stack_wallet/lib/services/mixins/paynym_wallet_interface.dart

import 'dart:convert';
import 'dart:math';
import 'dart:typed_data';

import 'package:bip32/bip32.dart' as bip32;
import 'package:bip47/bip47.dart';
import 'package:bip47/src/util.dart';
import 'package:bitcoindart/bitcoindart.dart' as btc_dart;
import 'package:bitcoindart/src/utils/constants/op.dart' as op;
import 'package:bitcoindart/src/utils/script.dart' as bscript;
import 'package:isar/isar.dart';
import 'package:pointycastle/digests/sha256.dart';
import 'package:stackwallet/db/main_db.dart';
import 'package:stackwallet/electrumx_rpc/electrumx.dart';
import 'package:stackwallet/exceptions/wallet/insufficient_balance_exception.dart';
import 'package:stackwallet/exceptions/wallet/paynym_send_exception.dart';
import 'package:stackwallet/models/isar/models/isar_models.dart';
import 'package:stackwallet/utilities/bip32_utils.dart';
import 'package:stackwallet/utilities/bip47_utils.dart';
import 'package:stackwallet/utilities/enums/coin_enum.dart';
import 'package:stackwallet/utilities/enums/derive_path_type_enum.dart';
import 'package:stackwallet/utilities/flutter_secure_storage_interface.dart';
import 'package:stackwallet/utilities/format.dart';
import 'package:stackwallet/utilities/logger.dart';
import 'package:tuple/tuple.dart';

const kPaynymDerivePath = "m/47'/0'/0'";

mixin PaynymWalletInterface {
  // passed in wallet data
  late final String _walletId;
  late final String _walletName;
  late final btc_dart.NetworkType _network;
  late final Coin _coin;
  late final MainDB _db;
  late final ElectrumX _electrumXClient;
  late final SecureStorageInterface _secureStorage;
  late final int _dustLimitP2PKH;
  late final int _minConfirms;

  // passed in wallet functions
  late final Future<String?> Function() _getMnemonicString;
  late final Future<String?> Function() _getMnemonicPassphrase;
  late final Future<int> Function() _getChainHeight;
  late final Future<String> Function() _getCurrentChangeAddress;
  late final int Function({
    required int vSize,
    required int feeRatePerKB,
  }) _estimateTxFee;
  late final Future<Map<String, dynamic>> Function({
    required String address,
    required int satoshiAmount,
    Map<String, dynamic>? args,
  }) _prepareSend;
  late final Future<int> Function({
    required String address,
  }) _getTxCount;
  late final Future<Map<String, dynamic>> Function(
    List<UTXO> utxosToUse,
  ) _fetchBuildTxData;
  late final Future<void> Function() _refresh;
  late final Future<void> Function() _checkChangeAddressForTransactions;
  late final Future<void> Function({
    required int chain,
    required String address,
    required String pubKey,
    required String wif,
    required DerivePathType derivePathType,
  }) _addDerivation;

  // initializer
  void initPaynymWalletInterface({
    required String walletId,
    required String walletName,
    required btc_dart.NetworkType network,
    required Coin coin,
    required MainDB db,
    required ElectrumX electrumXClient,
    required SecureStorageInterface secureStorage,
    required int dustLimitP2PKH,
    required int minConfirms,
    required Future<String?> Function() getMnemonicString,
    required Future<String?> Function() getMnemonicPassphrase,
    required Future<int> Function() getChainHeight,
    required Future<String> Function() getCurrentChangeAddress,
    required int Function({
      required int vSize,
      required int feeRatePerKB,
    })
        estimateTxFee,
    required Future<Map<String, dynamic>> Function({
      required String address,
      required int satoshiAmount,
      Map<String, dynamic>? args,
    })
        prepareSend,
    required Future<int> Function({
      required String address,
    })
        getTxCount,
    required Future<Map<String, dynamic>> Function(
      List<UTXO> utxosToUse,
    )
        fetchBuildTxData,
    required Future<void> Function() refresh,
    required Future<void> Function() checkChangeAddressForTransactions,
    required Future<void> Function({
      required int chain,
      required String address,
      required String pubKey,
      required String wif,
      required DerivePathType derivePathType,
    })
        addDerivation,
  }) {
    _walletId = walletId;
    _walletName = walletName;
    _network = network;
    _coin = coin;
    _db = db;
    _electrumXClient = electrumXClient;
    _secureStorage = secureStorage;
    _dustLimitP2PKH = dustLimitP2PKH;
    _minConfirms = minConfirms;
    _getMnemonicString = getMnemonicString;
    _getMnemonicPassphrase = getMnemonicPassphrase;
    _getChainHeight = getChainHeight;
    _getCurrentChangeAddress = getCurrentChangeAddress;
    _estimateTxFee = estimateTxFee;
    _prepareSend = prepareSend;
    _getTxCount = getTxCount;
    _fetchBuildTxData = fetchBuildTxData;
    _refresh = refresh;
    _checkChangeAddressForTransactions = checkChangeAddressForTransactions;
    _addDerivation = addDerivation;
  }

