Clean up settings/preferences controller (#2237)

* Add missing fields group on preferences page

* Clean up settings/preferences controller

* Extract a UserSettingsDecorator

spec/lib/user_settings_decorator_spec.rb

@@ -0,0 +1,45 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+describe UserSettingsDecorator do
+  describe 'update' do
+    let(:user) { Fabricate(:user) }
+    let(:settings) { described_class.new(user) }
+
+    it 'updates the user settings value for email notifications' do
+      values = { 'notification_emails' => { 'follow' => '1' } }
+
+      settings.update(values)
+      expect(user.settings['notification_emails']['follow']).to eq true
+    end
+
+    it 'updates the user settings value for interactions' do
+      values = { 'interactions' => { 'must_be_follower' => '0' } }
+
+      settings.update(values)
+      expect(user.settings['interactions']['must_be_follower']).to eq false
+    end
+
+    it 'updates the user settings value for privacy' do
+      values = { 'setting_default_privacy' => 'public' }
+
+      settings.update(values)
+      expect(user.settings['default_privacy']).to eq 'public'
+    end
+
+    it 'updates the user settings value for boost modal' do
+      values = { 'setting_boost_modal' => '1' }
+
+      settings.update(values)
+      expect(user.settings['boost_modal']).to eq true
+    end
+
+    it 'updates the user settings value for gif auto play' do
+      values = { 'setting_auto_play_gif' => '0' }
+
+      settings.update(values)
+      expect(user.settings['auto_play_gif']).to eq false
+    end
+  end
+end