//         queue implemented as an array

#ifndef POINTER_QUEUE
#define POINTER_QUEUE

#include <exception>

template <typename T>
class QueueNode {
public:
  T data;
  QueueNode<T> *next;

  QueueNode(const T& el) 
    : data(el), next(nullptr) {}
};

class QueueEmptyException : public std::exception
{
public:
  QueueEmptyException() noexcept {}

  const char* what() const { return "Queue is empty."; }
};

template<class T>
class PointerQueue {
public:
    PointerQueue() { 
    front = back = nullptr; 
  }
  PointerQueue(const PointerQueue<T>& other) = delete;
  PointerQueue(PointerQueue<T>&& other) = delete;
  ~PointerQueue() {
    while(front != nullptr) {
      QueueNode<T>* toDelete = front;
      front = toDelete->next;
      delete toDelete;
    }
  }
  
  PointerQueue<T>& operator=(const PointerQueue<T>& other) = delete;
  PointerQueue<T>& operator=(PointerQueue<T>&& other) = delete;
  
    void enqueue(T);
    T dequeue();
    bool isEmpty() { 
    return front == nullptr; 
  }
private:
  QueueNode<T> *front, *back;
};

template<class T>
void PointerQueue<T>::enqueue(T el) {
  if(front == nullptr) 
    front = back = new QueueNode(el);
  else {
    back->next = new QueueNode(el);
    back = back->next;
  }
}

template<class T>
T PointerQueue<T>::dequeue() {   
  if(front == nullptr)
    throw QueueEmptyException();
  QueueNode<T>* toRemove = front;
  front = front->next;
  T data = toRemove->data;
  delete toRemove;
  return data;
}

#endif