  // convenience getter
  btc_dart.NetworkType get networkType => _network;

  Future<Address> currentReceivingPaynymAddress(PaymentCode sender) async {
    final keys = await lookupKey(sender.toString());
    final address = await _db
        .getAddresses(_walletId)
        .filter()
        .subTypeEqualTo(AddressSubType.paynymReceive)
        .and()
        .anyOf<String, Address>(keys, (q, String e) => q.otherDataEqualTo(e))
        .sortByDerivationIndexDesc()
        .findFirst();

    if (address == null) {
      final generatedAddress = await _generatePaynymReceivingAddress(sender, 0);

      final existing = await _db
          .getAddresses(_walletId)
          .filter()
          .valueEqualTo(generatedAddress.value)
          .findFirst();

      if (existing == null) {
        // Add that new address
        await _db.putAddress(generatedAddress);
      } else {
        // we need to update the address
        await _db.updateAddress(existing, generatedAddress);
      }

      return currentReceivingPaynymAddress(sender);
    } else {
      return address;
    }
  }

  Future<Address> _generatePaynymReceivingAddress(
    PaymentCode sender,
    int index,
  ) async {
    final myPrivateKey = await deriveReceivingPrivateKey(
      mnemonic: (await _getMnemonicString())!,
      mnemonicPassphrase: (await _getMnemonicPassphrase())!,
      index: index,
    );

    final paymentAddress = PaymentAddress.initWithPrivateKey(
      myPrivateKey,
      sender,
      0,
    );
    final pair = paymentAddress.getReceiveAddressKeyPair();
    final address = await generatePaynymReceivingAddressFromKeyPair(
      pair: pair,
      derivationIndex: index,
      derivePathType: DerivePathType.bip44,
      fromPaymentCode: sender,
    );
    return address;
  }

  Future<void> checkCurrentPaynymReceivingAddressForTransactions(
      PaymentCode sender) async {
    final address = await currentReceivingPaynymAddress(sender);
    final txCount = await _getTxCount(address: address.value);
    if (txCount > 0) {
      // generate next address and add to db
      final nextAddress = await _generatePaynymReceivingAddress(
        sender,
        address.derivationIndex + 1,
      );

      final existing = await _db
          .getAddresses(_walletId)
          .filter()
          .valueEqualTo(nextAddress.value)
          .findFirst();

      if (existing == null) {
        // Add that new address
        await _db.putAddress(nextAddress);
      } else {
        // we need to update the address
        await _db.updateAddress(existing, nextAddress);
      }
      // keep checking until address with no tx history is set as current
      await checkCurrentPaynymReceivingAddressForTransactions(sender);
    }
  }

  Future<void> checkAllCurrentReceivingPaynymAddressesForTransactions() async {
    final codes = await getAllPaymentCodesFromNotificationTransactions();
    final List<Future<void>> futures = [];
    for (final code in codes) {
      futures.add(checkCurrentPaynymReceivingAddressForTransactions(code));
    }
    await Future.wait(futures);
  }

  // generate bip32 payment code root
  Future<bip32.BIP32> _getRootNode({
    required String mnemonic,
    required String mnemonicPassphrase,
  }) async {
    final root = await Bip32Utils.getBip32Root(
      mnemonic,
      mnemonicPassphrase,
      _network,
    );
    return root;
  }

  Future<Uint8List> deriveNotificationPrivateKey({
    required String mnemonic,
    required String mnemonicPassphrase,
  }) async {
    final root = await _getRootNode(
      mnemonic: mnemonic,
      mnemonicPassphrase: mnemonicPassphrase,
    );
    final node = root.derivePath(kPaynymDerivePath).derive(0);
    return node.privateKey!;
  }

  Future<Uint8List> deriveReceivingPrivateKey({
    required String mnemonic,
    required String mnemonicPassphrase,
    required int index,
  }) async {
    final root = await _getRootNode(
      mnemonic: mnemonic,
      mnemonicPassphrase: mnemonicPassphrase,
    );
    final node = root.derivePath(kPaynymDerivePath).derive(index);
    return node.privateKey!;
  }

  /// fetch or generate this wallet's bip47 payment code
  Future<PaymentCode> getPaymentCode(
    DerivePathType derivePathType,
  ) async {
    final address = await getMyNotificationAddress(derivePathType);
    final pCodeString = await paymentCodeStringByKey(address.otherData!);
    final paymentCode = PaymentCode.fromPaymentCode(
      pCodeString!,
      _network,
    );
    return paymentCode;
  }

  Future<Uint8List> signWithNotificationKey(Uint8List data) async {
    final privateKey = await deriveNotificationPrivateKey(
      mnemonic: (await _getMnemonicString())!,
      mnemonicPassphrase: (await _getMnemonicPassphrase())!,
    );
    final pair = btc_dart.ECPair.fromPrivateKey(privateKey, network: _network);
    final signed = pair.sign(SHA256Digest().process(data));
    return signed;
  }

  Future<String> signStringWithNotificationKey(String data) async {
    final bytes =
        await signWithNotificationKey(Uint8List.fromList(utf8.encode(data)));
    return Format.uint8listToString(bytes);
  }

