AssetQueryString.php

<?php

declare (strict_types=1);
namespace Drupal\Core\Asset;

use Drupal\Component\Datetime\TimeInterface;
use Drupal\Core\State\StateInterface;

/**
 * Stores a cache busting query string service for asset URLs.
 *
 * The string changes on every update or full cache flush, forcing browsers to
 * load a new copy of the files, as the URL changed.
 */
class AssetQueryString implements AssetQueryStringInterface {
    
    /**
     * The key used for state.
     */
    const STATE_KEY = 'asset.css_js_query_string';
    
    /**
     * Creates a new AssetQueryString instance.
     *
     * @param \Drupal\Core\State\StateInterface $state
     *   State service.
     * @param \Drupal\Component\Datetime\TimeInterface $time
     *   System time service.
     */
    public function __construct(StateInterface $state, TimeInterface $time) {
    }
    
    /**
     * {@inheritdoc}
     */
    public function reset() : void {
        // The timestamp is converted to base 36 in order to make it more compact.
        $this->state
            ->set(self::STATE_KEY, base_convert(strval($this->time
            ->getRequestTime()), 10, 36));
    }
    
    /**
     * {@inheritdoc}
     */
    public function get() : string {
        return $this->state
            ->get(self::STATE_KEY, '0');
    }

}