# frozen_string_literal: true

require 'nokogiri'
require 'asciidoctor/extensions/asciidoctor_kroki/version'
require 'asciidoctor/extensions/asciidoctor_kroki/extension'

module Banzai
  module Filter
    # HTML that replaces all diagrams supported by Kroki with the corresponding img tags.
    # If the source content is large then the hidden attribute is added to the img tag.
    class KrokiFilter < HTML::Pipeline::Filter
      MAX_CHARACTER_LIMIT = 2000

      def call
        return doc unless settings.kroki_enabled

        diagram_selectors = ::Gitlab::Kroki.formats(settings)
                                .map do |diagram_type|
                                  %(pre[lang="#{diagram_type}"] > code,
                                  pre > code[lang="#{diagram_type}"])
                                end
                                .join(', ')

        xpath = Gitlab::Utils::Nokogiri.css_to_xpath(diagram_selectors)
        return doc unless doc.at_xpath(xpath)

        diagram_format = "svg"
        doc.xpath(xpath).each do |node|
          diagram_type = node.parent['lang'] || node['lang']
          diagram_src = node.content
          image_src = create_image_src(diagram_type, diagram_format, diagram_src)
          img_tag = Nokogiri::HTML::DocumentFragment.parse(%(<img src="#{image_src}" />))
          img_tag = img_tag.children.first

          next if img_tag.nil?

          lazy_load = diagram_src.length > MAX_CHARACTER_LIMIT
          img_tag.set_attribute('hidden', '') if lazy_load
          img_tag.set_attribute('class', 'js-render-kroki')

          img_tag.set_attribute('data-diagram', diagram_type)
          img_tag.set_attribute('data-diagram-src', "data:text/plain;base64,#{Base64.strict_encode64(diagram_src)}")

          node.parent.replace(img_tag)
        end

        doc
      end

      private

      def create_image_src(type, format, text)
        ::AsciidoctorExtensions::KrokiDiagram.new(type, format, text)
          .get_diagram_uri(settings.kroki_url)
      end

      def settings
        Gitlab::CurrentSettings.current_application_settings
      end
    end
  end
end