From 2dff0864f0288984446b73c8d9f60fc441f48b3d Mon Sep 17 00:00:00 2001
From: Dave Johnston <johnsto@gmail.com>
Date: Sat, 5 Apr 2014 20:42:58 +0100
Subject: [PATCH] Add header ID support and tests: # Header {#myid}

---
 block.go      | 16 ++++++++++++++--
 block_test.go | 48 ++++++++++++++++++++++++++++++++++++++++++++++++
 html.go       |  6 ++++--
 latex.go      |  2 +-
 markdown.go   |  3 ++-
 5 files changed, 69 insertions(+), 6 deletions(-)

diff --git a/block.go b/block.go
index 8681e63..e73cf02 100644
--- a/block.go
+++ b/block.go
@@ -186,6 +186,18 @@ func (p *parser) prefixHeader(out *bytes.Buffer, data []byte) int {
 	for end = i; data[end] != '\n'; end++ {
 	}
 	skip := end
+	id := ""
+	if p.flags&EXTENSION_HEADER_IDS != 0 {
+		j, k := 0, 0
+		for j = i; j < end - 1 && data[j] != '{' && data[j+1] != '#'; j++ {
+		}
+		for k = j + 1; k < end && data[k] != '}'; k++ {
+		}
+		if j < end && k < end {
+			id = string(data[j+2:k])
+			end = j
+		}
+	}
 	for end > 0 && data[end-1] == '#' {
 		end--
 	}
@@ -197,7 +209,7 @@ func (p *parser) prefixHeader(out *bytes.Buffer, data []byte) int {
 			p.inline(out, data[i:end])
 			return true
 		}
-		p.r.Header(out, work, level)
+		p.r.Header(out, work, level, id)
 	}
 	return skip
 }
@@ -1214,7 +1226,7 @@ func (p *parser) paragraph(out *bytes.Buffer, data []byte) int {
 						return true
 					}
 				}(out, p, data[prev:eol])
-				p.r.Header(out, work, level)
+				p.r.Header(out, work, level, "")
 
 				// find the end of the underline
 				for data[i] != '\n' {
diff --git a/block_test.go b/block_test.go
index ae4e1cc..20f29a1 100644
--- a/block_test.go
+++ b/block_test.go
@@ -177,6 +177,54 @@ func TestPrefixHeaderSpaceExtension(t *testing.T) {
 	doTestsBlock(t, tests, EXTENSION_SPACE_HEADERS)
 }
 
+func TestPrefixHeaderIdExtension(t *testing.T) {
+	var tests = []string{
+		"# Header 1 {#someid}\n",
+		"<h1 id=\"someid\">Header 1</h1>\n",
+
+		"# Header 1 {#someid}   \n",
+		"<h1 id=\"someid\">Header 1</h1>\n",
+
+		"# Header 1         {#someid}\n",
+		"<h1 id=\"someid\">Header 1</h1>\n",
+
+		"# Header 1 {#someid\n",
+		"<h1>Header 1 {#someid</h1>\n",
+
+		"## Header 2 {#someid}\n",
+		"<h2 id=\"someid\">Header 2</h2>\n",
+
+		"### Header 3 {#someid}\n",
+		"<h3 id=\"someid\">Header 3</h3>\n",
+
+		"#### Header 4 {#someid}\n",
+		"<h4 id=\"someid\">Header 4</h4>\n",
+
+		"##### Header 5 {#someid}\n",
+		"<h5 id=\"someid\">Header 5</h5>\n",
+
+		"###### Header 6 {#someid}\n",
+		"<h6 id=\"someid\">Header 6</h6>\n",
+
+		"####### Header 7 {#someid}\n",
+		"<h6 id=\"someid\"># Header 7</h6>\n",
+
+		"Hello\n# Header 1\nGoodbye\n",
+		"<p>Hello</p>\n\n<h1>Header 1</h1>\n\n<p>Goodbye</p>\n",
+
+		"* List\n# Header {#someid}\n* List\n",
+		"<ul>\n<li><p>List</p>\n\n<h1 id=\"someid\">Header</h1></li>\n\n<li><p>List</p></li>\n</ul>\n",
+
+		"* List\n#Header {#someid}\n* List\n",
+		"<ul>\n<li><p>List</p>\n\n<h1 id=\"someid\">Header</h1></li>\n\n<li><p>List</p></li>\n</ul>\n",
+
+		"*   List\n    * Nested list\n    # Nested header {#someid}\n",
+		"<ul>\n<li><p>List</p>\n\n<ul>\n<li><p>Nested list</p>\n\n" +
+			"<h1 id=\"someid\">Nested header</h1></li>\n</ul></li>\n</ul>\n",
+	}
+	doTestsBlock(t, tests, EXTENSION_HEADER_IDS)
+}
+
 func TestUnderlineHeaders(t *testing.T) {
 	var tests = []string{
 		"Header 1\n========\n",
diff --git a/html.go b/html.go
index 41220f5..5bba2a5 100644
--- a/html.go
+++ b/html.go
@@ -181,11 +181,13 @@ func (options *Html) GetFlags() int {
 	return options.flags
 }
 
-func (options *Html) Header(out *bytes.Buffer, text func() bool, level int) {
+func (options *Html) Header(out *bytes.Buffer, text func() bool, level int, id string) {
 	marker := out.Len()
 	doubleSpace(out)
 
-	if options.flags&HTML_TOC != 0 {
+	if id != "" {
+		out.WriteString(fmt.Sprintf("<h%d id=\"%s\">", level, id))
+	} else if options.flags&HTML_TOC != 0 {
 		// headerCount is incremented in htmlTocHeader
 		out.WriteString(fmt.Sprintf("<h%d id=\"toc_%d\">", level, options.headerCount))
 	} else {
diff --git a/latex.go b/latex.go
index da17234..8924aca 100644
--- a/latex.go
+++ b/latex.go
@@ -68,7 +68,7 @@ func (options *Latex) BlockHtml(out *bytes.Buffer, text []byte) {
 	out.WriteString("\n\\end{verbatim}\n")
 }
 
-func (options *Latex) Header(out *bytes.Buffer, text func() bool, level int) {
+func (options *Latex) Header(out *bytes.Buffer, text func() bool, level int, id string) {
 	marker := out.Len()
 
 	switch level {
diff --git a/markdown.go b/markdown.go
index 1b170e4..703bd88 100644
--- a/markdown.go
+++ b/markdown.go
@@ -39,6 +39,7 @@ const (
 	EXTENSION_TAB_SIZE_EIGHT                         // expand tabs to eight spaces instead of four
 	EXTENSION_FOOTNOTES                              // Pandoc-style footnotes
 	EXTENSION_NO_EMPTY_LINE_BEFORE_BLOCK             // No need to insert an empty line to start a (code, quote, order list, unorder list)block
+	EXTENSION_HEADER_IDS                             // specify header IDs  with {#id}
 )
 
 // These are the possible flag values for the link renderer.
@@ -133,7 +134,7 @@ type Renderer interface {
 	BlockCode(out *bytes.Buffer, text []byte, lang string)
 	BlockQuote(out *bytes.Buffer, text []byte)
 	BlockHtml(out *bytes.Buffer, text []byte)
-	Header(out *bytes.Buffer, text func() bool, level int)
+	Header(out *bytes.Buffer, text func() bool, level int, id string)
 	HRule(out *bytes.Buffer)
 	List(out *bytes.Buffer, text func() bool, flags int)
 	ListItem(out *bytes.Buffer, text []byte, flags int)