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<?php
/**
* This file contains classes implementing the queue feature.
*
* @author Qiang Xue <qiang.xue@gmail.com>
* @link http://www.yiiframework.com/
* @copyright Copyright &copy; 2008 Yii Software LLC
* @license http://www.yiiframework.com/license/
*/

/**
* CQueue implements a queue.
*
* The typical queue operations are implemented, which include
* {@link enqueue()}, {@link dequeue()} and {@link peek()}. In addition,
* {@link contains()} can be used to check if an item is contained
* in the queue. To obtain the number of the items in the queue,
* check the {@link getCount Count} property.
*
* Items in the queue may be traversed using foreach as follows,
* <pre>
* foreach($queue as $item) ...
* </pre>
*
* @author Qiang Xue <qiang.xue@gmail.com>
* @version $Id$
* @package system.collections
* @since 1.0
*/
class CQueue extends CComponent implements IteratorAggregate,Countable
{
/**
* internal data storage
* @var array
*/
private $_d=array();
/**
* number of items
* @var integer
*/
private $_c=0;

/**
* Constructor.
* Initializes the queue with an array or an iterable object.
* @param array the intial data. Default is null, meaning no initialization.
* @throws CException If data is not null and neither an array nor an iterator.
*/
public function __construct($data=null)
{
if($data!==null)
$this->copyFrom($data);
}

/**
* @return array the list of items in queue
*/
public function toArray()
{
return $this->_d;
}

/**
* Copies iterable data into the queue.
* Note, existing data in the list will be cleared first.
* @param mixed the data to be copied from, must be an array or object implementing Traversable
* @throws CException If data is neither an array nor a Traversable.
*/
public function copyFrom($data)
{
if(is_array($data) || ($data instanceof Traversable))
{
$this->clear();
foreach($data as $item)
{
$this->_d[]=$item;
++$this->_c;
}
}
else if($data!==null)
throw new CException(Yii::t('yii#Queue data must be an array or an object implementing Traversable.'));
}

/**
* Removes all items in the queue.
*/
public function clear()
{
$this->_c=0;
$this->_d=array();
}

/**
* @param mixed the item
* @return boolean whether the queue contains the item
*/
public function contains($item)
{
return array_search($item,$this->_d,true)!==false;
}

/**
* Returns the item at the top of the queue.
* @return mixed item at the top of the queue
* @throws CException if the queue is empty
*/
public function peek()
{
if($this->_c===0)
throw new CException(Yii::t('yii#The queue is empty.'));
else
return $this->_d[$this->_c-1];
}

/**
* Removes and returns the object at the beginning of the queue.
* @return mixed the item at the beginning of the queue
* @throws CException if the queue is empty
*/
public function dequeue()
{
if($this->_c===0)
throw new CException(Yii::t('yii#The queue is empty.'));
else
{
--$this->_c;
return array_shift($this->_d);
}
}

/**
* Adds an object to the end of the queue.
* @param mixed the item to be appended into the queue
*/
public function enqueue($item)
{
++$this->_c;
array_push($this->_d,$item);
}

/**
* Returns an iterator for traversing the items in the queue.
* This method is required by the interface IteratorAggregate.
* @return Iterator an iterator for traversing the items in the queue.
*/
public function getIterator()
{
return new CQueueIterator($this->_d);
}

/**
* @return integer the number of items in the queue
*/
public function getCount()
{
return $this->_c;
}

/**
* Returns the number of items in the queue.
* This method is required by Countable interface.
* @return integer number of items in the queue.
*/
public function count()
{
return $this->getCount();
}
}

/**
* CQueueIterator implements an interator for {@link CQueue}.
*
* It allows CQueue to return a new iterator for traversing the items in the queue.
*
* @author Qiang Xue <qiang.xue@gmail.com>
* @version $Id$
* @package system.collections
* @since 1.0
*/
class CQueueIterator implements Iterator
{
/**
* @var array the data to be iterated through
*/
private $_d;
/**
* @var integer index of the current item
*/
private $_i;
/**
* @var integer count of the data items
*/
private $_c;

/**
* Constructor.
* @param array the data to be iterated through
*/
public function __construct(&$data)
{
$this->_d=&$data;
$this->_i=0;
$this->_c=count($this->_d);
}

/**
* Rewinds internal array pointer.
* This method is required by the interface Iterator.
*/
public function rewind()
{
$this->_i=0;
}

/**
* Returns the key of the current array item.
* This method is required by the interface Iterator.
* @return integer the key of the current array item
*/
public function key()
{
return $this->_i;
}

/**
* Returns the current array item.
* This method is required by the interface Iterator.
* @return mixed the current array item
*/
public function current()
{
return $this->_d[$this->_i];
}

/**
* Moves the internal pointer to the next array item.
* This method is required by the interface Iterator.
*/
public function next()
{
$this->_i++;
}

/**
* Returns whether there is an item at current position.
* This method is required by the interface Iterator.
* @return boolean
*/
public function valid()
{
return $this->_i<$this->_c;
}
}
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