Clean up settings/preferences controller (#2237)

* Add missing fields group on preferences page

* Clean up settings/preferences controller

* Extract a UserSettingsDecorator

app/lib/user_settings_decorator.rb

@@ -0,0 +1,56 @@
+# frozen_string_literal: true
+
+class UserSettingsDecorator
+  attr_reader :user, :settings
+
+  def initialize(user)
+    @user = user
+  end
+
+  def update(settings)
+    @settings = settings
+    process_update
+  end
+
+  private
+
+  def process_update
+    user.settings['notification_emails'] = merged_notification_emails
+    user.settings['interactions'] = merged_interactions
+    user.settings['default_privacy'] = default_privacy_preference
+    user.settings['boost_modal'] = boost_modal_preference
+    user.settings['auto_play_gif'] = auto_play_gif_preference
+  end
+
+  def merged_notification_emails
+    user.settings['notification_emails'].merge coerced_settings('notification_emails').to_h
+  end
+
+  def merged_interactions
+    user.settings['interactions'].merge coerced_settings('interactions').to_h
+  end
+
+  def default_privacy_preference
+    settings['setting_default_privacy']
+  end
+
+  def boost_modal_preference
+    boolean_cast_setting 'setting_boost_modal'
+  end
+
+  def auto_play_gif_preference
+    boolean_cast_setting 'setting_auto_play_gif'
+  end
+
+  def boolean_cast_setting(key)
+    settings[key] == '1'
+  end
+
+  def coerced_settings(key)
+    coerce_values settings.fetch(key, {})
+  end
+
+  def coerce_values(params_hash)
+    params_hash.transform_values { |x| x == '1' }
+  end
+end