#398 Service Objects pro

def create
  auth = Authentication.new(params, env["omniauth.auth"])
  if auth.authenticated?
    session[:user_id] = auth.user.id
    redirect_to root_url, notice: "Logged in!"
  else
    flash.now.alert = "Username or password is invalid"
    render "new"
  end
end

class Authentication
  def initialize(params, omniauth = nil)
    @params = params
    @omniauth = omniauth
  end

  def user
    @user ||= @omniauth ? user_from_omniauth : user_with_password
  end

  def authenticated?
    user.present?
  end

private

  def user_from_omniauth
    User.where(@omniauth.slice(:provider, :uid)).first_or_initialize.tap do |user|
      user.provider = @omniauth[:provider]
      user.uid = @omniauth[:uid]
      user.username = @omniauth[:info][:nickname]
      user.save!
    end
  end

  def user_with_password
    user = User.find_by_username(@params[:username])
    user && user.authenticate(@params[:password])
  end
end

# not needed in Rails 4
config.autoload_paths += %W(#{config.root}/app/models/concerns)

include Authentication

class User
  module Authentication
    extend ActiveSupport::Concern

    included do
      has_secure_password
    end

    module ClassMethods
      def authenticate(username, password)
        user = find_by_username(username)
        user && user.authenticate(password)
      end

      def from_omniauth(auth)
        where(auth.slice(:provider, :uid)).first_or_initialize.tap do |user|
          user.provider = auth[:provider]
          user.uid = auth[:uid]
          user.username = auth[:info][:nickname]
          user.save!
        end
      end
    end
  end
end