<?php
namespace TYPO3\CMS\Core\Cache\Backend;

/**
 * This file is part of the TYPO3 CMS project.
 *
 * It is free software; you can redistribute it and/or modify it under
 * the terms of the GNU General Public License, either version 2
 * of the License, or any later version.
 *
 * For the full copyright and license information, please read the
 * LICENSE.txt file that was distributed with this source code.
 *
 * The TYPO3 project - inspiring people to share!
 */
/**
 * A caching backend which stores cache entries by using Memcached.
 *
 * This backend uses the following types of Memcache keys:
 * - tag_xxx
 * xxx is tag name, value is array of associated identifiers identifier. This
 * is "forward" tag index. It is mainly used for obtaining content by tag
 * (get identifier by tag -> get content by identifier)
 * - ident_xxx
 * xxx is identifier, value is array of associated tags. This is "reverse" tag
 * index. It provides quick access for all tags associated with this identifier
 * and used when removing the identifier
 *
 * Each key is prepended with a prefix. By default prefix consists from two parts
 * separated by underscore character and ends in yet another underscore character:
 * - "TYPO3"
 * - Current site path obtained from the PATH_site constant
 * This prefix makes sure that keys from the different installations do not
 * conflict.
 *
 * Note: When using the Memcached backend to store values of more than ~1 MB,
 * the data will be split into chunks to make them fit into the memcached limits.
 *
 * This file is a backport from FLOW3 by Ingo Renner.
 *
 * @author Robert Lemke <robert@typo3.org>
 * @author Christian Jul Jensen <julle@typo3.org>
 * @author Karsten Dambekalns <karsten@typo3.org>
 * @author Dmitry Dulepov <dmitry@typo3.org>
 * @api
 */
class MemcachedBackend extends \TYPO3\CMS\Core\Cache\Backend\AbstractBackend implements \TYPO3\CMS\Core\Cache\Backend\TaggableBackendInterface {

	/**
	 * Max bucket size, (1024*1024)-42 bytes
	 *
	 * @var int
	 */
	const MAX_BUCKET_SIZE = 1048534;
	/**
	 * Instance of the PHP Memcache class
	 *
	 * @var \Memcache
	 */
	protected $memcache;

	/**
	 * Array of Memcache server configurations
	 *
	 * @var array
	 */
	protected $servers = array();

	/**
	 * Indicates whether the memcache uses compression or not (requires zlib),
	 * either 0 or MEMCACHE_COMPRESSED
	 *
	 * @var int
	 */
	protected $flags;

	/**
	 * A prefix to separate stored data from other data possibly stored in the memcache
	 *
	 * @var string
	 */
	protected $identifierPrefix;

	/**
	 * Constructs this backend
	 *
	 * @param string $context FLOW3's application context
	 * @param array $options Configuration options - depends on the actual backend
	 * @throws \TYPO3\CMS\Core\Cache\Exception if memcache is not installed
	 */
	public function __construct($context, array $options = array()) {
		if (!extension_loaded('memcache')) {
			throw new \TYPO3\CMS\Core\Cache\Exception('The PHP extension "memcache" must be installed and loaded in ' . 'order to use the Memcached backend.', 1213987706);
		}
		parent::__construct($context, $options);
	}

	/**
	 * Setter for servers to be used. Expects an array,  the values are expected
	 * to be formatted like "<host>[:<port>]" or "unix://<path>"
	 *
	 * @param array $servers An array of servers to add.
	 * @return void
	 * @api
	 */
	protected function setServers(array $servers) {
		$this->servers = $servers;
	}

	/**
	 * Setter for compression flags bit
	 *
	 * @param boolean $useCompression
	 * @return void
	 * @api
	 */
	protected function setCompression($useCompression) {
		if ($useCompression === TRUE) {
			$this->flags ^= MEMCACHE_COMPRESSED;
		} else {
			$this->flags &= ~MEMCACHE_COMPRESSED;
		}
	}

	/**
	 * Initializes the identifier prefix
	 *
	 * @return void
	 * @throws \TYPO3\CMS\Core\Cache\Exception
	 */
	public function initializeObject() {
		if (!count($this->servers)) {
			throw new \TYPO3\CMS\Core\Cache\Exception('No servers were given to Memcache', 1213115903);
		}
		$this->memcache = new \Memcache();
		$defaultPort = ini_get('memcache.default_port');
		foreach ($this->servers as $server) {
			if (substr($server, 0, 7) == 'unix://') {
				$host = $server;
				$port = 0;
			} else {
				if (substr($server, 0, 6) === 'tcp://') {
					$server = substr($server, 6);
				}
				if (strpos($server, ':') !== FALSE) {
					list($host, $port) = explode(':', $server, 2);
				} else {
					$host = $server;
					$port = $defaultPort;
				}
			}
			$this->memcache->addserver($host, $port);
		}
	}

