From 34f98f362f54df17e7a6fa58ffcda5677bb0d234 Mon Sep 17 00:00:00 2001
From: Robin Ward <robin.ward@gmail.com>
Date: Thu, 28 Sep 2017 13:16:51 -0400
Subject: [PATCH] Add a plugin hook to specify a class on the body of the
 document

---
 app/helpers/application_helper.rb | 6 +++++-
 lib/plugin/instance.rb            | 6 ++++++
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/app/helpers/application_helper.rb b/app/helpers/application_helper.rb
index 803f82e27e4..8e81cfe5d55 100644
--- a/app/helpers/application_helper.rb
+++ b/app/helpers/application_helper.rb
@@ -8,12 +8,16 @@ require_dependency 'mobile_detection'
 require_dependency 'category_badge'
 require_dependency 'global_path'
 require_dependency 'emoji'
+require_dependency 'multisite_class_var'
 
 module ApplicationHelper
   include CurrentUser
   include CanonicalURL::Helpers
   include ConfigurableUrls
   include GlobalPath
+  include MultisiteClassVar
+
+  multisite_class_var(:extra_body_classes) { Set.new }
 
   def google_universal_analytics_json(ua_domain_name = nil)
     result = {}
@@ -75,7 +79,7 @@ module ApplicationHelper
   end
 
   def body_classes
-    result = []
+    result = ApplicationHelper.extra_body_classes.to_a
 
     if @category && @category.url.present?
       result << "category-#{@category.url.sub(/^\/c\//, '').gsub(/\//, '-')}"
diff --git a/lib/plugin/instance.rb b/lib/plugin/instance.rb
index 3eb44c76bd1..e84ab6e413e 100644
--- a/lib/plugin/instance.rb
+++ b/lib/plugin/instance.rb
@@ -103,6 +103,12 @@ class Plugin::Instance
     end
   end
 
+  def add_body_class(class_name)
+    reloadable_patch do |plugin|
+      ::ApplicationHelper.extra_body_classes << class_name if plugin.enabled?
+    end
+  end
+
   # Extend a class but check that the plugin is enabled
   # for class methods use `add_class_method`
   def add_to_class(class_name, attr, &block)