discourse/app/services/user_activator.rb

class UserActivator
  attr_reader :user, :request, :session, :cookies, :message

  def initialize(user, request, session, cookies)
    @user = user
    @session = session
    @cookies = cookies
    @request = request
    @settings = SiteSetting
    @hub = DiscourseHub
    @message = nil
  end

  def start
    register_username
  end

  def finish
    @message = activator.activate
  end

  private

  def activator
    factory.new(user, request, session, cookies)
  end

  def factory
    if @settings.must_approve_users?
      ApprovalActivator
    elsif !user.active?
      EmailActivator
    else
      LoginActivator
    end
  end

  def register_username
    if user.valid? && @settings.call_discourse_hub?
      @hub.register_username(user.username, user.email)
    end
  end
end

class ApprovalActivator < UserActivator
  def activate
    I18n.t("login.wait_approval")
  end
end

class EmailActivator < UserActivator
  def activate
    Jobs.enqueue(:user_email,
      type: :signup,
      user_id: user.id,
      email_token: user.email_tokens.first.token
    )
    I18n.t("login.activate_email", email: user.email)
  end
end

class LoginActivator < UserActivator
  include CurrentUser

  def activate
    log_on_user(user)
    user.enqueue_welcome_message('welcome_user')
    I18n.t("login.active")
  end
end