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* Remove outdated comment in common.js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

15 files changed, 64 insertions, 21 deletions

diff --git a/app/controllers/application_controller.rb b/app/controllers/application_controller.rb
index 0b40fb05b..d5eca6ffb 100644
--- a/app/controllers/application_controller.rb
+++ b/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)
 
diff --git a/app/controllers/settings/preferences_controller.rb b/app/controllers/settings/preferences_controller.rb
index f107f2b16..207c7b324 100644
--- a/app/controllers/settings/preferences_controller.rb
+++ b/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)
     )
diff --git a/app/javascript/packs/common.js b/app/javascript/packs/common.js
index ba7053f1f..4880f0242 100644
--- a/app/javascript/packs/common.js
+++ b/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();
diff --git a/app/lib/themes.rb b/app/lib/themes.rb
new file mode 100644
index 000000000..243ffb9ab
--- /dev/null
+++ b/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
diff --git a/app/lib/user_settings_decorator.rb b/app/lib/user_settings_decorator.rb
index 62046ed72..cb1b3c4a9 100644
--- a/app/lib/user_settings_decorator.rb
+++ b/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
diff --git a/app/models/user.rb b/app/models/user.rb
index 5e548c1ef..3bf069a31 100644
--- a/app/models/user.rb
+++ b/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
diff --git a/app/views/layouts/application.html.haml b/app/views/layouts/application.html.haml
index 88eff7d17..15012de7e 100755
--- a/app/views/layouts/application.html.haml
+++ b/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' }/
diff --git a/app/views/layouts/embedded.html.haml b/app/views/layouts/embedded.html.haml
index 46dab2d0f..ac11cfbe7 100644
--- a/app/views/layouts/embedded.html.haml
+++ b/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'
diff --git a/app/views/settings/preferences/show.html.haml b/app/views/settings/preferences/show.html.haml
index f42f92508..5efd538e4 100644
--- a/app/views/settings/preferences/show.html.haml
+++ b/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,
diff --git a/config/locales/en.yml b/config/locales/en.yml
index 9013f0ac9..0f3812aff 100644
--- a/config/locales/en.yml
+++ b/config/locales/en.yml
@@ -461,6 +461,8 @@ en:
     settings: Settings
     two_factor_authentication: Two-factor Authentication
     your_apps: Your applications
+  themes:
+    default: Mastodon
   statuses:
     open_in_web: Open in web
     over_character_limit: character limit of %{max} exceeded
diff --git a/config/locales/simple_form.en.yml b/config/locales/simple_form.en.yml
index fb8524a24..c535a22fe 100644
--- a/config/locales/simple_form.en.yml
+++ b/config/locales/simple_form.en.yml
@@ -13,6 +13,7 @@ en:
           one: <span class="note-counter">1</span> character left
           other: <span class="note-counter">%{count}</span> characters left
         setting_noindex: Affects your public profile and status pages
+        setting_theme: Affects how Mastodon looks when you're logged in from any device.
       imports:
         data: CSV file exported from another Mastodon instance
       sessions:
@@ -44,6 +45,7 @@ en:
         setting_noindex: Opt-out of search engine indexing
         setting_system_font_ui: Use system's default font
         setting_unfollow_modal: Show confirmation dialog before unfollowing someone
+        setting_theme: Site theme 
         severity: Severity
         type: Import type
         username: Username
diff --git a/config/settings.yml b/config/settings.yml
index ba63afa92..c437b4ccb 100644
--- a/config/settings.yml
+++ b/config/settings.yml
@@ -24,6 +24,7 @@ defaults: &defaults
   auto_play_gif: false
   system_font_ui: false
   noindex: false
+  theme: 'default'
   notification_emails:
     follow: false
     reblog: false
diff --git a/config/themes.yml b/config/themes.yml
new file mode 100644
index 000000000..a1049fae7
--- /dev/null
+++ b/config/themes.yml
@@ -0,0 +1 @@
+default: styles/application.scss
diff --git a/config/webpack/configuration.js b/config/webpack/configuration.js
index 6ef484c3a..822329490 100644
--- a/config/webpack/configuration.js
+++ b/config/webpack/configuration.js
@@ -9,6 +9,9 @@ const configPath = resolve('config', 'webpacker.yml');
 const loadersDir = join(__dirname, 'loaders');
 const settings = safeLoad(readFileSync(configPath), 'utf8')[env.NODE_ENV];
 
