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

enum {
    BYTES_PER_SAMPLE = 2
};

enum {
    MAX_SAMPLE = (~(~0 << (8*BYTES_PER_SAMPLE-1)))
};

typedef struct Command Command;

struct Command {
    FILE* fp;
    double leftProportion;
    Command* next;
};

static void
emitIntegerSample( double samp )
{
    int val = (int)( MAX_SAMPLE * samp );

    if ( val < -MAX_SAMPLE ) {
	val = -MAX_SAMPLE;
    } else if ( val > MAX_SAMPLE ) {
	val = MAX_SAMPLE;
    }

    fputc( ( val >> 8 ) & 0xFF, stdout );
    fputc( ( val >> 0 ) & 0xFF, stdout );
}

static void
emitFloatingSample( double samp )
{
    fwrite( (const char*)&samp, sizeof(samp), 1, stdout );
}

static void
cleanUpList( Command* list )
{
    while ( list != 0 ) {
	Command* next = list->next;
	pclose( list->fp );
	free( list );
	list = next;
    }
}

static unsigned int
addCommand( Command** commands, const char* str, double leftProportion )
{
    FILE* fp = popen( str, "r" );

    if ( fp == 0 ) {
	cleanUpList( *commands );
	fprintf( stderr, "Couldn't run <%s>\n", str );
	perror( "popen" );
	return __LINE__;
    } else {
	Command* nn = (Command*)malloc( sizeof(Command) );

	if ( nn == 0 ) {
	    pclose( fp );
	    cleanUpList( *commands );
	    fprintf( stderr, "Couldn't get memory\n" );
	    return __LINE__;
	}

	nn->fp = fp;
	nn->leftProportion = leftProportion;
	nn->next = *commands;
	*commands = nn;
    }

    return 0;
}

int
main( int argc, const char* argv[] )
{
    unsigned int help = 0;
    double gain = 1.00;
    void (*emitSample)( double ) = emitIntegerSample;
    unsigned int done = 0;
    Command* commands = 0;
    unsigned int commandCount = 0;
    double leftProportion = 0.5;
    unsigned int frequency = 8192;
    double length = -1.0;
    double fadeIn = 0.0;
    double fadeOut = 5.0;
    unsigned int stereo = 0;
    unsigned int ii;
    unsigned int lastSample;
    unsigned int fadeInEnd;
    unsigned int fadeOutSamples;
    unsigned int fadeOutStart;

    for ( ii=1; ii < argc; ++ii ) {
	if ( !strcmp( argv[ ii ], "-command" ) ) {
	    if ( addCommand( &commands, argv[ ++ii ], leftProportion ) != 0 ) {
		return __LINE__;
	    } else {
		++commandCount;
	    }
	} else if ( !strcmp( argv[ ii ], "-file" ) ) {
	    FILE* fp = fopen( argv[ ++ii ], "r" );

	    if ( fp == 0 ) {
		fprintf( stderr, "Unable to read file <%s>\n", argv[ii] );
		return __LINE__;
	    } else {
		char buf[ 8192 ];

		while ( fgets( buf, sizeof(buf), fp ) != 0 ) {
		    if ( buf[0] == '@' ) {
			leftProportion = strtod( &buf[1], 0 );
		    } else {
			if ( addCommand( &commands, buf, leftProportion )
			!= 0 ) {
			    fclose( fp );
			    return __LINE__;
			} else {
			    ++commandCount;
			}
		    }
		}