	/**
	 * Initializes the identifier prefix when setting the cache.
	 *
	 * @param \TYPO3\CMS\Core\Cache\Frontend\FrontendInterface $cache The frontend for this backend
	 * @return void
	 */
	public function setCache(\TYPO3\CMS\Core\Cache\Frontend\FrontendInterface $cache) {
		parent::setCache($cache);
		$identifierHash = substr(md5(PATH_site . $this->context . $this->cacheIdentifier), 0, 12);
		$this->identifierPrefix = 'TYPO3_' . $identifierHash . '_';
	}

	/**
	 * Saves data in the cache.
	 *
	 * @param string $entryIdentifier An identifier for this specific cache entry
	 * @param string $data The data to be stored
	 * @param array $tags Tags to associate with this cache entry
	 * @param integer $lifetime Lifetime of this cache entry in seconds. If NULL is specified, the default lifetime is used. "0" means unlimited lifetime.
	 * @return void
	 * @throws \TYPO3\CMS\Core\Cache\Exception if no cache frontend has been set.
	 * @throws \InvalidArgumentException if the identifier is not valid or the final memcached key is longer than 250 characters
	 * @throws \TYPO3\CMS\Core\Cache\Exception\InvalidDataException if $data is not a string
	 * @api
	 */
	public function set($entryIdentifier, $data, array $tags = array(), $lifetime = NULL) {
		if (strlen($this->identifierPrefix . $entryIdentifier) > 250) {
			throw new \InvalidArgumentException('Could not set value. Key more than 250 characters (' . $this->identifierPrefix . $entryIdentifier . ').', 1232969508);
		}
		if (!$this->cache instanceof \TYPO3\CMS\Core\Cache\Frontend\FrontendInterface) {
			throw new \TYPO3\CMS\Core\Cache\Exception('No cache frontend has been set yet via setCache().', 1207149215);
		}
		if (!is_string($data)) {
			throw new \TYPO3\CMS\Core\Cache\Exception\InvalidDataException('The specified data is of type "' . gettype($data) . '" but a string is expected.', 1207149231);
		}
		$tags[] = '%MEMCACHEBE%' . $this->cacheIdentifier;
		$expiration = $lifetime !== NULL ? $lifetime : $this->defaultLifetime;
		// Memcached consideres values over 2592000 sec (30 days) as UNIX timestamp
		// thus $expiration should be converted from lifetime to UNIX timestamp
		if ($expiration > 2592000) {
			$expiration += $GLOBALS['EXEC_TIME'];
		}
		try {
			if (strlen($data) > self::MAX_BUCKET_SIZE) {
				$data = str_split($data, 1024 * 1000);
				$success = TRUE;
				$chunkNumber = 1;
				foreach ($data as $chunk) {
					$success = $success && $this->memcache->set($this->identifierPrefix . $entryIdentifier . '_chunk_' . $chunkNumber, $chunk, $this->flags, $expiration);
					$chunkNumber++;
				}
				$success = $success && $this->memcache->set($this->identifierPrefix . $entryIdentifier, 'TYPO3*chunked:' . $chunkNumber, $this->flags, $expiration);
			} else {
				$success = $this->memcache->set($this->identifierPrefix . $entryIdentifier, $data, $this->flags, $expiration);
			}
			if ($success === TRUE) {
				$this->removeIdentifierFromAllTags($entryIdentifier);
				$this->addIdentifierToTags($entryIdentifier, $tags);
			} else {
				throw new \TYPO3\CMS\Core\Cache\Exception('Could not set data to memcache server.', 1275830266);
			}
		} catch (\Exception $exception) {
			\TYPO3\CMS\Core\Utility\GeneralUtility::sysLog('Memcache: could not set value. Reason: ' . $exception->getMessage(), 'Core', \TYPO3\CMS\Core\Utility\GeneralUtility::SYSLOG_SEVERITY_WARNING);
		}
	}

	/**
	 * Loads data from the cache.
	 *
	 * @param string $entryIdentifier An identifier which describes the cache entry to load
	 * @return mixed The cache entry's content as a string or FALSE if the cache entry could not be loaded
	 * @api
	 */
	public function get($entryIdentifier) {
		$value = $this->memcache->get($this->identifierPrefix . $entryIdentifier);
		if (substr($value, 0, 14) === 'TYPO3*chunked:') {
			list(, $chunkCount) = explode(':', $value);
			$value = '';
			for ($chunkNumber = 1; $chunkNumber < $chunkCount; $chunkNumber++) {
				$value .= $this->memcache->get($this->identifierPrefix . $entryIdentifier . '_chunk_' . $chunkNumber);
			}
		}
		return $value;
	}

	/**
	 * Checks if a cache entry with the specified identifier exists.
	 *
	 * @param string $entryIdentifier An identifier specifying the cache entry
	 * @return boolean TRUE if such an entry exists, FALSE if not
	 * @api
	 */
	public function has($entryIdentifier) {
		return $this->memcache->get($this->identifierPrefix . $entryIdentifier) !== FALSE;
	}

