/*
 * This module is for storing strings in a doubly-linked list
 * The strings can be alphabetized using a mergesort algorithm
 */ 


/* List nodes */
struct node_t {
    struct node_t *next;
    struct node_t *prev;
    char *string;
};
		    

/*
 * Frees an entire list of node_t's
 * list is a pointer to any node in the list.
 */
void free_list(struct node_t *list);

/*
 * Returns the number of nodes in the node_t list
 * list is a pointer to any node in the list.
 */
int get_count(struct node_t *list);

/*  
 * list is a pointer to any node in the list.
 * Returns the head of the node_t list.
 * Returns NULL if list is NULL.
 */  
struct node_t *get_head(struct node_t *list);

/*
 * list is a pointer to any node in the list.
 * Returns the tail of the node_t list.
 * Returns NULL if list is NULL.
 */
struct node_t *get_tail(struct node_t *list);

/*
 * Returns a node_t list of the files and directories in directory dir_path
 * Ignores files or directories beginning with '.'
 * Returns the head of the list upon success, NULL upon failure
 */
struct node_t *get_dir_list(char *dir_path);

/*
 * Adds a new node to the end of the node_t list list. 
 * list is a pointer to any node in the list.
 * If list is NULL, a new node is created. 
 * Places str in the new node. 
 * Returns a pointer to the tail upon success, NULL upon failure.
 * If you create a list, it is your responsibility to free it with free_list()
 */
struct node_t *append_string(struct node_t *list, char *str);

/*
 * Alphabetizes a list of node_t's according to ascii
 * head must be the head of the list
 * Returns a pointer to the head of the alphabetized list
 * You must free the list after you are finished 
 * with it with free_list()
 */
struct node_t *alpha_mergesort(struct node_t *head);

/*
 * Merges and alphabetizes (according to ascii) 2 node_t lists.
 * Typically only called by alpha_mergesort()
 */
struct node_t *alpha_merge(struct node_t *head1, struct node_t *head2);

/*
 * Divides a node_t list in half, returning a 
 * pointer to the second half.
 * head must be the head of the list
 */
struct node_t *divide_list(struct node_t *head);