log-in service example

sessions.rb

# session controller 
# receives callbacks with oauth
class SessionsController < ApplicationController

  skip_before_filter :login_required

  def create
    login.run!
    redirect_to root_path
  end

  private

  def auth_info
    request.env['omniauth.auth'].to_hash
  end

  def user_params
    raw_params = ActionController::Parameters.new(auth_info['info'])
    raw_params.permit(:first_name, :last_name, :email)
  end

  def login
    LogUserIn.new(session, user_params)
  end

end

# app/services/log_user_in.rb
# exsting user logged in with data
# non-existing user created (dispatched to creation service)

class LogUserIn

  attr_accessor :session, :data, :user, :email

  def initialize session, user_hash
    self.session = session
    self.data = user_hash
    self.email = data[:email]
  end

  def run!
    create_user unless user.present?
    session[:user_id] = user.id
  end

  def create_user
    registration.run!
    self.user = registration.user
  end

  def user
    @user ||= email && User.find_by(email: email)
  end

  private

  def registration
    RegisterUser.new(data) # same style service
  end

end