#include <stdio.h>
#include <stdint.h>
#include <string.h>
#include <math.h>
#include <errno.h>
#include <time.h>
#include <sys/time.h>
#include <alsa/asoundlib.h>

#define SAMPLE_RATE 8000

#define BUFFER_SIZE 512

/* 2 bytes per sample; 0.1 seconds long */
#define TONE_SIZE (2*SAMPLE_RATE/10)

#define TONE1_FREQ 800
#define TONE2_FREQ 440

static uint8_t tone1[TONE_SIZE];
static uint8_t tone2[TONE_SIZE];
static const uint8_t silence[BUFFER_SIZE];

static int set_params(snd_pcm_t *pcm_handle)
{
	snd_pcm_hw_params_t *hwparams;
	unsigned int rate = SAMPLE_RATE;
	snd_pcm_uframes_t bufsize = BUFFER_SIZE;

	snd_pcm_hw_params_alloca(&hwparams);

	if (snd_pcm_hw_params_any(pcm_handle, hwparams) < 0) {
		printf("Failed configuring device\n");
		return -1;
	}
	if (snd_pcm_hw_params_set_access(pcm_handle, hwparams, SND_PCM_ACCESS_RW_INTERLEAVED) < 0) {
		printf("Failed setting access mode\n");
		return -1;
	}
	if (snd_pcm_hw_params_set_format(pcm_handle, hwparams, SND_PCM_FORMAT_S16_LE) < 0) {
		printf("Failed setting format\n");
		return -1;
	}
	if (snd_pcm_hw_params_set_rate_near(pcm_handle, hwparams, &rate, 0) < 0) {
		printf("Failed setting sample rate\n");
		return -1;
	}
	if (snd_pcm_hw_params_set_buffer_size_near(pcm_handle, hwparams, &bufsize) < 0) {
		printf("Failed setting sample rate\n");
		return -1;
	}
	if (snd_pcm_hw_params_set_channels(pcm_handle, hwparams, 1) < 0) {
		printf("Failed setting channel number\n");
		return -1;
	}
	if (snd_pcm_hw_params(pcm_handle, hwparams) < 0) {
		printf("Failed applying hardware parameters\n");
		return -1;
	}

	return 0;
}

static void prepare_tones()
{
	int i, amplitude = 20;
	uint16_t sample;

	for(i=0; i<TONE_SIZE-1; i++) {
		sample = amplitude * sin(2*M_PI*TONE1_FREQ*i/SAMPLE_RATE);
		tone1[i] = sample % 256;
		tone1[i+1] = sample >> 8;
		sample = amplitude * sin(2*M_PI*TONE2_FREQ*i/SAMPLE_RATE);
		tone2[i] = sample % 256;
		tone2[i+1] = sample >> 8;
	}
}

static long timediff_us(struct timespec *ts1, struct timespec *ts2)
{
	struct timeval tv1, tv2, diff;

	TIMESPEC_TO_TIMEVAL(&tv1, ts1);
	TIMESPEC_TO_TIMEVAL(&tv2, ts2);

	timersub(&tv1, &tv2, &diff);

	return diff.tv_sec * 1000000 + diff.tv_usec;
}

static void play_tone(snd_pcm_t *pcm_handle, char tone)
{
	const uint8_t *tonebuf;
	int tonebuf_size;

	switch(tone) {
		case '1':
			tonebuf = tone1;
			tonebuf_size = sizeof(tone1);
			break;
		case '2':
			tonebuf = tone2;
			tonebuf_size = sizeof(tone2);
			break;
		case 's':
		default:
			tonebuf = silence;
			tonebuf_size = sizeof(silence);
			break;
	}
	while (snd_pcm_writei(pcm_handle, tonebuf, tonebuf_size / 2) < 0) {
		snd_pcm_prepare(pcm_handle);
		printf("underrun\n");
	}
}

static int play(snd_pcm_t *pcm_handle, const char *pattern, int bpm)
{
	int i = 0;
	double period_us;
	struct timespec cur_t, old_t = {};

	period_us = 1000000 * 60.0 / bpm;

	/* fill buffer with silence */
	snd_pcm_prepare(pcm_handle);
	play_tone(pcm_handle, 's');

	while(1) {
		if (clock_gettime(CLOCK_MONOTONIC, &cur_t) == -1) {
			printf("Failed getting time: %s\n", strerror(errno));
			return -1;
		}

		if (timediff_us(&cur_t, &old_t) >= period_us) {
			memcpy(&old_t, &cur_t, sizeof(struct timespec));
			play_tone(pcm_handle, pattern[i++ % strlen(pattern)]);
		} else {
			play_tone(pcm_handle, 's');
		}

		usleep(500);
	}
}

int main()
{
	snd_pcm_t *pcm_handle;

	if (snd_pcm_open(&pcm_handle, /*"default"*/ "plughw:1,0", SND_PCM_STREAM_PLAYBACK, 0) < 0) {
		printf("Failed opening device\n");
		return 1;
	}

	if (set_params(pcm_handle) < 0) {
		return 1;
	}

	prepare_tones();
	play(pcm_handle, "2111", 120);

	snd_pcm_close(pcm_handle);

	return 0;
}