stack_wallet/lib/wallets/wallet/wallet_mixin_interfaces/electrumx_interface.dart

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

import 'package:bip47/src/util.dart';
import 'package:bitcoindart/bitcoindart.dart' as bitcoindart;
import 'package:coinlib_flutter/coinlib_flutter.dart' as coinlib;
import 'package:decimal/decimal.dart';
import 'package:isar/isar.dart';
import 'package:stackwallet/electrumx_rpc/cached_electrumx_client.dart';
import 'package:stackwallet/electrumx_rpc/electrumx_client.dart';
import 'package:stackwallet/models/isar/models/isar_models.dart';
import 'package:stackwallet/models/paymint/fee_object_model.dart';
import 'package:stackwallet/models/signing_data.dart';
import 'package:stackwallet/utilities/amount/amount.dart';
import 'package:stackwallet/utilities/enums/coin_enum.dart';
import 'package:stackwallet/utilities/enums/derive_path_type_enum.dart';
import 'package:stackwallet/utilities/enums/fee_rate_type_enum.dart';
import 'package:stackwallet/utilities/logger.dart';
import 'package:stackwallet/wallets/crypto_currency/coins/firo.dart';
import 'package:stackwallet/wallets/models/tx_data.dart';
import 'package:stackwallet/wallets/wallet/intermediate/bip39_hd_wallet.dart';
import 'package:stackwallet/wallets/wallet/wallet_mixin_interfaces/paynym_interface.dart';
import 'package:uuid/uuid.dart';

mixin ElectrumXInterface on Bip39HDWallet {
  late ElectrumXClient electrumXClient;
  late CachedElectrumXClient electrumXCachedClient;

  double? _serverVersion;
  // Firo server added batching without incrementing version number...
  bool get serverCanBatch =>
      (_serverVersion != null && _serverVersion! >= 1.6) ||
      cryptoCurrency is Firo;

  List<({String address, Amount amount})> _helperRecipientsConvert(
      List<String> addrs, List<int> satValues) {
    final List<({String address, Amount amount})> results = [];

    for (int i = 0; i < addrs.length; i++) {
      results.add((
        address: addrs[i],
        amount: Amount(
          rawValue: BigInt.from(satValues[i]),
          fractionDigits: cryptoCurrency.fractionDigits,
        ),
      ));
    }

    return results;
  }

  Future<TxData> coinSelection({
    required TxData txData,
    required bool coinControl,
    required bool isSendAll,
    int additionalOutputs = 0,
    List<UTXO>? utxos,
  }) async {
    Logging.instance
        .log("Starting coinSelection ----------", level: LogLevel.Info);

    // TODO: multiple recipients one day
    assert(txData.recipients!.length == 1);

    final recipientAddress = txData.recipients!.first.address;
    final satoshiAmountToSend = txData.amount!.raw.toInt();
    final int? satsPerVByte = txData.satsPerVByte;
    final selectedTxFeeRate = txData.feeRateAmount!;

    final List<UTXO> availableOutputs =
        utxos ?? await mainDB.getUTXOs(walletId).findAll();
    final currentChainHeight = await chainHeight;
    final List<UTXO> spendableOutputs = [];
    int spendableSatoshiValue = 0;

    // Build list of spendable outputs and totaling their satoshi amount
    for (final utxo in availableOutputs) {
      if (utxo.isBlocked == false &&
          utxo.isConfirmed(currentChainHeight, cryptoCurrency.minConfirms) &&
          utxo.used != true) {
        spendableOutputs.add(utxo);
        spendableSatoshiValue += utxo.value;
      }
    }

    if (coinControl) {
      if (spendableOutputs.length < availableOutputs.length) {
        throw ArgumentError("Attempted to use an unavailable utxo");
      }
    }

    // don't care about sorting if using all utxos
    if (!coinControl) {
      // sort spendable by age (oldest first)
      spendableOutputs.sort((a, b) => b.blockTime!.compareTo(a.blockTime!));
    }

    Logging.instance.log("spendableOutputs.length: ${spendableOutputs.length}",
        level: LogLevel.Info);
    Logging.instance.log("availableOutputs.length: ${availableOutputs.length}",
        level: LogLevel.Info);
    Logging.instance
        .log("spendableOutputs: $spendableOutputs", level: LogLevel.Info);
    Logging.instance.log("spendableSatoshiValue: $spendableSatoshiValue",
        level: LogLevel.Info);
    Logging.instance
        .log("satoshiAmountToSend: $satoshiAmountToSend", level: LogLevel.Info);
    // If the amount the user is trying to send is smaller than the amount that they have spendable,
    // then return 1, which indicates that they have an insufficient balance.
    if (spendableSatoshiValue < satoshiAmountToSend) {
      // return 1;
      throw Exception("Insufficient balance");
      // If the amount the user wants to send is exactly equal to the amount they can spend, then return
      // 2, which indicates that they are not leaving enough over to pay the transaction fee
    } else if (spendableSatoshiValue == satoshiAmountToSend && !isSendAll) {
      throw Exception("Insufficient balance to pay transaction fee");
      // return 2;
    }
    // If neither of these statements pass, we assume that the user has a spendable balance greater
    // than the amount they're attempting to send. Note that this value still does not account for
    // the added transaction fee, which may require an extra input and will need to be checked for
    // later on.

    // Possible situation right here
    int satoshisBeingUsed = 0;
    int inputsBeingConsumed = 0;
    List<UTXO> utxoObjectsToUse = [];

    if (!coinControl) {
      for (var i = 0;
          satoshisBeingUsed < satoshiAmountToSend &&
              i < spendableOutputs.length;
          i++) {
        utxoObjectsToUse.add(spendableOutputs[i]);
        satoshisBeingUsed += spendableOutputs[i].value;
        inputsBeingConsumed += 1;
      }
      for (int i = 0;
          i < additionalOutputs &&
              inputsBeingConsumed < spendableOutputs.length;
          i++) {
        utxoObjectsToUse.add(spendableOutputs[inputsBeingConsumed]);
        satoshisBeingUsed += spendableOutputs[inputsBeingConsumed].value;
        inputsBeingConsumed += 1;
      }
    } else {
      satoshisBeingUsed = spendableSatoshiValue;
      utxoObjectsToUse = spendableOutputs;
      inputsBeingConsumed = spendableOutputs.length;
    }

    Logging.instance
        .log("satoshisBeingUsed: $satoshisBeingUsed", level: LogLevel.Info);
    Logging.instance
        .log("inputsBeingConsumed: $inputsBeingConsumed", level: LogLevel.Info);
    Logging.instance
        .log('utxoObjectsToUse: $utxoObjectsToUse', level: LogLevel.Info);

