minor refactoring for proposal recommendations

app/models/proposal.rb

@@ -59,25 +59,14 @@ class Proposal < ActiveRecord::Base
   scope :public_for_api,           -> { all }
 
   def self.recommendations(user)
-    proposals_list = where("author_id != ?", user.id).unsuccessful
-    proposals_list_with_tagged = self.proposals_with_tagged(user, proposals_list)
-
-    if proposals_list_with_tagged.any?
-      proposals_list = self.proposals_not_followed_by_user(user, proposals_list_with_tagged)
-    end
-
-    # proposals_list
-    proposals_list.distinct
+    tagged_with(user.interests, any: true).
+    where("author_id != ?", user.id).
+    unsuccessful.
+    not_followed_by_user(user)
   end
 
-  def self.proposals_with_tagged(user, proposals_list)
-    proposals_list.joins(:tags).where('taggings.taggable_type = ?', self.name)
-                               .where('tags.name IN (?)', user.interests)
-  end
-
-  def self.proposals_not_followed_by_user(user, proposals_list_with_tagged)
-    followed_proposals_ids = Proposal.followed_by_user(user).pluck(:id)
-    proposals_list_with_tagged.where("proposals.id NOT IN (?)", followed_proposals_ids)
+  def self.not_followed_by_user(user)
+    where.not(id: followed_by_user(user).pluck(:id))
   end
 
   def to_param