<?php
/*
 * Copyright 2008 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
require_once realpath(dirname(__FILE__) . '/../../../autoload.php');

/**
 * A persistent storage class based on the memcache, which is not
 * really very persistent, as soon as you restart your memcache daemon
 * the storage will be wiped.
 *
 * Will use either the memcache or memcached extensions, preferring
 * memcached.
 *
 * @author Chris Chabot <chabotc@google.com>
 */
class Google_Cache_Memcache extends Google_Cache_Abstract
{

    private $connection = false;

    private $mc = false;

    private $host;

    private $port;

    /**
     *
     * @var Google_Client the current client
     */
    private $client;

    public function __construct(Google_Client $client)
    {
        if (! function_exists('memcache_connect') && ! class_exists("Memcached")) {
            $error = "Memcache functions not available";
            $client->getLogger()->error($error);
            throw new Google_Cache_Exception($error);
        }
        $this->client = $client;
        if ($client->isAppEngine()) {
            // No credentials needed for GAE.
            $this->mc = new Memcached();
            $this->connection = true;
        } else {
            $this->host = $client->getClassConfig($this, 'host');
            $this->port = $client->getClassConfig($this, 'port');
            if (empty($this->host) || (empty($this->port) && (string) $this->port != "0")) {
                $error = "You need to supply a valid memcache host and port";
                $client->getLogger()->error($error);
                throw new Google_Cache_Exception($error);
            }
        }
    }

    /**
     * @inheritDoc
     */
    public function get($key, $expiration = false)
    {
        $this->connect();
        $ret = false;
        if ($this->mc) {
            $ret = $this->mc->get($key);
        } else {
            $ret = memcache_get($this->connection, $key);
        }
        if ($ret === false) {
            $this->client->getLogger()->debug('Memcache cache miss', array(
                'key' => $key
            ));
            return false;
        }
        if (is_numeric($expiration) && (time() - $ret['time'] > $expiration)) {
            $this->client->getLogger()->debug('Memcache cache miss (expired)', array(
                'key' => $key,
                'var' => $ret
            ));
            $this->delete($key);
            return false;
        }
        $this->client->getLogger()->debug('Memcache cache hit', array(
            'key' => $key,
            'var' => $ret
        ));
        return $ret['data'];
    }

    /**
     * @inheritDoc
     *
     * @param string $key            
     * @param string $value            
     * @throws Google_Cache_Exception
     */
    public function set($key, $value)
    {
        $this->connect();
        // we store it with the cache_time default expiration so objects will at
        // least get cleaned eventually.
        $data = array(
            'time' => time(),
            'data' => $value
        );
        $rc = false;
        if ($this->mc) {
            $rc = $this->mc->set($key, $data);
        } else {
            $rc = memcache_set($this->connection, $key, $data, false);
        }
        if ($rc == false) {
            $this->client->getLogger()->error('Memcache cache set failed', array(
                'key' => $key,
                'var' => $data
            ));
            throw new Google_Cache_Exception("Couldn't store data in cache");
        }
        $this->client->getLogger()->debug('Memcache cache set', array(
            'key' => $key,
            'var' => $data
        ));
    }

    /**
     * @inheritDoc
     *
     * @param String $key            
     */
    public function delete($key)
    {
        $this->connect();
        if ($this->mc) {
            $this->mc->delete($key, 0);
        } else {
            memcache_delete($this->connection, $key, 0);
        }
        $this->client->getLogger()->debug('Memcache cache delete', array(
            'key' => $key
        ));
    }

    /**
     * Lazy initialiser for memcache connection.
     * Uses pconnect for to take
     * advantage of the persistence pool where possible.
     */
    private function connect()
    {
        if ($this->connection) {
            return;
        }
        if (class_exists("Memcached")) {
            $this->mc = new Memcached();
            $this->mc->addServer($this->host, $this->port);
            $this->connection = true;
        } else {
            $this->connection = memcache_pconnect($this->host, $this->port);
        }
        if (! $this->connection) {
            $error = "Couldn't connect to memcache server";
            $this->client->getLogger()->error($error);
            throw new Google_Cache_Exception($error);
        }
    }
}