// A Queue class based on a DLL implementation.

// Work in this implementation is delegated to a DLList object.

// A queue can be implemented as a linked list by adding to one end and deleting from
// the other end. For example, AddToTail + DeleteHead or AddToHead + DeleteTail.
// DeleteTail should be avoided with singly linked lists.

#include "Header.h"

template <class T>
class QueueDLL
{
public:
	QueueDLL();
	~QueueDLL();

	void Enqueue(T& val);	// Adds an element to the queue.
	T Dequeue(void);		// Returns and removes from the queue the first
							// element added to the queue.

	T GetFirst(void);		// Returns the first element added to the queue.
	T GetLast(void);		// Returns the last element added to the queue.
	bool IsEmpty(void);
	void Clear(void);

private:
	DLList<T> list;
};


// Constructor.
// Automatically calls the constructor of the DLList.
template <class T>
QueueDLL<T>::QueueDLL(void)
{}

// Destructor.
// Automatically calls the destructor of the DLList.
template <class T>
QueueDLL<T>::~QueueDLL(void)
{}

template <class T>
void QueueDLL<T>::Enqueue(T& el)
{
	list.AddToTail(el);
}

template <class T>
T QueueDLL<T>::Dequeue()
{
	T el = list.GetHead();
	list.DeleteFromHead();
	return el;
}

template <class T>
T QueueDLL<T>::GetFirst()
{
	return list.GetHead();
}

template <class T>
T QueueDLL<T>::GetLast()
{
	return list.GetTail();
}

template <class T>
bool QueueDLL<T>::IsEmpty(void)
{
	return list.IsEmpty();
}