/* mixer.c   by Michael Thorpe   2018-06-23 */

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

#define SHORT_USAGE "mixer -h | { -[emv] | -[blor] <#> | <file> }* <file>"

struct channel {
	struct channel *next;
	unsigned int sample_rate; /* Not yet supported */
	unsigned int bits_per_sample;
	signed long left_gain_times_256;
	signed long right_gain_times_256;
	signed long current_sample;
	int little_endian;
	unsigned long saturations;
	char *name;
	FILE *f;
};

int main(int argc,char **argv) {
	int i,output_bits_per_sample=16,output_in_stereo=1,verbose=0,retval=0;
	struct channel *c;
	char buf[3],*s;
	signed long current_left_sample,current_right_sample,summand;
	unsigned long summing_saturations=0;
	unsigned long output_skip=0,output_length=0;
	struct channel default_channel={0,44100,16,256,256,0,0,0,0,0};

	for(i=1;i<argc;i++) {
		if(!strcmp(argv[i],"-h")) {
			fputs(
SHORT_USAGE "\n"
"      -b <#>  set input bits/sample for following file(s) (default: 16)\n"
"      -e      toggle endianness for following files/output (default: big-endian)\n"
"      -h      show this help message\n"
"      -l <#>  set left channel volume for following file(s) (default: 256)\n"
"      -m      toggle stereo/mono output (default: stereo)\n"
"      -o <#>  set output bits/sample (default: 16)\n"
"      -r <#>  set right channel volume for following file(s) (default: 256)\n"
"      -v      toggle verbosity\n"
"      <file>  name of a file, or - for stdin\n"
			,stdout);
			return(0);
		} else if(!strcmp(argv[i],"-e")) {
			default_channel.little_endian=!default_channel.little_endian;
		} else if(!strcmp(argv[i],"-m")) {
			output_in_stereo=!output_in_stereo;
		} else if(!strcmp(argv[i],"-v")) {
			verbose=!verbose;
		} else if(argv[i][0]=='-' && argv[i][1] && i<argc-1) {
			if(!strcmp(argv[i],"-b")) {
				default_channel.bits_per_sample=strtoul(argv[++i],&s,10);
				if(*s || default_channel.bits_per_sample==0 || 24<default_channel.bits_per_sample || default_channel.bits_per_sample&7) {
					fprintf(stderr,"Invalid number of bits per sample: %s\n",argv[i]);
					return(1);
				}
			} else if(!strcmp(argv[i],"-l")) {
				default_channel.left_gain_times_256=strtol(argv[++i],&s,10);
				if(*s) {
					fprintf(stderr,"Invalid left gain: %s\n",argv[i]);
					return(1);
				}
			} else if(!strcmp(argv[i],"-r")) {
				default_channel.right_gain_times_256=strtol(argv[++i],&s,10);
				if(*s) {
					fprintf(stderr,"Invalid right gain: %s\n",argv[i]);
					return(1);
				}
			} else if(!strcmp(argv[i],"-o")) {
				output_bits_per_sample=strtoul(argv[++i],&s,10);
				if(*s || output_bits_per_sample==0 || 24<output_bits_per_sample || output_bits_per_sample&7) {
					fprintf(stderr,"Invalid number of output bits: %s\n",argv[i]);
					return(1);
				}
			} else if(!strcmp(argv[i],"-s")) {
				output_skip=strtol(argv[++i],&s,10);
				if(*s) {
					fprintf(stderr,"Invalid output skip: %s\n",argv[i]);
					return(1);
				}
			} else if(!strcmp(argv[i],"-t")) {
				output_length=strtol(argv[++i],&s,10);
				if(*s) {
					fprintf(stderr,"Invalid output length: %s\n",argv[i]);
					return(1);
				}
			} else {
				fprintf(stderr,"Invalid argument: %s\n",argv[i]);
			}
		} else {
			c=(struct channel *)malloc(sizeof(struct channel));
			if(!c) {
				perror("malloc");
				return(1);
			}
			memcpy(c,&default_channel,sizeof(struct channel));
			c->name=argv[i];
			if(argv[i][0]=='-' && !argv[i][1])
