;; a person is a (make-person string number symbol list-of-person)
(define-struct person (name year eye children))

;; A list-of-person is either
;; empty, or
;; (cons person list-of-person)

(define SusanTree
  (make-person "Susan" 1920 'blue
               (list (make-person "Joe" 1938 'green empty)
                     (make-person "Helen" 1940 'brown
                                  (list (make-person "Hank" 1965 'green empty)
                                        (make-person "Cara" 1969 'brown empty)))
                     (make-person "Ricky" 1942 'blue empty))))


; ;; there are 2 data definitions, so need 2 templates
; 
; ;; person-template:  person .. -> ...
; ;; ...
; (define (person-template aper ...)
;   (person-name aper)
;   (person-year aper)
;   (person-eye aper)
;   (lop-template (person-children aper)...))
; 
; 
; ;; lop-template:  list-of-person ... -> ...
; ;; ...
; (define (lop-template alop ...)
;   (cond [(empty? alop)   ]
;         [(cons? alop)  (person-template (first alop)...)
;                        (lop-template (rest alop) ...)  ]))


;; count-older-blue:  person number -> number
;; produces the number of blue-eyed people in the tree who were born before the given year
(define (count-older-blue aper year)
  (cond [(and (< (person-year aper) year) (symbol=? (person-eye aper) 'blue))
         (+ 1 (old-blue-descendants (person-children aper) year))]
        [else (old-blue-descendants (person-children aper) year)]))



;; old-blue-descendants:  list-of-person number -> number
;; consumes a list of persons and produces the number of people in the list (and their descendants) who are blue-eyed
;; and born before the given year
(define (old-blue-descendants alop year)
  (cond [(empty? alop)  0 ]
        [(cons? alop)  (+ (count-older-blue (first alop) year)
                          (old-blue-descendants (rest alop) year) ) ]))

;; test cases
(check-expect (count-older-blue SusanTree 1950) 2)
(check-expect (count-older-blue SusanTree 1941) 1)