def parse_toc(html_content):
    """
    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)
    """
    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
