;; 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 15.6.1) (read-case-sensitive #t) (teachpacks ((lib "testing.ss" "teachpack" "htdp") (lib "371-tiles.ss" "installed-teachpacks") (lib "371-sb-world.ss" "installed-teachpacks"))) (htdp-settings #8(#t constructor repeating-decimal #f #t none #f ((lib "testing.ss" "teachpack" "htdp") (lib "371-tiles.ss" "installed-teachpacks") (lib "371-sb-world.ss" "installed-teachpacks")))))
; Worked exercise 15.6.1
; An animation of a picture that moves up, down, left, and right
; in response to the corresponding arrow keys

; Model: a posn representing the current location of the picture
; Handlers needed: redraw and key

; Useful constants:
(define WIDTH 300)
(define HEIGHT 300)
(define BACKGROUND (empty-scene WIDTH HEIGHT))
(define DOT (circle 3 "solid" "blue"))


; Redraw handler:
; show-picture: posn -> scene
(define (show-picture where)
  ; where             a posn       (make-posn 27 149)
  ; (posn-x where)    a number(x)  27
  ; (posn-y where)    a number(y)  149
  ; DOT               an image
  ; BACKGROUND        a scene
  ; right answer      a scene      (place-image DOT 27 149 BACKGROUND)
  (place-image DOT (posn-x where) (posn-y where) BACKGROUND)
  )
  
(check-expect (show-picture (make-posn 15 12))
              (place-image DOT 15 12 BACKGROUND))
(check-expect (show-picture (make-posn 27 149))
              (place-image DOT 27 149 BACKGROUND))

; 15.5.4 add-posns : posn posn -> posn
; Copied this so I can use it in handle-key
(define (add-posns here there)
  ; here               posn
  ; there              posn
  ; (posn-x here)      num
  ; (posn-y here)      num
  ; (posn-x there)     num
  ; (posn-y there)     num
  (make-posn (+ (posn-x here)
                (posn-x there))
             (+ (posn-y here)
                (posn-y there)))
  )
(check-expect (add-posns (make-posn 0 0) (make-posn 3 -2)) (make-posn 3 -2))
(check-expect (add-posns (make-posn 1 -2) (make-posn 2 7)) (make-posn 3 5))



; Key handler:
; handle-key: posn symbol-or-char -> posn\
(define (handle-key where key)
  ; where          a posn              (make-posn 12 19)
  ; key            a symbol or char    various
  ; (posn-x where) a number            12
  ; (posn-y where) a number            19
  (cond [(char? key)       where]
        [(symbol? key)
;         (cond [(symbol=? key 'right)
;                ; right answer         a posn   (make-posn 13 19)
;                (add-posn (make-posn 1 0) where)]
;               [(symbol=? key 'left)
;                ; right answer         a posn   (make-posn 11 19)
;                (add-posn (make-posn -1 0) where)]
;               [(symbol=? key 'up)
;                ; right answer         a posn   (make-posn 12 18)
;                (add-posn (make-posn 0 -1) where)]
;               [(symbol=? key 'down) 
;                ; right answer         a posn   (make-posn 12 20)
;                (add-posn (make-posn 0 1) where)]
;               [else   where]
;               )
         ; or alternatively,
         (add-posns where
                    (cond [(symbol=? key 'right) (make-posn 1 0)]
                          [(symbol=? key 'left) (make-posn -1 0)]
                          [(symbol=? key 'up) (make-posn 0 -1)]
                          [(symbol=? key 'down) (make-posn 0 1)]
                          [else (make-posn 0 0)]))
         ]
        ))
(check-expect (handle-key (make-posn 12 19) #\e) (make-posn 12 19))
(check-expect (handle-key (make-posn 12 19) 'left) (make-posn 11 19))
(check-expect (handle-key (make-posn 12 19) 'right) (make-posn 13 19))
(check-expect (handle-key (make-posn 12 19) 'up) (make-posn 12 18))
(check-expect (handle-key (make-posn 12 19) 'down) (make-posn 12 20))
(check-expect (handle-key (make-posn 12 19) 'home) (make-posn 12 19))

(generate-report)

(run-animation WIDTH HEIGHT
               (make-posn (quotient WIDTH 2) (quotient HEIGHT 2)) 1
               (on-redraw show-picture)
               (on-key handle-key))