private static Protos.Transaction.Pool getProtoPool(WalletTransaction wtx) {
   switch (wtx.getPool()) {
     case UNSPENT:
       return Protos.Transaction.Pool.UNSPENT;
     case SPENT:
       return Protos.Transaction.Pool.SPENT;
     case DEAD:
       return Protos.Transaction.Pool.DEAD;
     case PENDING:
       return Protos.Transaction.Pool.PENDING;
     default:
       throw new RuntimeException("Unreachable");
   }
 }
  private static Protos.Transaction makeTxProto(WalletTransaction wtx) {
    Transaction tx = wtx.getTransaction();
    Protos.Transaction.Builder txBuilder = Protos.Transaction.newBuilder();

    txBuilder
        .setPool(getProtoPool(wtx))
        .setHash(hashToByteString(tx.getHash()))
        .setVersion((int) tx.getVersion());

    if (tx.getUpdateTime() != null) {
      txBuilder.setUpdatedAt(tx.getUpdateTime().getTime());
    }

    if (tx.getLockTime() > 0) {
      txBuilder.setLockTime((int) tx.getLockTime());
    }

    // Handle inputs.
    for (TransactionInput input : tx.getInputs()) {
      Protos.TransactionInput.Builder inputBuilder =
          Protos.TransactionInput.newBuilder()
              .setScriptBytes(ByteString.copyFrom(input.getScriptBytes()))
              .setTransactionOutPointHash(hashToByteString(input.getOutpoint().getHash()))
              .setTransactionOutPointIndex((int) input.getOutpoint().getIndex());
      if (input.hasSequence()) inputBuilder.setSequence((int) input.getSequenceNumber());
      if (input.getValue() != null) inputBuilder.setValue(input.getValue().value);
      txBuilder.addTransactionInput(inputBuilder);
    }

    // Handle outputs.
    for (TransactionOutput output : tx.getOutputs()) {
      Protos.TransactionOutput.Builder outputBuilder =
          Protos.TransactionOutput.newBuilder()
              .setScriptBytes(ByteString.copyFrom(output.getScriptBytes()))
              .setValue(output.getValue().value);
      final TransactionInput spentBy = output.getSpentBy();
      if (spentBy != null) {
        Sha256Hash spendingHash = spentBy.getParentTransaction().getHash();
        int spentByTransactionIndex = spentBy.getParentTransaction().getInputs().indexOf(spentBy);
        outputBuilder
            .setSpentByTransactionHash(hashToByteString(spendingHash))
            .setSpentByTransactionIndex(spentByTransactionIndex);
      }
      txBuilder.addTransactionOutput(outputBuilder);
    }

    // Handle which blocks tx was seen in.
    final Map<Sha256Hash, Integer> appearsInHashes = tx.getAppearsInHashes();
    if (appearsInHashes != null) {
      for (Map.Entry<Sha256Hash, Integer> entry : appearsInHashes.entrySet()) {
        txBuilder.addBlockHash(hashToByteString(entry.getKey()));
        txBuilder.addBlockRelativityOffsets(entry.getValue());
      }
    }

    if (tx.hasConfidence()) {
      TransactionConfidence confidence = tx.getConfidence();
      Protos.TransactionConfidence.Builder confidenceBuilder =
          Protos.TransactionConfidence.newBuilder();
      writeConfidence(txBuilder, confidence, confidenceBuilder);
    }

    Protos.Transaction.Purpose purpose;
    switch (tx.getPurpose()) {
      case UNKNOWN:
        purpose = Protos.Transaction.Purpose.UNKNOWN;
        break;
      case USER_PAYMENT:
        purpose = Protos.Transaction.Purpose.USER_PAYMENT;
        break;
      case KEY_ROTATION:
        purpose = Protos.Transaction.Purpose.KEY_ROTATION;
        break;
      case ASSURANCE_CONTRACT_CLAIM:
        purpose = Protos.Transaction.Purpose.ASSURANCE_CONTRACT_CLAIM;
        break;
      case ASSURANCE_CONTRACT_PLEDGE:
        purpose = Protos.Transaction.Purpose.ASSURANCE_CONTRACT_PLEDGE;
        break;
      case ASSURANCE_CONTRACT_STUB:
        purpose = Protos.Transaction.Purpose.ASSURANCE_CONTRACT_STUB;
        break;
      default:
        throw new RuntimeException("New tx purpose serialization not implemented.");
    }
    txBuilder.setPurpose(purpose);

    ExchangeRate exchangeRate = tx.getExchangeRate();
    if (exchangeRate != null) {
      Protos.ExchangeRate.Builder exchangeRateBuilder =
          Protos.ExchangeRate.newBuilder()
              .setCoinValue(exchangeRate.coin.value)
              .setFiatValue(exchangeRate.fiat.value)
              .setFiatCurrencyCode(exchangeRate.fiat.currencyCode);
      txBuilder.setExchangeRate(exchangeRateBuilder);
    }

    if (tx.getMemo() != null) txBuilder.setMemo(tx.getMemo());

    return txBuilder.build();
  }