draft a service to handle users credits

app/services/users_credit_manager.rb

@@ -0,0 +1,82 @@
+class UsersCreditManager
+  attr_reader :manager
+
+  def initialize(reservation)
+    if reservation.reservable_type == "Training"
+      @manager = Training.new(reservation)
+    elsif reservation.reservable_type == "Machine"
+      @manager = Machine.new(reservation)
+    end
+  end
+
+  class Machine < Manager
+    def will_use_credits?
+    end
+
+    def credited_hours_number
+    end
+
+    def update
+      super
+    end
+
+    private
+      def _will_use_credits?
+      end
+  end
+
+  class Training < Manager
+    def will_use_credits?
+      _will_use_credits?[0]
+    end
+
+    def update
+      super
+      will_use_credits, training_credit = _will_use_credits?
+      if will_use_credits
+        user.credits << training_credit # we create a new UsersCredit object
+      end
+    end
+
+    private
+      def _will_use_credits?
+        # if there is a training_credit defined for this plan and this training
+        if training_credit = plan.training_credits.find_by(creditable_id: reservation.reservable_id)
+          # if user has not used all the plan credits
+          if user.training_credits.count < plan.training_credit_nb
+            return true, training_credit
+          end
+        end
+        return false, nil
+      end
+  end
+
+  private
+    class Manager
+      attr_reader :reservation
+
+      def initialize(reservation)
+        @reservation = reservation
+        @already_updated = false
+      end
+
+      def plan
+        user.subscribed_plan
+      end
+
+      def user
+        reservation.user
+      end
+
+      def update
+        if @already_updated
+          raise AlreadyUpdated, "update credit is not idempotent ! do not try to update twice."
+        else
+          @already_updated = true
+        end
+      end
+    end
+
+    class AlreadyUpdated < StandardError
+    end
+end