{{/* Build a flat list of all pages from nav data (handles both flat
     items and grouped items) and find prev/next. */}}
{{ $allPages := slice }}
{{ range hugo.Data.nav }}
  {{ range .items }}{{ $allPages = $allPages | append . }}{{ end }}
  {{ range .groups }}
    {{ range .items }}{{ $allPages = $allPages | append . }}{{ end }}
  {{ end }}
{{ end }}

{{ $currentURL := .RelPermalink }}
{{ $currentIndex := -1 }}
{{ range $i, $item := $allPages }}
  {{ if eq $currentURL (relURL (strings.TrimPrefix "/" $item.url)) }}
    {{ $currentIndex = $i }}
  {{ end }}
{{ end }}

{{ if ge $currentIndex 0 }}
<div class="page-nav">
  {{ if gt $currentIndex 0 }}
  {{ $prev := index $allPages (sub $currentIndex 1) }}
  <a href="{{ relURL (strings.TrimPrefix "/" $prev.url) }}">
    <span class="nav-label">← Previous</span>
    <span class="nav-title">{{ $prev.title }}</span>
  </a>
  {{ else }}
  <span></span>
  {{ end }}

  {{ if lt (add $currentIndex 1) (len $allPages) }}
  {{ $next := index $allPages (add $currentIndex 1) }}
  <a class="next" href="{{ relURL (strings.TrimPrefix "/" $next.url) }}">
    <span class="nav-label">Next →</span>
    <span class="nav-title">{{ $next.title }}</span>
  </a>
  {{ end }}
</div>
{{ end }}