def process_zipfile(zipfilename_or_stream)
      @sheet_files = []

      unless is_stream?(zipfilename_or_stream)
        zip_file = Zip::File.open(zipfilename_or_stream)
      else
        zip_file = Zip::CentralDirectory.new
        zip_file.read_from_stream zipfilename_or_stream
      end

      process_zipfile_entries zip_file.to_a.sort_by(&:name)
    end
def process_zipfile(zipfilename_or_stream)
      @sheet_files = []

      unless is_stream?(zipfilename_or_stream)
        zip_file = Zip::File.open(zipfilename_or_stream)
      else
        zip_file = Zip::CentralDirectory.new
        zip_file.read_from_stream zipfilename_or_stream
      end

      process_zipfile_entries zip_file.to_a.sort_by(&:name)
    end
Extracts all needed files from the zip file