<?php
/**
 * EGroupware API: Caching data
 *
 * @link http://www.egroupware.org
 * @license http://opensource.org/licenses/gpl-license.php GPL - GNU General Public License
 * @package api
 * @subpackage cache
 * @author Ralf Becker <RalfBecker-AT-outdoor-training.de>
 * @copyright (c) 2009-15 by Ralf Becker <RalfBecker-AT-outdoor-training.de>
 * @version $Id$
 */

/**
 * Class to manage caching in eGroupware.
 *
 * It allows to cache on 4 levels:
 * a) tree:     for all instances/domains runining on a certain source path
 * b) instance: for all sessions on a given instance
 * c) session:  for all requests of a session, same as egw_session::appsession()
 * d) request:  just for this request (same as using a static variable)
 *
 * There's a get, a set and a unset method for each level: eg. getTree() or setInstance(),
 * as well as a variant allowing to specify the level as first parameter: eg. unsetCache()
 *
 * getXXX($app,$location,$callback=null,array $callback_params,$expiration=0)
 * has three optional parameters allowing to specify:
 * 3. a callback if requested data is not yes stored. In that case the callback is called
 *    and it's value is stored in the cache AND retured
 * 4. parameters to pass to the callback as array, see call_user_func_array
 * 5. an expiration time in seconds to specify how long data should be cached,
 *    default 0 means infinit (this time is not garantied and not supported for all levels!)
 *
 * Data is stored under an application name and a location, like egw_session::appsession().
 * In fact data stored at cache level egw_cache::SESSION, is stored in the same way as
 * egw_session::appsession() so both methods can be used with each other.
 *
 * The $app parameter should be either the app or the class name, which both are unique.
 *
 * The tree and instance wide cache uses a certain provider class, to store the data
 * eg. in memcached or if there's nothing else configured in the filesystem (eGW's temp_dir).
 *
 * "Admin >> clear cache and register hooks" allways only clears instance level cache of
 * calling instance. It never clears tree level cache, which makes it important to set
 * resonable expiry times or think about an other means of clearing that particular item.
 * (Not clearing of tree-level cache is important, as regenerating it is an expensive
 * operation for a huge scale EGroupware hosting operation.)
 *
 * Apps needing to talk to multiple EGroupware instances (eg. Stylite Managementserver)
 * can use install_id of instance as $level parameter to (set|get|unset)Cache method.
 */
class egw_cache
{
	/**
	 * tree-wide storage
	 */
	const TREE = 'Tree';
	/**
	 * instance-wide storage
	 */
	const INSTANCE = 'Instance';
	/**
	 * session-wide storage
	 */
	const SESSION = 'Session';
	/**
	 * request-wide storage
	 */
	const REQUEST = 'Request';

	/**
	 * Default provider for tree and instance data
	 *
	 * Can be specified eg. in the header.inc.php by setting:
	 * $GLOBALS['egw_info']['server']['cache_provider_instance'] and optional
	 * $GLOBALS['egw_info']['server']['cache_provider_tree'] (defaults to instance)
	 *
	 * Default is set (if not set here) after class definition to egw_cache_apc or egw_cache_files,
	 * depending on function 'apc_fetch' exists or not
	 *
	 * @var array
	 */
	static $default_provider;	// = array('egw_cache_files');// array('egw_cache_memcache','localhost');

	/**
	 * Maximum expiration time, if set unlimited expiration (=0) or bigger expiration times are replaced with that time
	 *
	 * @var int
	 */
	static $max_expiration;

	/**
	 * Used to determine keys for tree- and instance-level caches
	 *
	 * @var string
	 */
	static $egw_server_root = EGW_SERVER_ROOT;

