//  Queue.cpp

#include "Queue.h"

Node::Node (const ElemType& el)
  : elem_ (el), next_ (NULL)
{
}

Queue::Queue ()
  : front_ (NULL), back_ (NULL)
{
}

bool Queue::isEmpty() const
{ 
   return front_ == NULL;
}

void Queue::insert (const ElemType& el)
{
   Node* temp = new Node (el);

   if (isEmpty())
     {
       front_ = back_ = temp;
     }
   else
     {
       back_->next_ = temp;
       back_ = temp;
     }
}

const ElemType& Queue::front () const
{
  if (!isEmpty())
    return front_->elem_;
  else
    {
     cerr << "Cannot access the front of an Empty Queue"
          << endl;
     exit(1);  //  perhaps use of an exception is better
    }
}


void Queue::remove ()
{
  if (!isEmpty())
     {
      Node* temp = front_;
      front = front_->next_;
      delete temp;
     }
  else
     {
       cerr << "Cannot remove an item from an empty queue"
            << endl;
     }
}

void Queue::clear()
{
  while (!isEmpty())
      remove();
}

Queue::~Queue()
{
  clear();
}

Queue::Queue(const Queue& q)
 : front_ (NULL), back_ (NULL)
{
  Node* temp = q.front_;

  while (temp != NULL)
    {
     insert(temp->elem_);
     temp = temp->next_;
    }
}

Queue& Queue::operator= (const Queue& rhs)
{
  if (this == &rhs)
     return *this;

  // deallocate the nodes currently in this
  clear();

  // create a copy of rhs
  Node* temp = rhs.front_;
  while (temp != NULL)
    {
     insert(temp->elem_);
     temp = temp->next_;
    }

  // return
  return *this;
}