/* ----------------------------------------------------------------------- *
 * Exercise 13-3: A set of functions that plays with words
 *                1) reverses the whole string
 *                2) reverses each word in the string, preserving original
 *                   word order 
 *                3) reverses the words in the string, preserving the order
 *                   of letters in words.
 *
 * Author: Suzi Anvin   
 * ----------------------------------------------------------------------- */

#include <stdio.h>
#include <string.h>

/* swap_chars takes pointers to 2 places in a string.  It swaps the poited at 
 * characters, then moves the pointers inwards, and continues swapping until 
 * all characters have been swapped, reversing the order of the parts of the 
 * string between the two pointers */
void swap_chars (char *first_ptr, char *end_ptr) 
{
  char tmp;	                /* holds one character for a character swap */
  while (first_ptr < end_ptr) { /* loop until the two pointers meet or cross */
    tmp = *end_ptr;		/* save the character at the end to tmp */
    *end_ptr = *first_ptr;	/* move the first character to the end */
    *first_ptr = tmp;		/* move the saved end chacater to the front */
    ++first_ptr;		/* move the pointers inward one step */
    --end_ptr;
  }
}

/* Reverse the order of characters in the entire string */
void reverse_string (char *first_ptr, int size)
{                        /* first_ptr points at the first char in the string */
			 /* size is the number of characters in the string */
  char *end_ptr;	 /* points at the last char in the string */

  end_ptr = first_ptr + size - 1;   /* point end_ptr at last character */
  swap_chars (first_ptr, end_ptr); /* reverse the order  of characters */
}

/* Reverse the order of characters within each word */
void reverse_word_chars (char *first_ptr)
{                         /* first_ptr points at first character in a word */
  char *end_ptr;	  /* points at last character in a word */
  char *space_ptr;	  /* points at the space after the word to be swapped*/
 
  space_ptr = first_ptr;
  while (*space_ptr != '\0') {      /* choose new words until end of string */
    while ( *space_ptr != ' ' && *space_ptr != '\0') {
      space_ptr++;   /* advance space_ptr to end of next word (' ' or '\0') */
    }
    end_ptr = space_ptr - 1;          /* set end of word */
    swap_chars (first_ptr, end_ptr);  /*reverse the order of the characters */
    ++space_ptr;       /* move space_ptr so it no longer points to a space! */
    first_ptr = space_ptr;            /* set beginning of next word */
  }
}

/* Reverse the order of words only*/
void reverse_word_order (char *string, int size)
{
  reverse_string (string, size);
  reverse_word_chars (string);
}

int main ()
{
  char user_string[100];	/* line of text user wants to modify */
  char option[5];		/* option entered by user */

  while (1) {
    fputs("Please type in the text you wish to modify:\n", stdout);
    fgets(user_string, sizeof(user_string), stdin);
    user_string[strlen(user_string)-1] = '\0'; /* trim off '\n' */
    fputs("Choose a text modification:\n"
	  "1) Reverse the order of characters in the entire string\n"
	  "2) Reverse the order of characters within each word\n"
	  "3) Reverse the order of words only\n", stdout);
    while (1) {
      fgets(option, sizeof(option), stdin);
      switch (option[0]) {
      case '1': /* Reverse the order of characters in the entire string */
	reverse_string(user_string, strlen(user_string));
	break;
      case '2':	/* Reverse the order of characters within each word */
	reverse_word_chars(user_string);
	break;
      case '3': /* Reverse the order of words only */
	reverse_word_order(user_string, strlen(user_string));
	break;
      default:
	fputs("Error: Unknown text modification.  Enter 1, 2, or 3", stdout); 
	continue; /* go back to beginning of loop to re-enter option code*/
      }
      printf("Your string:\n%s\n", user_string);
      break; 
    }
    fputs("type Q to quit or [enter] to continue: ", stdout);
    fgets(option, sizeof(option), stdin);
    if (option[0] == 'Q' || option[0] == 'q')
      break;
  }
  return (0);
}