;; SNAKE!

(define GRID-SQSIZE 10)
(define BOARD-HEIGHT 20) ;; in grid squares
(define BOARD-WIDTH 30) ;; in grid squares

(define BACKGROUND (empty-scene (* GRID-SQSIZE BOARD-WIDTH)
                                (* GRID-SQSIZE BOARD-HEIGHT)))

(define TICK-RATE 0.3)
(define SEG-RADIUS (quotient GRID-SQSIZE 2))
(define SEG-IMAGE (circle SEG-RADIUS "solid" "red"))

(define FOOD-RADIUS (floor (* 0.9 SEG-RADIUS)))
(define FOOD-IMAGE (circle FOOD-RADIUS "solid" "green"))



;; Snake World


(define-struct world (snake food))
;; A World is a (make-world Snake Food)

;; A Food is a Posn (in grid square coords)

(define-struct snake (segs direction))
;; A Snake is a (make-snake Segs Direction)

;; A Segs is one of: 
;; - empty
;; - (cons Posn Segs)  ;; where posn is in grid square coords
;;   A Snake must contain at least one segment 
;;   The head is the first element in Segs

;; A NESegs is one of: 
;; - (cons Posn empty)
;; - (cons Posn NESegs)

;; A Direction is one of: 
;; - "up"
;; - "down" 
;; - "left"
;; - "right"


;; Initial wish-list 
;; world->scene : World -> Image
;; render the current world

;; food+scene : Food Image -> Image 
;; adds the food to a scene

;; snake+scene: Snake Image -> Image
;; add the snake to the scene

;; world->world : World -> World
;; produce the next world

;; snake-slither : Snake -> Snake
;; move snake in direction it's headed in

;; snake-grow : Snake -> Snake
;; grow the snake 


;; eating? : World -> Boolean
;; is this an eating scenario?

;; key-handler : World KeyEvt -> World

;; place-image-on-grid : Image Number Number 

;; game-over? : World -> Boolean
;; wall-collide? : Snake -> Boolean 
;; self-collide? : Snake -> Boolean 

;; create-food : World -> World
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

(define food1 (make-posn 5 3))
(define snake1 (make-snake (cons (make-posn 6 10) empty)
                           "left"))
(define world1 (make-world snake1 food1))


;; world->scene : World -> Image
;; render the current world
(define (world->scene w)
  ...)



;; food+scene : Food Image -> Image 
;; adds the food to a scene

;; snake+scene: Snake Image -> Image
;; add the snake to the scene

;; **** Your job: construct examples for world->scene, food+scene, snake+scene ****


#;(big-bang world0
          (to-draw world->scene)
          (on-tick world->world)
          (on-key key-handler)
          (stop-when game-over?))