Untitled

;;;--------------------------------
;;;Exercise 7
(define-struct photos [top bottom])
; ImageCollection is one of: 
; – #false 
; – (make-photos Image ImageCollection)
; interpretation: represents a collection of photos where #false is a
; collection with no photos and make-photos has at least one photo.
; - photos-top is the photo on the top of the stack of photos
; - photos-bottom represents the remaining photos
(define p0 #false)
(define p1 (make-photos . p0))
(define p2 (make-photos . p1))
(define p3 (make-photos . p2))
(define p4 (make-photos . p3))
(define p5 (make-photos . p4))

(define (photos-temp p)
  (...
   (cond [(boolean? p) ...]
         [(photos? p)
          ... (photos-top p)
          ... (photos-temp (photos-bottom p))])))

;;;p-size: ImageCollection -> Nat
;;;Returns the total number of images in a ImageCollection
(check-expect (p-size p1) 1)
(check-expect (p-size p3) 3)
(check-expect (p-size p5) 5)
(define (p-size p)
   (cond [(boolean? p) 0]
         [(photos? p)
          (add1 (p-size (photos-bottom p)))]))


;----------------------------------------------------
(define-struct cr (index images))
; A CR (Camera Roll) is a (make-cr PositiveNumber ImageCollection)
; interpretation: 
;  The index represents the position of the current image.
;  The index must be between 0 and the number of images in ImageCollection.
(define cr0 (make-cr 0 p0))
(define cr1 (make-cr 0 p1))
(define cr2 (make-cr 1 p2))
(define cr3 (make-cr 2 p3))
(define cr4 (make-cr 1 p4))
(define cr5 (make-cr 3 p5))

#;
(define (cr-temp cr)
  (... (cr-index cr))
  (... (photos-temp (cr-images cr))))

;;;NEED FUNCTION THAT TAKES IN CAMERA ROLL, LOOKS AT INDEX, GOES THAT MANY DEEP INTO THE IMAGECOLLECTION
;;;how do we go a variable amount deep?



(define Blacksquare (square 100 "solid" "black"))
;;;display-photo: CR -> Image
;;;takes in a Camera Roll and returns the current image
;;;returns a black square if no images in camera roll
;(check-expect (display-photo cr0) Blacksquare)
(check-expect (display-photo cr2) (photos-top p1))
(check-expect (display-photo cr5) (photos-top p3))

#;
(define (display-photo cr)
  (cond [(boolean? (cr-images cr)) Blacksquare]
        [(photos? (cr-images cr)) (photos-top (cr-images cr))]))

;;;change-photo: CR a-key -> CR
(define (change-photo cr a-key)
  (cond
    [(string=? a-key "left") (prev-photo cr)]
    [(string=? a-key "right") (next-photo cr)]
    [else cr]))

;;;prev-photo: CR -> CR
;;;Subtracts one from the index of a Camera Roll
(check-expect (prev-photo cr5) (make-cr 2 p5))
(check-expect (prev-photo cr3) (make-cr 1 p3))

(define (prev-photo cr)
  (if (> (cr-index cr) 0)
  (make-cr (- (cr-index cr) 1) (cr-images cr))
  cr))

;;;next-photo: CR -> CR
;;;Adds one to the index of a Camera Roll
(check-expect (next-photo cr5) (make-cr 4 p5))
(check-expect (next-photo cr3) (make-cr 3 p3))

(define (next-photo cr)
  (if (< (cr-index cr) (p-size (cr-images cr)))
  (make-cr (+ (cr-index cr) 1) (cr-images cr))
  cr))