class AttributeHelper

class AttributeHelper {
    
    /**
     * This class should not be instantiated.
     */
    private function __construct() {
    }
    
    /**
     * Checks if the given attribute collection has an attribute.
     *
     * @param string $name
     *   The name of the attribute to check for.
     * @param \Drupal\Core\Template\Attribute|array $collection
     *   An Attribute object or an array of attributes.
     *
     * @return bool
     *   TRUE if the attribute exists, FALSE otherwise.
     *
     * @throws \InvalidArgumentException
     *   When the input $collection is neither an Attribute object nor an array.
     */
    public static function attributeExists($name, $collection) {
        if ($collection instanceof Attribute) {
            return $collection->hasAttribute($name);
        }
        elseif (is_array($collection)) {
            return array_key_exists($name, $collection);
        }
        throw new \InvalidArgumentException('Invalid collection argument');
    }
    
    /**
     * Merges two attribute collections.
     *
     * @param \Drupal\Core\Template\Attribute|array $a
     *   First Attribute object or array to merge. The returned value type will
     *   be the same as the type of this argument.
     * @param \Drupal\Core\Template\Attribute|array $b
     *   Second Attribute object or array to merge.
     *
     * @return \Drupal\Core\Template\Attribute|array
     *   The merged attributes, as an Attribute object or an array.
     *
     * @throws \InvalidArgumentException
     *   If at least one collection argument is neither an Attribute object nor an
     *   array.
     */
    public static function mergeCollections($a, $b) {
        if (!($a instanceof Attribute || is_array($a)) || !($b instanceof Attribute || is_array($b))) {
            throw new \InvalidArgumentException('Invalid collection argument');
        }
        // If both collections are arrays, just merge them.
        if (is_array($a) && is_array($b)) {
            return NestedArray::mergeDeep($a, $b);
        }
        // If at least one collections is an Attribute object, merge through
        // Attribute::merge.
        $merge_a = $a instanceof Attribute ? $a : new Attribute($a);
        $merge_b = $b instanceof Attribute ? $b : new Attribute($b);
        $merge_a->merge($merge_b);
        return $a instanceof Attribute ? $merge_a : $merge_a->toArray();
    }

}