    // numberOfOutputs' length must always be equal to that of recipientsArray and recipientsAmtArray
    List<String> recipientsArray = [recipientAddress];
    List<int> recipientsAmtArray = [satoshiAmountToSend];

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

    if (isSendAll) {
      Logging.instance
          .log("Attempting to send all $cryptoCurrency", level: LogLevel.Info);
      if (txData.recipients!.length != 1) {
        throw Exception(
          "Send all to more than one recipient not yet supported",
        );
      }

      final int vSizeForOneOutput = buildTransaction(
        utxoSigningData: utxoSigningData,
        txData: txData.copyWith(
          recipients: _helperRecipientsConvert(
            [recipientAddress],
            [satoshisBeingUsed - 1],
          ),
        ),
      ).vSize!;
      int feeForOneOutput = satsPerVByte != null
          ? (satsPerVByte * vSizeForOneOutput)
          : estimateTxFee(
              vSize: vSizeForOneOutput,
              feeRatePerKB: selectedTxFeeRate,
            );

      if (satsPerVByte == null) {
        final int roughEstimate = roughFeeEstimate(
          spendableOutputs.length,
          1,
          selectedTxFeeRate,
        ).raw.toInt();
        if (feeForOneOutput < roughEstimate) {
          feeForOneOutput = roughEstimate;
        }
      }

      final int amount = satoshiAmountToSend - feeForOneOutput;
      final data = buildTransaction(
        txData: txData.copyWith(
          recipients: _helperRecipientsConvert(
            [recipientAddress],
            [amount],
          ),
        ),
        utxoSigningData: utxoSigningData,
      );

      return data.copyWith(
        fee: Amount(
          rawValue: BigInt.from(feeForOneOutput),
          fractionDigits: cryptoCurrency.fractionDigits,
        ),
        usedUTXOs: utxoSigningData.map((e) => e.utxo).toList(),
      );
    }

    final int vSizeForOneOutput;
    try {
      vSizeForOneOutput = buildTransaction(
        utxoSigningData: utxoSigningData,
        txData: txData.copyWith(
          recipients: _helperRecipientsConvert(
            [recipientAddress],
            [satoshisBeingUsed - 1],
          ),
        ),
      ).vSize!;
    } catch (e) {
      Logging.instance.log("vSizeForOneOutput: $e", level: LogLevel.Error);
      rethrow;
    }

    final int vSizeForTwoOutPuts;
    try {
      vSizeForTwoOutPuts = buildTransaction(
        utxoSigningData: utxoSigningData,
        txData: txData.copyWith(
          recipients: _helperRecipientsConvert(
            [recipientAddress, (await getCurrentChangeAddress())!.value],
            [
              satoshiAmountToSend,
              max(0, satoshisBeingUsed - satoshiAmountToSend - 1)
            ],
          ),
        ),
      ).vSize!;
    } catch (e) {
      Logging.instance.log("vSizeForTwoOutPuts: $e", level: LogLevel.Error);
      rethrow;
    }

    // Assume 1 output, only for recipient and no change
    final feeForOneOutput = satsPerVByte != null
        ? (satsPerVByte * vSizeForOneOutput)
        : estimateTxFee(
            vSize: vSizeForOneOutput,
            feeRatePerKB: selectedTxFeeRate,
          );
    // Assume 2 outputs, one for recipient and one for change
    final feeForTwoOutputs = satsPerVByte != null
        ? (satsPerVByte * vSizeForTwoOutPuts)
        : estimateTxFee(
            vSize: vSizeForTwoOutPuts,
            feeRatePerKB: selectedTxFeeRate,
          );

    Logging.instance
        .log("feeForTwoOutputs: $feeForTwoOutputs", level: LogLevel.Info);
    Logging.instance
        .log("feeForOneOutput: $feeForOneOutput", level: LogLevel.Info);

    if (satoshisBeingUsed - satoshiAmountToSend > feeForOneOutput) {
      if (satoshisBeingUsed - satoshiAmountToSend >
          feeForOneOutput + cryptoCurrency.dustLimit.raw.toInt()) {
        // Here, we know that theoretically, we may be able to include another output(change) but we first need to
        // factor in the value of this output in satoshis.
        int changeOutputSize =
            satoshisBeingUsed - satoshiAmountToSend - feeForTwoOutputs;
        // We check to see if the user can pay for the new transaction with 2 outputs instead of one. If they can and
        // the second output's size > cryptoCurrency.dustLimit satoshis, we perform the mechanics required to properly generate and use a new
        // change address.
        if (changeOutputSize > cryptoCurrency.dustLimit.raw.toInt() &&
            satoshisBeingUsed - satoshiAmountToSend - changeOutputSize ==
                feeForTwoOutputs) {
          // generate new change address if current change address has been used
          await checkChangeAddressForTransactions();
          final String newChangeAddress =
              (await getCurrentChangeAddress())!.value;

          int feeBeingPaid =
              satoshisBeingUsed - satoshiAmountToSend - changeOutputSize;

          recipientsArray.add(newChangeAddress);
          recipientsAmtArray.add(changeOutputSize);
          // At this point, we have the outputs we're going to use, the amounts to send along with which addresses
          // we intend to send these amounts to. We have enough to send instructions to build the transaction.
          Logging.instance.log('2 outputs in tx', level: LogLevel.Info);
          Logging.instance
              .log('Input size: $satoshisBeingUsed', level: LogLevel.Info);
          Logging.instance.log('Recipient output size: $satoshiAmountToSend',
              level: LogLevel.Info);
          Logging.instance.log('Change Output Size: $changeOutputSize',
              level: LogLevel.Info);
          Logging.instance.log(
              'Difference (fee being paid): $feeBeingPaid sats',
              level: LogLevel.Info);
          Logging.instance
              .log('Estimated fee: $feeForTwoOutputs', level: LogLevel.Info);

          var txn = buildTransaction(
            utxoSigningData: utxoSigningData,
            txData: txData.copyWith(
              recipients: _helperRecipientsConvert(
                recipientsArray,
                recipientsAmtArray,
              ),
            ),
          );

