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/**
 * MODULE NOTES:
 *
 * The Deque is a very small, very efficient container object
 * than can hold elements of type void*, offering the following features:
 *    Its interface supports pushing and popping of elements.
 *    It can iterate (via an interator class) its elements.
 *    When full, it can efficiently resize dynamically.
 *
 *
 * NOTE: The only bit of trickery here is that this deque is
 * built upon a ring-buffer. Like all ring buffers, the first
 * element may not be at index[0]. The mOrigin member determines
 * where the first child is. This point is quietly hidden from
 * customers of this class.
 *
 */

#ifndef _NSDEQUE
#define _NSDEQUE

#include "nscore.h"

/**
 * The nsDequeFunctor class is used when you want to create
 * callbacks between the deque and your generic code.
 * Use these objects in a call to ForEach();
 *
 */

class nsDequeFunctor{
public:
  virtual void* operator()(void* anObject)=0;
};

/******************************************************
 * Here comes the nsDeque class itself...
 ******************************************************/

/**
 * The deque (double-ended queue) class is a common container type,
 * whose behavior mimics a line in your favorite checkout stand.
 * Classic CS describes the common behavior of a queue as FIFO.
 * A deque allows insertion and removal at both ends of
 * the container.
 *
 * The deque stores pointers to items.
 */

class nsDequeIterator;

class NS_COM nsDeque {
  friend class nsDequeIterator;
  public:
   nsDeque(nsDequeFunctor* aDeallocator);
  ~nsDeque();

  /**
   * Returns the number of elements currently stored in
   * this deque.
   *
   * @return  number of elements currently in the deque
   */
  inline PRInt32 GetSize() const {return mSize;}

  /**
   * Appends new member at the end of the deque.
   *
   * @param   item to store in deque
   * @return  *this
   */
  nsDeque& Push(void* aItem);

  /**
   * Inserts new member at the front of the deque.
   *
   * @param   item to store in deque
   * @return  *this
   */
  nsDeque& PushFront(void* aItem);

  /**
   * Remove and return the last item in the container.
   *
   * @return  the item that was the last item in container
   */
  void* Pop();

  /**
   * Remove and return the first item in the container.
   *
   * @return  the item that was first item in container
   */
  void* PopFront();

  /**
   * Retrieve the bottom item without removing it.
   *
   * @return  the first item in container
   */

  void* Peek();
  /**
   * Return topmost item without removing it.
   *
   * @return  the first item in container
   */
  void* PeekFront();

  /**
   * Retrieve the i'th member from the deque without removing it.
   *
   * @param   index of desired item
   * @return  i'th element in list
   */
  void* ObjectAt(int aIndex) const;

  /**
   * Remove all items from container without destroying them.
   *
   * @return  *this
   */
  nsDeque& Empty();

  /**
   * Remove and delete all items from container.
   * Deletes are handled by the deallocator nsDequeFunctor
   * which is specified at deque construction.
   *
   * @return  *this
   */
  nsDeque& Erase();

  /**
   * Creates a new iterator, pointing to the first
   * item in the deque.
   *
   * @return  new dequeIterator
   */
  nsDequeIterator Begin() const;

  /**
   * Creates a new iterator, pointing to the last
   * item in the deque.
   *
   * @return  new dequeIterator
   */
  nsDequeIterator End() const;

  void* Last() const;
  /**
   * Call this method when you want to iterate all the
   * members of the container, passing a functor along
   * to call your code.
   *
   * @param   aFunctor object to call for each member
   * @return  *this
   */
  void ForEach(nsDequeFunctor& aFunctor) const;

  /**
   * Call this method when you want to iterate all the
   * members of the container, calling the functor you 
   * passed with each member. This process will interrupt
   * if your function returns non 0 to this method.
   *
   * @param   aFunctor object to call for each member
   * @return  first nonzero result of aFunctor or 0.
   */
  const void* FirstThat(nsDequeFunctor& aFunctor) const;

  void SetDeallocator(nsDequeFunctor* aDeallocator);

protected:
  PRInt32         mSize;
  PRInt32         mCapacity;
  PRInt32         mOrigin;
  nsDequeFunctor* mDeallocator;
  void*           mBuffer[8];
  void**          mData;

private:

  /**
   * Simple default constructor (PRIVATE)
   */
  nsDeque();

  /**
   * Copy constructor (PRIVATE)
   *
   * @param another deque
   */
  nsDeque(const nsDeque& other);

