Uses rubyzip on rails 3

# app/models/downloader.rb
require 'zip/zip'
require 'zip/zipfilesystem'

class Downloader
  attr_accessor :file_ids

  TEMP_PATH = "#{Rails.root.to_s}/public/temp_zips"

  def self.remove_temp(file_path)
    system "rm #{file_path}"
  end

  # ids should like this "1#2#3"
  def initialize(ids)
    ids ||= ''
    @file_ids = ids.split('#')
  end

  def add_file_id(file_id)
    return if @file_ids.include?(file_id)
    @file_ids << file_id
  end

  def delete_file_id(file_id)
    return unless @file_ids.include?(file_id)
    @file_ids.delete(file_id)
  end

  def files_list
    list = []
    @file_ids.each do |id|
      list << ProductDoc.find(id)
    end

    list
  end

  def compress
    file_path = "#{TEMP_PATH}/test-#{Time.now.strftime('%Y%m%d%I%L')}.zip"
    Zip::ZipFile.open(file_path, Zip::ZipFile::CREATE) do |zip|
      files_list.each do |file|
        path = file.document.path
        zip.add(File.basename(path), path)
      end
    end
    return file_path
  end
end

def download_zip
  zipfile = downloader.compress
  if File.exist?(zipfile)
    send_file zipfile, :type => 'application/zip', :filename => "Test-#{Time.now.strftime('%Y%m%d%I')}.zip", :disposition => 'attachment'
    Downloader.delay(run_at: 30.minutes.from_now).remove_temp(zipfile)
    cookies[:download_list] = nil
  end
end

# app/controllers/application_controller.rb
helper_method :downloader
def downloader
  return @downloader if @downloader
  @downloader = Downloader.new(cookies[:download_list])
end