/*
 * File:
 *   list.h
 * Author:
 *   Lindsey Kuper
 * Summary:
 *   Structures and function prototypes for a generic circular doubly-linked 
 *   list.
 */

#ifndef _LIST_H_
#define _LIST_H_

typedef struct node {
  void *contents;
  struct node *prev;
  struct node *next;
} node;

typedef struct LIST {
  node *head;
  node *current;
  int length;
} *list;

/* Procedure:
 *   getCurrentContents
 * Parameters:
 *   ls, a list. 
 * Purpose:
 *   Get the contents of the current element of ls, if it exists.
 * Produces:
 *   currentcontents, a void pointer.
 * Preconditions: 
 *   None.
 * Postconditions:
 *   If the current element of ls does not exist,  currentcontents is null.  
 *   Otherwise, current contents points to the contents of the current element
 *   of ls.
 */
void *getCurrentContents(list ls);

/* Procedure:
 *   deleteCurrent
 * Parameters:
 *   ls, a list.
 * Purpose: 
 *   Deletes the current element of ls, if it exists, and frees the memory that
 *   was associated with it.
 * Produces:
 *   success, an integer.
 * Preconditions:
 *   ls exists.
 * Postconditions:
 *   If the current element of ls does not exist:
 *     success is 0
 *     ls is unchanged
 *   Otherwise: 
 *     the "old" current element of ls has been removed from ls
 *     the cursor is on the element of ls immediately following the "old"
 *       current element, if it exists
 *     success is nonzero 
 */
int deleteCurrent(list ls);
int advance(list ls);
int addAfterCurrent(list ls, void *val);
int moveCursorToFront(list ls);

#endif /* _LIST_H_ */