	/**
	 * Add some data in the cache, only if the key does not yet exist
	 *
	 * @param string $level use egw_cache::(TREE|INSTANCE)
	 * @param string $app application storing data
	 * @param string $location location name for data
	 * @param mixed $data
	 * @param int $expiration =0 expiration time in seconds, default 0 = never
	 * @return boolean true if data could be stored, false otherwise incl. key already existed
	 */
	static public function addCache($level,$app,$location,$data,$expiration=0)
	{
		//error_log(__METHOD__."('$level','$app','$location',".array2string($data).",$expiration)");
		switch($level)
		{
			case self::SESSION:
			case self::REQUEST:
				throw new egw_exception_wrong_parameter(__METHOD__."('$level', ...) unsupported level parameter!");

			case self::INSTANCE:
			case self::TREE:
			default:
				if (!($provider = self::get_provider($level)))
				{
					return false;
				}
				// limit expiration to configured maximum time
				if (isset(self::$max_expiration) && (!$expiration || $expiration > self::$max_expiration))
				{
					$expiration = self::$max_expiration;
				}
				return $provider->add(self::keys($level,$app,$location),$data,$expiration);
		}
		throw new egw_exception_wrong_parameter(__METHOD__."() unknown level '$level'!");
	}

	/**
	 * Set some data in the cache
	 *
	 * @param string $level use egw_cache::(TREE|INSTANCE|SESSION|REQUEST)
	 * @param string $app application storing data
	 * @param string $location location name for data
	 * @param mixed $data
	 * @param int $expiration =0 expiration time in seconds, default 0 = never
	 * @return boolean true if data could be stored, false otherwise
	 */
	static public function setCache($level,$app,$location,$data,$expiration=0)
	{
		//error_log(__METHOD__."('$level','$app','$location',".array2string($data).",$expiration)");
		switch($level)
		{
			case self::SESSION:
			case self::REQUEST:
				return call_user_func(array(__CLASS__,'set'.$level),$app,$location,$data,$expiration);

			case self::INSTANCE:
			case self::TREE:
			default:
				if (!($provider = self::get_provider($level)))
				{
					return false;
				}
				// limit expiration to configured maximum time
				if (isset(self::$max_expiration) && (!$expiration || $expiration > self::$max_expiration))
				{
					$expiration = self::$max_expiration;
				}
				return $provider->set(self::keys($level,$app,$location),$data,$expiration);
		}
		throw new egw_exception_wrong_parameter(__METHOD__."() unknown level '$level'!");
	}

	/**
	 * Get some data from the cache
	 *
	 * @param string $level use egw_cache::(TREE|INSTANCE|SESSION|REQUEST)
	 * @param string $app application storing data
	 * @param string|array $location location(s) name for data
	 * @param callback $callback =null callback to get/create the value, if it's not cache
	 * @param array $callback_params =array() array with parameters for the callback
	 * @param int $expiration =0 expiration time in seconds, default 0 = never
	 * @return mixed NULL if data not found in cache (and no callback specified) or
	 * 	if $location is an array: location => data pairs for existing location-data, non-existing is not returned
	 */
	static public function getCache($level,$app,$location,$callback=null,array $callback_params=array(),$expiration=0)
	{
		switch($level)
		{
			case self::SESSION:
			case self::REQUEST:
				foreach((array)$location as $l)
				{
					$data[$l] = call_user_func(array(__CLASS__,'get'.$level),$app,$l,$callback,$callback_params,$expiration);
				}
				return is_array($location) ? $data : $data[$l];

			case self::INSTANCE:
			case self::TREE:
			default:
				if (!($provider = self::get_provider($level)))
				{
					return null;
				}
				try {
					if (is_array($location))
					{
						if (!is_null($callback))
						{
							throw new egw_exception_wrong_parameter(__METHOD__."() you can NOT use multiple locations (\$location parameter is an array) together with a callback!");
						}
						if (is_a($provider, 'egw_cache_provider_multiple'))
						{
							$data = $provider->mget($keys=self::keys($level,$app,$location));
						}
						else	// default implementation calls get multiple times
						{
							$data = array();
							foreach($location as $l)
							{
								$data[$l] = $provider->get($keys=self::keys($level,$app,$l));
								if (!isset($data[$l])) unset($data[$l]);
							}
						}
					}
					else
					{
						$data = $provider->get($keys=self::keys($level,$app,$location));
						if (is_null($data) && !is_null($callback))
						{
							$data = call_user_func_array($callback,$callback_params);
							// limit expiration to configured maximum time
							if (isset(self::$max_expiration) && (!$expiration || $expiration > self::$max_expiration))
							{
								$expiration = self::$max_expiration;
							}
							$provider->set($keys,$data,$expiration);
						}
					}
				}
				catch(Exception $e) {
					unset($e);
					$data = null;
				}
				return $data;
		}
		throw new egw_exception_wrong_parameter(__METHOD__."() unknown level '$level'!");
	}

