(define-interface finite-queues-interface
  (export make-finite-queue
	  finite-queue-empty? finite-queue-full?
	  add-to-finite-queue!
	  remove-from-finite-queue!))

(define-structure finite-queues finite-queues-interface
  (open scheme
	srfi-9
	big-util)
  (begin
    (define-record-type :finite-queue
      (really-make-buffer max-size vector size begin end)
      finite-queue?
      (max-size finite-queue-max-size)
      (vector finite-queue-vector)
      (size finite-queue-size set-finite-queue-size!)
      (begin finite-queue-begin set-finite-queue-begin!)
      (end finite-queue-end set-finite-queue-end!))
  
    (define (make-finite-queue max-size)
      (really-make-buffer max-size
			  (make-vector max-size)
			  0
			  0 0))

    (define (finite-queue-empty? finite-queue)
      (zero? (finite-queue-size finite-queue)))

    (define (finite-queue-full? finite-queue)
      (= (finite-queue-size finite-queue)
	 (finite-queue-max-size finite-queue)))

    (define (add-to-finite-queue! finite-queue element)
      (if (finite-queue-full? finite-queue)
	  (error "add-to-finite-queue!"))
      (let ((end (finite-queue-end finite-queue)))
	(vector-set! (finite-queue-vector finite-queue)
		     end
		     element)
	(set-finite-queue-end! finite-queue
			       (if (= (+ end 1)
				      (finite-queue-max-size finite-queue))
				   0
				   (+ end 1)))
	(set-finite-queue-size! finite-queue
				(+ 1
				   (finite-queue-size finite-queue)))))

    (define (remove-from-finite-queue! finite-queue)
      (if (finite-queue-empty? finite-queue)
	  (error "remove-from-finite-queue!"))
      (let* ((begin (finite-queue-begin finite-queue)))
	(set-finite-queue-begin! finite-queue
				 (if (= (+ begin 1)
					(finite-queue-max-size finite-queue))
				     0
				     (+ begin 1)))
	(set-finite-queue-size! finite-queue
				(- (finite-queue-size finite-queue)
				   1))
	(vector-ref (finite-queue-vector finite-queue)
		    begin)))
    ))