style(course): add reference_timeline_for

Author: purfectliterature

app/models/course.rb

@@ -262,6 +262,11 @@ def email_settings_with_enabled_components
     setting_emails.where(component: email_settings_enabled_components)
   end
 
+  def reference_timeline_for(course_user)
+    # TODO: [PR#5491] Return only `default_reference_timeline.id` if Multiple Reference Timelines component is disabled.
+    course_user&.reference_timeline_id || default_reference_timeline.id
+  end
+
   private
 
   # Set default values

app/models/course/lesson_plan/item.rb

@@ -135,7 +135,7 @@ def personal_time_for(course_user)
 
   def reference_time_for(course_user)
     default_reference_timeline_id = course.default_reference_timeline.id
-    reference_timeline_id = course_user&.reference_timeline_id || default_reference_timeline_id
+    reference_timeline_id = course.reference_timeline_for(course_user)
 
     # This reversion anticipates if course_user is on a non-default timeline which does not override the
     # default time for this lesson plan item.

app/views/course/users/_user_list_data.json.jbuilder

@@ -7,8 +7,7 @@ json.name course_user.name.strip
 json.imageUrl user_image(course_user.user)
 json.email course_user.user.email
 
-reference_timeline_id = course_user.reference_timeline_id
-json.referenceTimelineId reference_timeline_id || current_course.default_reference_timeline.id
+json.referenceTimelineId current_course.reference_timeline_for(course_user)
 json.timelineAlgorithm course_user.timeline_algorithm if should_show_timeline
 
 json.role course_user.role