<?php
/**
 * This source file is part of the open source project
 * ExpressionEngine (https://expressionengine.com)
 *
 * @link      https://expressionengine.com/
 * @copyright Copyright (c) 2003-2022, Packet Tide, LLC (https://www.packettide.com)
 * @license   https://expressionengine.com/license Licensed under Apache License, Version 2.0
 */

/**
 * Memcached Caching
 */
class EE_Cache_memcached extends CI_Driver
{
    /**
     * Holds the memcached object
     *
     * @var object
     */
    protected $_memcached = null;

    /**
     * Keeps current namespaces in memory
     *
     * @var array
     */
    protected $_namespaces = array();

    /**
     * Look for a value in the cache. If it exists, return the data
     * if not, return FALSE
     *
     * @param	string	$key 		Key name
     * @param	const	$scope		Cache::LOCAL_SCOPE or Cache::GLOBAL_SCOPE
     *		 for local or global scoping of the cache item
     * @param	bool	$namespace 	Whether or not to namespace the key
     * @return	mixed	value matching $id or FALSE on failure
     */
    public function get($key, $scope = Cache::LOCAL_SCOPE, $namespace = true)
    {
        $key = ($namespace) ? $this->_namespaced_key($key, $scope) : $this->unique_key($key, $scope);

        $data = $this->_memcached->get($key);

        return is_array($data) ? $data[0] : false;
    }

    /**
     * Save value to cache
     *
     * @param	string	$key		Key name
     * @param	mixed	$data		Data to store
     * @param	int		$ttl = 60	Cache TTL (in seconds)
     * @param	const	$scope		Cache::LOCAL_SCOPE or Cache::GLOBAL_SCOPE
     *		 for local or global scoping of the cache item
     * @param	bool	$namespace 	Whether or not to namespace the key
     * @return	bool	TRUE on success, FALSE on failure
     */
    public function save($key, $data, $ttl = 60, $scope = Cache::LOCAL_SCOPE, $namespace = true)
    {
        $key = ($namespace) ? $this->_namespaced_key($key, $scope) : $this->unique_key($key, $scope);

        // Memcache does not allow a TTL more than 30 days, anything over will
        // cause set() to return FALSE; and Memcached interprets any TTL over
        // 30 days to be a Unix timestamp, so we'll cap the TTL at 30 days
        if ($ttl > 2592000) {
            $ttl = 2592000;
        }

        $data = array($data, ee()->localize->now, $ttl);

        if (get_class($this->_memcached) === 'Memcached') {
            return $this->_memcached->set($key, $data, $ttl);
        } elseif (get_class($this->_memcached) === 'Memcache') {
            return $this->_memcached->set($key, $data, 0, $ttl);
        }

        return false;
    }

    /**
     * Delete from cache
     *
     * @param	string	$key	Key name
     * @param	const	$scope	Cache::LOCAL_SCOPE or Cache::GLOBAL_SCOPE
     *		 for local or global scoping of the cache item
     * @return	bool	TRUE on success, FALSE on failure
     */
    public function delete($key, $scope = Cache::LOCAL_SCOPE)
    {
        // Delete namespace contents
        if (strrpos($key, Cache::NAMESPACE_SEPARATOR, strlen($key) - 1) !== false) {
            $this->_create_new_namespace($key, $scope);

            return true;
        }

        // Delete specific key
        return $this->_memcached->delete($this->_namespaced_key($key, $scope));
    }

    /**
     * Clean the cache
     *
     * @param	const	$scope	Cache::LOCAL_SCOPE or Cache::GLOBAL_SCOPE
     *		 for local or global scoping of the cache item
     * @return	bool	TRUE on success, FALSE on failure
     */
    public function clean($scope = Cache::LOCAL_SCOPE)
    {
        $this->_create_new_namespace('', $scope, true);

        return true;
    }

    /**
     * Cache Info
     *
     * @return	mixed	array on success, false on failure
     */
    public function cache_info()
    {
        if ($this->_memcached instanceof Memcached) {
            return $this->_memcached->getStats();
        }

        if ($this->_memcached instanceof Memcache) {
            return $this->_memcached->getExtendedStats();
        }
    }

    /**
     * Get Cache Metadata
     *
     * @param	string	$key		Key to get cache metadata on
     * @param	const	$scope	Cache::LOCAL_SCOPE or Cache::GLOBAL_SCOPE
     *		 for local or global scoping of the cache item
     * @return	mixed	Cache item metadata
     */
    public function get_metadata($key, $scope = Cache::LOCAL_SCOPE)
    {
        $stored = $this->_memcached->get($this->_namespaced_key($key, $scope));

        if ($stored == false or count($stored) !== 3) {
            return false;
        }

        list($data, $time, $ttl) = $stored;

        return array(
            'expire' => $time + $ttl,
            'mtime' => $time,
            'data' => $data
        );
    }

    /**
     * Setup memcached.
     *
     * @return	bool
     */
    protected function _setup_memcached()
    {
        $defaults = array(
            'host' => '127.0.0.1',
            'port' => 11211,
            'weight' => 1
        );

