rss: add per-tag Atom feed at /rss/tags/:tag/updates.xml

- rss#tag_updates action: filters Page.heads by tag name, default
  locale, 20 items, same caching as updates feed
- tag_updates.xml.builder: Atom feed with CGI.escapeHTML on title
  and summary, consistent with updates.xml.builder
- tags/show.html.erb: add subscription link above article list
- routes: two routes per existing pattern (format-less + .:format
  constrained to /xml/)

2 files changed, 33 insertions, 0 deletions

diff --git a/app/views/rss/tag_updates.xml.builder b/app/views/rss/tag_updates.xml.builder
new file mode 100644
index 0000000..6491cfc
--- /dev/null
+++ b/app/views/rss/tag_updates.xml.builder
@@ -0,0 +1,27 @@
+xml.instruct!
+
+xml.feed(:xmlns => "http://www.w3.org/2005/Atom", "xml:base" => @host) do
+  xml.title("Chaos Computer Club: #{@tag}")
+  xml.link(:href => "#{@host}/")
+  xml.link(:rel => "self", :href => "#{@host}/rss/tags/#{@tag}/updates.xml")
+  xml.updated(@items.first.published_at.xmlschema) unless @items.empty?
+  xml.author do
+    xml.name("Chaos Computer Club e. V.")
+  end
+  xml.id("#{@host}/rss/tags/#{@tag}/updates")
+
+  @items.each do |item|
+    xml.entry do
+      xml.title(CGI.escapeHTML(item.title.to_s))
+      xml.link(
+        :href => content_url(:page_path => item.node.unique_path),
+        :rel  => "alternate",
+        :type => "text/html"
+      )
+      xml.id(content_url(:page_path => item.node.feed_id))
+      xml.updated(item.updated_at.xmlschema)
+      xml.published(item.published_at.xmlschema)
+      xml.summary(CGI.escapeHTML(item.abstract.to_s))
+    end
+  end
+end
diff --git a/app/views/tags/show.html.erb b/app/views/tags/show.html.erb
index b09cc15..3a23522 100644
--- a/app/views/tags/show.html.erb
+++ b/app/views/tags/show.html.erb
@@ -1,5 +1,11 @@
 <h2><%= t(:show_tag_headline) %> »<%=h @tag %>«</h2>
 
+<p class="feed_link">
+  <%= link_to "Subscribe to updates tagged »#{@tag}«",
+        rss_tag_url(:tag => @tag, :format => :xml),
+        :type => "application/atom+xml" %>
+</p>
+
 <%= 
     render(
       :partial => 'custom/partials/no_date_and_author',