Assign users into A/B groups

app/controllers/sessions_controller.rb

@@ -22,7 +22,7 @@ class SessionsController < ApplicationController
     store_nonce(params[:oauth_nonce])
     if params[:custom_redirect_target]
       redirect_to(URI.parse(params[:custom_redirect_target].to_s).path)
-    elsif PairProgramming23Study.participate?
+    elsif PairProgramming23Study.participate?(current_user, @exercise)
       redirect_to(new_exercise_programming_group_path(@exercise))
     else
       redirect_to(implement_exercise_path(@exercise),

lib/pair_programming23_study.rb

@@ -2,9 +2,27 @@
 
 class PairProgramming23Study
   ENABLE = ENV.fetch('PAIR_PROGRAMMING_23_STUDY', nil) == 'true'
+  STUDY_GROUP_IDS = [368, 451].freeze
 
-  def self.participate?
+  def self.participate?(user, exercise)
-    # TODO: Decide which users are in the study
+    ENABLE || participate_in_pp?(user, exercise)
-    ENABLE
+  end
+
+  def self.participate_in_pp?(user, exercise)
+    # All easy tasks of the first week to be solved by the participants on their own
+    if experiment_course?(user.current_study_group_id) && [636, 647, 648, 649, 637, 638, 623, 639, 650, 625, 624, 651, 653, 654, 655, 664, 656].exclude?(exercise.id)
+      user_group = user.id % 3 # => 0, 1, 2
+      case user_group
+        when 0, 1
+          return true
+        else # 2
+          return false
+      end
+    end
+    false
+  end
+
+  def self.experiment_course?(study_group_id)
+    STUDY_GROUP_IDS.include? study_group_id
   end
 end