/* listDeletions.c provides functions to delete nodes from a linked list.
 * @authro Eric Otoo, Wanlin Liu
 * Version 2.0 of February, 19, 2000
 */
#include "list.h"

/* deletecurrent(list ls) : deletes the current node of the list
 * Parmaeters             : a pointer to the list.
 * Pre                    : the current node cannot be the head
 * Post                   : current points to the next node if current is 
 *                          not the tail, otherwise current points to tail.
 * Returns                : 1 if current is successfully deleted, else 0.
 */                                                       
int deletecurrent(list ls) {
  /* A pointer to save current, so we can free it later.*/
  nodep p;
  /* If the current node is the dummy node, we cannot delete it.*/
  if(list->head == list->current) {  
    printf("Canont delete current, current is the head.\n");
    return 0;
}
  /*If the current is the tail, delete it and update tail and current.*/
  else if (list->current == list->tail) {
    list->tail = list->tail->pre;
    free(list->tail->next);
    list->tail->next = null;
  }
  /*Otherwise, delete and update current.*/
  else {
    p = ls->current;
    p->pre->next = p->next;
    p->next-pre = p->pre;
    advance(ls);
    free(p);    
  }
  return 1;
}/*deletecurrent(list)*/


/* find_nth_node(list ls, int n) : finds the nth node in a given list.
 * Parameters                    : the pointer to the list, a positive
 *                                 integer indicating the position the node.
 * Returns                       : 1 if the node is found, 0 if not
 * Pre                           : n cannot exceed the length of the node
 * Post                          : current points to the nth node if found
 *                               : otherwise, current position is unknown.
 */
int find_nth_node(list ls, int n){
  if (n<1)
    return 0;
  reset(ls);
  while (n--) {
    /*If the end of the list has not been reached, move forward.*/
    if((advance(ls)) == 0)
      return 0;
  }
  return 1;
}/* find_nth_node */


/* delete_nth_node(list ls, int n) : deletes the nth node in ls.
 * Parameters                      : a pointer to the list, 
 * Pre                             : n cannot exceed the length of the list.
 * Returns                         : 1 if node is successfully deleted,
 *                                   0 if the task fails.
 */
int delete_nth_node(list ls, int n){
  /* If the nth node cannot be located, return 0.*/
  if (find_nth_node(ls, n) == 0){
      printf("Unable to delete.\n");
      return 0;
  }
  /* If the nth node is found, delete it.*/
  else{
    deletecurrent(ls);
  }
}/*delete_nth_node(list, int) 


/* delete_elements(list ls, char[] str) : deletes all occurrences of the 
 *                                        string from the list
 * Parameters                           : a pointer to the list and a string
 * Returns                              : number of nodes deleted.
 */
list delete_elements(list ls, char[] str{
  int count;
  /* set the current to the head of the list.*/
  reset(ls);
  /* Go through the list and delete the strings.*/
  while(ls->current != ls->tail) {
    if((strcmp(getcurrent(ls), str)) == 0) {
      deletecurrent(ls);
      count++;
    }/* if */
  }/* while */
  return count;
}/* delete_ element */


/* delete_element takes the pointer to the first node and a string that is to be
 * deleted and deletes the first occurence of the string from the list.
 */
int delete_element(list ls, char[] str{
  int count;
  reset(ls);
  /* Go through the list and delete the strings.*/
  while(ls->current != ls->tail) {
    if((strcmp(getcurrent(ls), str)) == 0) {
      deletecurrent(ls);
      count++;
      return count;
    }/* if */
  }/* while */
  return count;
}