caches_page :small, :large

  def small
    render_promotion_thumbnail do |img|
      img.crop_resized!(100, 100, Magick::NorthWestGravity)
    end
  end

  def large
    render_promotion_thumbnail do |img|
      img.crop!(0, 0, 580, 190)
    end
  end

  private

  def render_promotion_thumbnail
    headers['Cache-Control'] = 'public'

    promotion = Promotion.find(params[:id])
    image_path = "#{RAILS_ROOT}/public/#{promotion.thumbnail}"
    image_path = "#{RAILS_ROOT}/public/images/promo-thumbnail-example.gif" unless File.exists?(image_path)
    img = Magick::Image.read(image_path).first

    yield(img)

    img.format = 'PNG'
    img.strip!

    send_data(img.to_blob, :type => 'image/png', :disposition => 'inline')

    GC.start
  end