<?php
/**
 * @link http://www.yiiframework.com/
 * @copyright Copyright (c) 2008 Yii Software LLC
 * @license http://www.yiiframework.com/license/
 */

namespace yii\caching;

/**
 * ZendDataCache provides Zend data caching in terms of an application component.
 *
 * To use this application component, the [Zend Data Cache PHP extension](http://www.zend.com/en/products/server/)
 * must be loaded.
 *
 * See [[Cache]] for common cache operations that ZendDataCache supports.
 *
 * @author Qiang Xue <qiang.xue@gmail.com>
 * @since 2.0
 */
class ZendDataCache extends Cache
{
	/**
	 * Checks whether a specified key exists in the cache.
	 * This can be faster than getting the value from the cache if the data is big.
	 * In case a cache does not support this feature natively, this method will try to simulate it
	 * but has no performance improvement over getting it.
	 * Note that this method does not check whether the dependency associated
	 * with the cached data, if there is any, has changed. So a call to [[get]]
	 * may return false while exists returns true.
	 * @param mixed $key a key identifying the cached value. This can be a simple string or
	 * a complex data structure consisting of factors representing the key.
	 * @return boolean true if a value exists in cache, false if the value is not in the cache or expired.
	 */
	public function exists($key)
	{
		$key = $this->buildKey($key);
		$value = $this->getValue($key);
		return $value !== null;
	}

	/**
	 * Retrieves a value from cache with a specified key.
	 * This is the implementation of the method declared in the parent class.
	 * @param string $key a unique key identifying the cached value
	 * @return string|boolean the value stored in cache, false if the value is not in the cache or expired.
	 */
	protected function getValue($key)
	{
		$result = zend_shm_cache_fetch($key);
		return $result === null ? false : $result;
	}

	/**
	 * Stores a value identified by a key in cache.
	 * This is the implementation of the method declared in the parent class.
	 *
	 * @param string $key the key identifying the value to be cached
	 * @param string $value the value to be cached
	 * @param integer $expire the number of seconds in which the cached value will expire. 0 means never expire.
	 * @return boolean true if the value is successfully stored into cache, false otherwise
	 */
	protected function setValue($key, $value, $expire)
	{
		return zend_shm_cache_store($key, $value, $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 $key the key identifying the value to be cached
	 * @param string $value the value to be cached
	 * @param integer $expire the number of seconds in which the cached value will expire. 0 means never expire.
	 * @return boolean true if the value is successfully stored into cache, false otherwise
	 */
	protected function addValue($key, $value, $expire)
	{
		return zend_shm_cache_fetch($key) === null ? $this->setValue($key, $value, $expire) : false;
	}

	/**
	 * Deletes a value with the specified key from cache
	 * This is the implementation of the method declared in the parent class.
	 * @param string $key the key of the value to be deleted
	 * @return boolean if no error happens during deletion
	 */
	protected function deleteValue($key)
	{
		return zend_shm_cache_delete($key);
	}

	/**
	 * Deletes all values from cache.
	 * This is the implementation of the method declared in the parent class.
	 * @return boolean whether the flush operation was successful.
	 */
	protected function flushValues()
	{
		return zend_shm_cache_clear();
	}
}