/* This program performs a simple rotation of the alphabet on 
** the standard input and writes it out on standard out.
**
** The command line arguments are:
** -n #  where # is the rotation number.  Default is 0.
** -l #  use # as the alphabet length
*/


#include <stdio.h>
#include <ctype.h>

#define ALPHLENGTH   26
#define MAXLENGTH   256
#define DEFROT        0
#define TRUE          1
#define FALSE         0

void rotate_char();


int
main(argc, argv)
int argc;
char **argv;
{
  int rotnum = DEFROT;
  int manyflag = FALSE;
  int alphabet_length = ALPHLENGTH;
  char *word = NULL;
  char c;

  --argc, ++argv;
  while(argc){
    if(**argv != '-'){
      if(word){
	(void) printf("Bad option: %s\n", *argv);
      }
      else{
	word = *argv;
      }
      --argc, ++argv;
    }
    else{
      switch(*++*argv){
	case 'n':
	  --argc, ++argv;
	  if(sscanf(*argv, "%d", &rotnum) != 1){
	    (void) printf("Bad argument value.\n");
	    rotnum = DEFROT;
	  }
	  --argc, ++argv;
	  break;
	case 'l':
	  --argc, ++argv;
	  if(sscanf(*argv, "%d", &alphabet_length) != 1){
	    (void) printf("Bad argument value.\n");
	    alphabet_length = ALPHLENGTH;
	  }
	  --argc, ++argv;
	  break;
      }
    }
  }

  /* Now perform the rotation.
  */

  rotnum %= alphabet_length;

  if(rotnum == 0)
    manyflag = TRUE;

  if(!word){
    while( (c = getchar()) != EOF){
      if(manyflag){
	for(rotnum = 0; rotnum < alphabet_length; rotnum++){
	  if(c != '\n'){
	    rotate_char(c, rotnum, alphabet_length);
	    (void) putchar(' ');
	  }
	}
	(void) putchar('\n');
      }
	
      else
	rotate_char(c, rotnum, alphabet_length);
    }
  }
  /* Otherwise the word was entered on the command line.
  */

  else{
    while(*word){
      if(manyflag){
	for(rotnum = 0; rotnum < alphabet_length; rotnum++){
	  rotate_char(*word, rotnum, alphabet_length);
	  (void) putchar(' ');
	}
	(void) putchar('\n');
      }
      else 
	rotate_char(*word, rotnum, alphabet_length);
      word++;
    }
    (void) putchar('\n');
  }
}

void
rotate_char(c, rotnum, alphabet_length)
char c;
int rotnum;
int alphabet_length;
{
  
  if(isalpha(c)){
    /* If c is in the first 26-n characters of the alphabet, then add
    ** n to its value.  otherwise subtract 26-n from its value.
    */

    if(isupper(c))
      if( (int) c - 'A' < alphabet_length-rotnum)
	c += rotnum;
      else
	c += rotnum-alphabet_length;
    else
      if( (int) c - 'a' < alphabet_length-rotnum)
	c += rotnum;
      else
	c += rotnum-alphabet_length;
  }

  (void) putchar(c);
}