DEV: Dedicated route for current user notification counts (#26106)

Co-authored-by: Alan Guo Xiang Tan <gxtan1990@gmail.com>

app/serializers/user_notification_total_serializer.rb

@@ -0,0 +1,65 @@
+# frozen_string_literal: true
+
+class UserNotificationTotalSerializer < ApplicationSerializer
+  attributes :username,
+             :unread_notifications,
+             :unread_personal_messages,
+             :unseen_reviewables,
+             :topic_tracking,
+             :group_inboxes
+
+  def unread_notifications
+    object.all_unread_notifications_count - new_personal_messages_notifications_count
+  end
+
+  def include_unread_personal_messages?
+    object.in_any_groups?(SiteSetting.personal_message_enabled_groups_map)
+  end
+
+  def unread_personal_messages
+    new_personal_messages_notifications_count
+  end
+
+  def include_unseen_reviewables?
+    scope.user.staff?
+  end
+
+  def unseen_reviewables
+    Reviewable.unseen_reviewable_count(object)
+  end
+
+  def topic_tracking
+    TopicTrackingState.report_totals(object)
+  end
+
+  def group_inboxes
+    group_inbox_data =
+      Notification
+        .unread
+        .where(
+          user_id: scope.user.id,
+          notification_type: Notification.types[:group_message_summary],
+        )
+        .pluck(:data)
+
+    results = []
+
+    return results if group_inbox_data.blank?
+
+    group_inbox_data.map do |json|
+      data = JSON.parse(json, symbolize_names: true)
+
+      results << {
+        group_id: data[:group_id],
+        group_name: data[:group_name],
+        count: data[:inbox_count],
+      }
+    end
+
+    results
+  end
+
+  def new_personal_messages_notifications_count
+    @new_personal_messages_notifications_count ||= object.new_personal_messages_notifications_count
+  end
+end