website/layouts/partials/page_navigation.html

{{ $current := .context }}

<!-- choose different bottom up step -->
<!-- in this case page.parent is index -->
{{ $g_parent := "" }}
{{ if $current.IsPage }}
{{ $g_parent = $current.Parent.Parent }}
{{ else }}
{{ $g_parent = $current.Parent}}
{{ end }}

<!-- SECTION1 -->
<!-- important! here we need call .Pages to include both pure page and _index -->
{{ $p_section := $g_parent.Pages.ByWeight }}
{{ $length := len $p_section }}
<!-- page prev -->
{{ if .prev }}
{{ $first := index $p_section 0}}

<!-- check if is already the first section -->
<!-- if is first section,we need to bottom up -->
{{ if $current.InSection $first.CurrentSection }}
<!-- bottom up -->
{{ partial "page_navigation" (dict "context" $g_parent "prev" true)}}

<!--if not the first section just go to pre section last page (last page of pre section of p_section)-->
{{else}}

<!-- find current page's section position -->
{{ $curIndex := 0 }}
{{ range $i, $p_sec := $p_section}}
{{ if eq $p_sec $current.CurrentSection}}
{{ $curIndex = $i }}
{{ end }}
{{ end }}

{{ $prevPage := index $p_section (sub $curIndex 1) }}
{{ partial "findLastInPreSection" $prevPage}}

{{ end }} <!-- close of check page prev bottom up -->
<!-- SECTION1 -->

<!-- page next -->
{{ else }}

<!-- SECTION2 -->
{{ $last := index $p_section (sub $length 1)}}

<!-- if is last section,we need to bottom up -->
{{ if $current.InSection $last.CurrentSection }}

<!-- bottom up -->
{{ partial "page_navigation" (dict "context" $g_parent "prev" false)}}

<!--if not the last section just go to next section -->
{{ else }}

{{ $curIndex := 0 }}
{{ range $i, $p_sec := $p_section}}
{{ if eq $p_sec $current.CurrentSection}}
{{ $curIndex = $i }}
{{ end }}
{{ end }}

{{ $nextPage := index $p_section (add $curIndex 1) }}
{{ partial "findFirstInNextSection" $nextPage}}

{{ end }} <!-- close of check next bottom up -->
<!-- SECTION2 -->

{{ end }}