class CssSubscriber

class CssSubscriber implements EventSubscriberInterface {
    
    /**
     * Scan the asset, count the selectors and save selector count to asset array.
     *
     * The counting method is very rough and may have inaccuracies - especially if
     * there are media queries in the file. Since we only care about the maximum,
     * this is acceptable since that reduces performance hit and an exact number
     * is unimportant.
     *
     * @param \Drupal\advagg\Asset\AssetOptimizationEvent $asset
     *   The asset optimization event.
     */
    public function scan(AssetOptimizationEvent $asset) {
        $asset_array = $asset->getAsset();
        $asset_array['selectors'] = substr_count($asset->getContent(), '{');
        $asset->setAsset($asset_array);
    }
    
    /**
     * {@inheritdoc}
     */
    public static function getSubscribedEvents() {
        return [
            AssetOptimizationEvent::CSS => [
                'scan',
                100,
            ],
        ];
    }

}