#include <assert.h>  // Provides assert
#include <stdlib.h>  // Provides NULL and size_t
#include "link2.h"   // Linked list toolkit 

template <class Item>
class Stack
{
    public:
        Stack( ) { top_ptr = NULL; }
        Stack(const Stack& source);
        ~Stack( ) { list_clear(top_ptr); }
        void push(const Item& entry);
        Item pop( );
        void operator =(const Stack& source);
        size_t size( ) const { return list_length(top_ptr); }
        bool is_empty( ) const { return top_ptr == NULL; }
        Item peek( ) const;
    private:
        Node<Item> *top_ptr;  // Points to top of stack
};

template <class Item>
Stack<Item>::Stack(const Stack<Item>& source)
{
    Node<Item> *tail_ptr; // Needed for argument of list_copy
    list_copy(source.top_ptr, top_ptr, tail_ptr);
}

template <class Item>
void Stack<Item>::push(const Item& entry) 
{
    list_head_insert(top_ptr, entry);
}

template <class Item>
Item Stack<Item>::pop( )
{
    Item answer;

    assert(!is_empty( ));
    answer = top_ptr->data;
    list_head_remove(top_ptr);
    return answer;
}

template <class Item>
void Stack<Item>::operator =(const Stack<Item>& source) 
{
    Node<Item> *tail_ptr; // Needed for argument of list_copy

    if (source.top_ptr == top_ptr) // Handle self-assignment
        return;

    list_clear(top_ptr);
    list_copy(source.top_ptr, top_ptr, tail_ptr);
}

// peek()