          // make sure minimum fee is accurate if that is being used
          if (txn.vSize! - feeBeingPaid == 1) {
            int changeOutputSize =
                satoshisBeingUsed - satoshiAmountToSend - txn.vSize!;
            feeBeingPaid =
                satoshisBeingUsed - satoshiAmountToSend - changeOutputSize;
            recipientsAmtArray.removeLast();
            recipientsAmtArray.add(changeOutputSize);
            Logging.instance.log('Adjusted Input size: $satoshisBeingUsed',
                level: LogLevel.Info);
            Logging.instance.log(
                'Adjusted Recipient output size: $satoshiAmountToSend',
                level: LogLevel.Info);
            Logging.instance.log(
                'Adjusted Change Output Size: $changeOutputSize',
                level: LogLevel.Info);
            Logging.instance.log(
                'Adjusted Difference (fee being paid): $feeBeingPaid sats',
                level: LogLevel.Info);
            Logging.instance.log('Adjusted Estimated fee: $feeForTwoOutputs',
                level: LogLevel.Info);
            txn = buildTransaction(
              utxoSigningData: utxoSigningData,
              txData: txData.copyWith(
                recipients: _helperRecipientsConvert(
                  recipientsArray,
                  recipientsAmtArray,
                ),
              ),
            );
          }

          return txn.copyWith(
            fee: Amount(
              rawValue: BigInt.from(feeBeingPaid),
              fractionDigits: cryptoCurrency.fractionDigits,
            ),
            usedUTXOs: utxoSigningData.map((e) => e.utxo).toList(),
          );
        } else {
          // Something went wrong here. It either overshot or undershot the estimated fee amount or the changeOutputSize
          // is smaller than or equal to cryptoCurrency.dustLimit. Revert to single output transaction.
          Logging.instance.log('1 output in tx', level: LogLevel.Info);
          Logging.instance
              .log('Input size: $satoshisBeingUsed', level: LogLevel.Info);
          Logging.instance.log('Recipient output size: $satoshiAmountToSend',
              level: LogLevel.Info);
          Logging.instance.log(
              'Difference (fee being paid): ${satoshisBeingUsed - satoshiAmountToSend} sats',
              level: LogLevel.Info);
          Logging.instance
              .log('Estimated fee: $feeForOneOutput', level: LogLevel.Info);
          final txn = buildTransaction(
            utxoSigningData: utxoSigningData,
            txData: txData.copyWith(
              recipients: _helperRecipientsConvert(
                recipientsArray,
                recipientsAmtArray,
              ),
            ),
          );

          return txn.copyWith(
            fee: Amount(
              rawValue: BigInt.from(satoshisBeingUsed - satoshiAmountToSend),
              fractionDigits: cryptoCurrency.fractionDigits,
            ),
            usedUTXOs: utxoSigningData.map((e) => e.utxo).toList(),
          );
        }
      } else {
        // No additional outputs needed since adding one would mean that it'd be smaller than cryptoCurrency.dustLimit sats
        // which makes it uneconomical to add to the transaction. Here, we pass data directly to instruct
        // the wallet to begin crafting the transaction that the user requested.
        Logging.instance.log('1 output in tx', level: LogLevel.Info);
        Logging.instance
            .log('Input size: $satoshisBeingUsed', level: LogLevel.Info);
        Logging.instance.log('Recipient output size: $satoshiAmountToSend',
            level: LogLevel.Info);
        Logging.instance.log(
            'Difference (fee being paid): ${satoshisBeingUsed - satoshiAmountToSend} sats',
            level: LogLevel.Info);
        Logging.instance
            .log('Estimated fee: $feeForOneOutput', level: LogLevel.Info);
        final txn = buildTransaction(
          utxoSigningData: utxoSigningData,
          txData: txData.copyWith(
            recipients: _helperRecipientsConvert(
              recipientsArray,
              recipientsAmtArray,
            ),
          ),
        );

        return txn.copyWith(
          fee: Amount(
            rawValue: BigInt.from(satoshisBeingUsed - satoshiAmountToSend),
            fractionDigits: cryptoCurrency.fractionDigits,
          ),
          usedUTXOs: utxoSigningData.map((e) => e.utxo).toList(),
        );
      }
    } else if (satoshisBeingUsed - satoshiAmountToSend == feeForOneOutput) {
      // In this scenario, no additional change output is needed since inputs - outputs equal exactly
      // what we need to pay for fees. Here, we pass data directly to instruct the wallet to begin
      // crafting the transaction that the user requested.
      Logging.instance.log('1 output in tx', level: LogLevel.Info);
      Logging.instance
          .log('Input size: $satoshisBeingUsed', level: LogLevel.Info);
      Logging.instance.log('Recipient output size: $satoshiAmountToSend',
          level: LogLevel.Info);
      Logging.instance.log(
          'Fee being paid: ${satoshisBeingUsed - satoshiAmountToSend} sats',
          level: LogLevel.Info);
      Logging.instance
          .log('Estimated fee: $feeForOneOutput', level: LogLevel.Info);
      final txn = buildTransaction(
        utxoSigningData: utxoSigningData,
        txData: txData.copyWith(
          recipients: _helperRecipientsConvert(
            recipientsArray,
            recipientsAmtArray,
          ),
        ),
      );
      return txn.copyWith(
        fee: Amount(
          rawValue: BigInt.from(feeForOneOutput),
          fractionDigits: cryptoCurrency.fractionDigits,
        ),
        usedUTXOs: utxoSigningData.map((e) => e.utxo).toList(),
      );
    } else {
      // Remember that returning 2 indicates that the user does not have a sufficient balance to
      // pay for the transaction fee. Ideally, at this stage, we should check if the user has any
      // additional outputs they're able to spend and then recalculate fees.
      Logging.instance.log(
          'Cannot pay tx fee - checking for more outputs and trying again',
          level: LogLevel.Warning);
      // try adding more outputs
      if (spendableOutputs.length > inputsBeingConsumed) {
        return coinSelection(
          txData: txData,
          isSendAll: isSendAll,
          additionalOutputs: additionalOutputs + 1,
          utxos: utxos,
          coinControl: coinControl,
        );
      }
      throw Exception("Insufficient balance to pay transaction fee");
      // return 2;
    }
  }

  Future<List<SigningData>> fetchBuildTxData(
    List<UTXO> utxosToUse,
  ) async {
    // return data
    List<SigningData> signingData = [];

    try {
      // Populating the addresses to check
      for (var i = 0; i < utxosToUse.length; i++) {
        final derivePathType =
            cryptoCurrency.addressType(address: utxosToUse[i].address!);

        signingData.add(
          SigningData(
            derivePathType: derivePathType,
            utxo: utxosToUse[i],
          ),
        );
      }

      final convertedNetwork = bitcoindart.NetworkType(
        messagePrefix: cryptoCurrency.networkParams.messagePrefix,
        bech32: cryptoCurrency.networkParams.bech32Hrp,
        bip32: bitcoindart.Bip32Type(
          public: cryptoCurrency.networkParams.pubHDPrefix,
          private: cryptoCurrency.networkParams.privHDPrefix,
        ),
        pubKeyHash: cryptoCurrency.networkParams.p2pkhPrefix,
        scriptHash: cryptoCurrency.networkParams.p2shPrefix,
        wif: cryptoCurrency.networkParams.wifPrefix,
      );

