[WiP] Add presenter and serializer to make use of shallow serializers

app/presenters/grouped_notifications_presenter.rb

@@ -0,0 +1,34 @@
+# frozen_string_literal: true
+
+class GroupedNotificationsPresenter < ActiveModelSerializers::Model
+  def initialize(grouped_notifications)
+    super()
+
+    @grouped_notifications = grouped_notifications
+  end
+
+  def notification_groups
+    @grouped_notifications
+  end
+
+  def statuses
+    @grouped_notifications.filter_map(&:target_status)
+  end
+
+  def accounts
+    @grouped_notifications.flat_map do |group|
+      accounts = group.sample_accounts.dup
+
+      case group.type
+      when :favourite, :reblog, :status, :mention, :poll, :update
+        accounts << group.target_status&.account
+      when :'admin.report'
+        accounts << group.report&.target_account
+      when :moderation_warning
+        accounts << group.account_warning&.target_account
+      end
+
+      accounts.compact
+    end.uniq(&:id)
+  end
+end

app/serializers/rest/dedup_notification_group_serializer.rb

@@ -0,0 +1,7 @@
+# frozen_string_literal: true
+
+class REST::DedupNotificationGroupSerializer < ActiveModel::Serializer
+  has_many :accounts, serializer: REST::Shallow::AccountSerializer
+  has_many :statuses, serializer: REST::Shallow::StatusSerializer
+  has_many :notification_groups, serializer: REST::Shallow::NotificationGroupSerializer
+end