/* filecut.c

   my own version of file cut utility, which does not have a memory
   requirement */

#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <limits.h>

#define BUFFER_SIZE	5000000

int main(int argc, char *argv[])
{
  struct stat filestat;
  FILE *infile, *outfile;
  off_t len, offset;
  off_t insize;
  unsigned char buf[BUFFER_SIZE];
  int i;
  int num_reads, tail_len;


  /* checking command line parameters */
  if (argc != 4 && argc != 5) {
    fprintf(stderr, "Usage: filecut infile outfile length [offset]\n");
    exit(1);
  }
  if ( (infile=fopen(argv[1], "rb")) == NULL ) {
    fprintf(stderr, "Can not open input file!\n");
    exit(1);
  }
  if ( (outfile=fopen(argv[2], "wb")) == NULL ) {
    fprintf(stderr, "Can not open output file!\n");
    exit(1);
  }
  if ( (len=atol(argv[3])) < 0 ) {
    fprintf(stderr, "Invalid length specification!\n");
    exit(1);
  }
  if (argc == 5) {
    if ( (offset=atol(argv[4])) < 0 ) {
      fprintf(stderr, "Invalid offset specification!\n");
      exit(1);
    }
  }
  else
    offset = 0;

  /* get entir file length */
  if ( stat(argv[1], &filestat) ) {
    fprintf(stderr, "Can not get input file length\n");
    exit(1);
  }
  insize = filestat.st_size;
  if (insize < (offset+len) ) {
    fprintf(stderr, "Offset + Len is larger than filesize\n");
    exit(1);
  }

  /* cut file */
  if ( offset != 0 )
    fseek(infile, offset, SEEK_SET);
  num_reads = len / BUFFER_SIZE;
  tail_len = len % BUFFER_SIZE;
  for (i=0;i<num_reads;i++) {
    printf("Reading buffer %d from %s\n", i+1, argv[1]);
    fread(buf, sizeof(unsigned char), BUFFER_SIZE, infile);
    printf("Writing buffer %d to %s\n", i+1, argv[2]);
    fwrite(buf, sizeof(unsigned char), BUFFER_SIZE, outfile);
  }
  fread(buf, sizeof(unsigned char), tail_len, infile);
  fwrite(buf, sizeof(unsigned char), tail_len, outfile); 

  /* clean up */
  fclose(infile);
  fclose(outfile);
  return(0);

}