<?php
/**
 * Extends the Yii class 'CCache' to store cached data in mongoDB.
 *
 * PHP version 5.2+
 * MongoDB version >= 1.5.3
 * required extensions: MongoYii (for the configuration of the mongoDB connection)
 *
 * @author Zoltan Rajcsanyi <rajcsanyiz@gmail.com>
 * @copyright 2013 Zoltan Rajcsanyi
 * @license New BSD License
 * @category Database
 * @version 1.0
 */

/**
 * EMongoCache implements a cache application component by storing cached data in a mongodb.
 *
 * EMongoDBCache stores cache data in a collection named {@link collectionName}.
 * If the collection does not exist, it will be automatically created.
 *
 * See {@link CCache} manual for common cache operations that are supported by EMongoCache.
 */
class EMongoCache extends CCache
{
	public $connectionID;

	/**
	 * @var string name of the collection to store cache content. Defaults to 'YiiCache'.
	 * The items are stored withe following structure:
	 * <pre>
	 *  key: string,
	 *  value: string
	 *  expire: integer
	 * </pre>
	 */
	public $collectionName = 'YiiCache';
	
	public $ensureIndex = true;  //set to false after first use of the cache

	/**
	 * @var EMongoClient the DB connection instance
	 */
	private $_db;

	private $_gcProbability = 100;
	
	private $_gced = false;

	/**
	 * Initializes this application component.
	 * ensureIndex 'key' if $ensureIndex = true
	 * Set $ensureIndex to false after first use to increase performance
	 *
	 * This method is required by the {@link IApplicationComponent} interface.
	 * It ensures the existence of the cache DB table.
	 * It also removes expired data items from the cache.
	 */
	public function init()
	{
		parent::init();

		if($this->ensureIndex){
			$this->getCollection()->ensureIndex( array('key' => 1));  // create index on "key"
		}
	}
	 
	/**
	 * @return EMongoClient the DB connection instance
	 * @throws CException if {@link connectionID} does not point to a valid application component.
	 */
	protected function getDbConnection()
	{
		if($this->_db !== null){
			return $this->_db;
		}elseif(($id = $this->connectionID) !== null){
			if(($this->_db = Yii::app()->getComponent($id)) instanceof EMongoClient){
				return $this->_db;
			}else{
				throw new CException(
					Yii::t(
						'yii', 
						'EMongoCache.connectionID "{id}" is invalid. Please make sure it refers to the ID of a EMongoClient application component.',
						array('{id}'=>$id)
					)
				);
			}
		}else{
			return $this->_db = Yii::app()->getComponent('mongodb');
		}
	}

	/**
	 * Returns current MongoCollection object
	 *
	 * @return MongoCollection
	 */
	protected function getCollection()
	{
		return $this->getDbConnection()->{$this->collectionName};
	}

	/**
	 * @return integer the probability (parts per million) that garbage collection (GC) should be performed
	 * when storing a piece of data in the cache. Defaults to 100, meaning 0.01% chance.
	 * @since 1.0.9
	 */
	public function getGCProbability()
	{
		return $this->_gcProbability;
	}

	/**
	 * @param integer $value the probability (parts per million) that garbage collection (GC) should be performed
	 * when storing a piece of data in the cache. Defaults to 100, meaning 0.01% chance.
	 * This number should be between 0 and 1000000. A value 0 meaning no GC will be performed at all.
	 * @since 1.0.9
	 */
	public function setGCProbability($value)
	{
		$value=(int)$value;

		if($value < 0){
			$value = 0;
		}elseif($value > 1000000){
			$value = 1000000;
		}

		$this->_gcProbability=$value;
	}

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

		$criteria = array(
			'key' => (string)$key,
			'$or' =>  array(
				array('expire' => 0),
				array('expire' => array('$gt'=> $time)),
			),
		);

		$data = $this->getCollection()->findOne($criteria);

		return $data === null ? '' : $data['value'];
	}

	/**
	 * Retrieves multiple values from cache with the specified keys.
	 * @param array $keys a list of keys identifying the cached values
	 * @return array a list of cached values indexed by the keys
	 */
	protected function getValues($keys)
	{
		if(empty($keys)){
			return array();
		}

		$results = array();
		$time = time();

		$criteria = array(
			'key' => array('$in' => $keys),
			'$or' => array(
				array('expire' => 0),
				array('expire' => array('$gt'=> $time)),
			),
		);

		$data = $this->getCollection()->find($criteria);

		if(!empty($data) && $data->count()){
			foreach($data as $id => $value){
				$results[$value['key']] = $value['value'];
			}
		}

		return $results;
	}

	/**
	 * 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 $this->addValue($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.
	 *
	 * If the key exists the value will be updated, otherwise inserted
	 *
	 * @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, $expire)
	{
		if(!$this->_gced && mt_rand(0,1000000) < $this->_gcProbability){
			$this->gc();
			$this->_gced = true;
		}

		if($expire > 0){
			$expire += time();
		}else{
			$expire = 0;
		}

		$criteria = array('key' => (string)$key);

		$data = array(
			'key' => (string)$key,
			'value' => (string)$value,
			'expire' => (int)$expire,
		);

		$options = array('upsert' => true);

		try{
			return $this->getCollection()->update($criteria, $data, $options);
		}catch(Exception $e){
			return 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)
	{
		$criteria = array('key' => (string)$key);
		$data = $this->getCollection()->remove($criteria);
		return true;
	}

	/**
	 * Removes the expired data values.
	 */
	protected function gc()
	{
		//delete expired entries
		$criteria = array(
			'expired' => array('$gt' => 0),
			'expired' => array('$lt' => time()),
		);

		$this->getCollection()->remove($criteria);
	}

	/**
	 * 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()
	{
		$this->getCollection()->remove();
		return true;
	}
}