protected function getManifest()
    {
        if (! is_null($this->manifest)) {
            return $this->manifest;
        }

        if (! file_exists($this->manifestPath)) {
            $this->build();
        }

        $this->files->get($this->manifestPath);

        return $this->manifest = file_exists($this->manifestPath) ?
            $this->files->getRequire($this->manifestPath) : [];
    }