//-------------------------------------------------------------------
//	mknoises.cpp
//
//	This program generates the Pulse Code Modulation data for a
//	stereophonic demonstration for one second of 'white noise',
//	(using the 'rand()' library-function to generate pulse-data
//	first for the left channel and then for the right channel). 
//	You can play the 'noises.wav' file with our 'pcmplay' tool.
// 
//		     compile using:  $ make mknoises 
//		     execute using:  $ mknoises
//
//	NOTE: This program is a revision of our 'makewave.cpp' demo
//	which created a Waveform Audio File for a single channel of
//	audio playback.  Here the audio file's data-chunk has twice 
//	the previous size because each 'sample' describes the 8-bit
//	intensity for a left-hand channel and a right-hand channel.
//
//	programmer: ALLAN CRUSE
//	written on: 14 SEP 2005
//-------------------------------------------------------------------

#include <stdio.h>	// for printf(), perror() 
#include <fcntl.h>	// for open() 
#include <stdlib.h>	// for exit() 
#include <unistd.h>	// for write(), close() 

#define SAMPLE_RATE	8000
#define SAMPLE_SIZE	2
#define NUM_SAMPLES	SAMPLE_RATE

unsigned char	pulsecode[ NUM_SAMPLES * SAMPLE_SIZE ];
char 	filename[] = "noises.wav";


int main( int argc, char **argv )
{
	// specify our default parameters for tone generation
	int	sampleRate = SAMPLE_RATE;
	int	numSamples = NUM_SAMPLES;
	int	amplitude = 64;
	int	silence = 128;

	// generate the pulse-code data for the stereo demonstration
	int	period = NUM_SAMPLES / 2;
	for (int sample = 0; sample < NUM_SAMPLES; sample++)
		{
		int	pulse = rand() % amplitude;
		int	signal_left  = ( sample < period ) ? 1 : 0;
		int	signal_right = ( sample < period ) ? 0 : 1;
		int	pulse_left  = pulse * signal_left; 
		int	pulse_right = pulse * signal_right;
		pulsecode[ 2*sample + 0 ] = silence + pulse_left;
		pulsecode[ 2*sample + 1 ] = silence + pulse_right;
		}	

	//----------------------------------------------
	// now store the pulse-code data as a .wav file
	//----------------------------------------------

	// setup the .wav file parameters
	int	formatTag = 1; 
	int	nChannels = 2;
	int	fmt_ChunkSize = 16;
	int	dataChunkSize = numSamples * nChannels;
	int	riffChunkSize = 4 + (8+fmt_ChunkSize) + (8+dataChunkSize);
	int	bitsPerSample = 8;
	int	samplesPerSec = sampleRate;
	int	avBytesPerSec = samplesPerSec * nChannels;
	int	frameAlignmnt = nChannels * (bitsPerSample/8);

	// open the .wav file for writing
	int	fd = open( filename, O_WRONLY | O_CREAT | O_TRUNC, 0666 );
	if ( fd < 0 ) { perror( filename ); exit(1); }

	// write the RIFF chunk
	write( fd, "RIFF", 4 );
	write( fd, &riffChunkSize, 4 );
	write( fd, "WAVE", 4 );

	// write the FORMAT chunk
	write( fd, "fmt ", 4 );
	write( fd, &fmt_ChunkSize, 4 );
	write( fd, &formatTag, 2 );
	write( fd, &nChannels, 2 );
	write( fd, &samplesPerSec, 4 );
	write( fd, &avBytesPerSec, 4 );
	write( fd, &frameAlignmnt, 2 );
	write( fd, &bitsPerSample, 2 );
	
	// write the DATA chunk
	write( fd, "data", 4 );
	write( fd, &dataChunkSize, 4 );

	unsigned char	*dat = pulsecode;
	int		morebytes = dataChunkSize;
	while ( morebytes > 0 )
		{
		int	nbytes = write( fd, dat, morebytes );
		if ( nbytes < 0 ) break;
		morebytes -= nbytes;
		dat += nbytes;
		}

	// close the .wav file 
	close( fd );

	// show the filename and filesize to our user
	printf( "\npulse-code data saved as \'%s\' ", filename );
	printf( "(%d bytes) \n\n", 8+riffChunkSize );
}