Rails controller concern to help with rendering mobile views

mobile_concern.rb

#
# Add this to your Gemfile
# gem 'rack-mobile-detect', :require => 'rack/mobile-detect'
#
module MobileConcern
  extend ActiveSupport::Concern

  included do
    # Call this from a controller to enable mobile for a given action
    # Example: enable_mobile :only => [:show]
    def self.enable_mobile(*before_filter_args)
      before_action(MobileHelper, *before_filter_args)
      # set layout to 'nil', which sets the default layout
      layout(Proc.new { |controller| controller.mobile_helper.enabled? ? 'mobile' : nil })
    end
  end

  # Only method leaked into the Controller
  # This instance variable is set by the filer if activated, otherwise the 'null' object is created
  def mobile_helper
    @mobile_helper ||= MobileHelper.new(self)
  end

  class MobileHelper
    PARAM_KEY = :mobile
    PARAM_VALUES = {
      mobile: '1',
      desktop: '0'
    }
    COOKIE_KEY = 'mobile_pref'
    COOKIE_VALUES = {
      mobile: 'mobile',
      desktop: 'desktop'
    }

    # Called from the before_action callback
    def self.before(controller)
      self.new(controller).tap { |helper|
        # Give the controller access to this helper
        controller.instance_variable_set(:@mobile_helper, helper)
      }.filter!
    end

    attr_reader :controller, :views_path
    def initialize(controller, views_path = 'app/views/mobile')
      @controller = controller
      @views_path = views_path
      @enabled = false
    end

    def filter!
      self.set_mobile_pref_from_params
      self.enable! if self.show_mobile_version?
      self.controller.logger.debug("mobile = #{self.enabled? ? 'enabled' : 'disabled'}")
    end

    def enabled?
      @enabled
    end

    def show_mobile_version?
      self.param_mobile? || self.cookie_mobile? || (self.mobile_device? && !self.param_desktop? && !self.cookie_desktop?)
    end

    def enable!
      @enabled = true
      self.controller.prepend_view_path(File.join(Rails.root, self.views_path)) # see 'set_layout' for how layout is set
    end

    def set_mobile_pref_from_params
      self.mobile_cookie = COOKIE_VALUES[:mobile] if self.param_mobile?
      self.mobile_cookie = COOKIE_VALUES[:desktop] if self.param_desktop?
    end

    def mobile_device_name
      @mobile_device_name ||= self.controller.request.headers.fetch(Rack::MobileDetect::X_HEADER, '').downcase
    end

    def mobile_param
      @mobile_param ||= self.controller.params.fetch(PARAM_KEY, nil)
    end

    def mobile_cookie
      @mobile_cookie ||= self.controller.send(:cookies).fetch(COOKIE_KEY, nil)
    end

    def mobile_cookie=(val)
      self.controller.send(:cookies)[COOKIE_KEY] = {:value => val, :expires => 30.days.from_now} if val
    end

    def mobile_device?
      # TODO: move the ignored devices to a config
      self.mobile_device_name.present? && self.mobile_device_name.downcase != 'ipad'
    end

    def param_mobile?
      self.mobile_param == PARAM_VALUES[:mobile]
    end

    def param_desktop?
      self.mobile_param == PARAM_VALUES[:desktop]
    end

    def cookie_mobile?
      self.mobile_cookie == COOKIE_VALUES[:mobile]
    end

    def cookie_desktop?
      self.mobile_cookie == COOKIE_VALUES[:desktop]
    end
  end
end