module GitHubParser
  extend self

  class HTMLWithPantsRenderer < Redcarpet::Render::HTML
    include Redcarpet::Render::SmartyPants

    def block_code(code, language)
      if language
        language.sub!(/\Alang(uage)?-/, '')
        %{<pre class="language-#{language}"><code class="language-#{language}">#{html_escape(code)}</code></pre>}
      else
        %{<pre><code>#{html_escape(code)}</code></pre>}
      end
    end

    private

    # This is a method copy/pasted from redcarpet/lib/redcarpet.rb
    # It's a private instance method on the Render::Safe class which inherits
    # from the HTML renderer.
    # I'm not sure why our tests expect escaped code while we inherit from the
    # HTML renderer and not the Safe renderer though.
    def html_escape(string)
      string.gsub(/['&\"<>\/]/, {
        '&' => '&amp;',
        '<' => '&lt;',
        '>' => '&gt;',
        '"' => '&quot;',
        "'" => '&#x27;',
        "/" => '&#x2F;',
      })
    end
  end

  def self.parse(markdown)
    html = github_parser.render(markdown.to_s)
    doc = Nokogiri::HTML5::DocumentFragment.parse(html)
    special_blocks(doc)
    doc
  end

  private

  def self.github_parser
    @@github_parser ||= Redcarpet::Markdown.new(HTMLWithPantsRenderer, fenced_code_blocks: true, tables: true, no_intra_emphasis: true)
  end

  def self.special_blocks(doc)
    doc.css('blockquote>p:first').each do |node|
      if match = node.inner_html.match(/\A\W*(callout|warning|note)\W/)
        node.parent.name = 'div'
        node.parent['class'] = match[1]

        new_html = node.inner_html.gsub(/\A\W*(callout|warning|note)\W/, '')

        # Assigning inner_html directly causes encoding issues in old libxml versions,
        # workaround from https://github.com/sparklemotion/nokogiri/issues/458#issuecomment-3136620
        node.children = Nokogiri::HTML.fragment(new_html, 'utf-8')
      end
    end
  end
end