Source for file Queue.class.php

<?php
 
//require_once(HARMONI."utilities/Queue.interface.php");
/**
 * A generic queue of objects. It provides iterator functions next() and hasNext().
 *
 * @package harmoni.utilities
 * 
 * @copyright Copyright &copy; 2005, Middlebury College
 * @license http://www.gnu.org/copyleft/gpl.html GNU General Public License (GPL)
 *
 * @version $Id: Queue.class.php,v 1.5 2007/09/04 20:25:54 adamfranco Exp $
 */
class Queue {
 
    /**
     * An array used to store the elements of the queue.
     * @var array $_queue An array used to store the elements of the queue.
     */
    var $_queue;
 
    /**
     * The position in the array of the next element of the queue that will be returned when next() is called.
     * @var integer $_nextPosition The position in the array of the next element of the queue that will be returned when next() is called.
     */
    var $_nextPosition;
 
    /**
     * The start position of the queue in the array. In a reversed queue, this
     * would be the last element of the array. In a normal queue, this would equal
     * zero.
     * @var integer $_startPosition The start position of the queue in the array.
     */
    var $_startPosition;
 
    /**
     * The order of extraction from the queue.
     * Indicates whether the order in which objects are extracted from the queue
     * is FIFO ($_reversed = false) or FILO ($_reversed = true).
     * 
     * @var boolean $_reversed TRUE, if the queue is reversed.
     */
    var $_reversed;
    
 
    /**
     * Constructor. Create a new Queue.
     * 
     * @param boolean $reversed The order of extraction from the queue.
     * @access public
     */
    function Queue($reversed = false){
        $this->_reversed = $reversed;
        $this->clear();
    }
 
    
    
    /**
     * Clear the queue.
     *
     * @access public
     */
    function clear() {
        $this->_queue = array();
        
        // these will be set correctly when the first element gets added        
        $this->_startPosition = null;
        $this->_nextPosition = null;
    }
 
    
    
    /**
     * Add an object to the queue. The queue is automatically rewound at the end.
     * @param object $object The object to add to the queue.
     * @access public
     */
    function add($object) {
        $this->_queue[] =$object;
 
        // if we just inserted the first element in the queue, then reset the position indices
        if ($this->getSize() == 1) {
            $this->_startPosition = 0;
            $this->_nextPosition = 0;
        }
        // if the inserted element is not the first, then just adjust _startPosition if
        // the queue is reversed
        elseif ($this->_reversed)
            $this->_startPosition++;
 
        // when adding a new element, the queue is automatically rewound
        $this->rewind();
    }
 
    
    /**
     * Get the current element and increase the position by one.
     * @return object Object at the current position in the queue and increase the position by one.
     * @access public
     */
    function next() {
        // get next element
        $object =$this->_queue[$this->_nextPosition];
 
        // adjust _nextPosition depending on the queue type
        if($this->_reversed)
            $this->_nextPosition--; 
        else
            $this->_nextPosition++;
            
        return $object;
    }
 
    /**
     * @return boolean Whether there exists an object in the queue at the current position.
     * @access public
     */
    function hasNext() {
        return (isset($this->_queue[$this->_nextPosition])) ? true : false;
    }
    
    /**
     * Get the size of the queue.
     * @return integer The size of the queue
     * @access public
     */
    function getSize() {
        return count($this->_queue);
    }
 
    /**
     * Rewind the queue if it is not reversed
     * @return boolean True on sucess, false on failure (queue is reversed).
     * @access public
     */
    function rewind() { 
        $this->_nextPosition = $this->_startPosition;
    }
}
 
 
?>