        // Try to use user-configured Memcache config, otherwise we'll try
        // to use the defaults
        if (is_array(ee()->config->item('memcached'))) {
            $memcache_config = ee()->config->item('memcached');
        } else {
            $memcache_config = array($defaults);
        }

        // We prefer to use Memcached
        if (class_exists('Memcached', false)) {
            $this->_memcached = new Memcached();
        } elseif (class_exists('Memcache', false)) {
            $this->_memcached = new Memcache();
        } else {
            return false;
        }

        ee()->load->helper('array');

        // Add servers to Memcache
        foreach ($memcache_config as $server) {
            $host = element('host', $server, $defaults['host']);
            $port = element('port', $server, $defaults['port']);
            $weight = element('weight', $server, $defaults['weight']);

            if (get_class($this->_memcached) === 'Memcached') {
                $this->_memcached->addServer($host, $port, $weight);
            } else {
                // Third parameter is persistance and defaults to TRUE.
                $this->_memcached->addServer($host, $port, true, $weight);
            }
        }

        // Check each server to see if it's reporting the time; if at least
        // one server reports the time, we'll consider this driver ok to use
        if (is_array($this->cache_info())) {
            foreach ($this->cache_info() as $server) {
                if (! empty($server['time'])) {
                    // Attempt to get previously-created namespaces and assign to class variable
                    $this->_namespaces = $this->get('namespaces', Cache::GLOBAL_SCOPE, false);

                    return true;
                }
            }
        }

        return false;
    }

    /**
     * Is supported
     *
     * Returns FALSE if memcached is not supported on the system.
     * If it is, we setup the memcached object & return TRUE
     *
     * @return	bool
     */
    public function is_supported()
    {
        if (! extension_loaded('memcached') && ! extension_loaded('memcache')) {
            log_message('debug', 'The Memcached Extension must be loaded to use Memcached Cache.');

            return false;
        }

        // If already instantiated, don't reinstantiate Memcache just to tell
        // the caller if Memcache is supported
        if (! is_null($this->_memcached)) {
            return true;
        }

        return $this->_setup_memcached();
    }

    /**
     * Creates a properly namespaced key ready for storage or retreval of any
     * cache item.
     *
     * For example, given a key of "/page/contact" and a scope of CACHE_LOCAL,
     * would return a key similar to:
     *
     *     http://site.com:12345678:/page/contact
     *
     * This is so that a Memcached server serving many EE installs can use the
     * same keys, conflict free. But it also serves to create namespaces within
     * the cache store that we can indiviaully manange. For more information on
     * this, see the doc block for _create_new_namespace above.
     *
     * @param	string	$key	Key name
     * @param	const	$scope	Cache::LOCAL_SCOPE or Cache::GLOBAL_SCOPE
     *		 for local or global scoping of the cache item
     * @return	string	Key that has been prefixed with the proper namespace
     *					and make unique to this site
     */
    protected function _namespaced_key($key, $scope = Cache::LOCAL_SCOPE)
    {
        $root_key = $this->unique_key('', $scope);

        // If the current scope does not have namespaces setup, create one
        if (! isset($this->_namespaces[$root_key]['root_namespace'])) {
            $this->_create_new_namespace('', $scope, true);
        }

        // If the key contains our namespace separator character...
        if (strpos($key, Cache::NAMESPACE_SEPARATOR) !== false) {
            // Separate the namespace from the cache key name
            $namespace = substr($key, 0, strrpos($key, Cache::NAMESPACE_SEPARATOR) + 1);

            // Get new namespace string
            $namespace = $this->_get_namespace($namespace, $scope);

            // Remove namespace from key
            $key = substr($key, strrpos($key, Cache::NAMESPACE_SEPARATOR) + 1);
        }
        // Key is not namespaced, give it the namespace identifier of the
        // root namespace of the scope
        else {
            $namespace = $this->_namespaces[$root_key]['root_namespace'];
        }

        return $this->unique_key($namespace . ':' . $key, $scope);
    }

    /**
     * Takes a namespace string and converts it to a string we need to use to
     * access namespaced keys in Memcached. For example, given we are passed
     * this:
     *
     * 	  /some/nested/namespace/
     *
     * Each part of a namespace needs to be associated with its current version
     * (see docs for _create_new_namespace() for more), so we'll return
     * something like this:
     *
     * 	  /some:12345/nested:12346/namespace:12347/
     *
     * @param	string	$namespace	Namespace string, separated from key
     * @param	const	$scope		Cache::LOCAL_SCOPE or Cache::GLOBAL_SCOPE
     *		 for local or global scoping of the cache item
     * @return	string	New namespace/prefix for keys to be stored in this
     *					namespace
     */
    protected function _get_namespace($namespace, $scope)
    {
        // Get the current unique scope string
        $root_key = $this->unique_key('', $scope);

