federate emoji reactions

this is kind of experimental, but it should work
in theory.  at least i tested it with a remove
akkoma instance and it didn't crash.

app/controllers/api/v1/statuses/reactions_controller.rb

@@ -8,12 +8,12 @@ class Api::V1::Statuses::ReactionsController < Api::BaseController
   before_action :set_reaction, except: :update
 
   def update
-    @status.status_reactions.create!(account: current_account, name: params[:id])
+    StatusReactionService.new.call(current_account, @status, params[:id])
     render_empty
   end
 
   def destroy
-    @reaction.destroy!
+    StatusUnreactionService.new.call(current_account, @status)
     render_empty
   end
 

app/lib/activitypub/activity.rb

@@ -39,6 +39,8 @@ class ActivityPub::Activity
         ActivityPub::Activity::Follow
       when 'Like'
         ActivityPub::Activity::Like
+      when 'EmojiReact'
+        ActivityPub::Activity::EmojiReact
       when 'Block'
         ActivityPub::Activity::Block
       when 'Update'

app/lib/activitypub/activity/emoji_react.rb

@@ -0,0 +1,14 @@
+# frozen_string_literal: true
+
+class ActivityPub::Activity::EmojiReact < ActivityPub::Activity
+  def perform
+    original_status = status_from_uri(object_uri)
+    name = @json['content']
+    return if original_status.nil? ||
+      !original_status.account.local? ||
+      delete_arrived_first?(@json['id']) ||
+      @account.reacted?(original_status, name)
+
+    original_status.status_reactions.create!(account: @account, name: name)
+  end
+end

app/models/concerns/account_interactions.rb

@@ -243,6 +243,10 @@ module AccountInteractions
     status.proper.favourites.where(account: self).exists?
   end
 
+  def reacted?(status, name, custom_emoji = nil)
+    status.proper.status_reactions.where(account: self, name: name, custom_emoji: custom_emoji).exists?
+  end
+
   def bookmarked?(status)
     status.proper.bookmarks.where(account: self).exists?
   end

app/models/status.rb

@@ -71,7 +71,7 @@ class Status < ApplicationRecord
   has_many :mentioned_accounts, through: :mentions, source: :account, class_name: 'Account'
   has_many :active_mentions, -> { active }, class_name: 'Mention', inverse_of: :status
   has_many :media_attachments, dependent: :nullify
-  has_many :status_reactions, dependent: :destroy
+  has_many :status_reactions, inverse_of: :status, dependent: :destroy
 
   has_and_belongs_to_many :tags
   has_and_belongs_to_many :preview_cards

app/serializers/activitypub/emoji_reaction_serializer.rb

@@ -0,0 +1,36 @@
+# frozen_string_literal: true
+
+class ActivityPub::EmojiReactionSerializer < ActivityPub::Serializer
+  attributes :id, :type, :actor, :content
+  attribute :virtual_object, key: :object
+
+  has_one :custom_emoji, key: :tag, serializer: ActivityPub::EmojiSerializer, unless: -> { object.custom_emoji.nil? }
+
+  def id
+    [ActivityPub::TagManager.instance.uri_for(object.account), '#emoji_reactions/', object.id].join
+  end
+
+  def type
+    'EmojiReact'
+  end
+
+  def actor
+    ActivityPub::TagManager.instance.uri_for(object.account)
+  end
+
+  def virtual_object
+    ActivityPub::TagManager.instance.uri_for(object.status)
+  end
+
+  def content
+    if object.custom_emoji.nil?
+      object.name
+    else
+      ":#{object.name}:"
+    end
+  end
+
+  def reaction
+    content
+  end
+end

app/serializers/activitypub/undo_emoji_reaction_serializer.rb

@@ -0,0 +1,19 @@
+# frozen_string_literal: true
+
+class ActivityPub::UndoEmojiReactionSerializer < ActivityPub::Serializer
+  attributes :id, :type, :actor
+
+  has_one :object, serializer: ActivityPub::EmojiReactionSerializer
+
+  def id
+    [ActivityPub::TagManager.instance.uri_for(object.account), '#emoji_reactions/', object.id, '/undo'].join
+  end
+
+  def type
+    'Undo'
+  end
+
+  def actor
+    ActivityPub::TagManager.instance.uri_for(object.account)
+  end
+end

app/services/status_reaction_service.rb

@@ -0,0 +1,27 @@
+# frozen_string_literal: true
+
+class StatusReactionService < BaseService
+  include Authorization
+  include Payloadable
+
+  def call(account, status, emoji)
+    reaction = StatusReaction.find_by(account: account, status: status)
+    return reaction unless reaction.nil?
+
+    name, domain = emoji.split("@")
+
+    custom_emoji = CustomEmoji.find_by(shortcode: name, domain: domain)
+    reaction = StatusReaction.create!(account: account, status: status, name: name, custom_emoji: custom_emoji)
+
+    json = Oj.dump(serialize_payload(reaction, ActivityPub::EmojiReactionSerializer))
+    if status.account.local?
+      ActivityPub::RawDistributionWorker.perform_async(json, status.account.id)
+    else
+      ActivityPub::DeliveryWorker.perform_async(json, reaction.account_id, status.account.inbox_url)
+    end
+
+    ActivityTracker.increment('activity:interactions')
+
+    reaction
+  end
+end

app/services/status_unreaction_service.rb

@@ -0,0 +1,21 @@
+# frozen_string_literal: true
+
+class StatusUnreactionService < BaseService
+  include Payloadable
+
+  def call(account, status)
+    reaction = StatusReaction.find_by(account: account, status: status)
+    return if reaction.nil?
+
+    reaction.destroy!
+
+    json = Oj.dump(serialize_payload(reaction, ActivityPub::UndoEmojiReactionSerializer))
+    if status.account.local?
+      ActivityPub::RawDistributionWorker.perform_async(json, status.account.id)
+    else
+      ActivityPub::DeliveryWorker.perform_async(json, reaction.account_id, status.account.inbox_url)
+    end
+
+    reaction
+  end
+end