/*
 * File:
 *   list.c
 */

#include <stdlib.h>
#include "list.h"

list newList() {
  /* Allocate space for the list. */
  list foo = (list) malloc(sizeof(struct LIST));
  /* Sanity check. */
  if (!foo) return 0;
  /* Initialize the fields. */
  foo->head = (node *) NULL;
  foo->current = (node *) NULL;
  foo->length = 0;
  /* Return the new list. */
  return foo;
} /* newList() */

void *getCurrentContents(list ls) {
  if ((ls) && (ls->current) && (ls->current->contents))
    return ls->current->contents;
  return NULL;
} /* getCurrentContents(list) */

int addAfterCurrent(list ls, void *val) {
  node *new = (node *)malloc(sizeof(node));
  if (!new) return 0;
  new->contents = val;
  /* If there is a current element... */
  if (ls->current) {
    /* Rearrange pointers. */
    new->next = ls->current->next;
    if (ls->current->next) 
      ls->current->next->prev = new;
    new->prev = ls->current;
    ls->current->next = new;  
    ++(ls->length);
  }
  else {
    /* Otherwise, create the first element. */
    new->next = new;
    new->prev = new;
    ls->head = new;
    ls->current = new;
    ls->current->next = new;
    ls->current->prev = new;
    ls->length = 1;
  }
  return 1;
} /* addAfterCurrent(list, void *) */

int advance(list ls) {
  /* If the list is empty, give up. */
  if ((!ls->current) || (!ls->current->next))
    return 0;
  ls->current = ls->current->next;
  return 1;
} /* advance(list) */

int deleteCurrent(list ls) {
  node *tmp = ls->current;
  /* Verify that the list is nonempty. */
  if (!ls->current) return 0;
  /* If the list has one element, set everything to null. */
  if (ls->length == 1) {
    ls->current->next = NULL;
    ls->current->prev = NULL;
    ls->current = NULL;
    ls->head = NULL;
    ls->length = 0;
  }
  /* List has more than one element */
  else {
    ls->current->prev->next = ls->current->next;
    ls->current->next->prev = ls->current->prev;
    /* Advance current */
    ls->current = ls->current->next;
    /* Decrease the length. */
    --(ls->length);
    /* That's it, we're done. */
  }
  /* Free the memory associated with the current element. */
  free(tmp);
  tmp = NULL;
  return 1;
} /* deleteCurrent(list) */

int moveCursorToHead(list ls) {
  if ((!ls) || (!ls->head) || (!ls->current)) return 0;
  ls->current = ls->head;
  return 1;
} /* moveCursorToHead(list) */