        // Namespaces are stored in the array without leading slash as a
        // kind of normalization
        $namespace = ltrim($namespace, Cache::NAMESPACE_SEPARATOR);

        // Set up the namespace if it doesn't exist
        if (! isset($this->_namespaces[$root_key][$namespace])) {
            $this->_create_new_namespace($namespace, $scope);
        }

        // Cut up namespace into its respective parts (split by namespace
        // separator character) and get ready to build the new namespace
        // string
        $namespace_array = $this->_namespaces[$root_key];
        $namespace = trim($namespace, Cache::NAMESPACE_SEPARATOR);
        $parts = explode(Cache::NAMESPACE_SEPARATOR, $namespace);
        $namespace_lookup = '';
        $namespace_string = Cache::NAMESPACE_SEPARATOR;

        // For each part of the namespace, get its current unique identifier
        // and build a new namespace string
        foreach ($parts as $part) {
            // Work our way down the namespace tree
            $namespace_lookup .= $part . Cache::NAMESPACE_SEPARATOR;

            if (isset($namespace_array[$namespace_lookup])) {
                $namespace_string .= $part
                    . ':'
                    . $namespace_array[$namespace_lookup]
                    . Cache::NAMESPACE_SEPARATOR;
            }
        }

        return $namespace_string;
    }

    /**
     * Create a new namespace, which essentially invalidates an old/expired
     * namespace.
     *
     * Memcache(d) does not provide a way to delete or invalidate cache items
     * based on a wildcard pattern, and we do not way to iterate over every key
     * stored in numerous Memcached servers to figure out what to delete. So
     * we're using Memcached's recommended namespacing method of prefixing keys
     * with a random number.
     *
     * For example, for page caches, our namespace may be "/page/". We cannot
     * tell Memcached to delete all keys beginning with "/page/", so we attach
     * a number to the namespace, like so: "/page:12345/". If we want to clear
     * the page cache, we change the number ("/page:12346/") so that items
     * requested from the cache are effectively not existent, thus acting like
     * a cleared cache.
     *
     * It may be easiest to think of it like versioning. All past versions
     * continue to live in the cache store until automatically purged by
     * Memcached, but as we clear namespaces, we basically create new versions
     * of them for new things to be stored in.
     *
     * @param	string	$namespace	Namespace string, separated from key
     * @param	const	$scope		Cache::LOCAL_SCOPE or Cache::GLOBAL_SCOPE
     *		 for local or global scoping of the cache item
     * @param	bool	$clear_scope	Whether or not to clear the current scope
     * @return	void
     */
    protected function _create_new_namespace($namespace, $scope, $clear_scope = false)
    {
        // Get the current unique scope string
        $root_key = $this->unique_key('', $scope);

        // If no root namespace exists for the current scope, create one and
        // wipe out all other namespaces; or if the $clear_scope parameter is
        // set, in which case we are clearing the cache for the current scope
        if (! isset($this->_namespaces[$root_key]['root_namespace']) || $clear_scope) {
            $this->_namespaces[$root_key] = array(
                'root_namespace' => $this->_generate_unique_id()
            );
        }

        // If we're not creating a new cache for the current scope, we must be
        // creating a new namespace under the current scope
        if (! $clear_scope) {
            // Cut up namespace into its respective parts (split by namespace
            // separator character) and get ready to create the new namespace
            $namespace_array = &$this->_namespaces[$root_key];
            $namespace = trim($namespace, Cache::NAMESPACE_SEPARATOR);

            // Remove other array keys under this namespace
            foreach ($namespace_array as $key => $value) {
                if (strpos($key, $namespace . Cache::NAMESPACE_SEPARATOR) === 0) {
                    unset($namespace_array[$key]);
                }
            }

            $parts = explode(Cache::NAMESPACE_SEPARATOR, $namespace);
            $namespace_lookup = '';

            // Foreach part that doesn't exist, we'll create it; or if we run
            // into the specific namespace being asked to renew, renew it
            foreach ($parts as $part) {
                // Work our way down the namespace tree; they're stored in a
                // flat array for easier lookup
                $namespace_lookup .= $part . Cache::NAMESPACE_SEPARATOR;

                if (! isset($namespace_array[$namespace_lookup])
                    or $namespace . Cache::NAMESPACE_SEPARATOR == $namespace_lookup) {
                    $namespace_array[$namespace_lookup] = $this->_generate_unique_id();
                }
            }
        }

        // Save our class namespaces array to Memcached so we can access it on
        // subsequent page loads
        $this->save(
            'namespaces',
            $this->_namespaces,
            0,
            Cache::GLOBAL_SCOPE,
            false // Don't namespace this key
        );
    }

    /**
     * Generates a unique identifier for the namespace. We'll use the current
     * time concatenated with a random number, that way we're pretty much
     * guaranteed not to use an existing namespace.
     *
     * @return	string	Unique identifying string for a namespace
     */
    protected function _generate_unique_id()
    {
        return ee()->localize->now . rand(1, 10000);
    }
}

// EOF
