Add support for multiple themes (#4959)

* Add support for selecting a theme

* Fix codeclimate issues

* Look up site default style if current user is not available due to e.g. not being logged in

* Remove outdated comment in common.js

* Address requested changes in themes PR

* Fix codeclimate issues

* Explicitly check current_account in application controller and only check theme availability if non-nil

* codeclimate

* explicit precedence with &&

* Fix code style in application_controller according to @nightpool's suggestion, use default style in embedded.html.haml

* codeclimate: indentation + return

app/controllers/application_controller.rb

@@ -12,6 +12,7 @@ class ApplicationController < ActionController::Base
 
   helper_method :current_account
   helper_method :current_session
+  helper_method :current_theme
   helper_method :single_user_mode?
 
   rescue_from ActionController::RoutingError, with: :not_found
@@ -77,6 +78,11 @@ class ApplicationController < ActionController::Base
     @current_session ||= SessionActivation.find_by(session_id: cookies.signed['_session_id'])
   end
 
+  def current_theme
+    return Setting.default_settings['theme'] unless Themes.instance.names.include? current_user&.setting_theme
+    current_user.setting_theme
+  end
+
   def cache_collection(raw, klass)
     return raw unless klass.respond_to?(:with_includes)
 

app/controllers/settings/preferences_controller.rb

@@ -41,6 +41,7 @@ class Settings::PreferencesController < ApplicationController
       :setting_auto_play_gif,
       :setting_system_font_ui,
       :setting_noindex,
+      :setting_theme,
       notification_emails: %i(follow follow_request reblog favourite mention digest),
       interactions: %i(must_be_follower must_be_following)
     )

app/javascript/packs/common.js

@@ -1,9 +1,6 @@
 import { start } from 'rails-ujs';
 
-// import default stylesheet with variables
 require('font-awesome/css/font-awesome.css');
-require('mastodon-application-style');
-
 require.context('../images/', true);
 
 start();

app/lib/themes.rb

@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+
+require 'singleton'
+require 'yaml'
+
+class Themes
+  include Singleton
+
+  def initialize
+    @conf = YAML.load_file(Rails.root.join('config', 'themes.yml'))
+  end
+
+  def names
+    @conf.keys
+  end
+end

app/lib/user_settings_decorator.rb

@@ -25,6 +25,7 @@ class UserSettingsDecorator
     user.settings['auto_play_gif'] = auto_play_gif_preference
     user.settings['system_font_ui'] = system_font_ui_preference
     user.settings['noindex'] = noindex_preference
+    user.settings['theme'] = theme_preference
   end
 
   def merged_notification_emails
@@ -67,6 +68,10 @@ class UserSettingsDecorator
     boolean_cast_setting 'setting_noindex'
   end
 
+  def theme_preference
+    settings['setting_theme']
+  end
+
   def boolean_cast_setting(key)
     settings[key] == '1'
   end

app/models/user.rb

@@ -110,6 +110,10 @@ class User < ApplicationRecord
     settings.noindex
   end
 
+  def setting_theme
+    settings.theme
+  end
+
   def token_for_app(a)
     return nil if a.nil? || a.owner != self
     Doorkeeper::AccessToken

app/views/layouts/application.html.haml

@@ -19,6 +19,7 @@
       = title
 
     = stylesheet_pack_tag 'common', media: 'all'
+    = stylesheet_pack_tag current_theme, media: 'all'
     = javascript_pack_tag 'common', integrity: true, crossorigin: 'anonymous'
 
     %link{ href: asset_pack_path('features/getting_started.js'), crossorigin: 'anonymous', rel: 'preload', as: 'script' }/

app/views/layouts/embedded.html.haml

@@ -5,6 +5,7 @@
     %meta{ name: 'robots', content: 'noindex' }/
 
     = stylesheet_pack_tag 'common', media: 'all'
+    = stylesheet_pack_tag Setting.default_settings['theme'], media: 'all'
     = javascript_pack_tag 'common', integrity: true, crossorigin: 'anonymous'
     = javascript_pack_tag "locale_#{I18n.locale}", integrity: true, crossorigin: 'anonymous'
     = javascript_pack_tag 'public', integrity: true, crossorigin: 'anonymous'

app/views/settings/preferences/show.html.haml

@@ -5,6 +5,8 @@
   = render 'shared/error_messages', object: current_user
 
   .fields-group
+    = f.input :setting_theme, collection: Themes.instance.names, label_method: lambda { |theme| safe_join([I18n.t("themes.#{theme}", default: theme)])}, wrapper: :with_label, include_blank: false
+
     = f.input :locale,
       collection: I18n.available_locales,
       wrapper: :with_label,