discourse/app/services/anonymous_shadow_creator.rb

class AnonymousShadowCreator

  def self.get_master(user)
    return unless user
    return unless SiteSetting.allow_anonymous_posting

    if (master_id = user.custom_fields["master_id"].to_i) > 0
      User.find_by(id: master_id)
    end
  end

  def self.get(user)
    return unless user
    return unless SiteSetting.allow_anonymous_posting
    return if user.trust_level < SiteSetting.anonymous_posting_min_trust_level
    return if SiteSetting.must_approve_users? && !user.approved?

    if (shadow_id = user.custom_fields["shadow_id"].to_i) > 0
      shadow = User.find_by(id: shadow_id)

      if shadow && (shadow.post_count + shadow.topic_count) > 0 &&
          shadow.last_posted_at < SiteSetting.anonymous_account_duration_minutes.minutes.ago
        shadow = nil
      end

      shadow || create_shadow(user)
    else
      create_shadow(user)
    end
  end

  def self.create_shadow(user)
    username = UserNameSuggester.suggest(I18n.t(:anonymous).downcase)

    User.transaction do
      shadow = User.create!(
        password: SecureRandom.hex,
        email: "#{SecureRandom.hex}@anon.#{Discourse.current_hostname}",
        skip_email_validation: true,
        name: username, # prevents error when names are required
        username: username,
        active: true,
        trust_level: 1,
        manual_locked_trust_level: 1,
        approved: true,
        approved_at: 1.day.ago,
        created_at: 1.day.ago # bypass new user restrictions
      )

      shadow.user_option.update_columns(
        email_messages_level: UserOption.email_level_types[:never],
        email_digests: false
      )

      shadow.email_tokens.update_all(confirmed: true)
      shadow.activate

      # can not hold dupes
      UserCustomField.where(user_id: user.id, name: "shadow_id").destroy_all

      UserCustomField.create!(user_id: user.id, name: "shadow_id", value: shadow.id)
      UserCustomField.create!(user_id: shadow.id, name: "master_id", value: user.id)

      shadow.reload
      user.reload

      shadow
    end
  end
end