#include <stdexcept>
#include <utility>

#include "stack.h"

Stack::Stack() : first(nullptr)
{
}


bool Stack::empty() const
{
  return first == nullptr;
}

void Stack::push(int const& i)
{
  first = new Element(i, first);
}

void Stack::pop()
{
  if ( empty() )
  {
    throw Empty_Stack("empty stack");
  }
  Element* victim{ first };
  first = victim->next;
  victim->next = nullptr;
  delete victim;
}

int Stack::top() const
{
  if ( empty() )
  {
    throw Empty_Stack("empty stack");
  }
  return first->data;
}

Stack::Element::Element(int const& i, Element* n)
  : data{i}, next{n}
{
}