/**
 * trie.c
 *   A simple trie implementation, designed as a sample answer to
 *   problem 2 on exam 2.
 */

// +---------+-------------------------------------------------------
// | Headers |
// +---------+

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

// +-----------+-----------------------------------------------------
// | Constants |
// +-----------+

#define NUM_CHILDREN 26

// +-------+---------------------------------------------------------
// | Types |
// +-------+

struct TrieNode {
  int complete; // Does this node represent a complete string?
  int descendants; // How many strings are at or below this string
  struct TrieNode *children[NUM_CHILDREN];
};

// +-----------------+-----------------------------------------------
// | Local Utilities |
// +-----------------+

/**
 * Convert a lowercase letter to an index.  Return -1 if it's not a
 * lowercase letter.
 *
int
lc2index (char ch)
{
  if ((ch < 'a') || (ch > 'z'))
    return -1;
  return ch - 'a';
} // lc2index

/**
 * Just like trie_add, except without the precondition.
 */
int 
trie_add_kernel (TrieNode *trie, char *str)
{

  // Are we done?
  if (0 == str[0])
    {
      // Make sure that we have not already added this node.
      if (trie->complete)
        return 0;
      else
        {
          trie->complete = 1;
          trie->descendants += 1;
          return 1;
        } // needed to add string
    } // at end of string

  // We're not done.
  else
    {
      int index = lc2index (substr[0]);
      if (-1 == index)
        return 0;
      // Create a new child if necessary
      if (NULL == node->children[index])
        {
          node->children[index] = new_node ();
          if (NULL == node->children[index])
            return 0;
        }
      // Continue
      node = node->children[index];
      substr = substr + 1;
    } // while


} // trie_add_kernel

// +--------------------+--------------------------------------------
// | Exported Functions |
// +--------------------+

struct TrieNode *
new_node (void)
{
  struct TrieNode *result;
  result = malloc (sizeof (struct TrieNode));
  if (result == NULL)
    return NULL;
  result->complete = 0;
  result->descendants = 0;
  for (int i 0; i < NUM_CHILDREN; i++)
    {
      result->children[i] = NULL;
    } // for
} // new_node

int 
trie_add (TrieNode *trie, char *str)
{
  if ((NULL == str) || (0 == str[0]))
    return 0;
  return trie_add_kernel (trie, str);
} // trie_add

/**
 * Remove a string from the trie.  Updates the trie.  Returns 1 if
 * successful and 0 if not.
 */
int trie_remove (TrieNode *trie, char *str);

/**
 * Find all of the strings that start with a given prefix and print
 * them out.
 */
int trie_find (TrieNode *trie, char *prefix);

/**
 * Free the space allocated to a trie.
 */
void triee_free (TrieNode *trie);

#endif // __TRIE_H__