      final root = await getRootHDNode();

      for (final sd in signingData) {
        coinlib.HDPrivateKey? keys;
        final address = await mainDB.getAddress(walletId, sd.utxo.address!);
        if (address?.derivationPath != null) {
          if (address!.subType == AddressSubType.paynymReceive) {
            // TODO paynym
            // final code = await paymentCodeStringByKey(address.otherData!);
            //
            // final bip47base = await getBip47BaseNode();
            //
            // final privateKey = await getPrivateKeyForPaynymReceivingAddress(
            //   paymentCodeString: code!,
            //   index: address.derivationIndex,
            // );
            //
            // keys = coinlib.HDPrivateKey.fromKeyAndChainCode(
            //   privateKey,
            //   bip47base.chainCode,
            // );
          } else {
            keys = root.derivePath(address.derivationPath!.value);
          }
        }

        if (keys == null) {
          throw Exception(
              "Failed to fetch signing data. Local db corrupt. Rescan wallet.");
        }

        // final coinlib.Input input;

        final pubKey = keys.publicKey.data;
        final bitcoindart.PaymentData data;

        switch (sd.derivePathType) {
          case DerivePathType.bip44:
            // input = coinlib.P2PKHInput(
            //   prevOut: coinlib.OutPoint.fromHex(sd.utxo.txid, sd.utxo.vout),
            //   publicKey: keys.publicKey,
            // );

            data = bitcoindart
                .P2PKH(
                  data: bitcoindart.PaymentData(
                    pubkey: pubKey,
                  ),
                  network: convertedNetwork,
                )
                .data;
            break;
          //
          // case DerivePathType.bip49:
          //
          //   input = P2s
          //
          //   final p2wpkh = P2WPKH(
          //     data: PaymentData(
          //       pubkey: Format.stringToUint8List(pubKey),
          //     ),
          //     network: _network,
          //   ).data;
          //   redeemScript = p2wpkh.output;
          //   data = P2SH(
          //     data: PaymentData(redeem: p2wpkh),
          //     network: _network,
          //   ).data;
          //   break;

          case DerivePathType.bip84:
            // input = coinlib.P2WPKHInput(
            //   prevOut: coinlib.OutPoint.fromHex(sd.utxo.txid, sd.utxo.vout),
            //   publicKey: keys.publicKey,
            // );
            data = bitcoindart
                .P2WPKH(
                  data: bitcoindart.PaymentData(
                    pubkey: pubKey,
                  ),
                  network: convertedNetwork,
                )
                .data;
            break;

          default:
            throw Exception("DerivePathType unsupported");
        }

        // sd.output = input.script!.compiled;
        sd.output = data.output!;
        sd.keyPair = bitcoindart.ECPair.fromPrivateKey(
          keys.privateKey.data,
          compressed: keys.privateKey.compressed,
          network: convertedNetwork,
        );
      }

      return signingData;
    } catch (e, s) {
      Logging.instance
          .log("fetchBuildTxData() threw: $e,\n$s", level: LogLevel.Error);
      rethrow;
    }
  }

  /// Builds and signs a transaction
  TxData buildTransaction({
    required TxData txData,
    required List<SigningData> utxoSigningData,
  }) {
    Logging.instance
        .log("Starting buildTransaction ----------", level: LogLevel.Info);

    // TODO: use coinlib

    final txb = bitcoindart.TransactionBuilder(
      network: bitcoindart.testnet,
    );
    txb.setVersion(1);

    // Add transaction inputs
    for (var i = 0; i < utxoSigningData.length; i++) {
      final txid = utxoSigningData[i].utxo.txid;
      txb.addInput(
        txid,
        utxoSigningData[i].utxo.vout,
        null,
        utxoSigningData[i].output!,
      );
    }

    // Add transaction output
    for (var i = 0; i < txData.recipients!.length; i++) {
      txb.addOutput(
        txData.recipients![i].address,
        txData.recipients![i].amount.raw.toInt(),
      );
    }

    try {
      // Sign the transaction accordingly
      for (var i = 0; i < utxoSigningData.length; i++) {
        txb.sign(
          vin: i,
          keyPair: utxoSigningData[i].keyPair!,
          witnessValue: utxoSigningData[i].utxo.value,
          redeemScript: utxoSigningData[i].redeemScript,
        );
      }
    } catch (e, s) {
      Logging.instance.log("Caught exception while signing transaction: $e\n$s",
          level: LogLevel.Error);
      rethrow;
    }

    final builtTx = txb.build();
    final vSize = builtTx.virtualSize();

    return txData.copyWith(
      raw: builtTx.toHex(),
      vSize: vSize,
    );
  }

  Future<int> fetchChainHeight() async {
    try {
      final result = await electrumXClient.getBlockHeadTip();
      return result["height"] as int;
    } catch (e) {
      rethrow;
    }
  }

  Future<int> fetchTxCount({required String addressScriptHash}) async {
    final transactions =
        await electrumXClient.getHistory(scripthash: addressScriptHash);
    return transactions.length;
  }

  Future<Map<String, int>> fetchTxCountBatched({
    required Map<String, String> addresses,
  }) async {
    try {
      final Map<String, List<dynamic>> args = {};
      for (final entry in addresses.entries) {
        args[entry.key] = [
          cryptoCurrency.addressToScriptHash(address: entry.value),
        ];
      }
      final response = await electrumXClient.getBatchHistory(args: args);

      final Map<String, int> result = {};
      for (final entry in response.entries) {
        result[entry.key] = entry.value.length;
      }
      return result;
    } catch (e, s) {
      Logging.instance.log(
          "Exception rethrown in _getBatchTxCount(address: $addresses: $e\n$s",
          level: LogLevel.Error);
      rethrow;
    }
  }

  Future<List<({Transaction transaction, Address address})>>
      fetchTransactionsV1({
    required List<Address> addresses,
    required int currentChainHeight,
  }) async {
    final List<({String txHash, int height, String address})> allTxHashes =
        (await fetchHistory(addresses.map((e) => e.value).toList()))
            .map(
              (e) => (
                txHash: e["tx_hash"] as String,
                height: e["height"] as int,
                address: e["address"] as String,
              ),
            )
            .toList();

    List<Map<String, dynamic>> allTransactions = [];

    for (final data in allTxHashes) {
      final tx = await electrumXCachedClient.getTransaction(
        txHash: data.txHash,
        verbose: true,
        coin: cryptoCurrency.coin,
      );