				c->f=stdin;
			else
				c->f=fopen(argv[i],"rb");
			if(!c->f) {
				perror("open");
				return(1);
			}
			default_channel.next=c;
		}
	}
	if(!default_channel.next) {
		fputs("usage: " SHORT_USAGE "\n",stderr);
		return(1);
	}
	while(1) {
		current_left_sample=0;
		current_right_sample=0;
		for(c=default_channel.next;c;c=c->next) {
			if(c->little_endian) {
				buf[2]=buf[1]=buf[0]=0;
				if(1 != fread(buf+3-(c->bits_per_sample>>3),c->bits_per_sample>>3,1,c->f))
					goto no_more_samples;
				c->current_sample=(((signed int)(signed char)buf[2])<<16)+(((unsigned int)(unsigned char)buf[1])<<8)+((unsigned int)(unsigned char)buf[0]);
			} else {
				buf[2]=buf[1]=0;
				if(1 != fread(buf,c->bits_per_sample>>3,1,c->f))
					goto no_more_samples;
				c->current_sample=(((signed int)(signed char)buf[0])<<16)+(((unsigned int)(unsigned char)buf[1])<<8)+((unsigned int)(unsigned char)buf[2]);
			}
			if(c->current_sample&0x800000)
				c->current_sample|=~0xFFFFFF;
			summand=(c->current_sample*c->left_gain_times_256)/256L;
			if(c->left_gain_times_256) {
				if((summand<0)^(c->current_sample<0)^(c->left_gain_times_256<0)) {
					if(verbose)
						fputc('.',stderr);
					c->saturations++;
				}
				current_left_sample+=summand;
			}
			if(c->right_gain_times_256) {
				summand=(c->current_sample*c->right_gain_times_256)/256L;
				if((summand<0)^(c->current_sample<0)^(c->right_gain_times_256<0)) {
					if(verbose)
						fputc('.',stderr);
					c->saturations++;
				}
				current_right_sample+=summand;
			}
		}
		if(current_left_sample<-0x800000 || 0x800000<=current_left_sample) {
			if(verbose)
				fprintf(stderr,"Summing saturation: %8.8lX\n",current_left_sample&0xFFFFFFFF);
			current_left_sample=current_left_sample<0?-0x800000:0x7FFFFF;
			summing_saturations++;
		}
		if(output_skip) {
			output_skip--;
			continue;
		}
		if(default_channel.little_endian) {
			if(output_bits_per_sample>16)
				putchar(current_left_sample);
			if(output_bits_per_sample>8)
				putchar(current_left_sample>>8);
			putchar(current_left_sample>>16);
		} else {
			putchar(current_left_sample>>16);
			if(output_bits_per_sample>8)
				putchar(current_left_sample>>8);
			if(output_bits_per_sample>16)
				putchar(current_left_sample);
		}
		if(output_in_stereo) {
			if(current_right_sample<-0x800000 || 0x800000<=current_right_sample) {
				if(verbose)
					fprintf(stderr,"Summing saturation: %6.6lX\n",(current_right_sample>>8)&0xFFFFFFL);
				current_right_sample=current_right_sample<0?-0x800000:0x7FFFFF;
				summing_saturations++;
			}
			if(default_channel.little_endian) {
				if(output_bits_per_sample>16)
					putchar(current_right_sample);
				if(output_bits_per_sample>8)
					putchar(current_right_sample>>8);
				putchar(current_right_sample>>16);
			} else {
				putchar(current_right_sample>>16);
				if(output_bits_per_sample>8)
					putchar(current_right_sample>>8);
				if(output_bits_per_sample>16)
					putchar(current_right_sample);
			}
		}
		if(output_length && !--output_length)
			goto no_more_samples;
	}
no_more_samples:
	if(summing_saturations) {
		if(verbose)
			fputc('\n',stderr);
		fprintf(stderr,"Saturated %lu times when summing\n",summing_saturations);
		retval=1;
	}
	for(c=default_channel.next;c;c=c->next) {
		if(c->saturations) {
			fprintf(stderr,"Channel %s saturated %lu times\n",c->name,c->saturations);
			retval=1;
		}
	}
	return(retval);
}