;;
;; particles2.al: create and kill particles on the fly
;;

(define *particles* '())
(define *ppf* 1) ; particles per frame created

(define (randR low high) (+ low (* (rand) (- high low))))

(define (make-one-particle)
  (list (list 'pp (vec3 0 0 0))
	(list 'pv (vec3 0 0 0))
	(list 'pa (vec3 0 0 0))
	(list 'age 0)
	(list 'lifespan 100)
	))

(define (add-particle p)
  (set! *particles* (cons p *particles*)))

(define (get-value p key)
  (list-ref (assq key p) 1))

(define (set-value p key val)
  (set-cdr! (assq key p) (list val)))

(define (update-particle p)
  (let ((pos (get-value p 'pp))
	(vel (get-value p 'pv))
	(acc (get-value p 'pa))
	(age (get-value p 'age))
	)
    (set-value p 'pp (+ pos vel))
    (set-value p 'pv (+ vel acc))
    (set-value p 'age (+ age 1))
    ))

(define (update-particles)
  (map update-particle *particles*))

(define (draw-particle p)
  (separator
    (translate (get-value p 'pp))
    (uscale .1)
    (sphere)))

(define (draw-particles)
  (map draw-particle *particles*))

(define (create-particle)
  (let (
	(p (make-one-particle))
	)
    (set-value p 'pp (vec3 0 -1 0))
    (set-value p 'pv (vec3 (randR -.03 .03) (randR .08 .12) 0))
    (set-value p 'pa (vec3 0 -.005 0))
    (set-value p 'lifespan (randR 10 50))
    (add-particle p)
    ))

(define (create-particles n)
  (for i 1 n 1
       (create-particle)))

(define (kill-particle? p)
  (if (> (get-value p 'age) (get-value p 'lifespan))
      '()
      (list p)
      ))

(define (kill-em p-list)
  (if (null? p-list)
      '()
      (append (kill-particle? (car p-list))
	      (kill-em (cdr p-list)))))

(define (kill-particles)	
  (set! *particles* (kill-em *particles*)))

(define (sim)
  (begin
    (for i 1 60 1
         (begin
	   (create-particles *ppf*)
	   (world
	     (draw-particles)
	     )
	   (update-particles)
	   (kill-particles)
	   ))))

(sim)