Extract commentable_path to an initializer

By doing so and including it in ActionDispatch::Routing::UrlFor, we make
it available in controllers, helpers and specs, and so we can remove the
duplication we had there with methods dealing with the same problem.

Even if monkey-patching is ugly, using a different module and executing
ActionDispatch::Routing::UrlFor.send(:include, MyModule) wouldn't make
the method available in the controller.

app/controllers/notifications_controller.rb

@@ -36,19 +36,11 @@ class NotificationsController < ApplicationController
   end
 
   private
-
     def linkable_resource_path(notification)
-      case notification.linkable_resource.class.name
+      if notification.linkable_resource.is_a?(AdminNotification)
-      when "Budget::Investment"
+        notification.linkable_resource.link || notifications_path
-        budget_investment_path @notification.linkable_resource.budget, @notification.linkable_resource
-      when "Topic"
-        community_topic_path @notification.linkable_resource.community, @notification.linkable_resource
       else
-        if @notification.linkable_resource.is_a?(AdminNotification)
+        polymorphic_hierarchy_path(notification.linkable_resource)
-          @notification.linkable_resource.link || notifications_path
-        else
-          url_for @notification.linkable_resource
-        end
       end
     end
 

app/helpers/comments_helper.rb

@@ -41,22 +41,7 @@ module CommentsHelper
   end
 
   def commentable_path(comment)
-    commentable = comment.commentable
+    polymorphic_hierarchy_path(comment.commentable)
-
-    case comment.commentable_type
-    when "Budget::Investment"
-      budget_investment_path(commentable.budget_id, commentable)
-    when "Legislation::Question"
-      legislation_process_question_path(commentable.process, commentable)
-    when "Legislation::Annotation"
-      legislation_process_draft_version_annotation_path(commentable.draft_version.process, commentable.draft_version, commentable)
-    when "Topic"
-      community_topic_path(commentable.community, commentable)
-    when "Legislation::Proposal"
-      legislation_process_proposal_path(commentable.legislation_process_id, commentable)
-    else
-      commentable
-    end
   end
 
   def user_level_class(comment)

config/initializers/routes_hierarchy.rb

@@ -0,0 +1,58 @@
+# This module is expanded in order to make it easier to use polymorphic
+# routes with nested resources.
+# HACK: is there a way to avoid monkey-patching here? Using helpers is
+# a similar use of a global namespace too...
+module ActionDispatch::Routing::UrlFor
+  def resource_hierarchy_for(resource)
+    case resource.class.name
+    when "Budget::Investment"
+      [resource.budget, resource]
+    when "Legislation::Annotation"
+      [resource.draft_version.process, resource.draft_version, resource]
+    when "Legislation::Proposal", "Legislation::Question"
+      [resource.process, resource]
+    when "Topic"
+      [resource.community, resource]
+    else
+      resource
+    end
+  end
+
+  def polymorphic_hierarchy_path(resource)
+    # Unfortunately, we can't use polymorphic routes because there
+    # are cases where polymorphic_path doesn't get the named routes properly.
+    # Example:
+    #
+    # polymorphic_path([legislation_proposal.process, legislation_proposal])
+    #
+    # That line tries to find legislation_process_legislation_proposal_path
+    # while the correct route would be legislation_process_proposal_path
+    #
+    # We probably need to define routes differently in order to be able to use
+    # polymorphic_path which might be possible with Rails 5.1 `direct` and
+    # `resolve` methods.
+
+    resources = resource_hierarchy_for(resource)
+
+    case resource.class.name
+    when "Budget::Investment"
+      # polymorphic_path would return budget_budget_investment_path
+      budget_investment_path(*resources)
+    when "Legislation::Annotation"
+      # polymorphic_path would return:
+      # "legislation_process_legislation_draft_version_legislation_annotation_path"
+      legislation_process_draft_version_annotation_path(*resources)
+    when "Legislation::Proposal"
+      # polymorphic_path would return legislation_process_legislation_proposal_path
+      legislation_process_proposal_path(*resources)
+    when "Legislation::Question"
+      # polymorphic_path would return legislation_process_legislation_question_path
+      legislation_process_question_path(*resources)
+    when "Poll::Question"
+      # polymorphic_path would return poll_question_path
+      question_path(*resources)
+    else
+      polymorphic_path(resources)
+    end
+  end
+end

spec/support/common_actions/notifications.rb

@@ -32,20 +32,7 @@ module Notifications
   end
 
   def path_for(resource)
-    nested_path_for(resource) || url_for([resource, only_path: true])
+    polymorphic_hierarchy_path(resource)
-  end
-
-  def nested_path_for(resource)
-    case resource.class.name
-    when "Legislation::Question"
-      legislation_process_question_path(resource.process, resource)
-    when "Legislation::Proposal"
-      legislation_process_proposal_path(resource.process, resource)
-    when "Budget::Investment"
-      budget_investment_path(resource.budget, resource)
-    else
-      false
-    end
   end
 
   def error_message(resource_model = nil)