		fclose( fp );
	    }
	} else if ( !strcmp( argv[ ii ], "-prop" ) ) {
	    leftProportion = strtod( argv[ ++ii ], 0 );
	} else if ( !strcmp( argv[ ii ], "-gain" ) ) {
	    gain = strtod( argv[ ++ii ], 0 );
	} else if ( !strcmp( argv[ ii ], "-freq" ) ) {
	    frequency = strtol( argv[ ++ii ], 0, 0 );
	} else if ( !strcmp( argv[ ii ], "-length" ) ) {
	    length = strtod( argv[ ++ii ], 0 );
	} else if ( !strcmp( argv[ ii ], "-fadeIn" ) ) {
	    fadeIn = strtod( argv[ ++ii ], 0 );
	} else if ( !strcmp( argv[ ii ], "-fadeOut" ) ) {
	    fadeOut = strtod( argv[ ++ii ], 0 );
	} else if ( !strcmp( argv[ ii ], "-float" ) ) {
	    emitSample = emitFloatingSample;
	} else if ( !strcmp( argv[ ii ], "-stereo" ) ) {
	    stereo = 1;
	} else {
	    fprintf( stderr, "Unknown argument <%s>\n", argv[ii] );
	    help = 1;
	}
    }

    if ( gain < 0.0000001 || commands == 0 ) {
	fprintf( stderr, "Bad parameters\n" );
	help = 1;
    }

    if ( help ) {
	fprintf( stderr, "Usage: %s\n", argv[0] );
	fprintf( stderr, "\t[\n" );
	fprintf( stderr, "\t\t[-prop proportionForLeftChannel]\n" );
	fprintf( stderr, "\t\t[-command commandToFork]\n" );
	fprintf( stderr, "\t\t...\n" );
	fprintf( stderr, "\t]\n" );
	fprintf( stderr, "\t[-gain gain]\n" );
	fprintf( stderr, "\t[-freq frequency]\n" );
	fprintf( stderr, "\t[-length lengthOfSong]\n" );
	fprintf( stderr, "\t[-fadeIn lengthOfFadeIn]\n" );
	fprintf( stderr, "\t[-fadeOut lengthOfFadeOut]\n" );
	fprintf( stderr, "\t[-float]\n" );
	fprintf( stderr, "\t[-stereo]\n" );
	fprintf( stderr, "\t[-help]\n" );
	return __LINE__;
    }

	/* adjust gain to avoid clipping */
    gain /= (double) commandCount;

    if ( length < 0.0 ) {
	lastSample = 0;
	fadeInEnd = 0;
	fadeOutSamples = 0;
	fadeOutStart = ~0;
    } else {
	lastSample = (unsigned int)( length * (double)frequency );
	fadeInEnd = (unsigned int)( fadeIn * (double)frequency );
	fadeOutSamples = (unsigned int)( fadeOut * (double)frequency );

	if ( lastSample >= fadeOutSamples ) {
	    fadeOutStart = lastSample - fadeOutSamples;
	} else {
	    fadeOutStart = 0;
	}

	if ( fadeOutStart < fadeInEnd ) {
	    fadeInEnd = fadeOutStart = ( fadeInEnd + fadeOutStart ) / 2;
	    fadeOutSamples = lastSample - fadeOutSamples;
	}
    }

    for ( ii=0; !done && ( ( lastSample == 0 ) || ii < lastSample ); ++ii ) {
	Command* ptr = commands;
	double leftSamp = 0.0;
	double rightSamp = 0.0;
	double effectiveGain = gain;

	while ( ptr != 0 ) {
	    double thisGuy;

	    if ( fread( (char*)&thisGuy, sizeof(double), 1, ptr->fp ) != 1 ) {
		done = 1;
		break;
	    }

	    leftSamp  += ptr->leftProportion * thisGuy;
	    rightSamp += ( 1.0 - ptr->leftProportion ) * thisGuy;

	    ptr = ptr->next;
	}

	if ( ii < fadeInEnd ) {
	    effectiveGain = gain * ( (double)ii ) / ( (double) fadeInEnd );
	} else if ( ii >= fadeOutStart ) {
	    effectiveGain = gain - gain
		* ( (double)( ii - fadeOutStart ) )
		    / ( (double) fadeOutSamples );
	}

	if ( stereo ) {
	    (*emitSample)( leftSamp * effectiveGain );
	    (*emitSample)( rightSamp * effectiveGain );
	} else {
	    (*emitSample)( ( leftSamp + rightSamp ) * effectiveGain );
	}
    }

    cleanUpList( commands );

    return 0;
}