  Future<Map<String, dynamic>> preparePaymentCodeSend(
      {required PaymentCode paymentCode,
      required int satoshiAmount,
      Map<String, dynamic>? args}) async {
    if (!(await hasConnected(paymentCode.toString()))) {
      throw PaynymSendException(
          "No notification transaction sent to $paymentCode");
    } else {
      final myPrivateKey = await deriveNotificationPrivateKey(
        mnemonic: (await _getMnemonicString())!,
        mnemonicPassphrase: (await _getMnemonicPassphrase())!,
      );
      final sendToAddress = await nextUnusedSendAddressFrom(
        pCode: paymentCode,
        privateKey: myPrivateKey,
      );

      return _prepareSend(
        address: sendToAddress.value,
        satoshiAmount: satoshiAmount,
        args: args,
      );
    }
  }

  /// get the next unused address to send to given the receiver's payment code
  /// and your own private key
  Future<Address> nextUnusedSendAddressFrom({
    required PaymentCode pCode,
    required Uint8List privateKey,
    int startIndex = 0,
  }) async {
    // https://en.bitcoin.it/wiki/BIP_0047#Path_levels
    const maxCount = 2147483647;

    for (int i = startIndex; i < maxCount; i++) {
      final keys = await lookupKey(pCode.toString());
      final address = await _db
          .getAddresses(_walletId)
          .filter()
          .subTypeEqualTo(AddressSubType.paynymSend)
          .and()
          .anyOf<String, Address>(keys, (q, String e) => q.otherDataEqualTo(e))
          .and()
          .derivationIndexEqualTo(i)
          .findFirst();

      if (address != null) {
        final count = await _getTxCount(address: address.value);
        // return address if unused, otherwise continue to next index
        if (count == 0) {
          return address;
        }
      } else {
        final pair = PaymentAddress.initWithPrivateKey(
          privateKey,
          pCode,
          i, // index to use
        ).getSendAddressKeyPair();

        // add address to local db
        final address = await generatePaynymSendAddressFromKeyPair(
          pair: pair,
          derivationIndex: i,
          derivePathType: DerivePathType.bip44,
          toPaymentCode: pCode,
        );

        final storedAddress = await _db.getAddress(_walletId, address.value);
        if (storedAddress == null) {
          await _db.putAddress(address);
        } else {
          await _db.updateAddress(storedAddress, address);
        }
        final count = await _getTxCount(address: address.value);
        // return address if unused, otherwise continue to next index
        if (count == 0) {
          return address;
        }
      }
    }

    throw PaynymSendException("Exhausted unused send addresses!");
  }

  Future<Map<String, dynamic>> prepareNotificationTx({
    required int selectedTxFeeRate,
    required String targetPaymentCodeString,
    int additionalOutputs = 0,
    List<UTXO>? utxos,
  }) async {
    final amountToSend = _dustLimitP2PKH;
    final List<UTXO> availableOutputs =
        utxos ?? await _db.getUTXOs(_walletId).findAll();
    final List<UTXO> spendableOutputs = [];
    int spendableSatoshiValue = 0;

    // Build list of spendable outputs and totaling their satoshi amount
    for (var i = 0; i < availableOutputs.length; i++) {
      if (availableOutputs[i].isBlocked == false &&
          availableOutputs[i]
                  .isConfirmed(await _getChainHeight(), _minConfirms) ==
              true) {
        spendableOutputs.add(availableOutputs[i]);
        spendableSatoshiValue += availableOutputs[i].value;
      }
    }

    if (spendableSatoshiValue < amountToSend) {
      // insufficient balance
      throw InsufficientBalanceException(
          "Spendable balance is less than the minimum required for a notification transaction.");
    } else if (spendableSatoshiValue == amountToSend) {
      // insufficient balance due to missing amount to cover fee
      throw InsufficientBalanceException(
          "Remaining balance does not cover the network fee.");
    }

    // sort spendable by age (oldest first)
    spendableOutputs.sort((a, b) => b.blockTime!.compareTo(a.blockTime!));

    int satoshisBeingUsed = 0;
    int outputsBeingUsed = 0;
    List<UTXO> utxoObjectsToUse = [];

    for (int i = 0;
        satoshisBeingUsed < amountToSend && i < spendableOutputs.length;
        i++) {
      utxoObjectsToUse.add(spendableOutputs[i]);
      satoshisBeingUsed += spendableOutputs[i].value;
      outputsBeingUsed += 1;
    }

    // add additional outputs if required
    for (int i = 0;
        i < additionalOutputs && outputsBeingUsed < spendableOutputs.length;
        i++) {
      utxoObjectsToUse.add(spendableOutputs[outputsBeingUsed]);
      satoshisBeingUsed += spendableOutputs[outputsBeingUsed].value;
      outputsBeingUsed += 1;
    }

