Support feed discovery and enumeration

This adds support for a Jinja function/filter, “atom_feeds”, which can be used
to enumerate all feeds defined in the project (“atom_feeds()”), or those
relevant to the page being generated (“atom_feeds(for_page=this)”).

This is convenient, e.g., to define a generic site header which automatically
displays a “subscribe” link on those pages which generate feeds.

Author: eigengrau

README.md

@@ -100,6 +100,18 @@ Link to the feed in a template like this:
 {{ 'blog@atom/main'|url }}
 ```
 
+The plugin also defines a function to enumerate all feeds or a subset of feeds
+relevant to the current page.
+
+```
+{% for feed in atom_feeds(for_page=this) %}
+    {{ feed | url }}
+{% endfor %}
+```
+
+When the argument `for_page` is omitted, the function will enumerate all feeds
+defined in your project.
+
 # Changes
 
 2016-06-02: Version 0.2. Python 3 compatibility (thanks to Dan Bauman),

lektor_atom.py

@@ -184,6 +184,9 @@ def get_atom_config(self, feed_id, key):
     def on_setup_env(self, **extra):
         self.env.add_build_program(AtomFeedSource, AtomFeedBuilderProgram)
 
+        self.env.jinja_env.filters['atom_feeds'] = self.atom_feeds
+        self.env.jinja_env.globals['atom_feeds'] = self.atom_feeds
+
         @self.env.virtualpathresolver('atom')
         def feed_path_resolver(node, pieces):
             if len(pieces) != 1:
@@ -204,3 +207,33 @@ def generate_feeds(source):
             for _id in self.get_config().sections():
                 if source.path == self.get_atom_config(_id, 'source_path'):
                     yield AtomFeedSource(source, _id, self)
+
+    def _all_feeds(self):
+        ctx = get_ctx()
+
+        feeds = []
+        for feed_id in self.get_config().sections():
+            path = self.get_atom_config(feed_id, 'source_path')
+            feed = ctx.pad.get('%s@atom/%s' % (path, feed_id))
+            if feed:
+                feeds.append(feed)
+
+        return feeds
+
+    def _feeds_for(self, page):
+        ctx = get_ctx()
+        record = page.record
+
+        feeds = []
+        for section in self.get_config().sections():
+            feed = ctx.pad.get('%s@atom/%s' % (record.path, section))
+            if feed:
+                feeds.append(feed)
+
+        return feeds
+
+    def atom_feeds(self, for_page=None):
+        if not for_page:
+            return self._all_feeds()
+        else:
+            return self._feeds_for(for_page)

tests/demo-project/configs/atom.ini

@@ -17,3 +17,13 @@ item_body_field = contents
 item_author_field = writer
 item_date_field = published
 item_model = custom-blog-post
+
+[feed-four]
+name = Feed Three (uncensored)
+source_path = /custom-blog
+filename = nsfw.xml
+item_title_field = headline
+item_body_field = contents
+item_author_field = writer
+item_date_field = published
+item_model = custom-blog-post

tests/demo-project/content/no-feed-content/contents.lr

@@ -0,0 +1,3 @@
+_model: page
+---
+contents: Buffalo buffalo Buffalo buffalo buffalo buffalo Buffalo buffalo (cf. Wikipedia)

tests/test_lektor_atom.py

@@ -1,5 +1,6 @@
 import os
 
+from lektor.context import Context
 from lxml import objectify
 
 
@@ -113,3 +114,41 @@ def test_dependencies(pad, builder, reporter):
         'configs/atom.ini',
     ])
 
+
+def feeds_from_template(pad, template):
+    with Context(pad=pad):
+        return set(
+            pad.env.jinja_env.from_string(template)
+                             .render()
+                             .split()
+        )
+
+
+def test_discover_all(pad):
+    template = r'''
+    {% for feed in atom_feeds() %}
+        {{ feed.feed_id }}
+    {% endfor %}
+    '''
+    all_feeds = set(['feed-one', 'feed-two',
+                     'feed-three', 'feed-four'])
+    feeds_discovered = feeds_from_template(pad, template)
+    assert feeds_discovered == all_feeds
+
+
+def test_discover_local(pad):
+    template_blog = r'''
+    {% for feed in atom_feeds(for_page=site.get('/custom-blog')) %}
+        {{ feed.feed_id }}
+    {% endfor %}
+    '''
+    feeds_blog = feeds_from_template(pad, template_blog)
+    assert feeds_blog == set(['feed-three', 'feed-four'])
+
+    template_noblog = r'''
+    {% for feed in atom_feeds(for_page=site.get('/no-feed-content')) %}
+        {{ feed.feed_id }}
+    {% endfor %}
+    '''
+    feeds_noblog = feeds_from_template(pad, template_noblog)
+    assert len(feeds_noblog) == 0