fix rails4 enums attribute issue

With a Rails 4 enum field the changed attributes hash contains the
mapped value and when prev[attr] assigns the value it will be lost.

lib/paper_trail/has_paper_trail.rb

@@ -342,9 +342,13 @@ module PaperTrail
         all_timestamp_attributes.each do |column|
           previous[column] = send(column) if self.class.column_names.include?(column.to_s) and not send(column).nil?
         end
+        enums = previous.respond_to?(:defined_enums) ? previous.defined_enums : {}
         previous.tap do |prev|
           prev.id = id # `dup` clears the `id` so we add that back
-          changed_attributes.select { |k,v| self.class.column_names.include?(k) }.each { |attr, before| prev[attr] = before }
+          changed_attributes.select { |k,v| self.class.column_names.include?(k) }.each { |attr, before|
+            before = enums[attr][before] unless enums[attr].nil?
+            prev[attr] = before
+          }
         end
       end
 

test/dummy/app/models/post_with_status.rb

@@ -0,0 +1,4 @@
+class PostWithStatus < ActiveRecord::Base
+  has_paper_trail
+  enum status: { draft: 0, published: 1, archived: 2 }
+end

test/dummy/db/migrate/20110208155312_set_up_test_tables.rb

@@ -92,6 +92,10 @@ class SetUpTestTables < ActiveRecord::Migration
       t.string :content
     end
 
+    create_table :post_with_statuses, :force => true do |t|
+      t.integer :status
+    end
+
     create_table :animals, :force => true do |t|
       t.string :name
       t.string :species   # single table inheritance column
@@ -100,7 +104,7 @@ class SetUpTestTables < ActiveRecord::Migration
     create_table :documents, :force => true do |t|
       t.string :name
     end
-    
+
     create_table :legacy_widgets, :force => true do |t|
       t.string    :name
       t.integer   :version

test/unit/model_test.rb

@@ -1376,6 +1376,16 @@ class HasPaperTrailModelTest < ActiveSupport::TestCase
     end
   end
 
+  context 'A record with enum fields' do
+    should "keep the integer in versions" do
+      post = PostWithStatus.create!(status: "draft")
+      assert post.draft?
+      post.published!
+      post.archived!
+      assert post.previous_version.published?
+    end
+  end
+
 
   private