(*

 * Author: Michael Shelley
 *)

object PredictionItem is
	components: stugi:StudentGI, chg:Change;
	description:
		(*
		 * A PredictionItem contains a boolean flag to indicate if the
		 * score has been changed for a particular GradedItem in a 
		 * Prediction's whatif list.
		 *);

end PredictionItem;

object Prediction is
	components: cls:Class, whatifs:PredictionItem*;
	description:
		(*
		 * A Prediction is only associated with one Student, the Student
		 * whose GraderID is associated with the gradebook retrieved by
		 * the Student from the instructor. clsGIlist is the list of
		 * GradedItems from a class and whatifs begin as the list of
		 * Student GradedItems (StudentGI) taken from the Gradebook.
		 *);

end Prediction;

object Change is boolean;
object ClsPercent is integer;
object Averages is integer*;

operation ComputeTotal is
	description:
		(*
		 * Compute the total of a Graded Item.
		 *);

        inputs: pred:Prediction;
        outputs: pred':Prediction;

	precondition:
		(*
		 * whatifs in Prediction is not empty.
		 *)
		((#(pred.whatifs)) > 0)

			and

		(*
		 * The value of a whatif grade entered by the user cannot exceed
		 * the points possible for that GradedItem in the class.
		 *
                 *)

                not(pred'.cls.tot > pred.cls.tot);

end ComputeTotal;

operation Avg is
	description:
		(*
		 * Computes average scores for ungraded GradedItems if the top
		 * most parent's score (total points for a particular GradedItem 
		 * category such as "Quizes") has been changed.
		 *);

        inputs: pred:Prediction;
        outputs: pred':Prediction;

	precondition:
		(*
		* whatifs in Prediction is not empty.
		*)
		((#(pred.whatifs)) > 0)
	
			and
	
		(*
		 * The value of a whatif grade entered by the user cannot exceed
		 * the points possible for that GradedItem in the class.
		 *)

                 not(pred'.cls.tot > pred.cls.tot)

                    and
			
		(*
		 * A total for a GradedItem category (top level Graded
		 * Item) has been changed.
		 *)
		forall (whatgi:PredictionItem)
			exists (whatgi in pred.whatifs)
				 ((whatgi.stugi.par = nil) & (whatgi.chg = true));
					
end Avg;