code: def parse_toc(html_content):
      
      from flask import current_app
      from veripress.model.toc import HtmlTocParser
  
      if current_app.config['SHOW_TOC']:
          toc_parser = HtmlTocParser()
          toc_parser.feed(html_content)
          toc_html = toc_parser.toc_html(
              depth=current_app.config['TOC_DEPTH'],
              lowest_level=current_app.config['TOC_LOWEST_LEVEL'])
          toc = toc_parser.toc(
              depth=current_app.config['TOC_DEPTH'],
              lowest_level=current_app.config['TOC_LOWEST_LEVEL'])
          return toc_parser.html, toc, toc_html
      else:
          return html_content, None, None
docs: Parse TOC of HTML content if the SHOW_TOC config is true.
  
      :param html_content: raw HTML content
      :return: tuple(processed HTML, toc list, toc HTML unordered list)