users_controller.rb

class UsersController < ApplicationController
  def create
    @user = UserSignupManager.perform(user_params, invitation_token)

    if @user.errors.blank?
      flash[:success] = "Welcome to Raysurfing. Hope you enjoy it!"
      redirect_to posts_path
    else
      flash[:error] = "Sorry there was an error with your regitration"
      render :new
    end
  end

  private

  def user_params
    params.require(:user).permit(:email, :name, :username)
  end

  def invitation_token
    params[:invitation_token]
  end
end

user_signup_manager.rb

class UserSignupManager
  attr_reader :invitation_token, :status, :user

  def initialize(user_params, invitation_token)
    @user = User.new(user_params)
    @invitation_token = invitation_token
  end

  def self.perform
    new(user_params, params[:invitation_token]).perform
  end

  def perform
    begin
      persistance_actions
      mailer_actions
      user
    rescue ActiveRecord::RecordInvalid => e
      user.errors[:base] << "#{e}"
      user
    end
  end

  private

  def persistance_actions
    ActiveRecord::Base.transaction do
      @user = user.save
      InvitationHandler.handle(user, invitation_token)
    end
  end

  def mailer_actions
    MilestoneChecker.check
    AppMailer.welcome_email(@user)
  end
end

invitation_handler.rb

class InvitationHandler
  attr_reader :user, :invitation_token

  def initialize(user, invitation_token)
    @user = user
    @invitation_token = invitation_token
  end

  def self.handle
    new.(user, invitation_token).handle
  end

  def handle
    return unless invitation_token

    follow_relationships
    stale_invitation
  end

  private

  def follow_relationships
    user.leaders << invitation_user
    invitation_user.followers << user
    invitation_user.update_points(500)
  end

  def stale_invitation
    invitation.update_attribute(:token, nil)
  end

  def inivitation_user
    @inivitation_user ||= Invitation.find_by(token: params[:invitation_token]).user
  end
end

milestone_checker.rb

class MilestoneChecker
  def self.check
    return unless User.count == 50000

    admins = User.where(admin: true)
    AppMailer.community_milestone_reached(admins)
  end
end