<?php
/**
 * @link http://www.yiiframework.com/
 * @copyright Copyright (c) 2008 Yii Software LLC
 * @license http://www.yiiframework.com/license/
 */

namespace yii\web;

use Yii;
use yii\caching\Cache;
use yii\base\InvalidConfigException;
use yii\di\Instance;

/**
 * CacheSession implements a session component using cache as storage medium.
 *
 * The cache being used can be any cache application component.
 * The ID of the cache application component is specified via [[cache]], which defaults to 'cache'.
 *
 * Beware, by definition cache storage are volatile, which means the data stored on them
 * may be swapped out and get lost. Therefore, you must make sure the cache used by this component
 * is NOT volatile. If you want to use database as storage medium, [[DbSession]] is a better choice.
 *
 * The following example shows how you can configure the application to use CacheSession:
 * Add the following to your application config under `components`:
 *
 * ~~~
 * 'session' => [
 *     'class' => 'yii\web\CacheSession',
 *     // 'cache' => 'mycache',
 * ]
 * ~~~
 *
 * @property boolean $useCustomStorage Whether to use custom storage. This property is read-only.
 *
 * @author Qiang Xue <qiang.xue@gmail.com>
 * @since 2.0
 */
class CacheSession extends Session
{
    /**
     * @var Cache|string the cache object or the application component ID of the cache object.
     * The session data will be stored using this cache object.
     *
     * After the CacheSession object is created, if you want to change this property,
     * you should only assign it with a cache object.
     */
    public $cache = 'cache';

    /**
     * Initializes the application component.
     */
    public function init()
    {
        parent::init();
        $this->cache = Instance::ensure($this->cache, Cache::className());
    }

    /**
     * Returns a value indicating whether to use custom session storage.
     * This method overrides the parent implementation and always returns true.
     * @return boolean whether to use custom storage.
     */
    public function getUseCustomStorage()
    {
        return true;
    }

    /**
     * Session read handler.
     * Do not call this method directly.
     * @param  string $id session ID
     * @return string the session data
     */
    public function readSession($id)
    {
        $data = $this->cache->get($this->calculateKey($id));

        return $data === false ? '' : $data;
    }

    /**
     * Session write handler.
     * Do not call this method directly.
     * @param  string  $id   session ID
     * @param  string  $data session data
     * @return boolean whether session write is successful
     */
    public function writeSession($id, $data)
    {
        return $this->cache->set($this->calculateKey($id), $data, $this->getTimeout());
    }

    /**
     * Session destroy handler.
     * Do not call this method directly.
     * @param  string  $id session ID
     * @return boolean whether session is destroyed successfully
     */
    public function destroySession($id)
    {
        return $this->cache->delete($this->calculateKey($id));
    }

    /**
     * Generates a unique key used for storing session data in cache.
     * @param  string $id session variable name
     * @return mixed  a safe cache key associated with the session variable name
     */
    protected function calculateKey($id)
    {
        return [__CLASS__, $id];
    }
}