    // gather required signing data
    final utxoSigningData = await _fetchBuildTxData(utxoObjectsToUse);

    final int vSizeForNoChange = (await _createNotificationTx(
            targetPaymentCodeString: targetPaymentCodeString,
            utxosToUse: utxoObjectsToUse,
            utxoSigningData: utxoSigningData,
            change: 0))
        .item2;

    final int vSizeForWithChange = (await _createNotificationTx(
            targetPaymentCodeString: targetPaymentCodeString,
            utxosToUse: utxoObjectsToUse,
            utxoSigningData: utxoSigningData,
            change: satoshisBeingUsed - amountToSend))
        .item2;

    // Assume 2 outputs, for recipient and payment code script
    int feeForNoChange = _estimateTxFee(
      vSize: vSizeForNoChange,
      feeRatePerKB: selectedTxFeeRate,
    );

    // Assume 3 outputs, for recipient, payment code script, and change
    int feeForWithChange = _estimateTxFee(
      vSize: vSizeForWithChange,
      feeRatePerKB: selectedTxFeeRate,
    );

    if (_coin == Coin.dogecoin || _coin == Coin.dogecoinTestNet) {
      if (feeForNoChange < vSizeForNoChange * 1000) {
        feeForNoChange = vSizeForNoChange * 1000;
      }
      if (feeForWithChange < vSizeForWithChange * 1000) {
        feeForWithChange = vSizeForWithChange * 1000;
      }
    }

    if (satoshisBeingUsed - amountToSend > feeForNoChange + _dustLimitP2PKH) {
      // try to add change output due to "left over" amount being greater than
      // the estimated fee + the dust limit
      int changeAmount = satoshisBeingUsed - amountToSend - feeForWithChange;

      // check estimates are correct and build notification tx
      if (changeAmount >= _dustLimitP2PKH &&
          satoshisBeingUsed - amountToSend - changeAmount == feeForWithChange) {
        var txn = await _createNotificationTx(
          targetPaymentCodeString: targetPaymentCodeString,
          utxosToUse: utxoObjectsToUse,
          utxoSigningData: utxoSigningData,
          change: changeAmount,
        );

        int feeBeingPaid = satoshisBeingUsed - amountToSend - changeAmount;

        // make sure minimum fee is accurate if that is being used
        if (txn.item2 - feeBeingPaid == 1) {
          changeAmount -= 1;
          feeBeingPaid += 1;
          txn = await _createNotificationTx(
            targetPaymentCodeString: targetPaymentCodeString,
            utxosToUse: utxoObjectsToUse,
            utxoSigningData: utxoSigningData,
            change: changeAmount,
          );
        }

        Map<String, dynamic> transactionObject = {
          "hex": txn.item1,
          "recipientPaynym": targetPaymentCodeString,
          "amount": amountToSend,
          "fee": feeBeingPaid,
          "vSize": txn.item2,
        };
        return transactionObject;
      } else {
        // something broke during fee estimation or the change amount is smaller
        // than the dust limit. Try without change
        final txn = await _createNotificationTx(
          targetPaymentCodeString: targetPaymentCodeString,
          utxosToUse: utxoObjectsToUse,
          utxoSigningData: utxoSigningData,
          change: 0,
        );

        int feeBeingPaid = satoshisBeingUsed - amountToSend;

        Map<String, dynamic> transactionObject = {
          "hex": txn.item1,
          "recipientPaynym": targetPaymentCodeString,
          "amount": amountToSend,
          "fee": feeBeingPaid,
          "vSize": txn.item2,
        };
        return transactionObject;
      }
    } else if (satoshisBeingUsed - amountToSend >= feeForNoChange) {
      // since we already checked if we need to add a change output we can just
      // build without change here
      final txn = await _createNotificationTx(
        targetPaymentCodeString: targetPaymentCodeString,
        utxosToUse: utxoObjectsToUse,
        utxoSigningData: utxoSigningData,
        change: 0,
      );

      int feeBeingPaid = satoshisBeingUsed - amountToSend;

      Map<String, dynamic> transactionObject = {
        "hex": txn.item1,
        "recipientPaynym": targetPaymentCodeString,
        "amount": amountToSend,
        "fee": feeBeingPaid,
        "vSize": txn.item2,
      };
      return transactionObject;
    } else {
      // if we get here we do not have enough funds to cover the tx total so we
      // check if we have any more available outputs and try again
      if (spendableOutputs.length > outputsBeingUsed) {
        return prepareNotificationTx(
          selectedTxFeeRate: selectedTxFeeRate,
          targetPaymentCodeString: targetPaymentCodeString,
          additionalOutputs: additionalOutputs + 1,
        );
      } else {
        throw InsufficientBalanceException(
            "Remaining balance does not cover the network fee.");
      }
    }
  }