      // check for duplicates before adding to list
      if (allTransactions
              .indexWhere((e) => e["txid"] == tx["txid"] as String) ==
          -1) {
        tx["address"] = addresses.firstWhere((e) => e.value == data.address);
        tx["height"] = data.height;
        allTransactions.add(tx);
      }
    }

    final List<({Transaction transaction, Address address})> txnsData = [];

    for (final txObject in allTransactions) {
      final data = await _parseTransactionV1(
        txObject,
        addresses,
      );

      txnsData.add(data);
    }

    return txnsData;
  }

  Future<ElectrumXNode> getCurrentElectrumXNode() async {
    final node = getCurrentNode();

    return ElectrumXNode(
      address: node.host,
      port: node.port,
      name: node.name,
      useSSL: node.useSSL,
      id: node.id,
    );
  }

  Future<void> updateElectrumX({required ElectrumXNode newNode}) async {
    final failovers = nodeService
        .failoverNodesFor(coin: cryptoCurrency.coin)
        .map((e) => ElectrumXNode(
              address: e.host,
              port: e.port,
              name: e.name,
              id: e.id,
              useSSL: e.useSSL,
            ))
        .toList();

    final newNode = await getCurrentElectrumXNode();
    electrumXClient = ElectrumXClient.from(
      node: newNode,
      prefs: prefs,
      failovers: failovers,
    );
    electrumXCachedClient = CachedElectrumXClient.from(
      electrumXClient: electrumXClient,
    );
  }

  //============================================================================

  Future<({List<Address> addresses, int index})> checkGapsBatched(
    int txCountBatchSize,
    coinlib.HDPrivateKey root,
    DerivePathType type,
    int chain,
  ) async {
    List<Address> addressArray = [];
    int gapCounter = 0;
    int highestIndexWithHistory = 0;

    for (int index = 0;
        index < cryptoCurrency.maxNumberOfIndexesToCheck &&
            gapCounter < cryptoCurrency.maxUnusedAddressGap;
        index += txCountBatchSize) {
      List<String> iterationsAddressArray = [];
      Logging.instance.log(
          "index: $index, \t GapCounter $chain ${type.name}: $gapCounter",
          level: LogLevel.Info);

      final _id = "k_$index";
      Map<String, String> txCountCallArgs = {};

      for (int j = 0; j < txCountBatchSize; j++) {
        final derivePath = cryptoCurrency.constructDerivePath(
          derivePathType: type,
          chain: chain,
          index: index + j,
        );

        final keys = root.derivePath(derivePath);

        final addressData = cryptoCurrency.getAddressForPublicKey(
          publicKey: keys.publicKey,
          derivePathType: type,
        );

        final addressString = convertAddressString(
          addressData.address.toString(),
        );

        final address = Address(
          walletId: walletId,
          value: addressString,
          publicKey: keys.publicKey.data,
          type: addressData.addressType,
          derivationIndex: index + j,
          derivationPath: DerivationPath()..value = derivePath,
          subType:
              chain == 0 ? AddressSubType.receiving : AddressSubType.change,
        );

        addressArray.add(address);

        txCountCallArgs.addAll({
          "${_id}_$j": addressString,
        });
      }

      // get address tx counts
      final counts = await fetchTxCountBatched(addresses: txCountCallArgs);

      // check and add appropriate addresses
      for (int k = 0; k < txCountBatchSize; k++) {
        int count = counts["${_id}_$k"]!;
        if (count > 0) {
          iterationsAddressArray.add(txCountCallArgs["${_id}_$k"]!);

          // update highest
          highestIndexWithHistory = index + k;

          // reset counter
          gapCounter = 0;
        }

        // increase counter when no tx history found
        if (count == 0) {
          gapCounter++;
        }
      }
      // // cache all the transactions while waiting for the current function to finish.
      // unawaited(getTransactionCacheEarly(addressArray));
    }
    return (index: highestIndexWithHistory, addresses: addressArray);
  }

  Future<({List<Address> addresses, int index})> checkGapsLinearly(
    coinlib.HDPrivateKey root,
    DerivePathType type,
    int chain,
  ) async {
    List<Address> addressArray = [];
    int gapCounter = 0;
    int index = 0;
    for (;
        index < cryptoCurrency.maxNumberOfIndexesToCheck &&
            gapCounter < cryptoCurrency.maxUnusedAddressGap;
        index++) {
      Logging.instance.log(
          "index: $index, \t GapCounter chain=$chain ${type.name}: $gapCounter",
          level: LogLevel.Info);

      final derivePath = cryptoCurrency.constructDerivePath(
        derivePathType: type,
        chain: chain,
        index: index,
      );
      final keys = root.derivePath(derivePath);
      final addressData = cryptoCurrency.getAddressForPublicKey(
        publicKey: keys.publicKey,
        derivePathType: type,
      );

      final addressString = convertAddressString(
        addressData.address.toString(),
      );

      final address = Address(
        walletId: walletId,
        value: addressString,
        publicKey: keys.publicKey.data,
        type: addressData.addressType,
        derivationIndex: index,
        derivationPath: DerivationPath()..value = derivePath,
        subType: chain == 0 ? AddressSubType.receiving : AddressSubType.change,
      );

      // get address tx count
      final count = await fetchTxCount(
        addressScriptHash: cryptoCurrency.addressToScriptHash(
          address: address.value,
        ),
      );

      // check and add appropriate addresses
      if (count > 0) {
        // add address to array
        addressArray.add(address);
        // reset counter
        gapCounter = 0;
        // add info to derivations
      } else {
        // increase counter when no tx history found
        gapCounter++;
      }
    }

    return (addresses: addressArray, index: index);
  }

  Future<List<Map<String, dynamic>>> fetchHistory(
    Iterable<String> allAddresses,
  ) async {
    try {
      List<Map<String, dynamic>> allTxHashes = [];

      if (serverCanBatch) {
        final Map<int, Map<String, List<dynamic>>> batches = {};
        final Map<String, String> requestIdToAddressMap = {};
        const batchSizeMax = 100;
        int batchNumber = 0;
        for (int i = 0; i < allAddresses.length; i++) {
          if (batches[batchNumber] == null) {
            batches[batchNumber] = {};
          }
          final scriptHash = cryptoCurrency.addressToScriptHash(
            address: allAddresses.elementAt(i),
          );
          final id = Logger.isTestEnv ? "$i" : const Uuid().v1();
          requestIdToAddressMap[id] = allAddresses.elementAt(i);
          batches[batchNumber]!.addAll({
            id: [scriptHash]
          });
          if (i % batchSizeMax == batchSizeMax - 1) {
            batchNumber++;
          }
        }

        for (int i = 0; i < batches.length; i++) {
          final response =
              await electrumXClient.getBatchHistory(args: batches[i]!);
          for (final entry in response.entries) {
            for (int j = 0; j < entry.value.length; j++) {
              entry.value[j]["address"] = requestIdToAddressMap[entry.key];
              if (!allTxHashes.contains(entry.value[j])) {
                allTxHashes.add(entry.value[j]);
              }
            }
          }
        }
      } else {
        for (int i = 0; i < allAddresses.length; i++) {
          final scriptHash = cryptoCurrency.addressToScriptHash(
            address: allAddresses.elementAt(1),
          );

          final response = await electrumXClient.getHistory(
            scripthash: scriptHash,
          );

          for (int j = 0; j < response.length; j++) {
            response[j]["address"] = allAddresses.elementAt(1);
            if (!allTxHashes.contains(response[j])) {
              allTxHashes.add(response[j]);
            }
          }
        }
      }

      return allTxHashes;
    } catch (e, s) {
      Logging.instance.log("_fetchHistory: $e\n$s", level: LogLevel.Error);
      rethrow;
    }
  }

