def facebook
        render_api 400, "Missing fields" and return unless check_params(facebook_params, [:id, :access_token])

        begin
          facebook_user = FbGraph2::User.me(params[:access_token]).fetch(fields: [:name, :email, :gender, :birthday, "picture.height(300)"])
          user = User.find_by_email(facebook_user.email)

          if user.nil?
            # crate
            meta = {
              name: facebook_user.name,
              gender: facebook_user.gender,
            }
            unless facebook_user.picture.is_silhouette
              meta[:facebook_picture] = facebook_user.picture.url
            end

            birthday = facebook_user.birthday rescue nil
            if birthday
              # TODO: check it works
              # birthday format is MM/dd/yyyy. change it to yyyy/MM/dd
              meta[:birthday] = Date.strptime(birthday, '%m/%d/%Y').strftime('%Y/%m/%d') rescue nil
            end

            user = User.create(email: facebook_user.email,
                               password: Devise.friendly_token,
                               auth_info: {
                                 type: "facebook",
                                 info: {
                                   id: facebook_params[:id]
                                 }
                               },
                               meta: meta)
            if user.save
              sign_in(user)
              render_api 201, user.as_json({:self => true})
            else
              render_api 400, user.errors.full_messages.as_json
            end
          else
            # authenticate
            if sign_in(user)
              if !facebook_user.birthday.nil? && current_user.meta['birthday'].nil?
                current_user.meta['birthday'] = facebook_user.birthday
                current_user.save!
              end
              render_api 200, current_user.as_json({:self => true})
            else
              render_api 500, "Failed to authenticate"
            end
          end
        rescue FbGraph2::Exception => e
          puts e
          render_api 500, "Failed to login with facebook"
        end
      end