html: Allow limiting level of headlines to be included in toc

The org mode toc OPTION does not just support true/false - it also allows
specifying the max headline level [1] to be included in the toc.

[1] headline level as seen in org mode - not the html tag level

org/document.go

@@ -169,7 +169,7 @@ func (d *Document) Get(key string) string {
 // - < (export timestamps)
 // - e (export org entities)
 // - f (export footnotes)
-// - toc (export table of content)
+// - toc (export table of content. an int limits the included org headline lvl)
 // - todo (export headline todo status)
 // - pri (export headline priority)
 // - tags (export headline tags)

org/html_writer.go

@@ -5,6 +5,7 @@ import (
 	"html"
 	"log"
 	"regexp"
+	"strconv"
 	"strings"
 	"unicode"
 
@@ -184,24 +185,32 @@ func (w *HTMLWriter) WriteFootnotes(d *Document) {
 
 func (w *HTMLWriter) WriteOutline(d *Document) {
 	if w.document.GetOption("toc") != "nil" && len(d.Outline.Children) != 0 {
+		maxLvl, _ := strconv.Atoi(w.document.GetOption("toc"))
 		w.WriteString("<nav>\n<ul>\n")
 		for _, section := range d.Outline.Children {
-			w.writeSection(section)
+			w.writeSection(section, maxLvl)
 		}
 		w.WriteString("</ul>\n</nav>\n")
 	}
 }
 
-func (w *HTMLWriter) writeSection(section *Section) {
+func (w *HTMLWriter) writeSection(section *Section, maxLvl int) {
+	if maxLvl != 0 && section.Headline.Lvl > maxLvl {
+		return
+	}
 	// NOTE: To satisfy hugo ExtractTOC() check we cannot use `<li>\n` here. Doesn't really matter, just a note.
 	w.WriteString("<li>")
 	h := section.Headline
 	title := cleanHeadlineTitleForHTMLAnchorRegexp.ReplaceAllString(w.WriteNodesAsString(h.Title...), "")
 	w.WriteString(fmt.Sprintf("<a href=\"#%s\">%s</a>\n", h.ID(), title))
-	if len(section.Children) != 0 {
+	hasChildren := false
+	for _, section := range section.Children {
+		hasChildren = hasChildren || maxLvl == 0 || section.Headline.Lvl <= maxLvl
+	}
+	if hasChildren {
 		w.WriteString("<ul>\n")
 		for _, section := range section.Children {
-			w.writeSection(section)
+			w.writeSection(section, maxLvl)
 		}
 		w.WriteString("</ul>\n")
 	}

org/testdata/headlines.html

@@ -14,6 +14,8 @@
 </li>
 <li><a href="#headline-7">malformed property drawer</a>
 </li>
+<li><a href="#headline-8">level limit for headlines to be included in the table of contents</a>
+</li>
 </ul>
 </nav>
 <h2 id="headline-1">
@@ -88,3 +90,22 @@ not a property
 <p>
 :END:
 </p>
+<h2 id="headline-8">
+level limit for headlines to be included in the table of contents
+</h2>
+<p>
+The toc option allows setting a <a href="https://orgmode.org/manual/Export-settings.html">level limit</a>. For this file we set it to 1 - which means that the following headlines
+won&#39;t be included in the table of contents.
+</p>
+<h3 id="headline-9">
+headline 2 not in toc
+</h3>
+<h4 id="headline-10">
+headline 3 not in toc
+</h4>
+<h3 id="headline-11">
+anoter headline 2 not in toc
+</h3>
+<p>
+you get the gist…
+</p>

org/testdata/headlines.org

@@ -1,4 +1,5 @@
 #+SETUPFILE: setup_file_org
+#+OPTIONS: toc:1
 * Simple Headline [1/2]
 - [X] checked
 - [ ] unchecked
@@ -31,3 +32,10 @@ By default =EXCLUDE_TAGS= is just =:noexport:=.
 :PROPERTIES:
 not a property
 :END:
+* level limit for headlines to be included in the table of contents
+The toc option allows setting a [[https://orgmode.org/manual/Export-settings.html][level limit]]. For this file we set it to 1 - which means that the following headlines
+won't be included in the table of contents.
+** headline 2 not in toc
+*** headline 3 not in toc
+** anoter headline 2 not in toc
+you get the gist...

org/testdata/headlines.pretty_org

@@ -1,4 +1,5 @@
 #+SETUPFILE: setup_file_org
+#+OPTIONS: toc:1
 * Simple Headline [1/2]
 - [X] checked
 - [ ] unchecked
@@ -31,3 +32,10 @@ By default =EXCLUDE_TAGS= is just =:noexport:=.
 :PROPERTIES:
 not a property
 :END:
+* level limit for headlines to be included in the table of contents
+The toc option allows setting a [[https://orgmode.org/manual/Export-settings.html][level limit]]. For this file we set it to 1 - which means that the following headlines
+won't be included in the table of contents.
+** headline 2 not in toc
+*** headline 3 not in toc
+** anoter headline 2 not in toc
+you get the gist...

org/testdata/misc.html

@@ -131,6 +131,7 @@ src block
 <div class="highlight">
 <pre>
 #+SETUPFILE: setup_file_org
+#+OPTIONS: toc:1
 * Simple Headline [1/2]
 - [X] checked
 - [ ] unchecked
@@ -163,6 +164,13 @@ By default =EXCLUDE_TAGS= is just =:noexport:=.
 :PROPERTIES:
 not a property
 :END:
+* level limit for headlines to be included in the table of contents
+The toc option allows setting a [[https://orgmode.org/manual/Export-settings.html][level limit]]. For this file we set it to 1 - which means that the following headlines
+won&#39;t be included in the table of contents.
+** headline 2 not in toc
+*** headline 3 not in toc
+** anoter headline 2 not in toc
+you get the gist...
 </pre>
 </div>
 </div>