#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <sys/soundcard.h>

#define DEVICE_NAME "/dev/dsp"

typedef struct {
  unsigned char *buffer;
  size_t size;
  int sample_rate;
} sound_t;

sound_t *
new_sound(int size, int sample_rate)
{
  sound_t *sb = (sound_t *) malloc(sizeof (sound_t));

  sb->buffer = (unsigned char *) malloc(sizeof (unsigned char) * size);
  sb->size = size;
  sb->sample_rate = sample_rate;

  return sb;
}

void
insert_sinus_tone(sound_t *sb, int frequency, int start, int length)
{
  int i;

  for (i = 0; i < length; ++i) {
    float f = sin((i * frequency) / (sb->sample_rate * 2 * M_PI));
    unsigned char sample = (unsigned char) ((f * 127) + 128);
    /* printf("%d %d\n", i, sample); */
    sb->buffer[start + i] = sample;
  }
}

void
free_sound(sound_t *sb)
{
  if (sb != 0) {
    if (sb->buffer != 0) {
      free(sb->buffer);
      sb->buffer = 0;
    }
    free(sb);
    sb = 0;
  }
}

int
init_audio()
{
  int audio_fd;

  if ((audio_fd = open(DEVICE_NAME, O_WRONLY, 0)) == -1) {
    perror(DEVICE_NAME);
    return (-1);
  }

  return audio_fd;
}

int
play_sound(int audio_fd, sound_t *sb)
{
  int len;

  if ((len = write(audio_fd, sb->buffer, sb->size)) == -1) {
    perror("write");
    return (-1);
  }

  if (len != sb->size) {
    fprintf(stderr, "buffer size: %i, len: %i\n", sb->size, len);
    return (-1);
  }

  return (0);
}

int
main(int argc, char **argv)
{
  int audio_fd, ret;
  sound_t *sb = 0;

  if ((audio_fd = init_audio()) == -1) {
    return (EXIT_FAILURE);
  }

  sb = new_sound(4096, 8000);
  insert_sinus_tone(sb, 44000, 0, 4096);

  if ((ret = play_sound(audio_fd, sb)) == -1) {
    free_sound(sb);
    close(audio_fd);
    return (EXIT_FAILURE);
  }

  free_sound(sb);
  close(audio_fd);
  return (EXIT_SUCCESS);
}