<?php
// This file is part of Moodle - http://moodle.org/
//
// Moodle is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// Moodle is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with Moodle.  If not, see <http://www.gnu.org/licenses/>.

/**
 * Memcached based session handler.
 *
 * @package    core
 * @copyright  2013 Petr Skoda {@link http://skodak.org}
 * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
 */

namespace core\session;

defined('MOODLE_INTERNAL') || die();

/**
 * Memcached based session handler.
 *
 * @package    core
 * @copyright  2013 Petr Skoda {@link http://skodak.org}
 * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
 */
class memcached extends handler {
    /** @var string $savepath save_path string  */
    protected $savepath;
    /** @var array $servers list of servers parsed from save_path */
    protected $servers;
    /** @var string $prefix session key prefix  */
    protected $prefix;

    /**
     * Create new instance of handler.
     */
    public function __construct() {
        global $CFG;

        if (empty($CFG->session_memcached_save_path)) {
            $this->savepath = '';
        } else {
            $this->savepath =  $CFG->session_memcached_save_path;
        }

        if (empty($this->savepath)) {
            $this->servers = array();
        } else {
            $this->servers = self::connection_string_to_servers($this->savepath);
        }

        if (empty($CFG->session_memcached_prefix)) {
            $this->prefix = ini_get('memcached.sess_prefix');
        } else {
            $this->prefix = $CFG->session_memcached_prefix;
        }
    }

    /**
     * Init session handler.
     */
    public function init() {
        if (!extension_loaded('memcached')) {
            throw new exception('sessionhandlerproblem', 'error', '', null, 'memcached extension is not loaded');
        }
        $version = phpversion('memcached');
        if (!$version or version_compare($version, '2.0') < 0) {
            throw new exception('sessionhandlerproblem', 'error', '', null, 'memcached extension version must be at least 2.0');
        }
        if (empty($this->savepath)) {
            throw new exception('sessionhandlerproblem', 'error', '', null, '$CFG->session_memcached_save_path must be specified in config.php');
        }

        // NOTE: we cannot set any lock acquiring timeout here - bad luck.
        ini_set('session.save_handler', 'memcached');
        ini_set('session.save_path', $this->savepath);
        ini_set('memcached.sess_prefix', $this->prefix);
        ini_set('memcached.sess_locking', '1'); // Locking is required!
    }

    /**
     * Check for existing session with id $sid.
     *
     * Note: this verifies the storage backend only, not the actual session records.
     *
     * @param string $sid
     * @return bool true if session found.
     */
    public function session_exists($sid) {
        if (!$this->servers) {
            return false;
        }

        $memcached = new \Memcached();
        $memcached->addServers($this->servers);
        $value = $memcached->get($this->prefix.$sid);
        $memcached->quit();

        return ($value !== false);
    }

    /**
     * Kill all active sessions, the core sessions table is
     * purged afterwards.
     */
    public function kill_all_sessions() {
        global $DB;
        if (!$this->servers) {
            return;
        }

        $memcached = new \Memcached();
        $memcached->addServers($this->servers);

        // Note: this can be significantly improved by fetching keys from memcached,
        //       but we need to make sure we are not deleting somebody else's sessions.

        $rs = $DB->get_recordset('sessions', array(), 'id DESC', 'id, sid');
        foreach ($rs as $record) {
            $memcached->delete($this->prefix.$record->sid);
        }
        $rs->close();

        $memcached->quit();
    }

    /**
     * Kill one session, the session record is removed afterwards.
     * @param string $sid
     */
    public function kill_session($sid) {
        if (!$this->servers) {
            return;
        }

        $memcached = new \Memcached();
        $memcached->addServers($this->servers);
        $memcached->delete($this->prefix.$sid);

        $memcached->quit();
    }

    /**
     * Convert a connection string to an array of servers
     *
     * EG: Converts: "abc:123, xyz:789" to
     *
     *  array(
     *      array('abc', '123'),
     *      array('xyz', '789'),
     *  )
     *
     * @copyright  2013 Moodlerooms Inc. (http://www.moodlerooms.com)
     * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
     * @author     Mark Nielsen
     *
     * @param string $str save_path value containing memcached connection string
     * @return array
     */
    protected static function connection_string_to_servers($str) {
        $servers = array();
        $parts   = explode(',', $str);
        foreach ($parts as $part) {
            $part = trim($part);
            $pos  = strrpos($part, ':');
            if ($pos !== false) {
                $host = substr($part, 0, $pos);
                $port = substr($part, ($pos + 1));
            } else {
                $host = $part;
                $port = 11211;
            }
            $servers[] = array($host, $port);
        }
        return $servers;
    }
}