protected function gatherCollections()
    {
        if ( ! is_null($collection = $this->input->getArgument('collection')))
        {
            if ( ! $this->environment->has($collection))
            {
                $this->comment('['.$collection.'] Collection not found.');

                return array();
            }

            $this->comment('Gathering assets for collection...');

            $collections = array($collection => $this->environment->collection($collection));
        }
        else
        {
            $this->comment('Gathering all collections to build...');

            $collections = $this->environment->all();
        }

        $this->line('');

        return $collections;
    }