  /// The optional (nullable) param [checkBlock] is a callback that can be used
  /// to check if a utxo should be marked as blocked
  Future<UTXO> parseUTXO({
    required Map<String, dynamic> jsonUTXO,
  }) async {
    final txn = await electrumXCachedClient.getTransaction(
      txHash: jsonUTXO["tx_hash"] as String,
      verbose: true,
      coin: cryptoCurrency.coin,
    );

    final vout = jsonUTXO["tx_pos"] as int;

    final outputs = txn["vout"] as List;

    String? scriptPubKey;
    String? utxoOwnerAddress;
    // get UTXO owner address
    for (final output in outputs) {
      if (output["n"] == vout) {
        scriptPubKey = output["scriptPubKey"]?["hex"] as String?;
        utxoOwnerAddress =
            output["scriptPubKey"]?["addresses"]?[0] as String? ??
                output["scriptPubKey"]?["address"] as String?;
      }
    }

    final checkBlockResult = checkBlockUTXO(jsonUTXO, scriptPubKey, txn);

    final utxo = UTXO(
      walletId: walletId,
      txid: txn["txid"] as String,
      vout: vout,
      value: jsonUTXO["value"] as int,
      name: "",
      isBlocked: checkBlockResult.blocked,
      blockedReason: checkBlockResult.blockedReason,
      isCoinbase: txn["is_coinbase"] as bool? ?? false,
      blockHash: txn["blockhash"] as String?,
      blockHeight: jsonUTXO["height"] as int?,
      blockTime: txn["blocktime"] as int?,
      address: utxoOwnerAddress,
    );

    return utxo;
  }

  Future<({Transaction transaction, Address address})> _parseTransactionV1(
    Map<String, dynamic> txData,
    List<Address> myAddresses,
  ) async {
    Set<String> receivingAddresses = myAddresses
        .where((e) =>
            e.subType == AddressSubType.receiving ||
            e.subType == AddressSubType.paynymReceive ||
            e.subType == AddressSubType.paynymNotification)
        .map((e) => e.value)
        .toSet();
    Set<String> changeAddresses = myAddresses
        .where((e) => e.subType == AddressSubType.change)
        .map((e) => e.value)
        .toSet();

    Set<String> inputAddresses = {};
    Set<String> outputAddresses = {};

    Amount totalInputValue = Amount(
      rawValue: BigInt.zero,
      fractionDigits: cryptoCurrency.coin.decimals,
    );
    Amount totalOutputValue = Amount(
      rawValue: BigInt.zero,
      fractionDigits: cryptoCurrency.coin.decimals,
    );

    Amount amountSentFromWallet = Amount(
      rawValue: BigInt.zero,
      fractionDigits: cryptoCurrency.coin.decimals,
    );
    Amount amountReceivedInWallet = Amount(
      rawValue: BigInt.zero,
      fractionDigits: cryptoCurrency.coin.decimals,
    );
    Amount changeAmount = Amount(
      rawValue: BigInt.zero,
      fractionDigits: cryptoCurrency.coin.decimals,
    );

    // parse inputs
    for (final input in txData["vin"] as List) {
      final prevTxid = input["txid"] as String;
      final prevOut = input["vout"] as int;

      // fetch input tx to get address
      final inputTx = await electrumXCachedClient.getTransaction(
        txHash: prevTxid,
        coin: cryptoCurrency.coin,
      );

      for (final output in inputTx["vout"] as List) {
        // check matching output
        if (prevOut == output["n"]) {
          // get value
          final value = Amount.fromDecimal(
            Decimal.parse(output["value"].toString()),
            fractionDigits: cryptoCurrency.coin.decimals,
          );

          // add value to total
          totalInputValue += value;

          // get input(prevOut) address
          final address = output["scriptPubKey"]?["addresses"]?[0] as String? ??
              output["scriptPubKey"]?["address"] as String?;

          if (address != null) {
            inputAddresses.add(address);

            // if input was from my wallet, add value to amount sent
            if (receivingAddresses.contains(address) ||
                changeAddresses.contains(address)) {
              amountSentFromWallet += value;
            }
          }
        }
      }
    }

    // parse outputs
    for (final output in txData["vout"] as List) {
      // get value
      final value = Amount.fromDecimal(
        Decimal.parse(output["value"].toString()),
        fractionDigits: cryptoCurrency.coin.decimals,
      );

      // add value to total
      totalOutputValue += value;

      // get output address
      final address = output["scriptPubKey"]?["addresses"]?[0] as String? ??
          output["scriptPubKey"]?["address"] as String?;
      if (address != null) {
        outputAddresses.add(address);

        // if output was to my wallet, add value to amount received
        if (receivingAddresses.contains(address)) {
          amountReceivedInWallet += value;
        } else if (changeAddresses.contains(address)) {
          changeAmount += value;
        }
      }
    }

    final mySentFromAddresses = [
      ...receivingAddresses.intersection(inputAddresses),
      ...changeAddresses.intersection(inputAddresses)
    ];
    final myReceivedOnAddresses =
        receivingAddresses.intersection(outputAddresses);
    final myChangeReceivedOnAddresses =
        changeAddresses.intersection(outputAddresses);

    final fee = totalInputValue - totalOutputValue;

    // this is the address initially used to fetch the txid
    Address transactionAddress = txData["address"] as Address;

    TransactionType type;
    Amount amount;
    if (mySentFromAddresses.isNotEmpty && myReceivedOnAddresses.isNotEmpty) {
      // tx is sent to self
      type = TransactionType.sentToSelf;

      // should be 0
      amount =
          amountSentFromWallet - amountReceivedInWallet - fee - changeAmount;
    } else if (mySentFromAddresses.isNotEmpty) {
      // outgoing tx
      type = TransactionType.outgoing;
      amount = amountSentFromWallet - changeAmount - fee;

