code: def generate_diff_html(self):
      
      if not os.path.exists(self.resource_directory):
        os.makedirs(self.resource_directory)
      self.copy_local_includes()
      div_html = ''
      for plot_div in sorted(self.plot_files):
        with open(plot_div, 'r') as div_file:
          div_html += '\n' + div_file.read()
      template_loader = FileSystemLoader(self.get_resources_location())
      template_environment = Environment(loader=template_loader)
      template_environment.filters['sanitize_string'] = naarad.utils.sanitize_string
      diff_html = template_environment.get_template(CONSTANTS.TEMPLATE_HEADER).render(custom_stylesheet_includes=CONSTANTS.STYLESHEET_INCLUDES,
                                                                                      custom_javascript_includes=CONSTANTS.JAVASCRIPT_INCLUDES,
                                                                                      resource_path=self.resource_path,
                                                                                      report_title='naarad diff report') + '\n'
      diff_html += template_environment.get_template(CONSTANTS.TEMPLATE_DIFF_PAGE).render(diff_data=self.diff_data, plot_div_content=div_html,
                                                                                          reports=self.reports, sla_failure_list=self.sla_failure_list,
                                                                                          sla_map=self.sla_map) + '\n'
      diff_html += template_environment.get_template(CONSTANTS.TEMPLATE_FOOTER).render()
      return diff_html
docs: Generate the summary diff report html from template
      :return: generated html to be written to disk