From 5cea9e413c60d8dd772f08183e7ce8ab90fa88a1 Mon Sep 17 00:00:00 2001
From: Emil Bay <github@tixz.dk>
Date: Sun, 20 Sep 2015 20:14:23 +0200
Subject: [PATCH] Append identical header ids with counter

This ensures unique HTML id's in line with the HTML spec, and allows anchors
to always reference the intended header.

Fixes #27
---
 lib/renderer.js                  | 19 ++++++++++++++++++-
 test/new/identical_header_1.html |  2 ++
 test/new/identical_header_1.text |  3 +++
 test/new/identical_header_2.html |  2 ++
 test/new/identical_header_2.text |  3 +++
 5 files changed, 28 insertions(+), 1 deletion(-)
 create mode 100644 test/new/identical_header_1.html
 create mode 100644 test/new/identical_header_1.text
 create mode 100644 test/new/identical_header_2.html
 create mode 100644 test/new/identical_header_2.text

diff --git a/lib/renderer.js b/lib/renderer.js
index 89f2db2..6c2d41f 100644
--- a/lib/renderer.js
+++ b/lib/renderer.js
@@ -15,6 +15,8 @@ var defaultOptions = {
 
 function Renderer(options) {
   this.options = options || defaultOptions;
+
+  this._idCounter = {}
 }
 
 Renderer.prototype.code = function(code, lang, escaped) {
@@ -56,7 +58,22 @@ Renderer.prototype._createId = function(str) {
   } catch (e) {
     str = str.replace(/[^\w]+/g, '-');
   }
-  return str.replace(/-$/, '');
+  str = str.replace(/-$/, '');
+
+  // make sure internal id has the current id registered. If not, initialize it
+  // at 0
+  if (this._idCounter[str] === undefined) {
+    this._idCounter[str] = 0;
+  }
+
+  // Increment the internal counter for the current id, and save new count
+  var cnt = ++this._idCounter[str];
+
+  if (cnt > 1) {
+    str = str + '-' + cnt
+  }
+
+  return str;
 };
 
 Renderer.prototype.heading = function(text, level, raw) {
diff --git a/test/new/identical_header_1.html b/test/new/identical_header_1.html
new file mode 100644
index 0000000..948d697
--- /dev/null
+++ b/test/new/identical_header_1.html
@@ -0,0 +1,2 @@
+<h1 id="identical-ids">Identical IDs</h1>
+<h1 id="identical-ids-2">Identical IDs</h1>
diff --git a/test/new/identical_header_1.text b/test/new/identical_header_1.text
new file mode 100644
index 0000000..4659a36
--- /dev/null
+++ b/test/new/identical_header_1.text
@@ -0,0 +1,3 @@
+# identical ids
+
+# identical ids
diff --git a/test/new/identical_header_2.html b/test/new/identical_header_2.html
new file mode 100644
index 0000000..948d697
--- /dev/null
+++ b/test/new/identical_header_2.html
@@ -0,0 +1,2 @@
+<h1 id="identical-ids">Identical IDs</h1>
+<h1 id="identical-ids-2">Identical IDs</h1>
diff --git a/test/new/identical_header_2.text b/test/new/identical_header_2.text
new file mode 100644
index 0000000..4659a36
--- /dev/null
+++ b/test/new/identical_header_2.text
@@ -0,0 +1,3 @@
+# identical ids
+
+# identical ids