; CS 131 - Week 3, Lecture 2
; modulo "prelude" example
;    (a variation from Week 2, Lecture 2 posted examples)

(require 2htdp/universe)
(require 2htdp/image)

; named constants for this animation

(define WIDTH 200)
(define HEIGHT 150)
(define BACKDROP
        (place-image (circle 30 "solid" "gold")
                     (- WIDTH 50)
                     (/ HEIGHT 3)
                     (empty-scene WIDTH HEIGHT)))

;----------------------
; let's say I want MANY purple stars of many sizes
; SO -- I'm going to write a function to do so

; signature: purple-star: number -> image
; purpose: expects a desired enclosing pentagon side length
;    in pixels, and produces a purple star of that size

(check-expect (purple-star 27)
              (star 27 "solid" "purple"))

(check-expect (purple-star 46)
              (star 46 "solid" "purple"))

(define (purple-star size)
  (star size "solid" "purple")
)

(purple-star 30)
(purple-star 4)

;---------------
; signature: get-1-bigger: number -> number
; purpose: expects a number, and produces the number
;     that is 1 bigger

(define (get-1-bigger a-number)
  (+ a-number 1)
)

(check-expect (get-1-bigger 15) 16)
(get-1-bigger 45)

;---------------
; what would happen if just the star's x-coordinate 
;    is determined by the current state?

; now it would be nice to have a named constant for
;    the star's size...

(define STAR-SIZE 30)

; signature: draw-star-scene3: number -> scene
; purpose: expects the current state of the universe,
;    and produces a scene with a purple star 
;    centered at ((modulo state WIDTH), HEIGHT/2)

(define (draw-star-scene3 a-number)
  (place-image
                   (purple-star STAR-SIZE)
                   (modulo a-number WIDTH)
                   (/ HEIGHT 2)
                   BACKDROP)
)


(check-expect (draw-star-scene3 15)
              (place-image
                   (purple-star STAR-SIZE)
                   15
                   (/ HEIGHT 2)
                   BACKDROP))
(check-expect (draw-star-scene3 47)
              (place-image
                   (purple-star STAR-SIZE)
                   47
                   (/ HEIGHT 2)
                   BACKDROP))
(check-expect (draw-star-scene3 (+ WIDTH 5))
              (place-image
                   (purple-star STAR-SIZE)
                   5
                   (/ HEIGHT 2)
                   BACKDROP))
(draw-star-scene3 15)

(big-bang 0
          (on-tick get-1-bigger 1/56)
          (on-draw draw-star-scene3))