+const themePath = resolve('config', 'themes.yml');
+const themes = safeLoad(readFileSync(themePath), 'utf8');
+
 function removeOuterSlashes(string) {
   return string.replace(/^\/*/, '').replace(/\/*$/, '');
 }
@@ -29,6 +32,7 @@ const output = {
 
 module.exports = {
   settings,
+  themes,
   env,
   loadersDir,
   output,
diff --git a/config/webpack/shared.js b/config/webpack/shared.js
index b097a5fe4..ea2da6aa7 100644
--- a/config/webpack/shared.js
+++ b/config/webpack/shared.js
@@ -1,13 +1,12 @@
 // Note: You must restart bin/webpack-dev-server for changes to take effect
 
-const { existsSync } = require('fs');
 const webpack = require('webpack');
 const { basename, dirname, join, relative, resolve, sep } = require('path');
 const { sync } = require('glob');
 const ExtractTextPlugin = require('extract-text-webpack-plugin');
 const ManifestPlugin = require('webpack-manifest-plugin');
 const extname = require('path-complete-extname');
-const { env, settings, output, loadersDir } = require('./configuration.js');
+const { env, settings, themes, output, loadersDir } = require('./configuration.js');
 const localePackPaths = require('./generateLocalePacks');
 
 const extensionGlob = `**/*{${settings.extensions.join(',')}}*`;
@@ -15,20 +14,25 @@ const entryPath = join(settings.source_path, settings.source_entry_path);
 const packPaths = sync(join(entryPath, extensionGlob));
 const entryPacks = [...packPaths, ...localePackPaths].filter(path => path !== join(entryPath, 'custom.js'));
 
-const customApplicationStyle = resolve(join(settings.source_path, 'styles/custom.scss'));
-const originalApplicationStyle = resolve(join(settings.source_path, 'styles/application.scss'));
+const themePaths = Object.keys(themes).reduce(
+  (themePaths, name) => {
+    themePaths[name] = resolve(join(settings.source_path, themes[name]));
+    return themePaths;
+  }, {});
 
 module.exports = {
-  entry: entryPacks.reduce(
-    (map, entry) => {
-      const localMap = map;
-      let namespace = relative(join(entryPath), dirname(entry));
-      if (namespace === join('..', '..', '..', 'tmp', 'packs')) {
-        namespace = ''; // generated by generateLocalePacks.js
-      }
-      localMap[join(namespace, basename(entry, extname(entry)))] = resolve(entry);
-      return localMap;
-    }, {}
+  entry: Object.assign(
+    entryPacks.reduce(
+      (map, entry) => {
+        const localMap = map;
+        let namespace = relative(join(entryPath), dirname(entry));
+        if (namespace === join('..', '..', '..', 'tmp', 'packs')) {
+          namespace = ''; // generated by generateLocalePacks.js
+        }
+        localMap[join(namespace, basename(entry, extname(entry)))] = resolve(entry);
+        return localMap;
+      }, {}
+    ), themePaths
   ),
 
   output: {
@@ -67,10 +71,6 @@ module.exports = {
   ],
 
   resolve: {
-    alias: {
-      'mastodon-application-style': existsSync(customApplicationStyle) ?
-                                    customApplicationStyle : originalApplicationStyle,
-    },
     extensions: settings.extensions,
     modules: [
       resolve(settings.source_path),