	/**
	 * Unset some data in the cache
	 *
	 * @param string $level use egw_cache::(TREE|INSTANCE|SESSION|REQUEST)
	 * @param string $app application storing data
	 * @param string $location location name for data
	 * @return boolean true if data was set, false if not (like isset())
	 */
	static public function unsetCache($level,$app,$location)
	{
		switch($level)
		{
			case self::SESSION:
			case self::REQUEST:
				return call_user_func(array(__CLASS__,'unset'.$level),$app,$location);

			case self::INSTANCE:
			case self::TREE:
			default:
				if (!($provider = self::get_provider($level, false)))
				{
					return false;
				}
				return $provider->delete(self::keys($level,$app,$location));
		}
		throw new egw_exception_wrong_parameter(__METHOD__."() unknown level '$level'!");
	}

	/**
	 * Set some data in the cache for the whole source tree (all instances)
	 *
	 * @param string $app application storing data
	 * @param string $location location name for data
	 * @param mixed $data
	 * @param int $expiration =0 expiration time in seconds, default 0 = never
	 * @return boolean true if data could be stored, false otherwise
	 */
	static public function setTree($app,$location,$data,$expiration=0)
	{
		//error_log(__METHOD__."('$app','$location',".array2string($data).",$expiration)");
		return self::setCache(self::TREE,$app,$location,$data,$expiration);
	}

	/**
	 * Get some data from the cache for the whole source tree (all instances)
	 *
	 * @param string $app application storing data
	 * @param string $location location name for data
	 * @param callback $callback =null callback to get/create the value, if it's not cache
	 * @param array $callback_params =array() array with parameters for the callback
	 * @param int $expiration =0 expiration time in seconds, default 0 = never
	 * @return mixed NULL if data not found in cache (and no callback specified)
	 */
	static public function getTree($app,$location,$callback=null,array $callback_params=array(),$expiration=0)
	{
		return self::getCache(self::TREE,$app,$location,$callback,$callback_params,$expiration);
	}

	/**
	 * Unset some data in the cache for the whole source tree (all instances)
	 *
	 * @param string $app application storing data
	 * @param string $location location name for data
	 * @return boolean true if data was set, false if not (like isset())
	 */
	static public function unsetTree($app,$location)
	{
		return self::unsetCache(self::TREE,$app,$location);
	}

	/**
	 * Set some data in the cache for the whole source tree (all instances)
	 *
	 * @param string $app application storing data
	 * @param string $location location name for data
	 * @param mixed $data
	 * @param int $expiration =0 expiration time in seconds, default 0 = never
	 * @return boolean true if data could be stored, false otherwise
	 */
	static public function setInstance($app,$location,$data,$expiration=0)
	{
		return self::setCache(self::INSTANCE,$app,$location,$data,$expiration);
	}

	/**
	 * Get some data from the cache for the whole source tree (all instances)
	 *
	 * @param string $app application storing data
	 * @param string $location location name for data
	 * @param callback $callback =null callback to get/create the value, if it's not cache
	 * @param array $callback_params =array() array with parameters for the callback
	 * @param int $expiration =0 expiration time in seconds, default 0 = never
	 * @return mixed NULL if data not found in cache (and no callback specified)
	 */
	static public function getInstance($app,$location,$callback=null,array $callback_params=array(),$expiration=0)
	{
		return self::getCache(self::INSTANCE,$app,$location,$callback,$callback_params,$expiration);
	}

	/**
	 * Unset some data in the cache for the whole source tree (all instances)
	 *
	 * @param string $app application storing data
	 * @param string $location location name for data
	 * @return boolean true if data was set, false if not (like isset())
	 */
	static public function unsetInstance($app,$location)
	{
		return self::unsetCache(self::INSTANCE,$app,$location);
	}

