{% comment %}
  Per-page version switcher (document pages only; rendered in the site header).

  Resolves each target channel honestly, in order:
    1. same channel-relative URL exists in the target channel,
    2. otherwise the page's WSTG ID exists there (renamed/renumbered path),
    3. otherwise the nearest existing ancestor section,
    4. otherwise the target channel's home ("no direct equivalent").
  Targets come from _data/version_map.yaml (generated by prepare_site.py),
  so a target is never invented for a page that does not exist.
{% endcomment %}
{% if page.channel_label and page.channel_path and site.data.version_map %}
{% assign vmap = site.data.version_map %}
{% assign cur_map = vmap.by_channel[page.collection_name] %}
{% assign chan_prefix = '/' | append: page.channel_path %}
{% assign rel = page.url | remove_first: chan_prefix %}
{% assign cur_id = cur_map[rel] %}
{% comment %} Badge tone reuses the channel banner colour classes (light + dark). {% endcomment %}
{% if page.collection_name == "latest" %}
  {% assign badge_tone = "latest" %}
{% elsif page.collection_name == "stable" or page.channel_label == site.stable_version %}
  {% assign badge_tone = "stable" %}
{% else %}
  {% assign badge_tone = "past" %}
{% endif %}
<details class="version-switcher version-switcher--{{ badge_tone }}">
  <summary class="version-switcher-summary channel-banner--{{ badge_tone }}">
    <span class="version-switcher-badge">{{ page.channel_label }}</span>
    <span class="version-switcher-caret" aria-hidden="true">&#9662;</span>
    <span class="visually-hidden">Switch version</span>
  </summary>
  <div class="version-switcher-panel">
    <p class="version-switcher-heading">Switch version</p>
    <ul class="version-switcher-list">
      {% assign vkeys = "latest,v42,v41" | split: "," %}
      {% assign vlabels = "Latest,v4.2,v4.1" | split: "," %}
      {% assign vpaths = "latest,v4.2,v4.1" | split: "," %}
      {% for vk in vkeys %}
        {% assign vlabel = vlabels[forloop.index0] %}
        {% assign vpath = vpaths[forloop.index0] %}
        {% if vk == page.collection_name %}
        <li class="version-switcher-item is-current">
          <span class="version-switcher-version">{{ vlabel }}</span>
          <span class="version-switcher-note">(You are here)</span>
        </li>
        {% else %}
          {% assign tmap = vmap.by_channel[vk] %}
          {% assign exact = tmap[rel] %}
          {% assign target = nil %}
          {% assign note = nil %}
          {% if exact != nil %}
            {% assign target = "/" | append: vpath | append: rel %}
            {% assign note = "Same page" %}
          {% endif %}
          {% if target == nil and cur_id and cur_id != "" %}
            {% assign byid = vmap.by_id[cur_id] %}
            {% assign id_url = byid[vk] %}
            {% if id_url %}
              {% assign target = id_url %}
              {% assign note = "Same scenario (renamed)" %}
            {% endif %}
          {% endif %}
          {% if target == nil %}
            {% comment %} Walk up to the nearest ancestor section that exists. {% endcomment %}
            {% assign segs = rel | split: "/" %}
            {% for i in (1..5) %}
              {% if target == nil %}
                {% assign n = segs | size | minus: 1 %}
                {% if n > 0 %}
                  {% assign segs = segs | slice: 0, n %}
                  {% assign probe = segs | join: "/" | append: "/" %}
                  {% if probe != "/" and tmap[probe] != nil %}
                    {% assign target = "/" | append: vpath | append: probe %}
                    {% assign note = "Nearest section" %}
                  {% endif %}
                {% endif %}
              {% endif %}
            {% endfor %}
          {% endif %}
          {% if target == nil %}
            {% assign target = "/" | append: vpath | append: "/" %}
            {% assign note = "No direct equivalent" %}
          {% endif %}
        {% if vk == "v42" %}
          {% assign v42_target = target %}
        {% endif %}
        <li class="version-switcher-item">
          <a class="version-switcher-version" href="{{ site.baseurl }}{{ target }}">{{ vlabel }}</a>
          <span class="version-switcher-note">({{ note }})</span>
        </li>
        {% endif %}
      {% endfor %}
      {% comment %}
        Stable is a path-preserving alias of v4.2 (every /stable/ page redirects
        there), so reuse the resolved v4.2 target under the /stable/ prefix.
      {% endcomment %}
      {% if page.collection_name == "v42" %}
        {% assign stable_rel = rel %}
      {% else %}
        {% assign stable_rel = v42_target | remove_first: "/v4.2" %}
      {% endif %}
      <li class="version-switcher-item">
        <a class="version-switcher-version" href="{{ site.baseurl }}/stable{{ stable_rel }}">Stable</a>
        <span class="version-switcher-note">(Now points to {{ site.stable_version }})</span>
      </li>
    </ul>
  </div>
</details>
{% endif %}