include asset host in theme json files

also include asset host in ENV.active_brand_config_json_url

closes CNVS-29764

test plan
- use a real s3 bucket for canvas cdn
- create a new theme
  - should have one custom image uploaded
  - should have some default images
- in the browser console `ENV.active_brand_config_jons_url` should
  include the asset host
- open the json url
  - default and custom image urls should work

Change-Id: I1dd1c11617db624e93686da706b94afee738df12
Reviewed-on: https://gerrit.instructure.com/81445
Reviewed-by: Ryan Shaw <ryan@instructure.com>
Tested-by: Jenkins
Product-Review: Ryan Shaw <ryan@instructure.com>
QA-Review: Jeremy Putnam <jeremyp@instructure.com>

Author: brentropy

app/helpers/application_helper.rb

@@ -710,7 +710,7 @@ def active_brand_config(opts={})
   def active_brand_config_json_url(opts={})
     path = active_brand_config(opts).try(:public_json_path)
     path ||= BrandableCSS.public_default_json_path
-    "/#{path}"
+    "#{Canvas::Cdn.config.host}/#{path}"
   end
 
   def brand_config_for_account(opts={})

lib/brandable_css.rb

@@ -7,9 +7,23 @@
 # stuff take FOREVER in the webpack build.  That means for the time being,
 # changes here if they happen may need to be mirrored in that file.
 
-module BrandableCSS
-  extend ActionView::Helpers::AssetTagHelper
+# this is to get urls that always have the asset host on them,
+# it was fixed in rails 4.1 so is unneeded once we are using 4.1+
+# at that point we can just use ActionController::Base.helpers.image_url below
+# see: https://github.com/rails/rails/issues/10051#issuecomment-26967074
+if CANVAS_RAILS4_0
+  class DummyControllerWithCorrectAssetUrls < ActionController::Base
+    def self.helpers
+      @helper_proxy ||= begin
+        proxy = ActionView::Base.new
+        proxy.config = config.inheritable_copy
+        proxy.extend(_helpers)
+      end
+    end
+  end
+end
 
+module BrandableCSS
   APP_ROOT = defined?(Rails) && Rails.root || Pathname.pwd
   CONFIG = YAML.load_file(APP_ROOT.join('config/brandable_css.yml')).freeze
   BRANDABLE_VARIABLES = JSON.parse(File.read(APP_ROOT.join(CONFIG['paths']['brandable_variables_json']))).freeze
@@ -90,7 +104,11 @@ def variables_map
     def variables_map_with_image_urls
       @variables_map_with_image_urls ||= variables_map.each_with_object({}) do |(key, config), memo|
         if config['type'] == 'image'
-          memo[key] = config.merge('default' => image_url(config['default']))
+          if CANVAS_RAILS4_0
+            memo[key] = config.merge('default' => DummyControllerWithCorrectAssetUrls.helpers.image_url(config['default']))
+          else
+            memo[key] = config.merge('default' => ActionController::Base.helpers.image_url(config['default']))
+          end
         else
           memo[key] = config
         end

spec/lib/brandable_css_spec.rb

@@ -26,11 +26,17 @@
 
     it "includes image_url asset path for default images" do
       # un-memoize so it calls image_url stub
-      BrandableCSS.remove_instance_variable(:@variables_map_with_image_urls)
-      image_name = "image.png"
-      BrandableCSS.stubs(:image_url).returns(image_name)
+      if BrandableCSS.instance_variable_get(:@variables_map_with_image_urls)
+        BrandableCSS.remove_instance_variable(:@variables_map_with_image_urls)
+      end
+      url = "https://test.host/image.png"
+      if CANVAS_RAILS4_0
+        DummyControllerWithCorrectAssetUrls.helpers.stubs(:image_url).returns(url)
+      else
+        ActionController::Base.helpers.stubs(:image_url).returns(url)
+      end
       tile_wide = BrandableCSS.all_brand_variable_values["ic-brand-msapplication-tile-wide"]
-      expect(tile_wide).to eq image_name
+      expect(tile_wide).to eq url
     end
 
     describe "when called with a brand config" do