#lang scheme

(require test-engine/scheme-tests)

(require 2htdp/universe)

(define (True x) true)

;; all geometric shapes support these methods in all contexts 
(define shape<%> 
  (interface ()
    area ;; -> Number
    ;; compute the area of this shape

    render ;; Scene -> Scene
    ;; add this shape to the given scene 
    ))

;; a circle 
(define circle%
  (class* object% (shape<%>)
    (init-field x  ; Number, x pixels of center from left
                y  ; Number, y pixels of center from top
		r  ; Number, radius
		c) ; ColorString 

    (define/public (area) (* pi r r))

    (define/public (render s) (place-image IMG x y s))
    (field [IMG (circle r "solid" c)])

    (super-new)))

;; a square parallel to sides of canvas 
(define square%
  (class* object% (shape<%>)
    (init-field x  ; Number, x pixels of upper-left from left
                y  ; Number, y pixels of upper-left from top
		l  ; Number, length of one side 
		c) ; ColorString 

    (define/public (area) (* l l))

    (define/public (render s) (place-image IMG x y s))
    (field [IMG (rectangle l l "solid" c)])
    
    (super-new)))

(define s1 (new circle% [x 10][y 20][r 40][c "red"]))
(define s2 (new square% [x 80][y 70][l 40][c "blue"]))
(define mt (empty-scene 100 100))

(check-within (send s1 area) (* pi 1600) .1)
(check-expect (send s2 area) 1600)
(check-expect (True (send s1 render mt)) true)
(check-expect (True (send s2 render mt)) true)
(test)