	/**
	 * Set some data in the cache for the whole source tree (all instances)
	 *
	 * @param string $app application storing data
	 * @param string $location location name for data
	 * @param mixed $data
	 * @param int $expiration =0 expiration time in seconds, default 0 = never
	 * @return boolean true if data could be stored, false otherwise
	 */
	static public function setSession($app,$location,$data,$expiration=0)
	{
		unset($expiration);	// not used, but required by function signature
		if (isset($_SESSION[egw_session::EGW_SESSION_ENCRYPTED]))
		{
			if (egw_session::ERROR_LOG_DEBUG) error_log(__METHOD__.' called after session was encrypted --> ignored!');
			return false;	// can no longer store something in the session, eg. because commit_session() was called
		}
		$_SESSION[egw_session::EGW_APPSESSION_VAR][$app][$location] = $data;

		return true;
	}

	/**
	 * Get some data from the cache for the whole source tree (all instances)
	 *
	 * Returns a reference to the var in the session!
	 *
	 * @param string $app application storing data
	 * @param string $location location name for data
	 * @param callback $callback =null callback to get/create the value, if it's not cache
	 * @param array $callback_params =array() array with parameters for the callback
	 * @param int $expiration =0 expiration time in seconds, default 0 = never
	 * @return mixed NULL if data not found in cache (and no callback specified)
	 */
	static public function &getSession($app,$location,$callback=null,array $callback_params=array(),$expiration=0)
	{
		unset($expiration);	// not used, but required by function signature
		if (isset($_SESSION[egw_session::EGW_SESSION_ENCRYPTED]))
		{
			if (egw_session::ERROR_LOG_DEBUG) error_log(__METHOD__.' called after session was encrypted --> ignored!');
			return null;	// can no longer store something in the session, eg. because commit_session() was called
		}
		if (!isset($_SESSION[egw_session::EGW_APPSESSION_VAR][$app][$location]) && !is_null($callback))
		{
			$_SESSION[egw_session::EGW_APPSESSION_VAR][$app][$location] = call_user_func_array($callback,$callback_params);
		}
		return $_SESSION[egw_session::EGW_APPSESSION_VAR][$app][$location];
	}

	/**
	 * Unset some data in the cache for the whole source tree (all instances)
	 *
	 * @param string $app application storing data
	 * @param string $location location name for data
	 * @return boolean true if data was set, false if not (like isset())
	 */
	static public function unsetSession($app,$location)
	{
		if (isset($_SESSION[egw_session::EGW_SESSION_ENCRYPTED]))
		{
			if (egw_session::ERROR_LOG_DEBUG) error_log(__METHOD__.' called after session was encrypted --> ignored!');
			return false;	// can no longer store something in the session, eg. because commit_session() was called
		}
		if (!isset($_SESSION[egw_session::EGW_APPSESSION_VAR][$app][$location]))
		{
			return false;
		}
		unset($_SESSION[egw_session::EGW_APPSESSION_VAR][$app][$location]);

		return true;
	}

	/**
	 * Static varible to cache request wide
	 *
	 * @var array
	 */
	private static $request_cache = array();

	/**
	 * Set some data in the cache for the whole source tree (all instances)
	 *
	 * @param string $app application storing data
	 * @param string $location location name for data
	 * @param mixed $data
	 * @param int $expiration =0 expiration time is NOT used for REQUEST!
	 * @return boolean true if data could be stored, false otherwise
	 */
	static public function setRequest($app,$location,$data,$expiration=0)
	{
		unset($expiration);	// not used, but required by function signature
		self::$request_cache[$app][$location] = $data;

		return true;
	}

	/**
	 * Get some data from the cache for the whole source tree (all instances)
	 *
	 * @param string $app application storing data
	 * @param string $location location name for data
	 * @param callback $callback =null callback to get/create the value, if it's not cache
	 * @param array $callback_params =array() array with parameters for the callback
	 * @param int $expiration =0 expiration time is NOT used for REQUEST!
	 * @return mixed NULL if data not found in cache (and no callback specified)
	 */
	static public function getRequest($app,$location,$callback=null,array $callback_params=array(),$expiration=0)
	{
		unset($expiration);	// not used, but required by function signature
		if (!isset(self::$request_cache[$app][$location]) && !is_null($callback))
		{
			self::$request_cache[$app][$location] = call_user_func_array($callback,$callback_params);
		}
		return self::$request_cache[$app][$location];
	}

