awesome.rb

module UniquelyIdentifiable
  extend ActiveSupport::Concern

  FINAL_BASE = 36
  INTERMEDIATE_BASE = 16
  SEPARATOR = 'a'

  def generate_uid
    real_id = self.id.to_s
    rl = (6 - real_id.length) / 2
    rl = 0 if rl < 0

    "#{SecureRandom.hex(rl)}#{SEPARATOR}#{real_id}".to_i(INTERMEDIATE_BASE).to_s(FINAL_BASE)
  end

  def generate_and_store_uid
    return nil unless persisted?
    update_attribute(:uid, generate_uid) unless self.uid.present?
    self.uid
  end

  module ClassMethods
    def parse_uid uid
      uid.to_i(FINAL_BASE).to_s(INTERMEDIATE_BASE).split(SEPARATOR).last.to_i
    end

    def find_with_uid uid
      find_by_id parse_uid(uid)
    end
  end
end