class AdvaggCssCollectionGrouper

class AdvaggCssCollectionGrouper extends CssCollectionGrouper implements AssetCollectionGrouperInterface {
    
    /**
     * Construct the grouper instance.
     *
     * @param \Drupal\Core\Config\ConfigFactoryInterface $config_factory
     *   A config factory for retrieving required config objects.
     */
    public function __construct(ConfigFactoryInterface $config_factory) {
        $this->config = $config_factory->get('advagg_bundler.settings');
    }
    
    /**
     * {@inheritdoc}
     */
    public function group(array $css_assets) {
        $max = $this->config
            ->get('css.max');
        // Only modify core grouping if bundler is enabled.
        if (!$this->config
            ->get('active') || !$max) {
            return parent::group($css_assets);
        }
        $logic = $this->config
            ->get('css.logic');
        $preprocess_count = count(array_filter(array_column($css_assets, 'preprocess')));
        $target = max($max - (count($css_assets) - $preprocess_count), 1);
        if ($logic === 0) {
            $split = round($preprocess_count / $target);
        }
        else {
            $split = array_sum(array_column($css_assets, 'size')) / $target;
        }
        $current_size = 0;
        $groups = [];
        // If a group can contain multiple items, we track the information that must
        // be the same for each item in the group, so that when we iterate the next
        // item, we can determine if it can be put into the current group, or if a
        // new group needs to be made for it.
        $current_group_keys = NULL;
        // When creating a new group, we pre-increment $i, so by initializing it to
        // -1, the first group will have index 0.
        $i = -1;
        foreach ($css_assets as $item) {
            // The browsers for which the CSS item needs to be loaded is part of the
            // information that determines when a new group is needed, but the order
            // of keys in the array doesn't matter, and we don't want a new group if
            // all that's different is that order.
            ksort($item['browsers']);
            // If the item can be grouped with other items, set $group_keys to an
            // array of information that must be the same for all items in its group.
            // If the item can't be grouped with other items, set $group_keys to
            // FALSE. We put items into a group that can be aggregated together:
            // whether they will be aggregated is up to the _drupal_css_aggregate()
            // function or an
            // override of that function specified in hook_css_alter(), but regardless
            // of the details of that function, a group represents items that can be
            // aggregated. Since a group may be rendered with a single HTML tag, all
            // items in the group must share the same information that would need to
            // be part of that HTML tag.
            switch ($item['type']) {
                case 'file':
                    // Group file items if their 'preprocess' flag is TRUE.
                    // Help ensure maximum reuse of aggregate files by only grouping
                    // together items that share the same 'group' value.
                    $group_keys = $item['preprocess'] ? [
                        $item['type'],
                        $item['group'],
                        $item['media'],
                        $item['browsers'],
                    ] : FALSE;
                    break;
                case 'external':
                    // Do not group external items.
                    $group_keys = FALSE;
                    break;
            }
            // If the group keys don't match the most recent group we're working with,
            // then a new group must be made.
            if ($group_keys !== $current_group_keys) {
                $i++;
                // Initialize the new group with the same properties as the first item
                // being placed into it. The item's 'data', 'weight' and 'basename'
                // properties are unique to the item and should not be carried over to
                // the group.
                $groups[$i] = $item;
                unset($groups[$i]['data'], $groups[$i]['weight'], $groups[$i]['basename']);
                $groups[$i]['items'] = [];
                $current_group_keys = $group_keys ? $group_keys : NULL;
            }
            // Add the item to the current group.
            $groups[$i]['items'][] = $item;
            if ($current_group_keys) {
                if ($logic === 0) {
                    if (count($groups[$i]['items']) >= $split) {
                        $current_group_keys = NULL;
                    }
                }
                else {
                    $current_size += isset($item['size']) ? $item['size'] : 0;
                    if ($current_size >= $split) {
                        $current_size = 0;
                        $current_group_keys = NULL;
                    }
                }
            }
            else {
                $current_size = 0;
            }
        }
        return $groups;
    }

}