/*
 * manipulate_hosts.c
 *
 * author: Patrick Neumann
 * version: 1.0 (02.11.2010)
 *
 * compile under (with):
 * - linux (http://gcc.gnu.org/)
 * - windows (http://www.mingw.org/)
 * - mac os x (work-in-progress)
 *
 * quick start guide:
 * 1. ping "www.microsoft.com" before
 * 2. run program
 * 3. ping "www.microsoft.com" afterwards
 * 4. compare outputs
 * 5. execute the program again
 * 6. now everything should be the same as before
 *
 * HINT: is not working on windows anymore because
 *         the anti virus tools from today detect that kind of modification!
 *
 */

#include <stdlib.h>
#include <stdio.h>
#include <string.h> // needed for the functions "strcpy", "strcat" und "strstr"
#define LINELENGTH 80
#ifdef __unix__
  #include <unistd.h> // needed for the function "access"
  #define WRITE W_OK
#else
  #include <io.h> // needed for the function "access"
  #define WRITE 02
#endif

int main(void) {
  #ifdef __unix__
    char oldfile[50] = "/etc/";
  #else
    char oldfile[50] = "C:\\WINDOWS\\system32\\drivers\\etc\\";
  #endif
  char newfile[50];
  strcpy( newfile, oldfile );
  strcat( oldfile, "hosts" );
  strcat( newfile, "newhosts" );
  char newline[50] = "149.20.20.133 www.microsoft.com";
  FILE *quelle, *ziel;
  char puffer[ LINELENGTH ];
  int counter = 0;

  // check if the source could be opened and be written (for the later "delete before rename")
  if( access( oldfile, WRITE ) == -1 ) {
    fprintf( stderr, "Will not be able to delete %s later.\n", oldfile );
    return EXIT_FAILURE;
  }

  // open source
  if( ( quelle=fopen( oldfile, "r" ) ) == NULL ) {
    fprintf( stderr, "Can not open %s.\n", oldfile );
    return EXIT_FAILURE;
  }

  // open target
  if( ( ziel=fopen( newfile, "w" ) ) == NULL ) {
    fprintf( stderr, "Can not open %s.\n", newfile );
    return EXIT_FAILURE;
  }

  while( fgets( puffer, LINELENGTH, quelle ) ) {
    // if text is not found, then ...
    if( strstr( puffer, newline ) == 0 ) {
       fputs( puffer, ziel );
    }
    // if text is found, then ...
    else {
      counter++;
    }
  }

  // if counter unchanged, then ...
  if( counter == 0 ) {
    fputs( newline, ziel );
    fputs( "\n", ziel );
    printf( "The line \"%s\" was added to %s.\n", newline, oldfile );
  }
  else {
    printf( "The line \"%s\" has been removed from %s.\n", newline, oldfile );
  }

  // close both files before deleting / renaming
  fclose(quelle);
  fclose(ziel);

  // delete original
  if( ( remove( oldfile ) ) == -1 ) {
    fprintf( stderr, "Error while deleting %s.\n", oldfile );
    return EXIT_FAILURE;
  }

  // rename manupulated copy to original
  if( ( rename( newfile, oldfile ) ) == -1 ) {
    fprintf( stderr, "Error while renaming %s.\n", newfile );
    return EXIT_FAILURE;
  }

  // so that the console esp. under windows does not disappear with "speed of light" again ...
  printf( "EXIT WITH RETURN..." );
  getchar();

  return EXIT_SUCCESS;
}