{{- /* Last modified: 2023-03-27T11:06:45-07:00 */}}

{{- /*
Copyright 2023 Veriphor LLC

Licensed under the Apache License, Version 2.0 (the "License"); you may not
use this file except in compliance with the License. You may obtain a copy of
the License at

https://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
License for the specific language governing permissions and limitations under
the License.
*/}}

{{- /*
Renders a table of contents by parsing rendered content.

In site configuration, set the default start level, end level, and the minimum
number of headings required to show the table of contents:

    [params.toc]
    startLevel = 2      # default is 2
    endLevel = 3        # default is 3
    minNumHeadings = 2  # default is 2

To display the table of contents on a page:

    +++
    title = 'Post 1'
    toc = true
    +++

To display the table of contents on a page, and override one or more of the
default settings:

    +++
    title = 'Post 1'
    [toc]
    startLevel = 2      # default is 2
    endLevel = 3        # default is 3
    minNumHeadings = 2  # default is 2
    +++

Change or localize the title with a "toc_title" key in your i18n file(s).

Start with these basic CSS rules to style the table of contents:

    a.toc-item {
      display: block;
    }
    a.toc-level-1 {
      margin-left: 0em;
    }
    a.toc-level-2 {
      margin-left: 1em;
    }
    a.toc-level-3 {
      margin-left: 2em;
    }
    a.toc-level-4 {
      margin-left: 3em;
    }
    a.toc-level-5 {
      margin-left: 4em;
    }
    a.toc-level-6 {
      margin-left: 5em;
    }

@context {page} .

@returns {template.HTML}

@example {{ partial "toc-parse-content.html" . }}
*/}}

{{- /* Initialize. */}}
{{- $partialName := "toc-parse-content" }}

{{- /* Verify minimum required version. */}}
{{- $minHugoVersion := "0.111.3" }}
{{- if lt hugo.Version $minHugoVersion }}
  {{- errorf "The %q partial requires Hugo v%s or later." $partialName $minHugoVersion }}
{{- end }}

{{- /* Determine content path for warning and error messages. */}}
{{- $contentPath := "" }}
{{- with .File }}
  {{- $contentPath = .Path }}
{{- else }}
  {{- $contentPath = .Path }}
{{- end }}

{{- /* Get configuration. */}}
{{- $minNumHeadings := 1 }}
{{- $startLevel := 2 }}
{{- $endLevel := or ($.Param "toc.endLevel" | int) 6 }}

{{- /* Get headings. */}}
{{- $headings := slice }}
{{- $ids := slice }}
{{- range findRE `(?is)<h\d.*?</h\d>` .Content }}
  {{- $level := substr . 2 1 | int }}
  {{- if and (ge $level $startLevel) (le $level $endLevel) }}
    {{- $text := replaceRE `(?is)<h\d.*?>(.+?)</h\d>` "$1" . }}
    {{- $text = trim $text " " | plainify }}
    {{- $id := "" }}
    {{- if findRE `\s+id=` . }}
      {{- $id = replaceRE `(?is).+?\s+id=(?:\x22|\x27)?(.*?)(?:\x22|\x27)?[\s>].+` "$1" . }}
      {{- $ids = $ids | append $id }}
      {{- if not $id }}
        {{- errorf "The %q partial detected that the %q heading has an empty ID attribute. See %s" $partialName $text $contentPath }}
      {{- end }}
    {{- else }}
      {{- errorf "The %q partial detected that the %q heading does not have an ID attribute. See %s" $partialName $text $contentPath }}
    {{- end }}
    {{- $headings = $headings | append (dict "id" $id "level" $level "text" $text) }}
  {{- end }}
{{- end }}

{{- /* Check for duplicate heading IDs. */}}
{{- $unique := slice }}
{{- $duplicates := slice }}
{{- range $ids }}
  {{- if in $unique . }}
    {{- $duplicates = $duplicates | append . }}
  {{- else }}
    {{- $unique = $unique | append . }}
  {{- end }}
{{- end }}
{{- with $duplicates }}
  {{- errorf "The %q partial detected duplicate heading IDs (%s) in %s" $partialName (delimit . ", ") $contentPath }}
{{- end }}

{{- /* Render */}}
{{ $page := . }}
{{- if (index .Params "table-of-contents") }}
  {{- with $headings }}
    {{- if ge (len .) $minNumHeadings }}
  <nav class="toc">
  <ul>
    {{- $counter := dict "h2" 0 "h3" 0 "h4" 0 "h5" 0 "h6" 0 }}
    {{- range . }}
      {{- $level := .level }}
      {{- range $i, $l := (seq (add $level 1) 6) }}
        {{- $counter = merge $counter (dict (printf "h%d" $l) 0) }}
      {{- end }}
      {{- $counter = merge $counter (dict (printf "h%d" $level) (add (index $counter (printf "h%d" $level)) 1)) }}
      {{- $num := slice }}
      {{- range $i, $l := (seq 2 6) }}
        {{- if ge $level $l }}
          {{- $num = $num | append (index $counter (printf "h%d" $l)) }}
        {{- end }}
      {{- end }}

      <li>
        <a href="{{ $.RelPermalink }}#{{ .id }}" class="toc-item toc-level-{{ sub .level 1 }}">
          {{ $isset := (isset $page.Params "toc-auto-numbering") }}
          {{ $local := (index $page.Params "toc-auto-numbering") }}
          {{ $global := (index $.Site.Params "toc-auto-numbering") }}
          {{ if (or (and $isset $local) (and $global (not $isset)) ) }}
          {{- range $num }}{{- if ne . 0 }}{{- . }}.{{- end }}{{- end }}
          {{ end }} {{ .text }}
        </a>
      </li>
    {{- end }}
  {{- end }}
  </ul>
  </nav>
  {{- end }}
{{- end }}