{%- comment -%}
Uses _data/versions.yml to scope out version history, conditionally
preparing each expected version path, depending on whether it's a current
index, old index, or a versioned non-index page.
Display can be disabled using `versioning: false` in a page's frontmatter.
{%- endcomment -%}
{%- assign latest_qry = site.data.versions | where: "latest", "true" -%}
{%- assign latest = latest_qry[0] -%}
{%- assign name_strip = page.name | remove: ".html" -%}
{%- assign name_split = name_strip | split: "-" -%}
{%- assign path_split = page.path | split: "/" -%}
{%- if page.url == "/" -%}{%- comment -%}site homepage{% endcomment %}
  {%- assign page_type = "latest-index" -%}
  {%- assign page_version = latest.slug -%}
{%- else -%}
  {%- if name_split[0] == "index" -%}{%- comment -%}older index{% endcomment %}
    {%- assign page_type = "old-index" -%}
    {%- capture page_version -%}{{name_split[1]}}-{{name_split[2]}}{%- endcapture -%}
  {%- else -%}
    {%- if page.collection -%}
      {%- assign col = site.collections | where: "label", page.collection -%}
      {%- if col[0].type == "version" -%}
        {%- comment -%}A page in a versioned collection{% endcomment %}
        {%- assign page_type = "versioned" -%}
        {%- assign page_version = page.collection -%}
      {%- else -%}
        {%- assign page_type = "unversioned" -%}
      {%- endif -%}
    {%- else -%}
      {%- assign page_type = "unversioned" -%}
      {%- assign page_version = latest.slug -%}
    {%- endif -%}
  {%- endif -%}
{%- endif %}
{% assign page_vsn_qry = site.data.versions | where: "slug", page_version %}
{% assign page_vsn_obj = page_vsn_qry[0] | default: latest %}