  // return tuple with string value equal to the raw tx hex and the int value
  // equal to its vSize
  Future<Tuple2<String, int>> _createNotificationTx({
    required String targetPaymentCodeString,
    required List<UTXO> utxosToUse,
    required Map<String, dynamic> utxoSigningData,
    required int change,
  }) async {
    final targetPaymentCode =
        PaymentCode.fromPaymentCode(targetPaymentCodeString, _network);
    final myCode = await getPaymentCode(DerivePathType.bip44);

    final utxo = utxosToUse.first;
    final txPoint = utxo.txid.fromHex.toList();
    final txPointIndex = utxo.vout;

    final rev = Uint8List(txPoint.length + 4);
    Util.copyBytes(Uint8List.fromList(txPoint), 0, rev, 0, txPoint.length);
    final buffer = rev.buffer.asByteData();
    buffer.setUint32(txPoint.length, txPointIndex, Endian.little);

    final myKeyPair = utxoSigningData[utxo.txid]["keyPair"] as btc_dart.ECPair;

    final S = SecretPoint(
      myKeyPair.privateKey!,
      targetPaymentCode.notificationPublicKey(),
    );

    final blindingMask = PaymentCode.getMask(S.ecdhSecret(), rev);

    final blindedPaymentCode = PaymentCode.blind(
      myCode.getPayload(),
      blindingMask,
    );

    final opReturnScript = bscript.compile([
      (op.OPS["OP_RETURN"] as int),
      blindedPaymentCode,
    ]);

    // build a notification tx
    final txb = btc_dart.TransactionBuilder(network: _network);
    txb.setVersion(1);

    txb.addInput(
      utxo.txid,
      txPointIndex,
      null,
      utxoSigningData[utxo.txid]["output"] as Uint8List,
    );

    // todo: modify address once segwit support is in our bip47
    txb.addOutput(
        targetPaymentCode.notificationAddressP2PKH(), _dustLimitP2PKH);
    txb.addOutput(opReturnScript, 0);

    // TODO: add possible change output and mark output as dangerous
    if (change > 0) {
      // generate new change address if current change address has been used
      await _checkChangeAddressForTransactions();
      final String changeAddress = await _getCurrentChangeAddress();
      txb.addOutput(changeAddress, change);
    }

    txb.sign(
      vin: 0,
      keyPair: myKeyPair,
      witnessValue: utxo.value,
      witnessScript: utxoSigningData[utxo.txid]["redeemScript"] as Uint8List?,
    );

    // sign rest of possible inputs
    for (var i = 1; i < utxosToUse.length; i++) {
      final txid = utxosToUse[i].txid;
      txb.sign(
        vin: i,
        keyPair: utxoSigningData[txid]["keyPair"] as btc_dart.ECPair,
        witnessValue: utxosToUse[i].value,
        witnessScript: utxoSigningData[utxo.txid]["redeemScript"] as Uint8List?,
      );
    }

    final builtTx = txb.build();

    return Tuple2(builtTx.toHex(), builtTx.virtualSize());
  }

  Future<String> broadcastNotificationTx(
      {required Map<String, dynamic> preparedTx}) async {
    try {
      Logging.instance.log("confirmNotificationTx txData: $preparedTx",
          level: LogLevel.Info);
      final txHash = await _electrumXClient.broadcastTransaction(
          rawTx: preparedTx["hex"] as String);
      Logging.instance.log("Sent txHash: $txHash", level: LogLevel.Info);

      // TODO: only refresh transaction data
      try {
        await _refresh();
      } catch (e) {
        Logging.instance.log(
          "refresh() failed in confirmNotificationTx ($_walletName::$_walletId): $e",
          level: LogLevel.Error,
        );
      }

      return txHash;
    } catch (e, s) {
      Logging.instance.log("Exception rethrown from confirmSend(): $e\n$s",
          level: LogLevel.Error);
      rethrow;
    }
  }

  // TODO optimize
  Future<bool> hasConnected(String paymentCodeString) async {
    final myNotificationAddress =
        await getMyNotificationAddress(DerivePathTypeExt.primaryFor(_coin));

    final txns = await _db
        .getTransactions(_walletId)
        .filter()
        .subTypeEqualTo(TransactionSubType.bip47Notification)
        .findAll();

    for (final tx in txns) {
      // quick check that may cause problems?
      if (tx.address.value?.value == myNotificationAddress.value) {
        return true;
      }

      final unBlindedPaymentCode = await unBlindedPaymentCodeFromTransaction(
        transaction: tx,
        myNotificationAddress: myNotificationAddress,
      );

      if (paymentCodeString == unBlindedPaymentCode.toString()) {
        return true;
      }

      if (tx.address.value?.otherData != null) {
        final code = await paymentCodeStringByKey(tx.address.value!.otherData!);
        if (code == paymentCodeString) {
          return true;
        }
      }
    }

    // otherwise return no
    return false;
  }

  Future<PaymentCode?> unBlindedPaymentCodeFromTransaction({
    required Transaction transaction,
    required Address myNotificationAddress,
  }) async {
    if (transaction.address.value != null &&
        transaction.address.value!.value != myNotificationAddress.value) {
      return null;
    }

    try {
      final blindedCodeBytes =
          Bip47Utils.getBlindedPaymentCodeBytesFrom(transaction);

