add backend support for status emoji reactions

turns out we can just reuse the code for
announcement reactions.

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

@@ -0,0 +1,29 @@
+# frozen_string_literal: true
+
+class Api::V1::Statuses::ReactionsController < Api::BaseController
+  before_action -> { doorkeeper_authorize! :write, :'write:favourites' }
+  before_action :require_user!
+
+  before_action :set_status
+  before_action :set_reaction, except: :update
+
+  def update
+    @status.status_reactions.create!(account: current_account, name: params[:id])
+    render_empty
+  end
+
+  def destroy
+    @reaction.destroy!
+    render_empty
+  end
+
+  private
+
+  def set_reaction
+    @reaction = @status.status_reactions.where(account: current_account).find_by!(name: params[:id])
+  end
+
+  def set_status
+    @status = Status.find(params[:status_id])
+  end
+end

app/models/status.rb

@@ -71,6 +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_and_belongs_to_many :tags
   has_and_belongs_to_many :preview_cards
@@ -292,6 +293,21 @@ class Status < ApplicationRecord
     @emojis = CustomEmoji.from_text(fields.join(' '), account.domain)
   end
 
+  def reactions(account = nil)
+    records = begin
+      scope = status_reactions.group(:status_id, :name, :custom_emoji_id).order(Arel.sql('MIN(created_at) ASC'))
+
+      if account.nil?
+        scope.select('name, custom_emoji_id, count(*) as count, false as me')
+      else
+        scope.select("name, custom_emoji_id, count(*) as count, exists(select 1 from status_reactions r where r.account_id = #{account.id} and r.status_id = status_reactions.status_id and r.name = status_reactions.name) as me")
+      end
+    end
+
+    ActiveRecord::Associations::Preloader.new.preload(records, :custom_emoji)
+    records
+  end
+
   def ordered_media_attachments
     if ordered_media_attachment_ids.nil?
       media_attachments

app/models/status_reaction.rb

@@ -0,0 +1,29 @@
+# frozen_string_literal: true
+# == Schema Information
+#
+# Table name: status_reactions
+#
+#  id              :bigint(8)        not null, primary key
+#  account_id      :bigint(8)        not null
+#  status_id       :bigint(8)        not null
+#  name            :string           default(""), not null
+#  custom_emoji_id :bigint(8)
+#  created_at      :datetime         not null
+#  updated_at      :datetime         not null
+#
+class StatusReaction < ApplicationRecord
+  belongs_to :account
+  belongs_to :status, inverse_of: :status_reactions
+  belongs_to :custom_emoji, optional: true
+
+  validates :name, presence: true
+  validates_with StatusReactionValidator
+
+  before_validation :set_custom_emoji
+
+  private
+
+  def set_custom_emoji
+    self.custom_emoji = CustomEmoji.local.find_by(disabled: false, shortcode: name) if name.present?
+  end
+end

app/serializers/rest/status_serializer.rb

@@ -28,6 +28,7 @@ class REST::StatusSerializer < ActiveModel::Serializer
   has_many :ordered_mentions, key: :mentions
   has_many :tags
   has_many :emojis, serializer: REST::CustomEmojiSerializer
+  has_many :reactions, serializer: REST::ReactionSerializer
 
   has_one :preview_card, key: :card, serializer: REST::PreviewCardSerializer
   has_one :preloadable_poll, key: :poll, serializer: REST::PollSerializer
@@ -148,6 +149,10 @@ class REST::StatusSerializer < ActiveModel::Serializer
     object.active_mentions.to_a.sort_by(&:id)
   end
 
+  def reactions
+    object.reactions(current_user&.account)
+  end
+
   class ApplicationSerializer < ActiveModel::Serializer
     attributes :name, :website
 

app/validators/status_reaction_validator.rb

@@ -0,0 +1,28 @@
+# frozen_string_literal: true
+
+class StatusReactionValidator < ActiveModel::Validator
+  SUPPORTED_EMOJIS = Oj.load_file(Rails.root.join('app', 'javascript', 'mastodon', 'features', 'emoji', 'emoji_map.json').to_s).keys.freeze
+
+  LIMIT = 8
+
+  def validate(reaction)
+    return if reaction.name.blank?
+
+    reaction.errors.add(:name, I18n.t('reactions.errors.unrecognized_emoji')) if reaction.custom_emoji_id.blank? && !unicode_emoji?(reaction.name)
+    reaction.errors.add(:base, I18n.t('reactions.errors.limit_reached')) if new_reaction?(reaction) && limit_reached?(reaction)
+  end
+
+  private
+
+  def unicode_emoji?(name)
+    SUPPORTED_EMOJIS.include?(name)
+  end
+
+  def new_reaction?(reaction)
+    !reaction.status.status_reactions.where(name: reaction.name).exists?
+  end
+
+  def limit_reached?(reaction)
+    reaction.status.status_reactions.where.not(name: reaction.name).count('distinct name') >= LIMIT
+  end
+end

db/migrate/20221124114030_create_status_reactions.rb

@@ -0,0 +1,14 @@
+class CreateStatusReactions < ActiveRecord::Migration[6.1]
+  def change
+    create_table :status_reactions do |t|
+      t.references :account, null: false, foreign_key: true
+      t.references :status, null: false, foreign_key: true
+      t.string :name, null: false, default: ''
+      t.references :custom_emoji, null: true, foreign_key: true
+
+      t.timestamps
+    end
+
+    add_index :status_reactions, [:account_id, :status_id, :name], unique: true, name: :index_status_reactions_on_account_id_and_status_id
+  end
+end

spec/fabricators/status_reaction_fabricator.rb

@@ -0,0 +1,6 @@
+Fabricator(:status_reaction) do
+  account      nil
+  status       nil
+  name         "MyString"
+  custom_emoji nil
+end

spec/models/status_reaction_spec.rb

@@ -0,0 +1,5 @@
+require 'rails_helper'
+
+RSpec.describe StatusReaction, type: :model do
+  pending "add some examples to (or delete) #{__FILE__}"
+end