	/**
	 * Removes all cache entries matching the specified identifier.
	 * Usually this only affects one entry but if - for what reason ever -
	 * old entries for the identifier still exist, they are removed as well.
	 *
	 * @param string $entryIdentifier Specifies the cache entry to remove
	 * @return boolean TRUE if (at least) an entry could be removed or FALSE if no entry was found
	 * @api
	 */
	public function remove($entryIdentifier) {
		$this->removeIdentifierFromAllTags($entryIdentifier);
		return $this->memcache->delete($this->identifierPrefix . $entryIdentifier, 0);
	}

	/**
	 * Finds and returns all cache entry identifiers which are tagged by the
	 * specified tag.
	 *
	 * @param string $tag The tag to search for
	 * @return array An array of entries with all matching entries. An empty array if no entries matched
	 * @api
	 */
	public function findIdentifiersByTag($tag) {
		$identifiers = $this->memcache->get($this->identifierPrefix . 'tag_' . $tag);
		if ($identifiers !== FALSE) {
			return (array) $identifiers;
		} else {
			return array();
		}
	}

	/**
	 * Removes all cache entries of this cache.
	 *
	 * @return void
	 * @throws \TYPO3\CMS\Core\Cache\Exception
	 * @api
	 */
	public function flush() {
		if (!$this->cache instanceof \TYPO3\CMS\Core\Cache\Frontend\FrontendInterface) {
			throw new \TYPO3\CMS\Core\Cache\Exception('No cache frontend has been set via setCache() yet.', 1204111376);
		}
		$this->flushByTag('%MEMCACHEBE%' . $this->cacheIdentifier);
	}

	/**
	 * Removes all cache entries of this cache which are tagged by the specified tag.
	 *
	 * @param string $tag The tag the entries must have
	 * @return void
	 * @api
	 */
	public function flushByTag($tag) {
		$identifiers = $this->findIdentifiersByTag($tag);
		foreach ($identifiers as $identifier) {
			$this->remove($identifier);
		}
	}

	/**
	 * Associates the identifier with the given tags
	 *
	 * @param string $entryIdentifier
	 * @param array $tags
	 * @return void
	 */
	protected function addIdentifierToTags($entryIdentifier, array $tags) {
		// Get identifier-to-tag index to look for updates
		$existingTags = $this->findTagsByIdentifier($entryIdentifier);
		$existingTagsUpdated = FALSE;

		foreach ($tags as $tag) {
			// Update tag-to-identifier index
			$identifiers = $this->findIdentifiersByTag($tag);
			if (!in_array($entryIdentifier, $identifiers, TRUE)) {
				$identifiers[] = $entryIdentifier;
				$this->memcache->set($this->identifierPrefix . 'tag_' . $tag, $identifiers);
			}
			// Test if identifier-to-tag index needs update
			if (!in_array($tag, $existingTags, TRUE)) {
				$existingTags[] = $tag;
				$existingTagsUpdated = TRUE;
			}
		}

		// Update identifier-to-tag index if needed
		if ($existingTagsUpdated) {
			$this->memcache->set($this->identifierPrefix . 'ident_' . $entryIdentifier, $existingTags);
		}
	}

	/**
	 * Removes association of the identifier with the given tags
	 *
	 * @param string $entryIdentifier
	 * @param array Array of tags
	 * @return void
	 */
	protected function removeIdentifierFromAllTags($entryIdentifier) {
		// Get tags for this identifier
		$tags = $this->findTagsByIdentifier($entryIdentifier);
		// Deassociate tags with this identifier
		foreach ($tags as $tag) {
			$identifiers = $this->findIdentifiersByTag($tag);
			// Formally array_search() below should never return FALSE due to
			// the behavior of findTagsByIdentifier(). But if reverse index is
			// corrupted, we still can get 'FALSE' from array_search(). This is
			// not a problem because we are removing this identifier from
			// anywhere.
			if (($key = array_search($entryIdentifier, $identifiers)) !== FALSE) {
				unset($identifiers[$key]);
				if (count($identifiers)) {
					$this->memcache->set($this->identifierPrefix . 'tag_' . $tag, $identifiers);
				} else {
					$this->memcache->delete($this->identifierPrefix . 'tag_' . $tag, 0);
				}
			}
		}
		// Clear reverse tag index for this identifier
		$this->memcache->delete($this->identifierPrefix . 'ident_' . $entryIdentifier, 0);
	}

	/**
	 * Finds all tags for the given identifier. This function uses reverse tag
	 * index to search for tags.
	 *
	 * @param string $identifier Identifier to find tags by
	 * @return array
	 * @api
	 */
	protected function findTagsByIdentifier($identifier) {
		$tags = $this->memcache->get($this->identifierPrefix . 'ident_' . $identifier);
		return $tags === FALSE ? array() : (array) $tags;
	}

	/**
	 * Does nothing, as memcached does GC itself
	 *
	 * @return void
	 * @api
	 */
	public function collectGarbage() {

	}

}
