Refactor access to latest submission

With these changes, it becomes easier to modify the access scopes given for various users.

Author: MrSerth

app/controllers/community_solutions_controller.rb

@@ -101,6 +101,6 @@ def set_community_solution_lock
 
   def set_exercise_and_submission
     @exercise = @community_solution.exercise
-    @submission = current_contributor.submissions.final.where(exercise: @community_solution.exercise).order(created_at: :desc).first
+    @submission = @community_solution.exercise.final_submission(current_contributor)
   end
 end

app/controllers/exercises_controller.rb

@@ -548,8 +548,7 @@ def external_user_statistics
         end
       end
     else
-      final_submissions = policy_scope(Submission).where(contributor: @external_user,
-        exercise_id: @exercise.id).final
+      final_submissions = policy_scope(Submission).where(contributor: @external_user, exercise: @exercise)
       submissions = []
       %i[before_deadline within_grace_period after_late_deadline].each do |filter|
         relevant_submission = final_submissions.send(filter).latest

app/controllers/user_exercise_feedbacks_controller.rb

@@ -59,7 +59,7 @@ def create
 
   def update
     submission = begin
-      current_contributor.submissions.where(exercise: @exercise).order(created_at: :desc).final.first
+      @exercise.final_submission(current_contributor)
     rescue StandardError
       nil
     end
@@ -116,10 +116,10 @@ def uef_params
                     params[:user_exercise_feedback][:exercise_id]
                   end
 
-    latest_submission = Submission
-      .where(contributor: current_contributor, exercise_id:)
-      .order(created_at: :desc).final.first
+    exercise = Exercise.find(exercise_id)
+    authorize(exercise, :implement?)
 
+    latest_submission = exercise.final_submission(current_contributor)
     authorize(latest_submission, :show?)
 
     params[:user_exercise_feedback]

app/views/exercises/statistics.html.slim

@@ -78,7 +78,7 @@ h1 = @exercise
               td = link_to_if symbol == :external_users && policy(contributor).statistics?, label, {controller: 'exercises', action: 'external_user_statistics', external_user_id: contributor.id, id: @exercise.id}
               td = us['maximum_score'] || 0
               td.align-middle
-                - latest_user_submission = submissions.where(contributor:).final.latest
+                - latest_user_submission = @exercise.final_submission(contributor)
                 - if latest_user_submission.present?
                   - if latest_user_submission.before_deadline?
                     .deadline-result.positive-result

app/views/external_users/statistics.html.slim

@@ -23,7 +23,7 @@ h1 = t('.title', user: @user.displayname)
               td = link_to exercise, controller: 'exercises', action: 'external_user_statistics', external_user_id: @user.id, id: exercise.id
               td = stats['maximum_score'] || 0
               td.align-middle
-                - latest_viewable_submission = submissions.where(exercise:).final.latest
+                - latest_viewable_submission = exercise.final_submission(@user)
                 - if latest_viewable_submission.present?
                   - if latest_viewable_submission.before_deadline?
                     .deadline-result.positive-result.before_deadline