def self.redeem_and_return(code)
    DB.transaction do

      dataset = DB[:fcm_promo_codes].where(promo_code: code)
      found_code = dataset.first
      return nil unless found_code

      return 20 unless found_code[:amount_released] == 0

      num_redeemed = DB[:fcm_promo_codes].where{amount_released > 0}.count
      prize_amount = prize_for(num_redeemed + 1)
      dataset.update(amount_released: prize_amount, redeemed_on:
                     Sequel.function(:NOW))
    end
  end