      // transaction does not contain a payment code
      if (blindedCodeBytes == null) {
        return null;
      }

      final designatedInput = transaction.inputs.first;

      final txPoint = designatedInput.txid.fromHex.toList();
      final txPointIndex = designatedInput.vout;

      final rev = Uint8List(txPoint.length + 4);
      Util.copyBytes(Uint8List.fromList(txPoint), 0, rev, 0, txPoint.length);
      final buffer = rev.buffer.asByteData();
      buffer.setUint32(txPoint.length, txPointIndex, Endian.little);

      final pubKey = designatedInput.scriptSigAsm!.split(" ")[1].fromHex;

      final myPrivateKey = await deriveNotificationPrivateKey(
        mnemonic: (await _getMnemonicString())!,
        mnemonicPassphrase: (await _getMnemonicPassphrase())!,
      );

      final S = SecretPoint(myPrivateKey, pubKey);

      final mask = PaymentCode.getMask(S.ecdhSecret(), rev);

      final unBlindedPayload = PaymentCode.blind(blindedCodeBytes, mask);

      final unBlindedPaymentCode =
          PaymentCode.initFromPayload(unBlindedPayload);

      return unBlindedPaymentCode;
    } catch (e) {
      Logging.instance.log(
        "unBlindedPaymentCodeFromTransaction() failed: $e",
        level: LogLevel.Warning,
      );
      return null;
    }
  }

  Future<List<PaymentCode>>
      getAllPaymentCodesFromNotificationTransactions() async {
    final myAddress =
        await getMyNotificationAddress(DerivePathTypeExt.primaryFor(_coin));
    final txns = await _db
        .getTransactions(_walletId)
        .filter()
        .subTypeEqualTo(TransactionSubType.bip47Notification)
        .findAll();

    List<PaymentCode> codes = [];

    for (final tx in txns) {
      // tx is sent so we can check the address's otherData for the code String
      if (tx.type == TransactionType.outgoing &&
          tx.address.value?.otherData != null) {
        final codeString =
            await paymentCodeStringByKey(tx.address.value!.otherData!);
        if (codeString != null &&
            codes.where((e) => e.toString() == codeString).isEmpty) {
          codes.add(PaymentCode.fromPaymentCode(codeString, _network));
        }
      } else {
        // otherwise we need to un blind the code
        final unBlinded = await unBlindedPaymentCodeFromTransaction(
          transaction: tx,
          myNotificationAddress: myAddress,
        );
        if (unBlinded != null &&
            codes.where((e) => e.toString() == unBlinded.toString()).isEmpty) {
          codes.add(unBlinded);
        }
      }
    }

    return codes;
  }

  Future<void> checkForNotificationTransactionsTo(
      Set<String> otherCodeStrings) async {
    final sentNotificationTransactions = await _db
        .getTransactions(_walletId)
        .filter()
        .subTypeEqualTo(TransactionSubType.bip47Notification)
        .and()
        .typeEqualTo(TransactionType.outgoing)
        .findAll();

    final List<PaymentCode> codes = [];
    for (final codeString in otherCodeStrings) {
      codes.add(PaymentCode.fromPaymentCode(codeString, _network));
    }

    for (final tx in sentNotificationTransactions) {
      if (tx.address.value != null && tx.address.value!.otherData == null) {
        final oldAddress =
            await _db.getAddress(_walletId, tx.address.value!.value);
        for (final code in codes) {
          final notificationAddress = code.notificationAddressP2PKH();
          if (notificationAddress == oldAddress!.value) {
            final address = Address(
              walletId: _walletId,
              value: notificationAddress,
              publicKey: [],
              derivationIndex: 0,
              derivationPath:
                  null, // might as well use null due to complexity of context
              type: oldAddress.type,
              subType: AddressSubType.paynymNotification,
              otherData: await storeCode(code.toString()),
            );
            await _db.updateAddress(oldAddress, address);
          }
        }
      }
    }
  }

  Future<void> restoreAllHistory({
    required int maxUnusedAddressGap,
    required int maxNumberOfIndexesToCheck,
    required Set<String> paymentCodeStrings,
  }) async {
    final codes = await getAllPaymentCodesFromNotificationTransactions();
    final List<PaymentCode> extraCodes = [];
    for (final codeString in paymentCodeStrings) {
      if (codes.where((e) => e.toString() == codeString).isEmpty) {
        final extraCode = PaymentCode.fromPaymentCode(codeString, _network);
        if (extraCode.isValid()) {
          extraCodes.add(extraCode);
        }
      }
    }

    codes.addAll(extraCodes);

    final List<Future<void>> futures = [];
    for (final code in codes) {
      futures.add(
        restoreHistoryWith(
          code,
          maxUnusedAddressGap,
          maxNumberOfIndexesToCheck,
        ),
      );
    }

    await Future.wait(futures);
  }

  Future<void> restoreHistoryWith(
    PaymentCode other,
    int maxUnusedAddressGap,
    int maxNumberOfIndexesToCheck,
  ) async {
    // https://en.bitcoin.it/wiki/BIP_0047#Path_levels
    const maxCount = 2147483647;
    assert(maxNumberOfIndexesToCheck < maxCount);

    final mnemonic = (await _getMnemonicString())!;
    final mnemonicPassphrase = (await _getMnemonicPassphrase())!;

    final mySendPrivateKey = await deriveNotificationPrivateKey(
      mnemonic: mnemonic,
      mnemonicPassphrase: mnemonicPassphrase,
    );
    final receivingNode = (await _getRootNode(
      mnemonic: mnemonic,
      mnemonicPassphrase: mnemonicPassphrase,
    ))
        .derivePath(kPaynymDerivePath);

