/* Reads two files, writes their bit-wise XOR. */
/* Last edited on 2013-09-04 18:34:50 by stolfi */

#define PROG_NAME "xor"
#define PROG_VERSION "1.0"

#define xor_C_copyright \
  "Copyright © 2013 Jorge Stolfi, State University of Campinas"

#define PROG_HELP \
  PROG_NAME " {FILE1} {FILE2} > {OUTFILE}"
 
#define xor_C_rights \
  xor_C_copyright ".\n" \
  "This file is provided 'as is'; the author and his employer are" \
  " not liable for any damages that may result from its use.  This" \
  " file can be used and modified for any purpose as long as" \
  " the copyright and this 'rights' note are preserved in" \
  " all copies and derived versions."
 
#define PROG_INFO \
  "SYNOPSIS\n" \
  "\n" \
  "  " PROG_HELP "\n" \
  "\n" \
  "DESCRIPTION\n" \
  "\n" \
  "  Reads two files named {FILE1} and {FILE2}, computes their" \
  " bitwise exclusive or (XOR), writes the result to standard" \
  " output.\n" \
  "\n" \
  "  Fails if file {FILE1} is longer than {FILE2}.\n" \
  "\n" \
  "  If either {FILE1} or {FILE2} is \"-\", assumes it is standard input.\n" \
  "\n" \
  "OPTIONS\n" \
  "\n" \
  "  -h\n" \
  "  --help\n" \
  "    Prints the SYNOPSIS above.\n" \
  "\n" \
  "  -i\n" \
  "  --info\n" \
  "    Prints this manpage.\n" \
  "\n" \
  "RIGHTS\n" \
  "\n" \
  "  " xor_C_rights "\n"
  
#define _GNU_SOURCE
#include <stdio.h>
#include <string.h>
#include <errno.h>

#include <cryptoy.h>
 
FILE *get_in_file(char *name);
  /* If {name} is "-", returns {stdin}, otherwise returns 
    an open file descriptor on file {name}.  in this second case,
    prints a message to {stderr} and returns NULL if the open failed. */

void arg_error(char *msg);
  /* Prints {PROG_NAME} and {msg} to {stderr}, then {PROG_HELP}. */

int main(int argc, char **argv);

int main(int argc, char **argv)
  {
    /* Command line options:  */
    int iarg = 1;
    while (iarg < argc)
      { if ((strcmp(argv[iarg],"-h") == 0)  || (strcmp(argv[iarg],"--help") == 0))
          { fprintf(stderr, "USAGE: %s\n", PROG_HELP); return 0; }
        else if ((strcmp(argv[iarg],"-i") == 0) || (strcmp(argv[iarg],"--info") == 0))
          { fprintf(stderr, "%s\n", PROG_INFO); return 0; }
        else 
          { break; }
        iarg++;
      }
    
    /* Command line arguments: */
    if ((argc - iarg) != 2) { arg_error("wrong number of arguments"); return 1; }
    FILE *a = get_in_file(argv[iarg]); iarg++;
    FILE *b = get_in_file(argv[iarg]); iarg++;
    if ((a == NULL) || (b == NULL)) { return 1; }
    if (a == b) { arg_error("cannot read both files from same file descriptor"); return 1;  }
    int nw = cryptoy_xor_files(a, b, stdout);
    if (nw < 0) 
      { fprintf(stderr, "aborted.\n"); return 1; }
    else
      { return 0; }
  }

FILE *get_in_file(char *name)
  {
    fprintf(stderr, "opening \"%s\"... \n", name);
    if (strlen(name) == 0)
      { fprintf(stderr, "%s: ** empty file name\n", PROG_NAME); return NULL; }
    else if (strcmp(name, "-") == 0)
      { return stdin; }
    else
      { FILE *d = fopen(name, "rb");
        if (d == NULL) { perror(PROG_NAME); }
        return d;
      }
  }

void arg_error(char *msg)
  {
    fprintf(stderr, "%s: ** %s\n", PROG_NAME, msg);
    fprintf(stderr, "%s\n", PROG_HELP);
  }