      // non wallet addresses found in tx outputs
      final nonWalletOutAddresses = outputAddresses.difference(
        myChangeReceivedOnAddresses,
      );

      if (nonWalletOutAddresses.isNotEmpty) {
        final possible = nonWalletOutAddresses.first;

        if (transactionAddress.value != possible) {
          transactionAddress = Address(
            walletId: myAddresses.first.walletId,
            value: possible,
            derivationIndex: -1,
            derivationPath: null,
            subType: AddressSubType.nonWallet,
            type: AddressType.nonWallet,
            publicKey: [],
          );
        }
      } else {
        // some other type of tx where the receiving address is
        // one of my change addresses

        type = TransactionType.sentToSelf;
        amount = changeAmount;
      }
    } else {
      // incoming tx
      type = TransactionType.incoming;
      amount = amountReceivedInWallet;
    }

    List<Output> outs = [];
    List<Input> ins = [];

    for (final json in txData["vin"] as List) {
      bool isCoinBase = json['coinbase'] != null;
      String? witness;
      if (json['witness'] != null && json['witness'] is String) {
        witness = json['witness'] as String;
      } else if (json['txinwitness'] != null) {
        if (json['txinwitness'] is List) {
          witness = jsonEncode(json['txinwitness']);
        }
      }
      final input = Input(
        txid: json['txid'] as String,
        vout: json['vout'] as int? ?? -1,
        scriptSig: json['scriptSig']?['hex'] as String?,
        scriptSigAsm: json['scriptSig']?['asm'] as String?,
        isCoinbase: isCoinBase ? isCoinBase : json['is_coinbase'] as bool?,
        sequence: json['sequence'] as int?,
        innerRedeemScriptAsm: json['innerRedeemscriptAsm'] as String?,
        witness: witness,
      );
      ins.add(input);
    }

    for (final json in txData["vout"] as List) {
      final output = Output(
        scriptPubKey: json['scriptPubKey']?['hex'] as String?,
        scriptPubKeyAsm: json['scriptPubKey']?['asm'] as String?,
        scriptPubKeyType: json['scriptPubKey']?['type'] as String?,
        scriptPubKeyAddress:
            json["scriptPubKey"]?["addresses"]?[0] as String? ??
                json['scriptPubKey']?['type'] as String? ??
                "",
        value: Amount.fromDecimal(
          Decimal.parse(json["value"].toString()),
          fractionDigits: cryptoCurrency.coin.decimals,
        ).raw.toInt(),
      );
      outs.add(output);
    }

    TransactionSubType txSubType = TransactionSubType.none;
    if (this is PaynymInterface && outs.length > 1 && ins.isNotEmpty) {
      for (int i = 0; i < outs.length; i++) {
        List<String>? scriptChunks = outs[i].scriptPubKeyAsm?.split(" ");
        if (scriptChunks?.length == 2 && scriptChunks?[0] == "OP_RETURN") {
          final blindedPaymentCode = scriptChunks![1];
          final bytes = blindedPaymentCode.fromHex;

          // https://en.bitcoin.it/wiki/BIP_0047#Sending
          if (bytes.length == 80 && bytes.first == 1) {
            txSubType = TransactionSubType.bip47Notification;
          }
        }
      }
    }

    final tx = Transaction(
      walletId: myAddresses.first.walletId,
      txid: txData["txid"] as String,
      timestamp: txData["blocktime"] as int? ??
          (DateTime.now().millisecondsSinceEpoch ~/ 1000),
      type: type,
      subType: txSubType,
      // amount may overflow. Deprecated. Use amountString
      amount: amount.raw.toInt(),
      amountString: amount.toJsonString(),
      fee: fee.raw.toInt(),
      height: txData["height"] as int?,
      isCancelled: false,
      isLelantus: false,
      slateId: null,
      otherData: null,
      nonce: null,
      inputs: ins,
      outputs: outs,
      numberOfMessages: null,
    );

    return (transaction: tx, address: transactionAddress);
  }

  //============================================================================

  @override
  Future<void> updateChainHeight() async {
    final height = await fetchChainHeight();
    await info.updateCachedChainHeight(
      newHeight: height,
      isar: mainDB.isar,
    );
  }

  @override
  Future<bool> pingCheck() async {
    try {
      final result = await electrumXClient.ping();
      return result;
    } catch (_) {
      return false;
    }
  }

  @override
  Future<void> updateNode() async {
    final node = await getCurrentElectrumXNode();
    await updateElectrumX(newNode: node);
  }

  FeeObject? _cachedFees;

  @override
  Future<FeeObject> get fees async {
    try {
      const int f = 1, m = 5, s = 20;

      final fast = await electrumXClient.estimateFee(blocks: f);
      final medium = await electrumXClient.estimateFee(blocks: m);
      final slow = await electrumXClient.estimateFee(blocks: s);

      final feeObject = FeeObject(
        numberOfBlocksFast: f,
        numberOfBlocksAverage: m,
        numberOfBlocksSlow: s,
        fast: Amount.fromDecimal(
          fast,
          fractionDigits: info.coin.decimals,
        ).raw.toInt(),
        medium: Amount.fromDecimal(
          medium,
          fractionDigits: info.coin.decimals,
        ).raw.toInt(),
        slow: Amount.fromDecimal(
          slow,
          fractionDigits: info.coin.decimals,
        ).raw.toInt(),
      );

      Logging.instance.log("fetched fees: $feeObject", level: LogLevel.Info);
      _cachedFees = feeObject;
      return _cachedFees!;
    } catch (e) {
      Logging.instance.log(
        "Exception rethrown from _getFees(): $e",
        level: LogLevel.Error,
      );
      if (_cachedFees == null) {
        rethrow;
      } else {
        return _cachedFees!;
      }
    }
  }

  @override
  Future<Amount> estimateFeeFor(Amount amount, int feeRate) async {
    final available = info.cachedBalance.spendable;
    final utxos = _spendableUTXOs(await mainDB.getUTXOs(walletId).findAll());

    if (available == amount) {
      return amount - (await _sweepAllEstimate(feeRate, utxos));
    } else if (amount <= Amount.zero || amount > available) {
      return roughFeeEstimate(1, 2, feeRate);
    }

