template GardeningContract
  with
    gardener    : Party
    beneficiary : Party
    amount      : Amount
    invoiceId   : Text
    optAchId    : Optional Text
  where
    signatory gardener, beneficiary

    agreement partyToText gardener <> " will mow " <> partyToText beneficiary
      <> "'s lawn for " <> show amount <> ". The ACH transaction "
      <> (if optAchId /= None then "has" else "has not") <> " been settled."

    controller beneficiary can
      SettleTransfer : ContractId GardeningContract
        with
          transferCid : TransferCid
        do
          assert (optAchId == None)
          transfer <- fetch transferCid
          assert (transfer.sender == beneficiary)
          assert (transfer.receiver == gardener)
          assert (transfer.amount == amount)
          assert (transfer.status == processed)
          assert (elem (Metadata with key = "invoiceId", value = invoiceId) transfer.metadata)
          create this with optAchId = Some transfer.individualAchId