# frozen_string_literal: true

# `CommonMark` markdown engine for GitLab's Banzai markdown filter.
# This module is used in Banzai::Filter::MarkdownFilter.
# Used gem is `commonmarker` which is a ruby wrapper for libcmark (CommonMark parser)
# including GitHub's GFM extensions.
# Homepage: https://github.com/gjtorikian/commonmarker

module Banzai
  module Filter
    module MarkdownEngines
      class CommonMark
        EXTENSIONS = [
          :autolink,      # provides support for automatically converting URLs to anchor tags.
          :strikethrough, # provides support for strikethroughs.
          :table          # provides support for tables.
        ].freeze

        PARSE_OPTIONS = [
          :FOOTNOTES,                  # parse footnotes.
          :STRIKETHROUGH_DOUBLE_TILDE, # parse strikethroughs by double tildes (as redcarpet does).
          :VALIDATE_UTF8               # replace illegal sequences with the replacement character U+FFFD.
        ].freeze

        RENDER_OPTIONS_C = [
          :GITHUB_PRE_LANG,  # use GitHub-style <pre lang> for fenced code blocks.
          :FOOTNOTES,        # render footnotes.
          :FULL_INFO_STRING, # include full info strings of code blocks in separate attribute.
          :UNSAFE            # allow raw/custom HTML and unsafe links.
        ].freeze

        # The `:GITHUB_PRE_LANG` option is not used intentionally because
        # it renders a fence block with language as `<pre lang="LANG"><code>some code\n</code></pre>`
        # while GitLab's syntax is `<pre><code lang="LANG">some code\n</code></pre>`.
        # If in the future the syntax is about to be made GitHub-compatible, please, add `:GITHUB_PRE_LANG` render option below
        # and remove `code_block` method from `lib/banzai/renderer/common_mark/html.rb`.
        RENDER_OPTIONS_RUBY = [
          # as of commonmarker 0.18.0, we need to use :UNSAFE to get the same as the original :DEFAULT
          # https://github.com/gjtorikian/commonmarker/pull/81
          :UNSAFE # allow raw/custom HTML and unsafe links.
        ].freeze

        def initialize(context)
          @context = context
          @renderer = Banzai::Renderer::CommonMark::HTML.new(options: render_options) if Feature.disabled?(:use_cmark_renderer)
        end

        def render(text)
          if Feature.enabled?(:use_cmark_renderer)
            CommonMarker.render_html(text, render_options, extensions)
          else
            doc = CommonMarker.render_doc(text, PARSE_OPTIONS, extensions)

            @renderer.render(doc)
          end
        end

        private

        def extensions
          if Feature.enabled?(:use_cmark_renderer)
            EXTENSIONS
          else
            EXTENSIONS + [
              :tagfilter # strips out several "unsafe" HTML tags from being used: https://github.github.com/gfm/#disallowed-raw-html-extension-
            ].freeze
          end
        end

        def render_options
          @context[:no_sourcepos] ? render_options_no_sourcepos : render_options_sourcepos
        end

        def render_options_no_sourcepos
          Feature.enabled?(:use_cmark_renderer) ? RENDER_OPTIONS_C : RENDER_OPTIONS_RUBY
        end

        def render_options_sourcepos
          render_options_no_sourcepos + [
            :SOURCEPOS # enable embedding of source position information
          ].freeze
        end
      end
    end
  end
end