<?php
/**
 * TMemCache class file
 *
 * @author Qiang Xue <qiang.xue@gmail.com>
 * @link http://www.pradosoft.com/
 * @copyright Copyright &copy; 2005 PradoSoft
 * @license http://www.pradosoft.com/license/
 * @version $Id$
 * @package System.Caching
 */

/**
 * TMemCache class
 *
 * TMemCache implements a cache application module based on {@link http://www.danga.com/memcached/ memcached}.
 *
 * TMemCache can be configured with the Host and Port properties, which
 * specify the host and port of the memcache server to be used.
 * By default, they take the value 'localhost' and 11211, respectively.
 * These properties must be set before {@link init} is invoked.
 *
 * The following basic cache operations are implemented:
 * - {@link get} : retrieve the value with a key (if any) from cache
 * - {@link set} : store the value with a key into cache
 * - {@link add} : store the value only if cache does not have this key
 * - {@link delete} : delete the value with the specified key from cache
 * - {@link flush} : delete all values from cache
 *
 * Each value is associated with an expiration time. The {@link get} operation
 * ensures that any expired value will not be returned. The expiration time can
 * be specified by the number of seconds (maximum 60*60*24*30)
 * or a UNIX timestamp. A expiration time 0 represents never expire.
 *
 * By definition, cache does not ensure the existence of a value
 * even if it never expires. Cache is not meant to be an persistent storage.
 *
 * Also note, there is no security measure to protected data in memcache.
 * All data in memcache can be accessed by any process running in the system.
 *
 * To use this module, the memcache PHP extension must be loaded.
 *
 * Some usage examples of TMemCache are as follows,
 * <code>
 * $cache=new TMemCache;  // TMemCache may also be loaded as a Prado application module
 * $cache->init(null);
 * $cache->add('object',$object);
 * $object2=$cache->get('object');
 * </code>
 *
 * If loaded, TMemCache will register itself with {@link TApplication} as the
 * cache module. It can be accessed via {@link TApplication::getCache()}.
 *
 * TMemCache may be configured in application configuration file as follows
 * <code>
 * <module id="cache" class="System.Caching.TMemCache" Host="localhost" Port="11211" />
 * </code>
 * where {@link getHost Host} and {@link getPort Port} are configurable properties
 * of TMemCache.
 *
 * @author Qiang Xue <qiang.xue@gmail.com>
 * @version $Id$
 * @package System.Caching
 * @since 3.0
 */
class TMemCache extends TCache
{
	/**
	 * @var boolean if the module is initialized
	 */
	private $_initialized=false;
	/**
	 * @var Memcache the Memcache instance
	 */
	private $_cache=null;
	/**
	 * @var string a unique prefix used to identify this cache instance from the others
	 */
	private $_prefix=null;
	/**
	 * @var string host name of the memcache server
	 */
	private $_host='localhost';
	/**
	 * @var integer the port number of the memcache server
	 */
	private $_port=11211;

	/**
	 * Destructor.
	 * Disconnect the memcache server.
	 */
	public function __destruct()
	{
		if($this->_cache!==null)
			$this->_cache->close();
	}

	/**
	 * Initializes this module.
	 * This method is required by the IModule interface. It makes sure that
	 * UniquePrefix has been set, creates a Memcache instance and connects
	 * to the memcache server.
	 * @param TApplication Prado application, can be null
	 * @param TXmlElement configuration for this module, can be null
	 * @throws TConfigurationException if memcache extension is not installed or memcache sever connection fails
	 */
	public function init($config)
	{
		if(!extension_loaded('memcache'))
			throw new TConfigurationException('memcache_extension_required');
		$this->_cache=new Memcache;
		if($this->_cache->connect($this->_host,$this->_port)===false)
			throw new TConfigurationException('memcache_connection_failed',$this->_host,$this->_port);
		$this->_initialized=true;
		parent::init($config);
	}

	/**
	 * @return string host name of the memcache server
	 */
	public function getHost()
	{
		return $this->_host;
	}

	/**
	 * @param string host name of the memcache server
	 * @throws TInvalidOperationException if the module is already initialized
	 */
	public function setHost($value)
	{
		if($this->_initialized)
			throw new TInvalidOperationException('memcache_host_unchangeable');
		else
			$this->_host=$value;
	}

	/**
	 * @return integer port number of the memcache server
	 */
	public function getPort()
	{
		return $this->_port;
	}

	/**
	 * @param integer port number of the memcache server
	 * @throws TInvalidOperationException if the module is already initialized
	 */
	public function setPort($value)
	{
		if($this->_initialized)
			throw new TInvalidOperationException('memcache_port_unchangeable');
		else
			$this->_port=TPropertyValue::ensureInteger($value);
	}

	/**
	 * Retrieves a value from cache with a specified key.
	 * This is the implementation of the method declared in the parent class.
	 * @param string a unique key identifying the cached value
	 * @return string the value stored in cache, false if the value is not in the cache or expired.
	 */
	protected function getValue($key)
	{
		return $this->_cache->get($key);
	}

	/**
	 * Stores a value identified by a key in cache.
	 * This is the implementation of the method declared in the parent class.
	 *
	 * @param string the key identifying the value to be cached
	 * @param string the value to be cached
	 * @param integer the number of seconds in which the cached value will expire. 0 means never expire.
	 * @return boolean true if the value is successfully stored into cache, false otherwise
	 */
	protected function setValue($key,$value,$expire)
	{
		return $this->_cache->set($key,$value,0,$expire);
	}

	/**
	 * Stores a value identified by a key into cache if the cache does not contain this key.
	 * This is the implementation of the method declared in the parent class.
	 *
	 * @param string the key identifying the value to be cached
	 * @param string the value to be cached
	 * @param integer the number of seconds in which the cached value will expire. 0 means never expire.
	 * @return boolean true if the value is successfully stored into cache, false otherwise
	 */
	protected function addValue($key,$value,$expire)
	{
		return $this->_cache->add($key,$value,0,$expire);
	}

	/**
	 * Deletes a value with the specified key from cache
	 * This is the implementation of the method declared in the parent class.
	 * @param string the key of the value to be deleted
	 * @return boolean if no error happens during deletion
	 */
	protected function deleteValue($key)
	{
		return $this->_cache->delete($key);
	}

	/**
	 * Deletes all values from cache.
	 * Be careful of performing this operation if the cache is shared by multiple applications.
	 */
	public function flush()
	{
		return $this->_cache->flush();
	}
}

?>