debian-mirror-gitlab/lib/banzai/filter/image_lazy_load_filter.rb

# frozen_string_literal: true

# Generated HTML is transformed back to GFM by app/assets/javascripts/behaviors/markdown/nodes/image.js
module Banzai
  module Filter
    # HTML filter that moves the value of image `src` attributes to `data-src`
    # so they can be lazy loaded.
    class ImageLazyLoadFilter < HTML::Pipeline::Filter
      def call
        doc.xpath('descendant-or-self::img').each do |img|
          img.add_class('lazy')
          img['data-src'] = img['src']
          img['src'] = LazyImageTagHelper.placeholder_image
        end

        doc
      end
    end
  end
end