	/**
	 * Unset some data in the cache for the whole source tree (all instances)
	 *
	 * @param string $app application storing data
	 * @param string $location location name for data
	 * @return boolean true if data was set, false if not (like isset())
	 */
	static public function unsetRequest($app,$location)
	{
		if (!isset(self::$request_cache[$app][$location]))
		{
			return false;
		}
		unset(self::$request_cache[$app][$location]);

		return true;
	}

	/**
	 * Get a caching provider for tree or instance level
	 *
	 * The returned provider already has an opened connection
	 *
	 * @param string $level egw_cache::(TREE|INSTANCE) or install_id
	 * @param boolean $log_not_found =true false do not log if no provider found, used eg. to supress error via unsetCache during installation
	 * @return egw_cache_provider
	 */
	static protected function get_provider($level, $log_not_found=true)
	{
		static $providers = array();

		if ($level != self::TREE) $level = self::INSTANCE;

		if (!isset($providers[$level]))
		{
			$params = $GLOBALS['egw_info']['server']['cache_provider_'.strtolower($level)];
			if (!isset($params) && $level == self::INSTANCE && isset(self::$default_provider))
			{
				$params = self::$default_provider;
			}
			if (!isset($params))
			{
				if ($level == self::TREE)	// if no tree level provider use the instance level one
				{
					$providers[$level] = self::get_provider(self::INSTANCE);
				}
				else
				{
					$providers[$level] = false;	// no provider specified
					$reason = 'no provider specified';
				}
			}
			elseif (!$params)
			{
					$providers[$level] = false;	// cache for $level disabled
					$reason = "cache for $level disabled";
			}
			else
			{
				if (!is_array($params)) $params = (array)$params;

				$class = array_shift($params);
				if (!class_exists($class))
				{
					$providers[$level] = false;	// provider class not found
					$reason = "provider $class not found";
				}
				else
				{
					try
					{
						$providers[$level] = new $class($params);
					}
					catch(Exception $e)
					{
						$providers[$level] = false;	// eg. could not open connection to backend
						$reason = "error instanciating provider $class: ".$e->getMessage();
					}
				}
			}
			if (!$providers[$level] && $log_not_found) error_log(__METHOD__."($level) no provider found ($reason)!".function_backtrace());
		}
		//error_log(__METHOD__."($level) = ".array2string($providers[$level]).', cache_provider='.array2string($GLOBALS['egw_info']['server']['cache_provider_'.strtolower($level)]));
		return $providers[$level];
	}

	/**
	 * Get a system configuration, even if in setup and it's not read
	 *
	 * @param string $name
	 * @param boolean $throw =true throw an exception, if we can't retriev the value
	 * @return string|boolean string with config or false if not found and !$throw
	 */
	static public function get_system_config($name,$throw=true)
	{
		if(!isset($GLOBALS['egw_info']['server'][$name]))
		{
			if (isset($GLOBALS['egw_setup']) && isset($GLOBALS['egw_setup']->db) || $GLOBALS['egw']->db)
			{
				$db = $GLOBALS['egw']->db ? $GLOBALS['egw']->db : $GLOBALS['egw_setup']->db;

				try {
					if (($rs = $db->select(config::TABLE,'config_value',array(
						'config_app'	=> 'phpgwapi',
						'config_name'	=> $name,
					),__LINE__,__FILE__)))
					{
						$GLOBALS['egw_info']['server'][$name] = $rs->fetchColumn();
					}
					else
					{
						error_log(__METHOD__."('$name', $throw) config value NOT found!");//.function_backtrace());
					}
				}
				catch(egw_exception_db $e)
				{
					if ($throw) error_log(__METHOD__."('$name', $throw) cound NOT query value: ".$e->getMessage());//.function_backtrace());
				}
			}
			if (!$GLOBALS['egw_info']['server'][$name] && $throw)
			{
				throw new Exception (__METHOD__."($name) \$GLOBALS['egw_info']['server']['$name'] is NOT set!");
			}
		}
		return $GLOBALS['egw_info']['server'][$name];
	}

