function CssCollectionGrouper::group

Puts multiple items into the same group if they are groupable. Items of the 'file' type are groupable if their 'preprocess' flag is TRUE, and items of the 'external' type are never groupable. Items with a media type of 'print' will be put into their own group so that they are not loaded on regular page requests. Items with a media type of 'all' or 'screen' will be grouped together (with media queries where necessary), to minimize the number of separate aggregates.

Also ensures that the process of grouping items does not change their relative order. This requirement may result in multiple groups for the same type and media, if needed to accommodate other items in between.

Overrides AssetCollectionGrouperInterface::group

File

core/lib/Drupal/Core/Asset/CssCollectionGrouper.php, line 25

Class

CssCollectionGrouper

Groups CSS assets.

Namespace

Code

public function group(array $css_assets) {
    $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) {
        // 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. The CSS optimizer
                // adds inline 'media' statements for everything except 'print', so
                // only vary groups based on that.
                $group_keys = $item['preprocess'] ? [
                    $item['type'],
                    $item['group'],
                    $item['media'] === 'print',
                ] : 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] = $item;
            if ($item['media'] !== 'print') {
                $groups[$i]['media'] = 'all';
            }
            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;
    }
    return $groups;
}