(require-library "graphics.ss" "graphics")

(define pi 3.1415926)

(define make-timer
  (lambda (seconds)
    (open-graphics)
    (let* ((v (open-viewport "Countdown Timer" 500 500))
           (red (make-rgb 1 0 0))
           (middle (make-posn 250 250))
           (radius 200))
      ((draw-viewport v) red)
      ((draw-string v)
       (make-posn 20 20) 
       (string-append "Pause " (number->string seconds) " seconds"))
      (clear-segments v middle radius seconds)
      (close-viewport v)
      (close-graphics))))

(define clear-segments 
  (lambda (v middle radius seconds)
    (let* ((step-angle (/ pi 90))
           (offset-seconds 3)
           (seconds-per-step (/ (- seconds offset-seconds) 180))
           (radius (+ radius 1))
           (phi0 (- (/ pi 2)))
           (clear-segment
            (lambda (i)
              (let* ((phi1 (+ phi0 (* i step-angle)))
                     (phi2 (+ phi1 step-angle)))           
                ((clear-solid-polygon v) 
                 (list (make-posn 0 0)
                       (make-posn (* radius (cos phi1)) (* radius (sin phi1)))
                       (make-posn (* radius (cos phi2)) (* radius (sin phi2))))
                 middle)))))
      (let loop ((step 0))
        (if (<= step 180)
            (begin
              (thread (lambda () (clear-segment step)))
              (sleep seconds-per-step)
              (loop (+ step 1)))))
      ((draw-viewport v) (make-rgb 0 1 0))
      (get-mouse-click v))))

(define pause
  (lambda (minutes)
    (make-timer (round (* 60 minutes)))))