;; the structure represents a student
;; name is a symbol, 
;; year-birth is a positive integer,
;; GPA is a non-negative real number <= 4.0 
(define-struct ummstudent (name year-birth GPA))

;; Template:
;;(ummstudent-name student) ....
;;(ummstudent-year-birth student) ....
;;(ummstudent-GPA student) ....

(define JoeSmith
  (make-ummstudent 'JoeSmith 1990 3.45))

(ummstudent-name JoeSmith) 
(ummstudent-year-birth JoeSmith)

(define JaneBrown 
  (make-ummstudent 'JaneBrown 1991 3.25))

;; Define test cases and fill in the body of the functions 



;; Contract: ummstudent, ummstudent -> symbol
;; Purpose: the function compares the ages
;; of two students and returns the name of 
;; the one who is older, based on the year of birth
;; If the two students were born in the same year,
;; the function returns a symbol 'BornSameYear
(define (isOlder student1 student2)
  (cond 
    [(= (ummstudent-year-birth student1) (ummstudent-year-birth student2)) 'BornSameYear]
    [(< (ummstudent-year-birth student1) (ummstudent-year-birth student2)) (ummstudent-name student1)]
    [else (ummstudent-name student2)]
  )
)

(check-expect (isOlder JoeSmith JaneBrown) 'JoeSmith)
(check-expect (isOlder JaneBrown JoeSmith) 'JoeSmith)
(check-expect (isOlder JoeSmith JoeSmith) 'BornSameYear)


;; Contract: ummstudent, ummstudent -> real
;; Purpose: the function retunrs the higher of the 
;; GPAs for the two students


;(check-expect (max-GPA JaneBrown JoeSmith) 3.45)
;(check-expect (max-GPA JaneBrown JaneBrown) 3.25)


;; Contract: ummstudent, real -> ummstudent
;; Purpose: the function takes a ummstudent structure
;; and returns a new ummstudent structure with the same 
;; student name and year of birth but with the new GPA
;; 
(define (update-GPA student new-GPA)
  (make-ummstudent (ummstudent-name student)
                   (ummstudent-year-birth student)
                   new-GPA
                   )
)

(check-expect (ummstudent-GPA (update-GPA JoeSmith 3.5)) 3.5)
(check-expect (ummstudent-name (update-GPA JoeSmith 3.5)) 'JoeSmith)
(check-expect (ummstudent-GPA JoeSmith) 3.45)



;; Contract: ummstudent -> boolean
;; Purpose: to check whether a given "ummstudent" structure 
;; is well-defined: the name is a symbol, the year 
;; is an integer between 1900 and 2000,
;; the GPA is a number between 0 and 4.0
(define (is-valid student)
  (and 
   (symbol? (ummstudent-name student)) ; check name
   (and (integer? (ummstudent-year-birth student)) ; check year-birth
        (<= (ummstudent-year-birth student) 2000)
        (>= (ummstudent-year-birth student) 1900)) 
   (and (real? (ummstudent-GPA student))  ; check GPA
        (<= (ummstudent-GPA student) 4.0)
        (>=  (ummstudent-GPA student) 0.0)
        )
  )
)

(check-expect (is-valid JoeSmith) true)
(check-expect (is-valid (make-ummstudent 5 'TheNineties -3.5)) false)
(check-expect (is-valid (make-ummstudent 'JoeSmith 'TheNineties 3.5)) false)
(check-expect (is-valid (make-ummstudent 'JoeSmith 1990 4.5)) false)

(define eternal-student (make-ummstudent 'NoOneRemembersHisName 1960 1.95))

;; age: ummstudent number -> number
;; age is a function that takes a perrson and current year 
;; and returns the age of this person by the end of the year

;; add tests