    List<Address> addresses = [];
    int receivingGapCounter = 0;
    int outgoingGapCounter = 0;

    for (int i = 0;
        i < maxNumberOfIndexesToCheck &&
            (receivingGapCounter < maxUnusedAddressGap ||
                outgoingGapCounter < maxUnusedAddressGap);
        i++) {
      if (outgoingGapCounter < maxUnusedAddressGap) {
        final paymentAddressSending = PaymentAddress.initWithPrivateKey(
          mySendPrivateKey,
          other,
          i, // index to use
        );
        final pair = paymentAddressSending.getSendAddressKeyPair();
        final address = await generatePaynymSendAddressFromKeyPair(
          pair: pair,
          derivationIndex: i,
          derivePathType: DerivePathType.bip44,
          toPaymentCode: other,
        );
        addresses.add(address);

        final count = await _getTxCount(address: address.value);

        if (count > 0) {
          outgoingGapCounter = 0;
        } else {
          outgoingGapCounter++;
        }
      }

      if (receivingGapCounter < maxUnusedAddressGap) {
        final myReceivingPrivateKey = receivingNode.derive(i).privateKey!;
        final paymentAddressReceiving = PaymentAddress.initWithPrivateKey(
          myReceivingPrivateKey,
          other,
          0,
        );
        final pair = paymentAddressReceiving.getReceiveAddressKeyPair();
        final address = await generatePaynymReceivingAddressFromKeyPair(
          pair: pair,
          derivationIndex: i,
          derivePathType: DerivePathType.bip44,
          fromPaymentCode: other,
        );
        addresses.add(address);

        final count = await _getTxCount(address: address.value);

        if (count > 0) {
          receivingGapCounter = 0;
        } else {
          receivingGapCounter++;
        }
      }
    }
    await _db.updateOrPutAddresses(addresses);
  }

  Future<Address> generatePaynymSendAddressFromKeyPair({
    required btc_dart.ECPair pair,
    required int derivationIndex,
    required DerivePathType derivePathType,
    required PaymentCode toPaymentCode,
  }) async {
    final data = btc_dart.PaymentData(pubkey: pair.publicKey);

    String addressString;
    switch (derivePathType) {
      case DerivePathType.bip44:
        addressString =
            btc_dart.P2PKH(data: data, network: _network).data.address!;
        break;

      // The following doesn't apply currently
      // case DerivePathType.bip49:
      //   addressString = btc_dart
      //       .P2SH(
      //         data: btc_dart.PaymentData(
      //             redeem: btc_dart
      //                 .P2WPKH(
      //                   data: data,
      //                   network: network,
      //                 )
      //                 .data),
      //         network: network,
      //       )
      //       .data
      //       .address!;
      //   break;
      //
      // case DerivePathType.bip84:
      //   addressString = btc_dart
      //       .P2WPKH(
      //         network: network,
      //         data: data,
      //       )
      //       .data
      //       .address!;
      //   break;
      default:
        throw UnimplementedError("segwit paynyms not implemented yet");
    }

    final address = Address(
      walletId: _walletId,
      value: addressString,
      publicKey: pair.publicKey,
      derivationIndex: derivationIndex,
      derivationPath:
          null, // might as well use null due to complexity of context
      type: AddressType.nonWallet,
      subType: AddressSubType.paynymSend,
      otherData: await storeCode(toPaymentCode.toString()),
    );

    return address;
  }

  Future<Address> generatePaynymReceivingAddressFromKeyPair({
    required btc_dart.ECPair pair,
    required int derivationIndex,
    required DerivePathType derivePathType,
    required PaymentCode fromPaymentCode,
  }) async {
    final data = btc_dart.PaymentData(pubkey: pair.publicKey);

    String addressString;
    AddressType addrType;
    switch (derivePathType) {
      case DerivePathType.bip44:
        addressString = btc_dart
            .P2PKH(
              data: data,
              network: _network,
            )
            .data
            .address!;
        addrType = AddressType.p2pkh;
        break;

      // The following doesn't apply currently
      // case DerivePathType.bip49:
      //   addressString = btc_dart
      //       .P2SH(
      //         data: btc_dart.PaymentData(
      //             redeem: btc_dart
      //                 .P2WPKH(
      //                   data: data,
      //                   network: network,
      //                 )
      //                 .data),
      //         network: network,
      //       )
      //       .data
      //       .address!;
      //   addrType = AddressType.p2sh;
      //   break;
      //
      // case DerivePathType.bip84:
      //   addressString = btc_dart
      //       .P2WPKH(
      //         network: network,
      //         data: data,
      //       )
      //       .data
      //       .address!;
      //   addrType = AddressType.p2wpkh;
      //   break;
      default:
        throw UnimplementedError("segwit paynyms not implemented yet");
    }

    final address = Address(
      walletId: _walletId,
      value: addressString,
      publicKey: pair.publicKey,
      derivationIndex: derivationIndex,
      derivationPath:
          null, // might as well use null due to complexity of context
      type: addrType,
      subType: AddressSubType.paynymReceive,
      otherData: await storeCode(fromPaymentCode.toString()),
    );

