;; The first three lines of this file were inserted by DrScheme. They record metadata
;; about the language level of this file in a form that our tools can easily process.
#reader(lib "htdp-beginner-reader.ss" "lang")((modname blob-world) (read-case-sensitive #t) (teachpacks ((lib "testing.ss" "teachpack" "htdp") (lib "universe.ss" "teachpack" "2htdp"))) (htdp-settings #(#t constructor repeating-decimal #f #t none #f ((lib "testing.ss" "teachpack" "htdp") (lib "universe.ss" "teachpack" "2htdp")))))
;; blob-world.ss

;; A Blob is (make-blob Posn Symbol)
;; Interpretation: a Blob is a disk at a given location and color
(define-struct blob (loc color))

;; examples of blobs
(define blob1 (make-blob (make-posn 30 40) 'red))
(define blob2 (make-blob (make-posn 130 40) 'blue))

;; draw an image of a blob on the  given scene
;; draw-blob: Blob Scene -> Scene
(define (draw-blob a-blob a-scene)
  (place-image (circle 10 'solid (blob-color a-blob)) 
               (posn-x (blob-loc a-blob))
               (posn-y (blob-loc a-blob))
               a-scene))

;; a visual test to draw the two blobs
(draw-blob blob1 (draw-blob blob2 (empty-scene 200 100)))

;; move the given posn by the given (dx, dy)
;; move-posn: Posn Number Number -> Posn
(define (move-posn p dx dy)
  (make-posn (+ (posn-x p) dx)
             (+ (posn-y p) dy)))

;; tests for the function move-posn
(check-expect (move-posn (make-posn 100 100) 20 40) (make-posn 120 140))

;; move the given blob by the given (dx, dy)
;; move-blob: Blob Number Number -> Blob
(define (move-blob a-blob dx dy)
  (make-blob (move-posn (blob-loc a-blob) dx dy)
             (blob-color a-blob)))

;; tests for the function move-blob
(check-expect (move-blob blob1 10 20)
              (make-blob (make-posn 40 60) 'red))

;;---------------------- BREAK --------------------------------------

;; The world consists of one blob
;; 'on-draw'        Draw the blob on a yellow rectangle 200 by 100
;; 'on-tick'        On tick of the clock the blob moves 3 pixels to the left
;; 'on-key'         Keep the blob stays within bounds using the right arrow key
;;      On each hit of the right arrow key the blob moves 3 pixels to the right
;; 'stop-world      The world ends when the blob gets out of bounds.

;; We work on each part one at a time:

;;------------------------------------------------------------------------
;; (on-draw draw-world)
;;
;; draw the blob on a yellow background
;; draw-world: Blob -> Scene
(define (draw-world a-blob)
  (draw-blob a-blob                                      ;; draw the blob
             (place-image 
                   (rectangle 200 100 'solid 'yellow)    ;; on a rectangle
                   100 50                                ;; centered pinhole
                   (empty-scene 200 100))))              ;; base is empty scene
             
;; a visual test for the draw=world function
(draw-world blob2)
            
;;------------------------------------------------------------------------
;; (on-tick tock speed)
;;
;; produce a blob moved 3 pixels to the left 
;; tock: Blob -> Blob
(define (tock a-blob)
  (move-blob a-blob -3 0))

;; test for the function tock
(check-expect (tock blob1) (make-blob (make-posn 27 40) 'red))

;;------------------------------------------------------------------------
;; Run the world with just the tick events
;;
;(big-bang blob2
;          (on-draw draw-world)
;          (on-tick tock 0.1))

;;------------------------------------------------------------------------
;; (on-key back ke)
;;
;; if right arrow is hit, move the blob right 3 pixels
;; back: Blob KeyEvent -> Blob
(define (back a-blob ke)
  (cond
    [(string=? ke "right") (move-blob a-blob 3 0)]
    [else a-blob]))

;; tests for the function back
(check-expect (back blob1 "right")
              (make-blob (make-posn 33 40) 'red))
(check-expect (back blob1 "left") blob1)

;;------------------------------------------------------------------------
;; Run the world with the tick events and key events
;;
;(big-bang blob2
;          (on-draw draw-world)
;          (on-tick tock 0.3)
;          (on-key back))

;;------------------------------------------------------------------------
;; (stop-when out-of-bounds?)
;;
;; is the blob out of bound on the left?
;; out-of-bounds?: Blob -> Boolean
(define (out-of-bounds? a-blob)
  (< (posn-x (blob-loc a-blob)) 0))

;; tests for the function out-of-bounds?
(check-expect (out-of-bounds? (make-blob (make-posn 33 40) 'red)) false)
(check-expect (out-of-bounds? (make-blob (make-posn -2 40) 'blue)) true)

;;-------------------------------------------------------------------------
;; Run the world with the tick events and key events and the world end test
;;
(big-bang blob1
          (on-draw draw-world)
          (on-tick tock 0.3)
          (on-key back)
          (stop-when out-of-bounds?))