(*
 *
 * Module Predict defines the objects and operations related to
 * predicting student grades using a gradesheet and an input
 *
 *)

module Predict;

  from Gradesheet import Gradesheet, StudentInfo, GradedItem;  
  

 (*
  *This function takes in two types of user entered grades Letter or Numbers.
  *Since the user may mix and match the grades with numbers and letter values
  *we only need one function that will produce letter grades or percentage
  *average values needed to attain a certain grade.
  *)

  operation PredictBoth
    in: g: Gradesheet, ul: UserDefinedLetterGrade, si:StudentInfo;
    out: si':StudentInfo;
   

    description: (* Puts X's for unimportant student info, and uses predictAll function for all
        values of UserDefinedLetterGrade and UserDefinedGradedItems.
    *);

    pre: exists (gi in si.GradedItem) gi =nil;
    
    post: 
	if(ul!=nil)
	then 
		si'.Grade = UserDefinedScore(si)/SumWeightsPossible(si)
	else
		forall(x:integer|(x>=1) and (x<#si.GradedItem))
			if(si.GradedItem[x]=nil) then
				si'.GradedItem[x].Points = (GetPercentNeeded(si,ul)*si.GradedItem[x].pointsPossible);
        
  end PredictBoth;




  object UserDefinedLetterGrade 
    components: ;
    description: (*
	This is when the user inputs a final letter grade desired, it may be any
        letter A to F with A-, B+-, C+-, D+-, and F as valid inputs.
    *);
  end UserDefinedLetterGrade;



  

  function UserDefinedScore(si:StudentInfo) = (
	if (#si =0) then
		if (si[1] !=nil) then 
			si.GradedItem[1].Points*si.GradedItem[1].Weight + UserDefinedScore(si[2:#si])
		else 
			UserDEfinedScore(si[2:#si])
	else 0;
	)
  end;


  function SumWeightsPossible(si:StudentInfo) = (
	if (#si =0) then
		if (si.GradedItem[1]=nil) then
			si.gradedItem[1].Weight + SumWeightsPossible(si[2:#si])
		else
			SumWeightsPossible(si[2:#si])
	else 0;
	) 
  end;





  function GetPercentNeeded(si:studentInfo, ul:UserDefinedLetterGrade) = (
	ul-UserDefinedScore(si);
	)
  end;


end Predict;