Always create a default study group for new consumers

app/models/consumer.rb

@@ -12,6 +12,13 @@ class Consumer < ApplicationRecord
   validates :oauth_key, presence: true, uniqueness: true
   validates :oauth_secret, presence: true
 
+  after_create :generate_internal_study_group
+
+  def generate_internal_study_group
+    StudyGroup.create!(consumer: self, name: "Default Study Group for #{name}", external_id: nil)
+  end
+  private :generate_internal_study_group
+
   def to_s
     name
   end

app/policies/study_group_policy.rb

@@ -5,10 +5,17 @@ class StudyGroupPolicy < AdminOnlyPolicy
     admin? || teacher?
   end
 
-  %i[show? destroy? edit? update? stream_la?].each do |action|
+  %i[show? edit? update? stream_la?].each do |action|
     define_method(action) { admin? || (@user.teacher? && @record.present? && @user.study_groups.exists?(@record.id)) }
   end
 
+  def destroy?
+    # A default study group should not get deleted without the consumer
+    return no_one if @record.external_id.blank?
+
+    admin? || teacher_in_study_group?
+  end
+
   class Scope < Scope
     def resolve
       if @user.admin?