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

namespace yii\caching;
use yii\base\InvalidConfigException;

/**
 * GroupDependency marks a cached data item with a group name.
 *
 * You may invalidate the cached data items with the same group name all at once
 * by calling [[invalidate()]].
 *
 * @author Qiang Xue <qiang.xue@gmail.com>
 * @since 2.0
 */
class GroupDependency extends Dependency
{
	/**
	 * @var string the group name. This property must be set.
	 */
	public $group;

	/**
	 * Generates the data needed to determine if dependency has been changed.
	 * This method does nothing in this class.
	 * @param Cache $cache the cache component that is currently evaluating this dependency
	 * @return mixed the data needed to determine if dependency has been changed.
	 * @throws InvalidConfigException if [[group]] is not set.
	 */
	protected function generateDependencyData($cache)
	{
		if ($this->group === null) {
			throw new InvalidConfigException('GroupDependency::group must be set');
		}
		$version = $cache->get([__CLASS__, $this->group]);
		if ($version === false) {
			$version = $this->invalidate($cache, $this->group);
		}
		return $version;
	}

	/**
	 * Performs the actual dependency checking.
	 * @param Cache $cache the cache component that is currently evaluating this dependency
	 * @return boolean whether the dependency is changed or not.
	 * @throws InvalidConfigException if [[group]] is not set.
	 */
	public function getHasChanged($cache)
	{
		if ($this->group === null) {
			throw new InvalidConfigException('GroupDependency::group must be set');
		}
		$version = $cache->get([__CLASS__, $this->group]);
		return $version === false || $version !== $this->data;
	}

	/**
	 * Invalidates all of the cached data items that have the same [[group]].
	 * @param Cache $cache the cache component that caches the data items
	 * @param string $group the group name
	 * @return string the current version number
	 */
	public static function invalidate($cache, $group)
	{
		$version = microtime();
		$cache->set([__CLASS__, $group], $version);
		return $version;
	}
}
