;; Example of how to program the world
;;------------------------------------

(define-struct my-world (loc radius))
;; MyWorld = (make-my-world Posn Number)
;; Interpretation: 
;; The world consists of a red circle
;; with the centre at loc and the specified radius

(define world0 (make-my-world (make-posn 100 100) 20))
(define world1 (make-my-world (make-posn 10 90) 4))


;; define how the worlds changes on each tick
;; World -> World
(define (tick-fcn w)
  (cond
    [(<= (my-world-radius w) 5) (make-my-world (my-world-loc w)
                                              5)]
    [else (make-my-world (my-world-loc w)
                         (- (my-world-radius w) 1))]))
           

;;; tests for tick
(check-expect (tick-fcn world0) (make-my-world (make-posn 100 100) 19))
(check-expect (tick-fcn world1) (make-my-world (make-posn 10 90) 5))

;; helper function to produce posn at a position changed by dx dy
;; move-posn: Posn Number Number -> Posn
(define (move-posn p dx dy)
  (make-posn (+ dx (posn-x p))
             (+ dy (posn-y p))))

(check-expect (move-posn (make-posn 20 20) 3 5) (make-posn 23 25))

;; define how the world responds to key events
;; World KeyEvent -> World
(define (ke-fcn w ke)
  (cond
    [(char? ke) w]    ;; ignore characters
    [(symbol=? ke 'left) 
     (make-my-world (move-posn (my-world-loc w) -3 0)
                    (my-world-radius w))]
    [(symbol=? ke 'right) 
     (make-my-world (move-posn (my-world-loc w) 3 0)
                    (my-world-radius w))]
    [else w]))

(check-expect (ke-fcn world0 "left") world0)
(check-expect (ke-fcn world0 'left) (make-my-world (make-posn 97 100) 20))
(check-expect (ke-fcn world0 'right) (make-my-world (make-posn 100 103) 20))
(check-expect (ke-fcn world0 'up) world0)
    
;; define how the world responds to muse clicks
;; World Number Number MouseEvent -> World
(define (mouse-fcn w mpx mpy mpe)
  (cond
    [(symbol=? mpe 'button-down) w]
    [(symbol=? mpe 'button-up) (make-my-world (make-posn mpx mpy) (my-world-radius w))]
    [(symbol=? mpe 'drag) (make-my-world (make-posn mpx mpy) (my-world-radius w))]
    [(symbol=? mpe 'move) w]
    [(symbol=? mpe 'enter) w]
    [(symbol=? mpe 'leave) w]))
    

(check-expect (mouse-fcn world0 50 40 'button-down) world0)
(check-expect (mouse-fcn world0 50 40 'button-up) 
              (make-my-world (make-posn 50 40) 20))
(check-expect (mouse-fcn world0 50 40 'drag) 
              (make-my-world (make-posn 50 40) 20))
(check-expect (mouse-fcn world0 50 40 'move) world0)
(check-expect (mouse-fcn world0 50 40 'enter) world0)
(check-expect (mouse-fcn world0 50 40 'leave) world0)


;; A MouseEvent is one of:
  ;; - 'button-down
  ;; - 'button-up
  ;; - 'drag
  ;; - 'move
  ;; - 'enter
  ;; - 'leave
                 
;; draw the current world onto the given scene
;; draw-fcn: World Image -> Image
(define (draw-fcn w scene)
  (place-image (circle (my-world-radius w) 'solid 'red)
               (posn-x (my-world-loc w)) (posn-y (my-world-loc w))
               scene))

;; verify that you get the expected drawing
(draw-fcn world0 (empty-scene 200 200))
(draw-fcn world1 (empty-scene 200 200))

;;------------ END OF THE STUDENT CODE -------------------------

;; --- run program run ---
(define WIDTH 200)
(define HEIGHT 200)

;; World -> Scene
;; place the image of the world in an empty scene
(define (world-scene w) 
  (draw-fcn w (empty-scene WIDTH HEIGHT)))

;; run the program with one tick per second
(big-bang WIDTH HEIGHT 1 world0)
(on-redraw world-scene)
(on-tick-event tick-fcn)
(on-key-event ke-fcn)
(on-mouse-event mouse-fcn)


;; on-mouse-event : (World Number Number MouseEvent -> World) -> true
;; (on-mouse-event clack) means that DrScheme must call clack 
;; on the current world, the current x and y coordinates of the mouse, 
;; and and a (representation of the) mouse event for every action 
;; of the mouse the programmer (user of the computer) makes; 
;; it uses the result as the next world