From c82d35c213e22f51590c006ea0990a528540772b Mon Sep 17 00:00:00 2001
From: John-Mark Gurney <jmg@funkthat.com>
Date: Fri, 16 Apr 2021 16:02:06 -0700
Subject: [PATCH] add a filter that will detect bare anchors and add a relative
 path..

The issue is that w/ mark'd sections, the anchors will be relative
to the imported doc and NOT the source document..  So the markdown
toc feature that adds anchors to header tags would create permanent
links that won't work in the long term.  This fixes them up.
---
 encthenet_plugins.py | 62 ++++++++++++++++++++++++++++++++++++++++++++
 layout/blog.j2       |  2 +-
 site.yaml            |  3 +++
 3 files changed, 66 insertions(+), 1 deletion(-)
 create mode 100644 encthenet_plugins.py

diff --git a/encthenet_plugins.py b/encthenet_plugins.py
new file mode 100644
index 0000000..86f9502
--- /dev/null
+++ b/encthenet_plugins.py
@@ -0,0 +1,62 @@
+from jinja2 import contextfilter, environmentfilter
+from jinja2.ext import Extension
+
+from io import StringIO
+from lxml import etree
+
+@contextfilter
+def rellinktoabs(context, value):
+	env = context.environment
+
+	# get the path for this context
+	rel_path = context['resource'].relative_path
+	content_url = env.globals['content_url'](context, rel_path)
+
+	html = etree.HTML(value)
+
+	# get all the fragment urls
+	r = html.xpath("//a[@href[starts-with(.,'#')]]")
+
+	for i in r:
+		# prefix them w/ the content_url
+		i.attrib['href'] = content_url + i.attrib['href']
+
+	return etree.tostring(html, encoding='unicode', method='html')
+
+# mostly copied from hyde.ext.templates.jinja.py Markdown
+# and using docs from:
+# https://jinja.palletsprojects.com/en/2.10.x/extensions/#example-extension
+# to get the filter installed
+
+class RelLinktoAbs(Extension):
+	"""
+	A wrapper around the rellinktoabs filter for syntactic sugar.
+	"""
+	tags = { 'rellinktoabs' }
+
+	def __init__(self, env):
+		super(RelLinktoAbs, self).__init__(env)
+
+		env.filters['rellinktoabs'] = rellinktoabs
+
+	def parse(self, parser):
+		"""
+		Parses the statements and defers to the callback
+		for rellinktoabs processing.
+		"""
+
+		lineno = next(parser.stream).lineno
+		body = parser.parse_statements(['name:endrellinktoabs'], drop_needle=True)
+
+		return nodes.CallBlock(
+		    self.call_method('_render_rellinktoabs'),
+		    [], [], body).set_lineno(lineno)
+
+	def _render_rellinktoabs(self, caller=None):
+		"""
+		Calls the rellinktoabs filter to transform the output.
+		"""
+		if not caller:
+			return ''
+		output = caller().strip()
+		return rellinktoabs(self.environment, output)
diff --git a/layout/blog.j2 b/layout/blog.j2
index 4c7cc83..b7abd26 100644
--- a/layout/blog.j2
+++ b/layout/blog.j2
@@ -23,7 +23,7 @@
 {% endif %}
 <div class="clear"/>
 <section>
-{% filter markdown|typogrify -%}
+{% filter markdown|typogrify|rellinktoabs -%}
 {% block post -%}{%- endblock %}
 {%- endfilter %}
 </section>
diff --git a/site.yaml b/site.yaml
index 377741f..fd13efd 100644
--- a/site.yaml
+++ b/site.yaml
@@ -13,6 +13,9 @@ context:
     data:
         tweet_via: encthenet
         title: encthenet ramblings
+jinja2:
+    extensions:
+        - encthenet_plugins.RelLinktoAbs
 markdown:
     extensions:
         - toc