	/**
	 * Flush (delete) whole (instance) cache or application/class specific part of it
	 *
	 * @param string $level =self::INSTANCE
	 * @param string $app =null
	 */
	static public function flush($level=self::INSTANCE, $app=null)
	{
		$ret = true;
		if (!($provider = self::get_provider($level)))
		{
			$ret = false;
		}
		else
		{
			if (!$provider->flush(self::keys($level, $app)))
			{
				if ($level == self::INSTANCE)
				{
					self::generate_instance_key();
				}
				else
				{
					$ret = false;
				}
			}
		}
		//error_log(__METHOD__."('$level', '$app') returning ".array2string($ret));
		return $ret;
	}

	/**
	 * Unset instance key, so it get read again and re-read install_id from database
	 */
	static public function unset_instance_key()
	{
		self::$instance_key = null;
		$GLOBALS['egw_info']['server']['install_id'] = egw_cache::get_system_config('install_id', false);
	}

	/**
	 * Key used for instance specific data
	 *
	 * @var string
	 */
	private static $instance_key;

	/**
	 * Generate a new instance key and by doing so effectivly flushes whole instance cache
	 *
	 * @param string $install_id =null default use install_id of current instance
	 * @return string new key also stored in self::$instance_key
	 */
	static public function generate_instance_key($install_id=null)
	{
		if (!isset($install_id))
		{
			self::$instance_key = null;
			$install_id = self::get_system_config('install_id');
		}
		$instance_key = self::INSTANCE.'-'.$install_id.'-'.microtime(true);
		self::setTree(__CLASS__, $install_id, $instance_key);

		//error_log(__METHOD__."(install_id='$install_id') returning '".$instance_key."'");
		return $instance_key;
	}

	/**
	 * Get keys array from $level, $app and $location
	 *
	 * @param string $level egw_cache::(TREE|INSTANCE) or instance_id
	 * @param string $app =null
	 * @param string $location =null
	 * @return array
	 */
	static public function keys($level, $app=null, $location=null)
	{
		static $tree_key = null;

		switch($level)
		{
			case self::TREE:
				if (!isset($tree_key))
				{
					$tree_key = $level.'-'.str_replace(array(':','/','\\'),'-', self::$egw_server_root);
					// add charset to key, if not utf-8 (as everything we store depends on charset!)
					if (($charset = self::get_system_config('system_charset',false)) && $charset != 'utf-8')
					{
						$tree_key .= '-'.$charset;
					}
				}
				$level_key = $tree_key;
				break;
			default:	// arbitrary install_id given --> check for current instance
				if ($level !== $GLOBALS['egw_info']['server']['install_id'])
				{
					$level_key = self::getTree(__CLASS__, $level);
					if (!isset($level_key)) $level_key = self::generate_instance_key($level);
					break;
				}
				// fall-through for current instance
			case self::INSTANCE:
				if (!isset(self::$instance_key))
				{
					self::$instance_key = self::getTree(__CLASS__, self::get_system_config('install_id'));
					//error_log(__METHOD__."('$level',...) instance_key read from tree-cache=".array2string(self::$instance_key));
					if (!isset(self::$instance_key)) self::$instance_key = self::generate_instance_key();
				}
				$level_key = self::$instance_key;
				break;
		}
		$keys = array($level_key);
		if (isset($app))
		{
			$keys[] = $app;
			if (isset($location)) $keys[] = $location;
		}
		return $keys;
	}

	/**
	 * Let everyone know the methods of this class should be used only statically
	 *
	 */
	function __construct()
	{
		throw new egw_exception_wrong_parameter("All methods of class ".__CLASS__." should be called static!");
	}
}

/**
 * Interface for a caching provider for tree and instance level
 *
 * The provider can eg. create subdirs under /tmp for each key
 * to store data as a file or concat them with a separator to
 * get a single string key to eg. store data in memcached
 */
interface egw_cache_provider
{
	/**
	 * Constructor, eg. opens the connection to the backend
	 *
	 * @throws Exception if connection to backend could not be established
	 * @param array $params eg. array(host,port) or array(directory) depending on the provider
	 */
	function __construct(array $params);

	/**
	 * Stores some data in the cache, if it does NOT already exists there
	 *
	 * @param array $keys eg. array($level,$app,$location)
	 * @param mixed $data
	 * @param int $expiration =0
	 * @return boolean true on success, false on error, incl. key already exists in cache
	 */
	function add(array $keys,$data,$expiration=0);

