#include <stdio.h>		/* Basic includes and definitions */
#include <stdlib.h>		/* Basic includes and definitions */
#include "dllist.h"

/*---------------------------------------------------------------------*
 * PROCEDURES FOR MANIPULATING DOUBLY LINKED LISTS 
 * Each list contains a sentinal node, so that     
 * the first item in list l is l->flink.  If l is  
 * empty, then l->flink = l->blink = l.            
 *---------------------------------------------------------------------*/

Dllist new_dllist ()
{
    Dllist d;

    d = (Dllist) malloc (sizeof (struct dllist));
    d->flink = d;
    d->blink = d;
    return d;
}

void dll_insert_b (Dllist node, Jval v)	/* Inserts before a given node */
{
    Dllist newnode;

    newnode = (Dllist) malloc (sizeof (struct dllist));
    newnode->val = v;

    newnode->flink = node;
    newnode->blink = node->blink;
    newnode->flink->blink = newnode;
    newnode->blink->flink = newnode;
}

void dll_insert_a (Dllist n, Jval val)	/* Inserts after a given node */
{
    dll_insert_b (n->flink, val);
}

void dll_append (Dllist l, Jval val)	/* Inserts at the end of the list */
{
    dll_insert_b (l, val);
}

void dll_prepend (Dllist l, Jval val)	/* Inserts at the beginning of the list */
{
    dll_insert_b (l->flink, val);
}


void dll_delete_node (Dllist node)	/* Deletes an arbitrary iterm */
{
    node->flink->blink = node->blink;
    node->blink->flink = node->flink;
    free (node);
}

int dll_empty (Dllist l)
{
    return (l->flink == l);
}

void free_dllist (Dllist l)
{
    while (!dll_empty (l))
	{
	    dll_delete_node (dll_first (l));
	}
    free (l);
}

Jval dll_val (Dllist l)
{
    return l->val;
}