Simple renderer for Markdown -> Liquid templates

liquid_markdown.rb

# frozen_string_literal: true

require 'action_view/template'

module LiquidMarkdown
  class Handler
    cattr_accessor :markdown_options, default: { autolink: true, tables: true, no_intra_emphasis: true }
    cattr_accessor :strict_liquid, default: true

    def self.call(template, source = nil)
      source ||= template.source
      "__lmd_source=begin;#{source.inspect};end.freeze; LiquidMarkdown::Handler.new(self, __lmd_source, local_assigns).render;"
    end

    def initialize(view, source, local_assigns)
      @view = view
      @source = source
      @local_assigns = local_assigns
    end

    def render
      _render
    end

    private
      attr_reader :source, :view, :local_assigns

      def _render
        if html?
          wrapped_sanitized_body
        else
          body
        end
      end

      def controller
        view.controller
      end

      def html?
        view.formats.include?(:html)
      end

      def wrapped_sanitized_body
        '<div class="lmd-rendered">%s</div>' % sanitizer.sanitize(body)
      end

      def sanitizer
        Rails::Html::WhiteListSanitizer.new
      end

      def body
        liquid_renderer.render!(liquid_assigns, liquid_render_options)
      end

      def liquid_renderer
        Liquid::Template.parse(liquid_template, liquid_parse_options)
      end

      def liquid_render_options
        {
          filters: liquid_filters,
          registers: liquid_registers,
          strict_variables: strict_liquid,
          strict_filters: strict_liquid
        }
      end

      def liquid_parse_options
        {
          error_mode: strict_liquid ? :strict : :lax
        }
      end

      def liquid_template
        if html?
          markdown_renderer.render(source)
        else
          source
        end
      end

      def liquid_assigns
        if controller.respond_to?(:liquid_assigns, true)
          controller.send(:liquid_assigns).stringify_keys
        else
          {}
        end.merge!(local_assigns.stringify_keys)
      end

      def liquid_filters
        if controller.respond_to?(:liquid_filters, true)
          controller.send(:liquid_filters)
        else
          []
        end
      end

      def liquid_registers
        {
          view: view,
          controller: controller
        }
      end

      def markdown_renderer
        Redcarpet::Markdown.new(Redcarpet::Render::HTML, markdown_options)
      end
  end
end

ActionView::Template.register_template_handler :lmd, LiquidMarkdown::Handler