Normalize Tags at Write Time

                  module TagNormalization
  extend ActiveSupport::Concern

  included do
    before_validation :normalize_tag_list
  end

  private

  def normalize_tag_list
    return unless respond_to?(:tag_list)

    self.tag_list = tag_list.map { |t| t.to_s.downcase.strip.gsub(/ +/, ' ') }
                             .reject(&:blank?)
                             .uniq
  end
end