Revert "Optimize getting exercises in a course"

This reverts commit 6e4282d.

Author: nygrenh

app/controllers/api/v8/courses/exercises_controller.rb

@@ -34,21 +34,8 @@ def index
           course = Course.find_by!(id: params[:course_id]) if params[:course_id]
           exercises = Exercise.includes(:available_points).where(course_id: course.id)
 
-          unlocked_exercises = course.unlocks
-                                     .where(user_id: current_user.id)
-                                     .where(['valid_after IS NULL OR valid_after < ?', Time.now])
-                                     .pluck(:exercise_name)
-
-          unless current_user.administrator? || current_user.teacher?(course.organization) || current_user.assistant?(course)
-            exercises = exercises.where(hidden: false, disabled_status: 0)
-            exercises = if unlocked_exercises.empty?
-                          exercises.where(unlock_spec: nil)
-                        else
-                          exercises.where(["unlock_spec IS NULL OR name IN (#{unlocked_exercises.map { |_| '?' }.join(', ')})", *unlocked_exercises])
-                        end.select { |e| e._fast_visible_to?(current_user) }
-          end
-
-          presentable = exercises.map do |ex|
+          visible = exercises.select { |ex| ex.visible_to?(current_user) }
+          presentable = visible.map do |ex|
             {
               id: ex.id,
               available_points: ex.available_points,
@@ -60,7 +47,8 @@ def index
             }
           end
 
-          render json: presentable
+          authorize_collection :read, visible
+          present(presentable)
         end
       end
     end