Simplify tag list reconstruct

app/models/chargeback/rates_cache.rb

@@ -3,22 +3,9 @@ class RatesCache
     def get(perf)
       @rates ||= {}
       @rates[perf.hash_features_affecting_rate] ||=
-        begin
-          prefix = tag_prefix(perf)
-          ChargebackRate.get_assigned_for_target(perf.resource,
-                                                 :tag_list => perf.tag_list_reconstruct.map! { |t| prefix + t },
-                                                 :parents  => perf.parents_determining_rate)
-        end
-    end
-
-    private
-
-    def tag_prefix(perf)
-      case perf.resource_type
-      when Container.name        then 'container_image'
-      when VmOrTemplate.name     then 'vm'
-      when ContainerProject.name then 'container_project'
-      end
+        ChargebackRate.get_assigned_for_target(perf.resource,
+                                               :tag_list => perf.tag_list_with_prefix,
+                                               :parents  => perf.parents_determining_rate)
     end
   end
 end

app/models/metric/chargeback_helper.rb

@@ -1,19 +1,30 @@
 module Metric::ChargebackHelper
+  TAG_MANAGED_PREFIX = "/tag/managed/".freeze
+
   def hash_features_affecting_rate
     tags = tag_names.split('|').reject { |n| n.starts_with?('folder_path_') }.sort.join('|')
     keys = [tags] + resource_parents.map(&:id)
     keys += [resource.container_image, timestamp] if resource_type == Container.name
     keys.join('_')
   end
 
-  def tag_list_reconstruct
-    tag_list = tag_names.split("|").inject([]) { |arr, t| arr << "/tag/managed/#{t}" }
+  def tag_prefix
+    klass_prefix = case resource_type
+                   when Container.name        then 'container_image'
+                   when VmOrTemplate.name     then 'vm'
+                   when ContainerProject.name then 'container_project'
+                   end
+
+    klass_prefix + TAG_MANAGED_PREFIX
+  end
 
-    if resource_type == Container.name
+  def tag_list_with_prefix
+    if resource.kind_of?(Container)
       state = resource.vim_performance_state_for_ts(timestamp.to_s)
-      tag_list += state.image_tag_names.split("|").inject([]) { |arr, t| arr << "/tag/managed/#{t}" } if state.present?
+      image_tag_name = "#{state.image_tag_names}|" if state
     end
-    tag_list
+
+    "#{image_tag_name}#{tag_names}".split("|").reject(&:empty?).map { |x| "#{tag_prefix}#{x}" }
   end
 
   def resource_parents