public function bust($file, $manifest = null)
    {
        if (! $manifest) {
            $manifest = $this->getDefaultManifest();
        }

        $dir = str_replace(
            static::$public,
            '',
            dirname($manifest)
        );

        $manifest = $this->loadManifest($manifest);

        if (isset($manifest->$file)) {
            return "/{$dir}/{$manifest->$file}";
        }

        throw new InvalidArgumentException(
            "File {$file} not defined in asset manifest."
        );
    }