moves method to repository model

app/models/project.rb

@@ -947,12 +947,6 @@ class Project < ActiveRecord::Base
   end
   def main_language
-    unless empty_repo?
-      Rails.cache.fetch([self, "language"]) do
-        Linguist::Repository.new(
-          @repository.rugged, 
-          @repository.rugged.head.target_id).language
-      end
-    end
+    @main_language = repository.main_language
   end
 end

app/models/repository.rb

@@ -812,6 +812,18 @@ class Repository
     raw_repository.ls_files(actual_ref)
   end
+  def main_language
+    return @main_language unless @main_language.nil? 
+
+    unless empty?
+      @main_language = cache.fetch(:main_language) do
+        Linguist::Repository.new(
+          rugged,
+          rugged.head.target_id).language
+      end
+    end
+  end
+
   private
   def cache