/*
 * Copyright (C) 2007-2012 Xagasoft, All rights reserved.
 *
 * This file is part of the libbu++ library and is released under the
 * terms of the license contained in the file LICENSE.
 */

#ifndef BU_SYNCHRO_QUEUE_H
#define BU_SYNCHRO_QUEUE_H

#include <pthread.h>

#include "bu/mutex.h"
#include "bu/condition.h"

namespace Bu
{
	/**
	 * A thread-safe queue class.  This class is a very simple queue with some
	 * cool extra functionality for use with the Synchro system.  The main extra
	 * that it provides is the option to either dequeue without blocking, with
	 * infinite blocking, or with timed blocking, which will return a value if
	 * something is enqueued within the specified time limit, or NULL if the
	 * time limit is exceded.
	 *@ingroup Threading Containers
	 */
	template <class T>
	class SynchroQueue
	{
	private:
		/**
		 * Helper struct.  Keeps track of linked-list items for the queue data.
		 */
		typedef struct Item
		{
			T pData;
			Item *pNext;
		} Item;

	public:
		/**
		 * Construct an empty queue.
		 */
		SynchroQueue() :
			pStart( NULL ),
			pEnd( NULL ),
			nSize( 0 )
		{
		}
		
		/**
		 * Destroy the queue.  This function will simply free all contained
		 * structures.  If you stored pointers in the queue, this will lose the
		 * pointers without cleaning up the memory they pointed to.  Make sure
		 * you're queue is empty before allowing it to be destroyed!
		 */
		~SynchroQueue()
		{
			cBlock.lock();
			Item *pCur = pStart;
			while( pCur )
			{
				Item *pTmp = pCur->pNext;
				delete pCur;
				pCur = pTmp;
			}
			cBlock.unlock();
		}

		/**
		 * Enqueue a pieces of data.  The new data will go at the end of the
		 * queue, and unless another piece of data is enqueued, will be the
		 * last piece of data to be dequeued.
		 *@param pData The data to enqueue.  If this is not a primitive data
		 * type it's probably best to use a pointer type.
		 */
		void enqueue( T pData )
		{
			cBlock.lock();

			if( pStart == NULL )
			{
				pStart = pEnd = new Item;
				pStart->pData = pData;
				pStart->pNext = NULL;
				nSize++;
			}
			else
			{
				pEnd->pNext = new Item;
				pEnd = pEnd->pNext;
				pEnd->pData = pData;
				pEnd->pNext = NULL;
				nSize++;
			}

			cBlock.signal();

			cBlock.unlock();
		}

		/**
		 * Dequeue the first item from the queue.  This function can operate in
		 * two different modes, blocking and non-blocking.  In non-blocking
		 * mode it will return immediately weather there was data in the queue
		 * or not.  If there was data it will remove it from the queue and
		 * return it to the caller.
		 *
		 * In blocking mode it will block forever wating for data to be
		 * enqueued.  When data finally is enqueued this function will return
		 * immediately with the new data.  The only way this function should
		 * ever return a null in blocking mode is if the calling thread was
		 * cancelled.  It's probably a good idea to check for NULL return
		 * values even if you use blocking, just to be on the safe side.
		 *@param bBlock Set to true to enable blocking, leave as false to work
		 * in non-blocking mode.
		 *@returns The next piece of data in the queue, or NULL if no data was
		 * in the queue.
		 */
		T dequeue( bool bBlock=false )
		{
			cBlock.lock();
			if( pStart == NULL )
			{
				if( bBlock )
				{
					for(;;)
					{
						if( pStart != NULL )
						{
							cBlock.unlock();
							break;
						}
						cBlock.wait();
					}
				
					T tmp = dequeue( false );
					
					cBlock.unlock();
					return tmp;

				}

				return NULL;
			}
			else
			{
				T pTmp = pStart->pData;
				Item *pDel = pStart;
				pStart = pStart->pNext;
				delete pDel;
				nSize--;
			
				cBlock.unlock();
				return pTmp;
			}
		}

		/**
		 * Operates just like the other dequeue function in blocking mode with
		 * one twist.  This function will block for at most nSec seconds and
		 * nUSec micro-seconds.  If the timer is up and no data is available,
		 * this will just return NULL.  If data is enqueued before the timeout
		 * expires, it will dequeue and exit immediately.
		 *@param nSec The number of seconds to wait, max.
		 *@param nUSec The number of micro-seconds to wait, max.
		 *@returns The next piece of data in the queue, or NULL if the timeout
		 * was exceeded.
		 */
		T dequeue( int nSec, int nUSec )
		{
			cBlock.lock();
			if( pStart == NULL )
			{
				cBlock.wait( nSec, nUSec );

				if( pStart == NULL )
				{
					cBlock.unlock();
					return NULL;
				}
			
				T pTmp = pStart->pData;
				Item *pDel = pStart;
				pStart = pStart->pNext;
				delete pDel;
				nSize--;
					
				cBlock.unlock();
				return pTmp;
			}
			else
			{
				T pTmp = pStart->pData;
				Item *pDel = pStart;
				pStart = pStart->pNext;
				delete pDel;
				nSize--;
			
				cBlock.unlock();
				return pTmp;
			}
		}

		/**
		 * Checks to see if the queue has data in it or not.  Note that there
		 * is no function to determine the length of the queue.  This data
		 * isn't kept track of.  If you really need to know, fix this.
		 *@returns True if the queue is empty, false if it has data in it.
		 */
		bool isEmpty()
		{
			cBlock.lock();
			bool bEmpty = (pStart == NULL );
			cBlock.unlock();

			return bEmpty;
		}

		long getSize()
		{
			cBlock.lock();
			long nRet = nSize;
			cBlock.unlock();

			return nRet;
		}

	private:
		Item *pStart;	/**< The start of the queue, the next element to dequeue. */
		Item *pEnd;		/**< The end of the queue, the last element to dequeue. */
		long nSize;		/**< The number of items in the queue. */

		Condition cBlock;	/**< The condition for blocking dequeues. */
	};
}

#endif