default ? reaction.Emoji : $":{reaction.Emoji}:"
+			};
+			if (reaction.EmojiURL != default)
+				react["tag"] = new JsonArray(new JsonObject
+				{
+					["type"] = "Emoji",
+					["name"] = $":{reaction.Emoji}:",
+					["icon"] = new JsonObject { ["type"] = "Image", ["url"] = reaction.EmojiURL }
+				});
+			return react;
+		}
+
+		async Task Tell(LocalActor me, PostEntity post, JsonObject activity, CancellationToken token)
+		{
+			var author = await _dbEntities.ForeignAvatars.Match(f => f.ActorURI == post.ActorURI).ExecuteFirstAsync(token);
+			if (!string.IsNullOrEmpty(author?.InboxURL))
+				await _delivery.Enqueue(me, new[] { author.InboxURL }, activity, token);
+		}
+
+		public sealed record Picked(string Name, string Url);
+
+		public static Picked Normalise(string content, List<Models.Post.CustomEmoji> emojis, bool requireKnownCustom = true)
+		{
+			var text = content?.Trim();
+			if (string.IsNullOrEmpty(text) || text.Length > 100)
+				return default;
+			if (text.StartsWith(':') && text.EndsWith(':') && text.Length > 2)
+			{
+				var shortcode = text.Trim(':');
+				var bare = shortcode.Split('@')[0];
+				var emoji = emojis.FirstOrDefault(e => e.Shortcode == shortcode) ?? emojis.FirstOrDefault(e => e.Shortcode.Split('@')[0] == bare);
+				if (emoji == default)
+					return requireKnownCustom ? default : new Picked(bare, default);
+				return new Picked(bare, emoji.URL);
+			}
+			if (text.Any(c => c < 128 || char.IsWhiteSpace(c)) || new StringInfo(text).LengthInTextElements != 1)
+				return default;
+			return new Picked(text, default);
+		}
+	}
+}