    final myCode = await getPaymentCode(DerivePathType.bip44);

    final bip32NetworkType = bip32.NetworkType(
      wif: _network.wif,
      bip32: bip32.Bip32Type(
        public: _network.bip32.public,
        private: _network.bip32.private,
      ),
    );

    final bip32.BIP32 node = bip32.BIP32.fromPrivateKey(
      pair.privateKey!,
      myCode.getChain(),
      bip32NetworkType,
    );

    await _addDerivation(
      chain: 0,
      address: address.value,
      derivePathType: DerivePathType.bip44,
      pubKey: Format.uint8listToString(node.publicKey),
      wif: node.toWIF(),
    );

    return address;
  }

  Future<Address> getMyNotificationAddress(
    DerivePathType derivePathType,
  ) async {
    // TODO: fix when segwit is here
    derivePathType = DerivePathType.bip44;

    AddressType type;
    switch (derivePathType) {
      case DerivePathType.bip44:
        type = AddressType.p2pkh;
        break;
      case DerivePathType.bip49:
        type = AddressType.p2sh;
        break;
      case DerivePathType.bip84:
        type = AddressType.p2wpkh;
        break;
      default:
        throw Exception("DerivePathType $derivePathType not supported");
    }

    final storedAddress = await _db
        .getAddresses(_walletId)
        .filter()
        .subTypeEqualTo(AddressSubType.paynymNotification)
        .and()
        .typeEqualTo(type)
        .and()
        .not()
        .typeEqualTo(AddressType.nonWallet)
        .findFirst();

    if (storedAddress != null) {
      return storedAddress;
    } else {
      final root = await _getRootNode(
        mnemonic: (await _getMnemonicString())!,
        mnemonicPassphrase: (await _getMnemonicPassphrase())!,
      );
      final node = root.derivePath(kPaynymDerivePath);
      final paymentCode = PaymentCode.initFromPubKey(
        node.publicKey,
        node.chainCode,
        _network,
      );

      String addressString;
      final data =
          btc_dart.PaymentData(pubkey: paymentCode.notificationPublicKey());
      switch (derivePathType) {
        case DerivePathType.bip44:
          addressString = btc_dart
              .P2PKH(
                data: data,
                network: _network,
              )
              .data
              .address!;
          break;
        // case DerivePathType.bip49:
        //   addressString = btc_dart
        //       .P2SH(
        //         data: btc_dart.PaymentData(
        //             redeem: btc_dart
        //                 .P2WPKH(
        //                   data: data,
        //                   network: network,
        //                 )
        //                 .data),
        //         network: network,
        //       )
        //       .data
        //       .address!;
        //   break;
        // case DerivePathType.bip84:
        //   addressString = btc_dart
        //       .P2WPKH(
        //         network: network,
        //         data: data,
        //       )
        //       .data
        //       .address!;
        //   break;
        default:
          throw UnimplementedError("segwit paynyms not implemented yet");
      }

      final address = Address(
        walletId: _walletId,
        value: addressString,
        publicKey: paymentCode.getPubKey(),
        derivationIndex: 0,
        derivationPath:
            null, // might as well use null due to complexity of context
        type: type,
        subType: AddressSubType.paynymNotification,
        otherData: await storeCode(paymentCode.toString()),
      );

      await _addDerivation(
        chain: 0,
        address: address.value,
        derivePathType: DerivePathType.bip44,
        pubKey: Format.uint8listToString(node.publicKey),
        wif: node.toWIF(),
      );

      await _db.putAddress(address);
      return address;
    }
  }

  /// look up a key that corresponds to a payment code string
  Future<List<String>> lookupKey(String paymentCodeString) async {
    final keys =
        (await _secureStorage.keys).where((e) => e.startsWith(kPCodeKeyPrefix));
    final List<String> result = [];
    for (final key in keys) {
      final value = await _secureStorage.read(key: key);
      if (value == paymentCodeString) {
        result.add(key);
      }
    }
    return result;
  }

  /// fetch a payment code string
  Future<String?> paymentCodeStringByKey(String key) async {
    final value = await _secureStorage.read(key: key);
    return value;
  }

  /// store payment code string and return the generated key used
  Future<String> storeCode(String paymentCodeString) async {
    final key = _generateKey();
    await _secureStorage.write(key: key, value: paymentCodeString);
    return key;
  }

  /// generate a new payment code string storage key
  String _generateKey() {
    final bytes = _randomBytes(24);
    return "$kPCodeKeyPrefix${bytes.toHex}";
  }

  // https://github.com/AaronFeickert/stack_wallet_backup/blob/master/lib/secure_storage.dart#L307-L311
  /// Generate cryptographically-secure random bytes
  Uint8List _randomBytes(int n) {
    final Random rng = Random.secure();
    return Uint8List.fromList(
        List<int>.generate(n, (_) => rng.nextInt(0xFF + 1)));
  }
}

const String kPCodeKeyPrefix = "pCode_key_";