Remove PairProgramming23Study and instead use LTI parameter

app/controllers/concerns/lti.rb

@@ -226,6 +226,7 @@ module Lti
     @lti_parameters.save!
 
     session[:external_user_id] = current_user.id
+    session[:pair_programming] = parameters[:custom_pair_programming] || false
   rescue ActiveRecord::RecordNotUnique, ActiveRecord::RecordInvalid
     retry
   end

app/controllers/exercises_controller.rb

@@ -305,6 +305,7 @@ class ExercisesController < ApplicationController
       # we are acting on behalf of a programming group
       if current_user.admin?
         session.delete(:pg_id)
+        session.delete(:pair_programming)
         @current_contributor = current_user
       else
         return redirect_back(
@@ -316,9 +317,9 @@ class ExercisesController < ApplicationController
       # we are just acting on behalf of a single user who has already worked on this exercise as part of a programming group **in the context of the current study group**
       session[:pg_id] = pg.id
       @current_contributor = pg
-    elsif session[:pg_id].blank? && PairProgramming23Study.participate_in_pp?(current_user, @exercise) && PairProgramming23Study::FORCED_EXERCISE_IDS.include?(@exercise.id)
+    elsif session[:pg_id].blank? && session[:pair_programming] == 'mandatory'
       return redirect_back(fallback_location: new_exercise_programming_group_path(@exercise))
-    elsif session[:pg_id].blank? && PairProgramming23Study.participate?(current_user, @exercise) && current_user.submissions.where(study_group_id: current_user.current_study_group_id, exercise: @exercise).none?
+    elsif session[:pg_id].blank? && session[:pair_programming] == 'optional' && current_user.submissions.where(study_group_id: current_user.current_study_group_id, exercise: @exercise).none?
       Event.find_or_create_by(category: 'pp_work_alone', user: current_user, exercise: @exercise, data: nil, file_id: nil)
       current_user.pair_programming_waiting_users&.find_by(exercise: @exercise)&.update(status: :worked_alone)
     end

app/controllers/sessions_controller.rb

@@ -19,12 +19,15 @@ class SessionsController < ApplicationController
   def create_through_lti
     return redirect_to_survey if params[:custom_survey_id]
 
-    session.delete(:pg_id) # Remove any previous pg_id from the session
+    # Remove any previous pg_id and pair_programming option from the session
+    session.delete(:pg_id)
+    session.delete(:pair_programming)
+
     store_lti_session_data(params)
     store_nonce(params[:oauth_nonce])
     if params[:custom_redirect_target]
       redirect_to(URI.parse(params[:custom_redirect_target].to_s).path)
-    elsif PairProgramming23Study.participate?(current_user, @exercise)
+    elsif params[:custom_pair_programming]
       redirect_to(new_exercise_programming_group_path(@exercise))
     else
       redirect_to(implement_exercise_path(@exercise),
@@ -57,6 +60,7 @@ class SessionsController < ApplicationController
       session.delete(:study_group_id)
       session.delete(:embed_options)
       session.delete(:pg_id)
+      session.delete(:pair_programming)
 
       # In case we have another session as an internal user, we set the study group for this one
       internal_user = find_or_login_current_user
@@ -98,7 +102,6 @@ class SessionsController < ApplicationController
         # add a user pseudo ID if applicable
         qp[:xi_pseudo_id] = Digest::SHA256.hexdigest(current_user.external_id)
         qp[:co_study_group_id] = current_user.current_study_group_id
-        qp[:co_pair_programming23_study] = PairProgramming23Study.participate_in_pp?(current_user, @exercise).to_s
         qp[:co_rfcs] = current_user.request_for_comments.includes(:submission).where(submission: {study_group_id: current_user.current_study_group_id}).size.to_s
         qp[:co_comments] = current_user.comments.includes(:submission).where(submission: {study_group_id: current_user.current_study_group_id}).size.to_s
       end