;Draws simple l-system consisting of an arbitrary 
;  list of +, -, and f where + and - are always 
;  right and left turns of 90 degrees and f is
;  always a straight line of 20 pixels. The state 
;  of the turtle is updated with the use of set!.

(load "writeln.scm")
(define drawSystem
  (lambda (cmdList)

    ;Turtle state
    (define x 0)
    (define y 0)
    (define angle 0)

    ;; Make an 800 x 500 frame
    (define frame (instantiate frame% 
       ("L-System") (width 800) (height 500))
    )


    (define draw-SetUp
      (lambda (dc)
        ;Set the background color to lavender.
        ;(send dc set-background 
        ;   (make-object color% 220 200 255)
        ;)
        (send dc clear)
        (send dc set-smoothing 'smoothed)
        (send dc set-pen red-pen)
        (set! x 400)
        (set! y 250)
        (set! angle 0)

      )
    )


    (define processf
      (lambda (dc)
        (define dx 0)
        (define dy 0)
    
        (cond 
          ((eq? angle 0)   (set! dy -20))
          ((eq? angle 90)  (set! dx  20))
          ((eq? angle 180) (set! dy  20))
          ((eq? angle 270) (set! dx -20))
        )
        (let ((x1 (+ x dx)) (y1 (+ y dy)))
        
          (send dc draw-line x y x1 y1)
          ;(writeln x y x1 y1 dx dy)
          (set! x x1)
          (set! y y1)
        )
      )
    )


    (define setAngle
      (lambda (delta)
        ;The use of modulo adds the delta to the 
        ;current value of angle and sets it to 
        ;290 of angle = -90 and to 0 if angle = 360. 
        ;(set! angle (+ angle x))
        ;(if (= angle -90) (set! angle 270))
        ;(if (= angle 360) (set! angle 0))
        (set! angle (modulo (+ angle delta) 360))
        ;(writeln x y angle)
      )
    )


    (define draw-cmdList 
      (lambda (dc mylist) 
        (cond 
          ((null? mylist) 0)
          (else
            (let ((c (car mylist)))
              (cond
                ((eq? c '+) (setAngle 90))
                ((eq? c '-) (setAngle -90))
                ((eq? c 'f) (processf dc))
              )
             
              (draw-cmdList dc (cdr mylist))
            )
          )
        )
      )
    )





    ;; Make the drawing area with a paint callback
    (define canvas 
      (instantiate canvas% (frame) 
        (paint-callback 
          (lambda (canvas dc) (reDrawEverything dc))
        )
      )
    )

    (define (reDrawEverything dc) 
      (draw-SetUp dc)
      (draw-cmdList dc cmdList)
    ) 

    ;Create a pen with color red, thickness 2, 
    ;  and line type solid
    (define red-pen 
      (instantiate pen% ("RED" 2 'solid))
    )


    ;; Show the frame
    (send frame show #t) 
  )
)

(drawSystem '(f + f - f + f - f + f))
(drawSystem '(f - f - f - f f + f + f + f))
(drawSystem '(f + f + f f + f f + f f f + f f f + f f f f + f f f f))
(drawSystem '(f - f - f f - f f - f f f - f f f - f f f f - f f f f))