	/**
	 * Stores some data in the cache
	 *
	 * @param array $keys eg. array($level,$app,$location)
	 * @param mixed $data
	 * @param int $expiration =0
	 * @return boolean true on success, false on error
	 */
	function set(array $keys,$data,$expiration=0);

	/**
	 * Get some data from the cache
	 *
	 * @param array $keys eg. array($level,$app,$location)
	 * @return mixed data stored or NULL if not found in cache
	 */
	function get(array $keys);

	/**
	 * Delete some data from the cache
	 *
	 * @param array $keys eg. array($level,$app,$location)
	 * @return boolean true on success, false on error (eg. $key not set)
	 */
	function delete(array $keys);

	/**
	 * Delete all data under given keys
	 *
	 * Providers can return false, if they do not support flushing part of the cache (eg. memcache)
	 *
	 * @param array $keys eg. array($level,$app,$location)
	 * @return boolean true on success, false on error (eg. $key not set)
	 */
	function flush(array $keys);
}

/**
 * Interface for a caching provider for tree and instance level
 *
 * The provider can eg. create subdirs under /tmp for each key
 * to store data as a file or concat them with a separator to
 * get a single string key to eg. store data in memcached
 */
interface egw_cache_provider_multiple
{
	/**
	 * Get multiple data from the cache
	 *
	 * @param array $keys eg. array of array($level,$app,array $locations)
	 * @return array key => data stored, not found keys are NOT returned
	 */
	function mget(array $keys);
}

abstract class egw_cache_provider_check implements egw_cache_provider
{
	/**
	 * Run several checks on a caching provider
	 *
	 * @param boolean $verbose =false true: echo failed checks
	 * @return int number of failed checks
	 */
	function check($verbose=false)
	{
		// set us up as provider for egw_cache class
		$GLOBALS['egw_info']['server']['install_id'] = md5(microtime(true));
		unset($GLOBALS['egw_info']['server']['cache_provider_instance']);
		unset($GLOBALS['egw_info']['server']['cache_provider_tree']);
		egw_cache::$default_provider = get_class($this);

		$failed = 0;
		foreach(array(
			egw_cache::TREE => 'tree',
			egw_cache::INSTANCE => 'instance',
		) as $level => $label)
		{
			$locations = array();
			foreach(array('string',123,true,false,null,array(),array(1,2,3)) as $data)
			{
				$location = md5(microtime(true).$label.serialize($data));
				$get_before_set = $this->get(array($level,__CLASS__,$location));
				if (!is_null($get_before_set))
				{
					if ($verbose) echo "$label: get_before_set=".array2string($get_before_set)." != NULL\n";
					++$failed;
				}
				if (($set = $this->set(array($level,__CLASS__,$location), $data, 10)) !== true)
				{
					if ($verbose) echo "$label: set returned ".array2string($set)." !== TRUE\n";
					++$failed;
				}
				$get_after_set = $this->get(array($level,__CLASS__,$location));
				if ($get_after_set !== $data)
				{
					if ($verbose) echo "$label: get_after_set=".array2string($get_after_set)." !== ".array2string($data)."\n";
					++$failed;
				}
				if (is_a($this, 'egw_cache_provider_multiple'))
				{
					$mget_after_set = $this->mget(array($level,__CLASS__,array($location)));
					if ($mget_after_set[$location] !== $data)
					{
						if ($verbose) echo "$label: mget_after_set['$location']=".array2string($mget_after_set[$location])." !== ".array2string($data)."\n";
						++$failed;
					}
				}
				$add_after_set = $this->add(array($level,__CLASS__,$location), 'other-data');
				if ($add_after_set !== false)
				{
					if ($verbose) echo "$label: add_after_set=".array2string($add_after_set)."\n";
					++$failed;
				}
				if (($delete = $this->delete(array($level,__CLASS__,$location))) !== true)
				{
					if ($verbose) echo "$label: delete returned ".array2string($delete)." !== TRUE\n";
					++$failed;
				}
				$get_after_delete = $this->get(array($level,__CLASS__,$location));
				if (!is_null($get_after_delete))
				{
					if ($verbose) echo "$label: get_after_delete=".array2string($get_after_delete)." != NULL\n";
					++$failed;
				}
				// prepare for mget of everything
				if (is_a($this, 'egw_cache_provider_multiple'))
				{
					$locations[$location] = $data;
					$mget_after_delete = $this->mget(array($level,__CLASS__,array($location)));
					if (isset($mget_after_delete[$location]))
					{
						if ($verbose) echo "$label: mget_after_delete['$location']=".array2string($mget_after_delete[$location])." != NULL\n";
						++$failed;
					}
				}
				elseif (!is_null($data))	// emulation can NOT distinquish between null and not set
				{
					$locations[$location] = $data;
				}
				$add_after_delete = $this->add(array($level,__CLASS__,$location), $data, 10);
				if ($add_after_delete !== true)
				{
					if ($verbose) echo "$label: add_after_delete=".array2string($add_after_delete)."\n";
					++$failed;
				}
				else
				{
					$get_after_add = $this->get(array($level,__CLASS__,$location));
					if ($get_after_add !== $data)
					{
						if ($verbose) echo "$label: get_after_add=".array2string($get_after_add)." !== ".array2string($data)."\n";
						++$failed;
					}
				}
			}
			// get all above in one request
			$keys = array_keys($locations);
			$keys_bogus = array_merge(array('not-set'),array_keys($locations),array('not-set-too'));
			if (is_a($this, 'egw_cache_provider_multiple'))
			{
				$mget = $this->mget(array($level,__CLASS__,$keys));
				$mget_bogus = $this->mget(array($level,__CLASS__,$keys_bogus));
			/* egw_cache::getCache() gives a different result, as it does NOT use $level direkt
			}
			else
			{
				$mget = egw_cache::getCache($level, __CLASS__, $keys);
				$mget_bogus = egw_cache::getCache($level, __CLASS__, $keys_bogus);
			}*/
				if ($mget !== $locations)
				{
					if ($verbose) echo "$label: mget=\n".array2string($mget)." !==\n".array2string($locations)."\n";
					++$failed;
				}
				if ($mget_bogus !== $locations)
				{
					if ($verbose) echo "$label: mget(".array2string($keys_bogus).")=\n".array2string($mget_bogus)." !==\n".array2string($locations)."\n";
					++$failed;
				}
			}
		}

