#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <math.h>

#include <time.h>
#include <fcntl.h>
#include <unistd.h>

#include <linux/soundcard.h>

#define UNIT_PITCH 2546.48
#define BASE_PITCH 440.0

int16_t generate_sample(int phase, double pitch)
{
	double result = 0;
	int i;
	for (i = 1; i <= 8; i++)
	{
		result += 1.0/(i*i)*sin(phase*pitch/UNIT_PITCH*i);
	}
	return result*10000;
}

/* A note is a 32-bit value used as follows:
     the least significant 8 bits are a number of octaves
     the next 8 bits are a number of fifths
     the next 8 bits are a number of thirds
*/

double pitch(uint32_t note)
{
	signed char octave = note;
	signed char fifth = (note >> 8);
	signed char third = (note >> 16);
	return BASE_PITCH * pow(2.0, octave) * pow(0.75, fifth) *
		pow(1.25, third);
}

uint32_t next(uint32_t prev, uint32_t base, double core_pitch, int m)
{
	signed char octave = prev;
	signed char fifth = (prev >> 8);
	signed char third = (prev >> 16);
	signed char bo = base;
	signed char bf = (base >> 8);
	signed char bt = (base >> 16);
	int pdo = 125;
	int pio = 125;
	int pdf = 160;
	int pif = 160;
	int pdt = 80;
	int pit = 80;
	if (pitch(prev) < core_pitch / 2)
	{
		pio += 180;
		pdo -= 90;
	}
	if (pitch(prev) > core_pitch / 2)
	{
		pdo += 180;
		pio -= 90;
	}
	if (fifth < bf)
	{
		pif += (m ? 120 : 240);
		pdf -= (m ? 60 : 120);
	}
	if (bf < fifth)
	{
		pdf += (m ? 120 : 240);
		pif -= (m ? 60 : 120);
	}
	if (third < bt)
	{
		pit += (m ? 160 : 240);
		pdt -= 80;
	}
	if (bt < third)
	{
		pdt += (m ? 160 : 240);
		pit -= 80;
	}
	int r = rand() % 1000;
	if (r < pdo)
		octave--;
	else if (r < pdo + pio)
		octave++;
	else if (r < pdo + pio + pdf)
		fifth--;
	else if (r < pdo + pio + pdf + pif)
		fifth++;
	else if (r < pdo + pio + pdf + pif + pdt)
		third--;
	else if (r < pdo + pio + pdf + pif + pdt + pit)
		third++;
	return (uint32_t)(unsigned char)octave |
		((uint32_t)(unsigned char)fifth << 8) |
		((uint32_t)(unsigned char)third << 16);
}

int main()
{
	srand(time(NULL));
	int i, out;
	out = open("/dev/dsp", O_WRONLY);
	if (out < 0)
	{
		perror("Could not open /dev/dsp: ");
		return 1;
	}
	int format = AFMT_S16_NE;
	if (ioctl(out, SNDCTL_DSP_SETFMT, &format) == -1)
	{
		perror("Could not set audio format: ");
		return 1;
	}
	if (format != AFMT_S16_LE)
	{
		fprintf(stderr,
	"Your sound-card does not support signed 16-bit native-endian audio");
		return 1;
	}
	int speed = 16000;
	if (ioctl(out, SNDCTL_DSP_SPEED, &speed) == -1)
	{
		perror("Could not set audio format: ");
		return 1;
	}
	if (speed < 15500 || speed > 16500)
	{
		fprintf(stderr, "Your sound-card does not support 16kHz audio");
		return 1;
	}
	uint32_t root = 0;
	uint32_t bass = -1;
	uint32_t cp1 = 0;
	uint32_t cp2 = 0;
	int d1 = 1;
	int d2 = 1;
	int d3 = 1;
	int16_t data[1000];
	while (1)
	{
		root = next(root, 0, 440.0, 0);
		for (i = 0; i < 64000; i++)
		{
			if (i % 16000 == 0)
			{
				d1--;
				if (d1 == 0)
				{
					int m = i / 16000;
					bass = next(bass, root, 220.0, m);
					d1 = rand()%(4-m)+1;
				}
			}
			if (i % 8000 == 0)
			{
				d2--;
				if (d2 == 0)
				{
					int m = i % 32000 / 8000;
					cp1 = next(cp1, bass, 330.0, m);
					d2 = rand()%(4-m)+1;
				}
			}
			if (i % 4000 == 0)
			{
				d3--;
				if (d3 == 0)
				{
					int m = i % 16000 / 4000;
					cp2 = next(cp2, bass, 440.0, m);
					d3 = rand()%(4-m)+1;
				}
			}
			data[i%1000] = generate_sample(i, pitch(bass)) +
					generate_sample(i, pitch(cp1)) +
					generate_sample(i, pitch(cp2));
			if (i % 1000 == 999)
			{
				if (write(out, data, 2000) < 0)
				{
					perror("Could not write to /dev/dsp: ");
					return 1;
				}
			}
		}
	}
	close(out);
}