/*
 Combines two files with byte boundaries.
 License: MIT.
*/

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

size_t copyfilev( FILE *outf, FILE *inf, unsigned char *bufo, const size_t bufs )
{
 size_t actr = 0, actw = 0, totr = 0;

 do
{
  actr = fread( bufo, 1, bufs, inf );
  actw = fwrite( bufo, 1, actr, outf );
  actr &= actw;
  totr += actr;
} while ( actr == bufs );

 return(totr);
}

int combin( FILE *arqo, FILE *arqi[2], unsigned char *bufm, const size_t readf[2], const size_t readl, const size_t bufs )
{
 int reti = 0;
 size_t bufr = bufs, buftr = 0, memloop = 1, mempos = 0, teste = 0, ui = 0;
 unsigned char uci = 0;
/* Cap the buffer. */
 memloop = bufs / readl;
 bufr = memloop * readl;

 for ( buftr = bufr; buftr == bufr; )
{
  buftr = 0;
/* Fill buffer. */
  for ( mempos = 0, ui = 0; ui < memloop; ui++ )
{

   for ( uci = 0; uci < 2; uci++ )
{
    teste = fread( &bufm[mempos], 1, readf[uci], arqi[uci] );
    buftr += teste;

    if ( teste != readf[uci] )
{
/* Check for bad combination. */
     if ( teste > 0 )
{
      reti = 1;
}
     break;
}

    mempos += teste;
}

   if ( uci != 2 )
{
    break;
}

}

  teste = fwrite( bufm, 1, buftr, arqo );
//  buftr &= teste;
  if ( teste != buftr )
{
   reti = 1;
   break;
}

}

#ifdef __DEBUG__
 printf( "Bufr: %lu\nBuftr: %lu\nMemloop: %lu\nMempos: %lu\nTeste loop 1: %lu\nUci: %u\n", bufr, buftr, memloop, mempos, teste, uci );
#endif
 uci ^= 1;
 teste = copyfilev( arqo, arqi[uci], bufm, bufs );
/* Check for bad combination, take two. */
 if ( teste > 0 )
{
  reti = 1;
}

#ifdef __DEBUG__
 printf( "Final teste: %lu\n", teste );
#endif
 return(reti);
}

int main( int argc, char **argv )
{
 FILE *arqi[2] = { 0, 0 };
 FILE *arqo = 0;
 char *errc = '\0', *file1n = '\0', *file2n = '\0', *fileon = '\0';
 int i = 0;
 size_t readf[2] = { 524288, 524288 };
 size_t bufs = 1048576, readl = 1048576, teste = 0;
 unsigned char *bufm = 0;
 unsigned char uci = 0;

 for ( ; i != -1; )
{
  i = getopt( argc, argv, "1:2:ho:r:" );

  switch ( i )
{
/* Detects overflow before it is too late. */
   case '1':
    readf[0] = strtoul( optarg, &errc, 10 );
    teste = ULONG_MAX - readf[0];

    if ( ( errc[0] != '\0' ) || ( teste < readf[1] ) )
{
     fprintf( stderr, "Invalid value combination.\n" );
     return(1);
}
    break;

   case '2':
    readf[1] = strtoul( optarg, &errc, 10 );
    teste = ULONG_MAX - readf[1];

    if ( ( errc[0] != '\0' ) || ( teste < readf[0] ) )
{
     fprintf( stderr, "Invalid value combination.\n" );
     return(1);
}
    break;

   case 'h':
    printf( "%s -1 input1_reads -2 input2_reads -r reading_size -o output -- file1 file2 [output]\n", argv[0] );
    return(0);

   case 'o':
    fileon = optarg;
    break;

   case 'r':
    bufs = strtoul( optarg, &errc, 10 );

    if ( errc[0] != '\0' )
{
     fprintf( stderr, "Wrong reading buffer value!\n" );
     return(1);
}
    break;

   case '?':
    if ( file1n == 0 )
{
     file1n = argv[optind - 1];
}
    else if ( file2n == 0 )
{
     file2n = argv[optind - 1];
}
    else if ( fileon == 0 )
{
     fileon = argv[optind - 1];
}
    else
{
     fprintf( stderr, "Unknown option \"%c\".\n", optopt );
     return(1);
}
    break;

   default:
    i = -1;
    break;
}

}

 for ( i = optind; i < argc; i++ )
{

  if ( file1n == 0 )
{
   file1n = argv[i];
}
  else if ( file2n == 0 )
{
   file2n = argv[i];
}
  else if ( fileon == 0 )
{
   fileon = argv[i];
}
  else
{
   break;
}

}

 readl = readf[0] + readf[1];

 if ( bufs < readl )
{
  fprintf( stderr, "Reading buffer size must hold at least one reading from each file!\n" );
  return(1);
}

 arqi[0] = fopen( file1n, "rb" );

 if ( arqi[0] == 0 )
{
  fprintf( stderr, "Couldn't open \"%s\"!\n", file1n );
  return(1);
}

 arqi[1] = fopen( file2n, "rb" );

 if ( arqi[1] == 0 )
{
  fprintf( stderr, "Couldn't open \"%s\"!\n", file2n );
  return(1);
}

 if ( fileon != 0 )
{
  arqo = fopen( fileon, "wb" );

  if ( arqo == 0 )
{
   fprintf( stderr, "Couldn't open \"%s\"!\n", fileon );
   return(1);
}

}
 else
{
  arqo = stdout;
}

 bufm = (unsigned char *)malloc( sizeof(unsigned char) * bufs );

 if ( bufm == 0 )
{
  fprintf( stderr, "Not enough memory for reading buffer!\n" );
  return(2);
}

/**/
 i = combin( arqo, arqi, bufm, readf, readl, bufs ) * 3;
 free(bufm);

 for ( uci = 0; uci < 2; uci++ )
{
  fclose(arqi[uci]);
}

 if ( fileon != 0 )
{
  fclose(arqo);
}

 return(i);
}