Show diff with current file in running backup page

app/controllers/concerns/setting_history_concern.rb

@@ -10,7 +10,7 @@ module SettingHistoryConcern
   def show
     current = @fluentd.agent.config
     target = @backup_file.content
-    @sdiff = Diff::LCS.sdiff(current.split("\n").map(&:rstrip), target.split("\n").map(&:rstrip))
+    @sdiff = Diff::LCS.sdiff(current.split("\n").map(&:rstrip), target.split("\n").map(&:rstrip)) if target
   end
 
   def reuse

app/views/fluentd/settings/running_backup/show.html.haml

@@ -12,9 +12,20 @@
 .row
   .col-xs-12
     - if @backup_file.content
+      %h2
+        = t('.page_title')
       %pre
         = preserve do
           = @backup_file.content
     - else
       %p
         =t('fluentd.common.never_started_yet', brand: fluentd_ui_brand)
+  - if @backup_file.content
+    .col-xs-12.diff
+      %h2
+        Diff:
+      %div
+        = t(".diff_discription")
+        %div.pull-right
+          = link_to t(".show_current"), daemon_setting_path(@fluentd)
+      = preserve render "/shared/settings/diff"

config/locales/translation_en.yml

@@ -263,12 +263,14 @@ en:
           page_title: "Reuse Setting History"
           target_config: "Target Config"
           current_config: "Current Config"
-          diff_discription: "diff between current config and target config(%{file_name})"
+          diff_discription: "diff between current config and target config(%{file_name}) (showing with '+' and '-' if any)"
           show_current: "> see current config"
       running_backup:
         title: "Running Config"
         show:
           page_title: "Running Config"
+          diff_discription: "diff between config and running config (showing with '+' and '-' if any)"
+          show_current: "> see current config"
 
   misc:
     information:

config/locales/translation_ja.yml

@@ -268,12 +268,14 @@ ja:
           page_title: "設定履歴 | 詳細"
           target_config: "対象設定"
           current_config: "現在の設定"
-          diff_discription: "現在の設定と対象設定(%{file_name})の差分"
+          diff_discription: "現在の設定と対象設定(%{file_name})の差分(+-で表示)"
           show_current: "> 現在の設定を見る"
       running_backup:
         title: "使用中の設定"
         show:
           page_title: "使用中の設定"
+          diff_discription: "現在の設定と使用中の設定の差分(+-で表示)"
+          show_current: "> 現在の設定を見る"
 
   misc:
     information:

spec/features/fluentd/setting/running_backup_spec.rb

@@ -36,6 +36,12 @@ describe "running_backup", stub: :daemon do
         expect(page).to have_text(I18n.t("terms.reuse"))
       end
 
+      it 'has diff' do
+        expect(page).to have_text("-   type http")
+        expect(page).to have_text("-   port 8899")
+        expect(page).to have_text("+   Running backup file content")
+      end
+
       it 'update config and redirect to setting#show' do
         click_link I18n.t("terms.reuse")