let subscriptionPeriod = 44000
let signature = tx.proofs[0]
let pk = tx.proofs[1]
let requiredAmount = 100000
#extracting the sender’s address from the transaction
let this = extract(tx.sender)

match tx {
   case d: DataTransaction =>
     #извлекаем дату последнего платежа
     #extracting the date of the most recent payment
     let lastPaymentHeight = extract(getInteger(this, d.data[0].key + "_lastPayment"))
     size(d.data) == 1 && d.data[0].value == "false" && lastPaymentHeight + subscriptionPeriod < height
     ||
     (
       let address = d.data[0].key

       #извлекаем трансфер-транзакцию по ID, указанному в пруфах
       #extracting the transfer transaction by the ID indicated in the proofs.
       let ttx = transactionById(d.proofs[0])

       size(d.data) == 2
           && d.data[0].value == "true"
           && d.data[1].key == address + "_lastPayment"
           && match ttx {
             case purchase : TransferTransaction =>
               d.data[1].value == transactionHeightById(purchase.id)
               && toBase58String(purchase.sender.bytes) == address
               && purchase.amount == requiredAmount
               && purchase.recipient == this
               #убеждаемся, что ассет waves
               #making sure the asset is WAVES
               && !isDefined(purchase.assetId)
         case _ => false
       }
     )
   case _ => false
}