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
    @message = nil
  end

  def start
  end

  def finish
    @message = activator.activate
  end

  private

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

  def factory
    invite = Invite.find_by(email: Email.downcase(@user.email))

    if !user.active?
      EmailActivator
    elsif SiteSetting.must_approve_users? && !(invite.present? && !invite.expired? && !invite.destroyed? && invite.link_valid?)
      ApprovalActivator
    else
      LoginActivator
    end
  end

end

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

class EmailActivator < UserActivator
  def activate
    email_token = user.email_tokens.unconfirmed.active.first
    email_token = user.email_tokens.create(email: user.email) if email_token.nil?

    Jobs.enqueue(:critical_user_email,
      type: :signup,
      user_id: user.id,
      email_token: email_token.token
    )
    I18n.t("login.activate_email", email: Rack::Utils.escape_html(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