Fix caching of social meta tags

Just use the url and the updated_at timestamp of the site to generate
the cache key for the head elements. Whilst this will mean that we add
cached head elements for pages that will be only viewed once such as
the signature validation page the LRU nature of Memcached means they
will be evicted first.

Also if the @Petition variable is set then use it for setting the meta
tags so that even if someone shares a thank you page or a signature
validation page then the URL shared by Facebook will be the main
petition url and not the url of the page they last visited.

Author: pixeltrix

app/helpers/cache_helper.rb

@@ -31,6 +31,7 @@ class Keys
       delegate :last_signature_at, to: :template
       delegate :petition_page?, to: :template
       delegate :page_title, to: :template
+      delegate :request, to: :template
 
       def initialize(template)
         @template = template
@@ -68,6 +69,10 @@ def site_updated_at
         Site.updated_at
       end
 
+      def url
+        request.original_url
+      end
+
       def for(keys)
         keys.map{ |key| [key, value_for(key)] }.uniq
       end

app/views/application/_social_meta.html.erb

@@ -2,32 +2,31 @@
 <%= open_graph_tag 'site_name', :site_name %>
 <%= open_graph_tag 'locale', 'en_GB' %>
 <%= open_graph_tag 'image', 'os-social/opengraph-image.png' %>
-<% if petition_page? %>
-<%= open_graph_tag 'url', petition_url(@petition) %>
-<%= open_graph_tag 'type', 'article' %>
-<%= open_graph_tag 'title', :title, petition: @petition.action %>
-<%= open_graph_tag 'description', @petition.background %>
-<% elsif archived_petition_page? %>
+<% if archived_petition_page? %>
 <%= open_graph_tag 'url', archived_petition_url(@petition) %>
 <%= open_graph_tag 'type', 'article' %>
 <%= open_graph_tag 'title', :archived_title, petition: @petition.title %>
 <%= open_graph_tag 'description', @petition.description %>
+<% elsif defined?(@petition) %>
+<%= open_graph_tag 'url', petition_url(@petition) %>
+<%= open_graph_tag 'type', 'article' %>
+<%= open_graph_tag 'title', :title, petition: @petition.action %>
+<%= open_graph_tag 'description', @petition.background %>
 <% else %>
 <%= open_graph_tag 'url', request.original_url %>
 <%= open_graph_tag 'type', 'website' %>
 <%= open_graph_tag 'title', page_title %>
 <% end %>
-
 <!-- Twitter -->
 <%= twitter_card_tag 'card', 'summary' %>
 <%= twitter_card_tag 'site', '@hocpetitions' %>
 <%= twitter_card_tag 'image', 'os-social/opengraph-image.png' %>
-<% if petition_page? %>
-<%= twitter_card_tag 'title', :title, petition: @petition.action %>
-<%= twitter_card_tag 'description', @petition.background %>
-<% elsif archived_petition_page? %>
+<% if archived_petition_page? %>
 <%= twitter_card_tag 'title', :title, petition: @petition.title %>
 <%= twitter_card_tag 'description', @petition.description %>
+<% elsif defined?(@petition) %>
+<%= twitter_card_tag 'title', :title, petition: @petition.action %>
+<%= twitter_card_tag 'description', @petition.background %>
 <% else %>
 <%= twitter_card_tag 'title', page_title %>
 <% end %>

config/fragments.yml

@@ -1,11 +1,7 @@
 head:
   keys:
     - :site_updated_at
-    - :last_signature_at
-    - :petition_page
-    - :archived_petition_page
-    - :page_title
-    - :petition
+    - :url
   options:
     expires_in: 300
 

spec/helpers/cache_helper_spec.rb

@@ -156,6 +156,15 @@
       end
     end
 
+    describe "#url" do
+      let(:request) { double(:request, original_url: "/petitions/123") }
+
+      it "delegates to the request's original_url method" do
+        expect(helper).to receive(:request).and_return(request)
+        expect(keys.url).to eq("/petitions/123")
+      end
+    end
+
     describe "#method_missing" do
       it "returns an assigned variable in the template context" do
         assign('signature_count', 32)