don't blow away the brandConfig someone else is working on

closes: CNVS-21804

this will also do a better job of cleaning up
the app/stylesheets/brandable_css_brands dir
(so when you compile sass, it won't do stuff
for brandConfigs that aren't being used anymore)

test plan:
open theme editor, make some changes, hit preview.
as a different user in a different browser,
open theme editor, make changes, press save.
now in the first window, try to hit save.
before it would break, now it will work

Change-Id: I094f737d35c854764a7c361bec4798b8a2203410
Reviewed-on: https://gerrit.instructure.com/58102
Reviewed-by: Mike Nomitch <mnomitch@instructure.com>
Product-Review: Jennifer Stern <jstern@instructure.com>
Tested-by: Jenkins
QA-Review: Nathan Rogowski <nathan@instructure.com>

app/controllers/brand_configs_controller.rb

@@ -14,6 +14,7 @@ class BrandConfigsController < ApplicationController
   end
 
   def create
+    old_md5 = session[:brand_config_md5]
     session[:brand_config_md5] = begin
       if params[:brand_config] == ''
         false
@@ -23,19 +24,22 @@ class BrandConfigsController < ApplicationController
         create_brand_config(variables).md5
       end
     end
+    BrandConfig.destroy_if_unused(old_md5)
     redirect_to brand_configs_new_path
   end
 
   def save_to_account
-    @domain_root_account.update_attributes!(brand_config_md5: session[:brand_config_md5].presence)
-    BrandConfig.clean_up_unused
-    session.delete(:brand_config_md5)
+    old_md5 = @domain_root_account.brand_config_md5
+    new_md5 = session.delete(:brand_config_md5).presence
+    @domain_root_account.brand_config = new_md5 && BrandConfig.find(new_md5)
+    @domain_root_account.save!
+    BrandConfig.destroy_if_unused(old_md5)
     redirect_to :back, notice: t('Success! All users on this domain will now see this branding.')
   end
 
   def destroy
     session.delete(:brand_config_md5)
-    BrandConfig.clean_up_unused
+    BrandConfig.destroy_if_unused(session.delete(:brand_config_md5))
     flash[:notice] = t('Theme editor changes have been cancelled.')
     render json: {success: true}
   end

app/models/brand_config.rb

@@ -35,18 +35,28 @@ class BrandConfig < ActiveRecord::Base
     end.compact.join("\n")
   end
 
-  def filename
-    File.join(CONFIG['paths']['branded_scss_folder'], md5, '_brand_variables.scss')
+  def scss_file
+    scss_dir.join('_brand_variables.scss')
+  end
+
+  def scss_dir
+    BrandableCSS.branded_scss_folder.join(md5)
   end
 
   def public_folder
     "dist/brandable_css/#{md5}"
   end
 
-  def save_file!
-    logger.info "saving BrandConfig: #{filename}"
-    FileUtils.mkdir_p(File.dirname(filename))
-    File.write(filename, to_scss)
+  def save_scss_file!
+    logger.info "saving brand variables file: #{scss_file}"
+    scss_dir.mkpath
+    scss_file.write(to_scss)
+  end
+
+  def remove_scss_file!
+    return unless scss_dir.exist?
+    logger.info "removing: #{scss_dir}"
+    scss_dir.rmtree
   end
 
   def compile_css!
@@ -58,16 +68,22 @@ class BrandConfig < ActiveRecord::Base
   end
 
   def save_and_sync_to_s3!
-    save_file!
+    save_scss_file!
     compile_css!
     sync_to_s3!
   end
 
-  def self.clean_up_unused
-    BrandConfig.
+  def self.destroy_if_unused(md5)
+    return unless md5
+    unused_brand_config = BrandConfig.
+      where(md5: md5).
       where('NOT EXISTS (SELECT 1 FROM accounts WHERE brand_config_md5=brand_configs.md5)').
       where('NOT share').
-      destroy_all
+      first
+    if unused_brand_config
+      unused_brand_config.destroy
+      unused_brand_config.remove_scss_file!
+    end
   end
 
 end

lib/brandable_css.rb

@@ -28,6 +28,10 @@ module BrandableCSS
       default
     end
 
+    def branded_scss_folder
+      Pathname.new(CONFIG['paths']['branded_scss_folder'])
+    end
+
     def variants
       @variants ||= CONFIG['variants'].map{|(k)| k }.freeze
     end

lib/tasks/brand_configs.rake

@@ -3,15 +3,15 @@ namespace :brand_configs do
        "Set BRAND_CONFIG_MD5=<whatever> to save just that one, otherwise writes a file for each BrandConfig in db."
   task :write => :environment do
     if md5 = ENV['BRAND_CONFIG_MD5']
-      BrandConfig.find(md5).save_file!
+      BrandConfig.find(md5).save_scss_file!
     else
       Rake::Task['brand_configs:clean'].invoke
-      BrandConfig.find_each(&:save_file!)
+      BrandConfig.find_each(&:save_scss_file!)
     end
   end
 
   desc "Remove all Brand Variable scss files"
   task :clean do
-    rm_rf BrandConfig::CONFIG['paths']['branded_scss_folder']
+    rm_rf BrandableCSS.branded_scss_folder
   end
 end