#include <assert.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <alsa/asoundlib.h>

#define RATE 48000

snd_pcm_uframes_t setup(snd_pcm_t ** pcm)
{
  snd_pcm_uframes_t bsize, psize;

  assert(snd_pcm_open(pcm, "default", SND_PCM_STREAM_PLAYBACK, 0) == 0);
  assert(snd_pcm_set_params(*pcm, SND_PCM_FORMAT_S16_LE,
                            SND_PCM_ACCESS_RW_INTERLEAVED,
                            1, RATE, 1, 250000) == 0);
  assert(snd_pcm_get_params(*pcm, &bsize, &psize) == 0);
  assert(bsize / psize >= 4);

  return psize;
}

void bwrite(snd_pcm_t * pcm, snd_pcm_sframes_t towrite)
{
  int r;
  char * garbage;

  garbage = calloc(1, towrite);
  r = snd_pcm_writei(pcm, garbage, towrite);
  free(garbage);

  if (r < 0) {
    fprintf(stderr, "bwrite error recovery\n");
    snd_pcm_recover(pcm, r, 1);
  }
}

snd_pcm_sframes_t fill(snd_pcm_t * pcm)
{
  snd_pcm_sframes_t avail;

  avail = snd_pcm_avail_update(pcm);
  if (avail < 0) {
    fprintf(stderr, "fill error recovery\n");
    snd_pcm_recover(pcm, avail, 1);
    avail = snd_pcm_avail_update(pcm);
  }
  if (avail) {
    bwrite(pcm, avail);
  }

  return avail;
}

int main(int argc, char * argv[])
{
  snd_pcm_t * pcm;
  snd_pcm_uframes_t psize;
  int pause = 0, count = 0, recovery = 0;

  if (argc == 2 && argv[1][0] == '-' && argv[1][1] == 'r') {
    recovery = 1;
  }

  /* set up a mono output device at RATE Hz with at least 4 periods */
  psize = setup(&pcm);

  /* prefill sound buffers and begin playback */
  fill(pcm);

  while (++count) {
    if (pause || count % 7 == 0) {
      fprintf(stderr, pause ? "resuming playback\n" : "pausing playback\n");
      pause = !pause;
      snd_pcm_pause(pcm, pause);

      /* if resuming playback and recovery enabled, fill sound buffers */
      if (recovery && !pause) {
        fprintf(stderr, "recovery, wrote %d frames\n", (int) fill(pcm));
      }
    }

    /* if not paused, write a period of sound data */
    if (!pause) {
      snd_pcm_sframes_t avail = snd_pcm_avail_update(pcm);
      bwrite(pcm, psize);
      fprintf(stderr, "playback, wrote %u frames (needed %d)\n", (unsigned int) psize, (int) avail);
    }

    /* sleep for half a period */
    usleep(psize * 1000000 / RATE / 2);
  }

  return 0;
}