index.html

<h4>Cycle PrevInSection/NextInSection Pages in Hugo Subsection</h4>

<p>Starting Point: Content organization</p>

<pre style="font-size: .8rem">
content/
|── _index.md
|── about.md
|── contact.md
└── portfolio/
    |── _index.md
    ├── project01/
    │   ├── _index.md
    │   ├── example01.md
    │   ├── example02.md
    │   ├── example03.md
    │   ├── example04.md
    │   ├── example05.md
    ├── project02/
    ...
</pre>

<hr>

<p>Psuedo Code<br><small>(Note default Hugo Prev/Next logic is +/-.<br>.Prev on the last page in a collection returns nil.<br>.Next on the first page in a collection returns nil.)</small></p>

<pre style="font-size: .8rem">
  if (current page is first page)
    Prev: link to last page
    Next: link to .PrevInSection
  else if (current page is last page)
    Prev: link to .NextInSection
    Next: link to first page
  else
    Prev: link to .NextInSection
    Next: link to .PrevInSection
  end
</pre>

<hr>

{{ $related := (.Site.RegularPages.RelatedTo ( keyVals "project" .Params.project)).ByTitle }}
{{ $currentPage := . }}

<p>Test if this page is first/last/current in subsection</p>

{{ with $related }}
<ol class="related-examples">
  {{ range $index, $element := $related }}
  {{ if eq (add $index 1) (len $related) }}
  <li>LAST <a href="{{ .RelPermalink }}" {{ if (eq $currentPage.RelPermalink .RelPermalink) }} class="current" {{ end }}>{{ .Title }}</a></li>
  {{ else if eq . (index $related 0) }}
  <li>FIRST <a href="{{ .RelPermalink }}" {{ if (eq $currentPage.RelPermalink .RelPermalink) }} class="current" {{ end }}>{{ .Title }}</a></li>
  {{ else }}
  <li><a href="{{ .RelPermalink }}" {{ if (eq $currentPage.RelPermalink .RelPermalink) }} class="current" {{ end }}>{{ .Title }}</a></li>
  {{ end }}
  {{ end }}
</ol>
{{ end }}

<hr>

<p>Add 2 more variables for code clarity</p>

{{ $firstItem := index $related 0 }}
{{ $lastItem := index $related (sub (len $related) 1) }}

{{ with $related }}
<ol class="related-examples">
  {{ range . }}
  {{ if eq . $lastItem }}
  <li>LAST <a href="{{ .RelPermalink }}" {{ if (eq $currentPage.RelPermalink .RelPermalink) }} class="current" {{ end }}>{{ .Title }}</a></li>
  {{ else if eq . $firstItem }}
  <li>FIRST <a href="{{ .RelPermalink }}" {{ if (eq $currentPage.RelPermalink .RelPermalink) }} class="current" {{ end }}>{{ .Title }}</a></li>
  {{ else }}
  <li><a href="{{ .RelPermalink }}" {{ if (eq $currentPage.RelPermalink .RelPermalink) }} class="current" {{ end }}>{{ .Title }}</a></li>
  {{ end }}
  {{ end }}
</ol>
{{ end }}

<hr>

<p>Example 1</p>

{{ if eq $currentPage $firstItem }}
Previous: <a href="{{ $lastItem.RelPermalink }}">{{ $lastItem.Title }}</a>
<br>
{{ if $currentPage.PrevInSection }}
Next: <a href="{{ $currentPage.PrevInSection.RelPermalink }}">{{ $currentPage.PrevInSection.Title }}</a>
{{ end }}
{{ else if eq $currentPage $lastItem }}
Previous: <a href="{{ .NextInSection.RelPermalink }}">{{ .NextInSection.Title }}</a>
<br>
Next: <a href="{{ $firstItem.RelPermalink }}">{{ $firstItem.Title }}</a>
{{ else }}
{{ if .NextInSection }}
Previous: <a href="{{ .NextInSection.RelPermalink }}">{{ .NextInSection.Title }}</a>
{{ end }}
<br>
{{ if .PrevInSection }}
Next: <a href="{{ .PrevInSection.RelPermalink }}">{{ .PrevInSection.Title }}</a>
{{ end }}
{{ end }}

<hr>

<p>Final Result: Example 2</p>

<p style="text-align: center;">
  {{ if eq $currentPage $firstItem }}
  &lt; <a href="{{ $lastItem.RelPermalink }}">Prev</a>
  |
  {{ if $currentPage.PrevInSection }}
  <a href="{{ $currentPage.PrevInSection.RelPermalink }}">Next</a> &gt;
  {{ end }}
  {{ else if eq $currentPage $lastItem }}
  &lt; <a href="{{ .NextInSection.RelPermalink }}">Prev</a>
  |
  <a href="{{ $firstItem.RelPermalink }}">Next</a> &gt;
  {{ else }}
  {{ if .NextInSection }}
  &lt; <a href="{{ .NextInSection.RelPermalink }}">Prev</a>
  {{ end }}
  |
  {{ if .PrevInSection }}
  <a href="{{ .PrevInSection.RelPermalink }}">Next</a> &gt;
  {{ end }}
  {{ end }}
</p>