		return $failed;
	}

	/**
	 * Delete all data under given keys
	 *
	 * Providers can return false, if they do not support flushing part of the cache (eg. memcache)
	 *
	 * @param array $keys eg. array($level,$app,$location)
	 * @return boolean true on success, false on error (eg. $key not set)
	 */
	function flush(array $keys)
	{
		unset($keys);	// required by function signature
		return false;
	}
}

// some testcode, if this file is called via it's URL
// can be run on command-line: sudo php -d apc.enable_cli=1 -f phpgwapi/inc/class.egw_cache.inc.php
/*if (isset($_SERVER['SCRIPT_FILENAME']) && realpath($_SERVER['SCRIPT_FILENAME']) == __FILE__)
{
	if (!isset($_SERVER['HTTP_HOST']))
	{
		chdir(dirname(__FILE__));	// to enable our relative pathes to work
	}
	$GLOBALS['egw_info'] = array(
		'flags' => array(
			'noapi' => true,
		),
	);
	include_once '../../header.inc.php';

	if (isset($_SERVER['HTTP_HOST'])) echo "<pre style='whitespace: nowrap'>\n";

	foreach(array(
		'egw_cache_apc' => array(),
		'egw_cache_memcache' => array('localhost'),
		'egw_cache_files' => array('/tmp'),
	) as $class => $param)
	{
		echo "Checking $class:\n";
		try {
			$start = microtime(true);
			$provider = new $class($param);
			$n = 100;
			for($i=1; $i <= $n; ++$i)
			{
				$failed = $provider->check($i == 1);
			}
			printf("$failed checks failed, $n iterations took %5.3f sec\n\n", microtime(true)-$start);
		}
		catch (Exception $e) {
			printf($e->getMessage()."\n\n");
		}
	}
}*/

// setting apc as default provider, if apc_fetch function exists AND further checks in egw_cache_apc recommed it
if (is_null(egw_cache::$default_provider))
{
	egw_cache::$default_provider = function_exists('apc_fetch') && egw_cache_apc::available() ? 'egw_cache_apc' : 'egw_cache_files';
}