#include <stdlib.h>
#include <stdio.h>
#include "dllist.h"

typedef struct
{
	Dllist *list;
} Stack;

void* new_stack()
{
	Stack *stack = (Stack*) malloc(sizeof(Stack));

	stack->list = new_dllist();

	return stack;
}

void* top(void *stack)
{
	Stack *s = (Stack*) stack;
	// Check to make sure the stack is not empty.
	if(! empty(s) )
		return dll_val( dll_first(s->list) );
	else
		return NULL;
}

int empty(void *stack)
{
	Stack *s = (Stack*) stack;
	return dll_empty( s->list );
}

void push(void *stack, void *v)
{
	Stack *s = (Stack*) stack;
	dll_prepend(s->list, v);
}


void* pop(void *stack)
{
	Stack *s = (Stack*) stack;
	void *v = top(s);
	
	// Only delete if the stack is not empty.
	if(! empty(s) )
		dll_delete_node( dll_first(s->list) );
	return v;
}

void free_stack(void *stack)
{
	Stack *s = (Stack*) stack;
	free_dllist(s->list);
	free(s);
}