{% set configured = site.extra.get("sidebar", {}).get("sections", []) %}
{% set found = namespace(names=[]) %}
{% for item in pages %}
  {% set name = item.meta.get("section") %}
  {% if name and name not in found.names %}
    {% set found.names = found.names + [name] %}
  {% endif %}
{% endfor %}
{% set ordered = namespace(names=[]) %}
{% for name in configured %}
  {% if name in found.names %}{% set ordered.names = ordered.names + [name] %}{% endif %}
{% endfor %}
{% for name in found.names | sort %}
  {% if name not in ordered.names %}{% set ordered.names = ordered.names + [name] %}{% endif %}
{% endfor %}
<aside class="sidebar">
  {% for name in ordered.names %}
    <section class="sidebar-section">
      <h2>{{ name | replace("-", " ") | title }}</h2>
      {% set items = namespace(list=[]) %}
      {% for item in pages %}
        {% if item.meta.get("section") == name %}{% set items.list = items.list + [item] %}{% endif %}
      {% endfor %}
      <ul>
        {% for item in items.list | sort(attribute="meta.order") %}
          <li{% if page is defined and item.url == page.url %} class="active"{% endif %}>
            <a href="{{ item.url }}">{{ item.meta.get("nav_title", item.title) }}</a>
          </li>
        {% endfor %}
      </ul>
    </section>
  {% endfor %}
</aside>