  /**
   * Deque assignment operator (PRIVATE)
   *
   * @param   another deque
   * @return  *this
   */
  nsDeque& operator=(const nsDeque& anOther);

  PRInt32 GrowCapacity();
};

/******************************************************
 * Here comes the nsDequeIterator class...
 ******************************************************/

class nsDequeIterator {
public:
  /**
   * DequeIterator is an object that knows how to iterate
   * (forward and backward) through a Deque. Normally,
   * you don't need to do this, but there are some special
   * cases where it is pretty handy.
   *
   * One warning: the iterator is not bound to an item,
   * it is bound to an index, so if you insert or remove
   * from the beginning while using an iterator
   * (which is not recommended) then the iterator will
   * point to a different item.  @see GetCurrent()
   *
   * Here you go.
   *
   * @param   aQueue is the deque object to be iterated
   * @param   aIndex is the starting position for your iteration
   */
  nsDequeIterator(const nsDeque& aQueue, int aIndex=0);

  /**
   * Create a copy of a DequeIterator
   *
   * @param   aCopy is another iterator to copy from
   */
  nsDequeIterator(const nsDequeIterator& aCopy);

  /**
   * Moves iterator to first element in the deque
   * @return  *this
   */
  nsDequeIterator& First();

  /**
   * Standard assignment operator for dequeiterator
   * @param   aCopy is another iterator to copy from
   * @return  *this
   */
  nsDequeIterator& operator=(const nsDequeIterator& aCopy);

  /**
   * preform ! operation against two iterators to test for equivalence
   * (or lack thereof)!
   *
   * @param   aIter is the object to be compared to
   * @return  TRUE if NOT equal.
   */
  PRBool operator!=(nsDequeIterator& aIter);

  /**
   * Compare two iterators for increasing order.
   *
   * @param   aIter is the other iterator to be compared to
   * @return  TRUE if this object points to an element before
   *          the element pointed to by aIter.
   *          FALSE if this and aIter are not iterating over
   *          the same deque.
   */
  PRBool operator<(nsDequeIterator& aIter);

  /**
   * Compare two iterators for equivalence.
   *
   * @param   aIter is the other iterator to be compared to
   * @return  TRUE if EQUAL
   */
  PRBool operator==(nsDequeIterator& aIter);

  /**
   * Compare two iterators for non strict decreasing order.
   *
   * @param   aIter is the other iterator to be compared to
   * @return  TRUE if this object points to the same element, or
   *          an element after the element pointed to by aIter.
   *          FALSE if this and aIter are not iterating over
   *          the same deque.
   */
  PRBool operator>=(nsDequeIterator& aIter);

  /**
   * Pre-increment operator
   * Iterator will advance one index towards the end.
   *
   * @return  object_at(++index)
   */
  void* operator++();

  /**
   * Post-increment operator
   * Iterator will advance one index towards the end.
   *
   * @param   param is ignored
   * @return  object_at(mIndex++)
   */
  void* operator++(int);

  /**
   * Pre-decrement operator
   * Iterator will advance one index towards the beginning.
   *
   * @return  object_at(--index)
   */
  void* operator--();

  /**
   * Post-decrement operator
   * Iterator will advance one index towards the beginning.
   *
   * @param   param is ignored
   * @return  object_at(index--)
   */
  void* operator--(int);

  /**
   * Retrieve the the iterator's notion of current node.
   *
   * Note that the iterator floats, so you don't need to do:
   * <code>++iter; aDeque.PopFront();</code>
   * Unless you actually want your iterator to jump 2 positions
   * relative to its origin.
   *
   * Picture: [1 2i 3 4]
   * PopFront()
   * Picture: [2 3i 4]
   * Note that I still happily points to object at the second index.
   *
   * @return  object at i'th index
   */
  void* GetCurrent();

  /**
   * Call this method when you want to iterate all the
   * members of the container, passing a functor along
   * to call your code.
   *
   * @param   aFunctor object to call for each member
   * @return  *this
   */
  void ForEach(nsDequeFunctor& aFunctor) const;

  /**
   * Call this method when you want to iterate all the
   * members of the container, calling the functor you 
   * passed with each member. This process will interrupt
   * if your function returns non 0 to this method.
   *
   * @param   aFunctor object to call for each member
   * @return  first nonzero result of aFunctor or 0.
   */
  const void* FirstThat(nsDequeFunctor& aFunctor) const;

  protected:

  PRInt32         mIndex;
  const nsDeque&  mDeque;
};
#endif
