#lang racket

(require ffi/vector
         (rename-in racket/contract [-> c->])

(define nat? exact-nonnegative-integer?)

(provide/contract [s16vec-play (c-> s16vector? nat? (or/c false? nat?) integer?
                                    (c-> void?))])

;; it would use less memory to use stream-play, but
;; there's an unacceptable 1/2-second lag in starting
;; a new place.

(define channels 2)

(define (s16vec-play s16vec start-frame pre-stop-frame sample-rate)
  (define total-frames (/ (s16vector-length s16vec) channels))
  (define stop-frame (or pre-stop-frame
  (check-args s16vec total-frames start-frame stop-frame)
  (define sound-frames (- stop-frame start-frame))  
  (define copying-info (make-copying-info s16vec start-frame stop-frame))
  (define sr/i (exact->inexact sample-rate))
  (define stream
     0             ;; input channels
     2             ;; output channels
     'paInt16      ;; sample format
     sr/i          ;; sample rate
     default-buffer-frames ;;frames-per-buffer
     copying-callback ;; callback (NULL means just wait for data)
  (pa-set-stream-finished-callback stream copying-info-free)
  (pa-start-stream stream)
  (define (stopper)
    (pa-maybe-stop-stream stream))

(define (check-args vec total-frames start-frame stop-frame)
  (unless (integer? total-frames)
    (raise-type-error 's16vec-play "vector of length divisible by 2" 0 vec start-frame stop-frame))
  (when (<= total-frames start-frame)
    (raise-type-error 's16vec-play "start frame < total number of frames" 1 vec start-frame stop-frame))
  (when (< total-frames stop-frame)
    (raise-type-error 's16vec-play "end frame < total number of frames" 2 vec start-frame stop-frame))
  (when (< stop-frame start-frame)
    (raise-type-error 's16vec-play "start frame <= end frame" 1 vec start-frame stop-frame)))

;; at 44100, this is close to 100ms, which should cover most
;; GC pauses.
(define default-buffer-frames 4096)