    Amount runningBalance = Amount(
      rawValue: BigInt.zero,
      fractionDigits: info.coin.decimals,
    );
    int inputCount = 0;
    for (final output in utxos) {
      if (!output.isBlocked) {
        runningBalance += Amount(
          rawValue: BigInt.from(output.value),
          fractionDigits: info.coin.decimals,
        );
        inputCount++;
        if (runningBalance > amount) {
          break;
        }
      }
    }

    final oneOutPutFee = roughFeeEstimate(inputCount, 1, feeRate);
    final twoOutPutFee = roughFeeEstimate(inputCount, 2, feeRate);

    if (runningBalance - amount > oneOutPutFee) {
      if (runningBalance - amount > oneOutPutFee + cryptoCurrency.dustLimit) {
        final change = runningBalance - amount - twoOutPutFee;
        if (change > cryptoCurrency.dustLimit &&
            runningBalance - amount - change == twoOutPutFee) {
          return runningBalance - amount - change;
        } else {
          return runningBalance - amount;
        }
      } else {
        return runningBalance - amount;
      }
    } else if (runningBalance - amount == oneOutPutFee) {
      return oneOutPutFee;
    } else {
      return twoOutPutFee;
    }
  }

  @override
  Future<void> checkReceivingAddressForTransactions() async {
    try {
      final currentReceiving = await getCurrentReceivingAddress();

      final bool needsGenerate;
      if (currentReceiving == null) {
        // no addresses in db yet for some reason.
        // Should not happen at this point...

        needsGenerate = true;
      } else {
        final txCount = await fetchTxCount(
          addressScriptHash: cryptoCurrency.addressToScriptHash(
            address: currentReceiving.value,
          ),
        );
        needsGenerate = txCount > 0 || currentReceiving.derivationIndex < 0;
      }

      if (needsGenerate) {
        await generateNewReceivingAddress();

        // TODO: get rid of this? Could cause problems (long loading/infinite loop or something)
        // keep checking until address with no tx history is set as current
        await checkReceivingAddressForTransactions();
      }
    } catch (e, s) {
      Logging.instance.log(
        "Exception rethrown from _checkReceivingAddressForTransactions"
        "($cryptoCurrency): $e\n$s",
        level: LogLevel.Error,
      );
      rethrow;
    }
  }

  @override
  Future<void> checkChangeAddressForTransactions() async {
    try {
      final currentChange = await getCurrentChangeAddress();

      final bool needsGenerate;
      if (currentChange == null) {
        // no addresses in db yet for some reason.
        // Should not happen at this point...

        needsGenerate = true;
      } else {
        final txCount = await fetchTxCount(
          addressScriptHash: cryptoCurrency.addressToScriptHash(
            address: currentChange.value,
          ),
        );
        needsGenerate = txCount > 0 || currentChange.derivationIndex < 0;
      }

      if (needsGenerate) {
        await generateNewChangeAddress();

        // TODO: get rid of this? Could cause problems (long loading/infinite loop or something)
        // keep checking until address with no tx history is set as current
        await checkChangeAddressForTransactions();
      }
    } catch (e, s) {
      Logging.instance.log(
        "Exception rethrown from _checkChangeAddressForTransactions"
        "($cryptoCurrency): $e\n$s",
        level: LogLevel.Error,
      );
      rethrow;
    }
  }

  @override
  Future<void> recover({required bool isRescan}) async {
    final root = await getRootHDNode();

    final List<Future<({int index, List<Address> addresses})>> receiveFutures =
        [];
    final List<Future<({int index, List<Address> addresses})>> changeFutures =
        [];

    const receiveChain = 0;
    const changeChain = 1;

    const txCountBatchSize = 12;

    try {
      await refreshMutex.protect(() async {
        if (isRescan) {
          // clear cache
          await electrumXCachedClient.clearSharedTransactionCache(
              coin: info.coin);
          // clear blockchain info
          await mainDB.deleteWalletBlockchainData(walletId);
        }

        // receiving addresses
        Logging.instance.log(
          "checking receiving addresses...",
          level: LogLevel.Info,
        );

        for (final type in cryptoCurrency.supportedDerivationPathTypes) {
          receiveFutures.add(
            serverCanBatch
                ? checkGapsBatched(
                    txCountBatchSize,
                    root,
                    type,
                    receiveChain,
                  )
                : checkGapsLinearly(
                    root,
                    type,
                    receiveChain,
                  ),
          );
        }

        // change addresses
        Logging.instance.log(
          "checking change addresses...",
          level: LogLevel.Info,
        );
        for (final type in cryptoCurrency.supportedDerivationPathTypes) {
          changeFutures.add(
            serverCanBatch
                ? checkGapsBatched(
                    txCountBatchSize,
                    root,
                    type,
                    changeChain,
                  )
                : checkGapsLinearly(
                    root,
                    type,
                    changeChain,
                  ),
          );
        }

        // io limitations may require running these linearly instead
        final futuresResult = await Future.wait([
          Future.wait(receiveFutures),
          Future.wait(changeFutures),
        ]);

        final receiveResults = futuresResult[0];
        final changeResults = futuresResult[1];

        final List<Address> addressesToStore = [];

        int highestReceivingIndexWithHistory = 0;

        for (final tuple in receiveResults) {
          if (tuple.addresses.isEmpty) {
            await checkReceivingAddressForTransactions();
          } else {
            highestReceivingIndexWithHistory = max(
              tuple.index,
              highestReceivingIndexWithHistory,
            );
            addressesToStore.addAll(tuple.addresses);
          }
        }

        int highestChangeIndexWithHistory = 0;
        // If restoring a wallet that never sent any funds with change, then set changeArray
        // manually. If we didn't do this, it'd store an empty array.
        for (final tuple in changeResults) {
          if (tuple.addresses.isEmpty) {
            await checkChangeAddressForTransactions();
          } else {
            highestChangeIndexWithHistory = max(
              tuple.index,
              highestChangeIndexWithHistory,
            );
            addressesToStore.addAll(tuple.addresses);
          }
        }

        // remove extra addresses to help minimize risk of creating a large gap
        addressesToStore.removeWhere((e) =>
            e.subType == AddressSubType.change &&
            e.derivationIndex > highestChangeIndexWithHistory);
        addressesToStore.removeWhere((e) =>
            e.subType == AddressSubType.receiving &&
            e.derivationIndex > highestReceivingIndexWithHistory);

        await mainDB.updateOrPutAddresses(addressesToStore);
      });

      await refresh();
    } catch (e, s) {
      Logging.instance.log(
          "Exception rethrown from electrumx_mixin recover(): $e\n$s",
          level: LogLevel.Info);

      rethrow;
    }
  }

  @override
  Future<void> updateUTXOs() async {
    final allAddresses = await fetchAddressesForElectrumXScan();

    try {
      final fetchedUtxoList = <List<Map<String, dynamic>>>[];

      if (serverCanBatch) {
        final Map<int, Map<String, List<dynamic>>> batches = {};
        const batchSizeMax = 10;
        int batchNumber = 0;
        for (int i = 0; i < allAddresses.length; i++) {
          if (batches[batchNumber] == null) {
            batches[batchNumber] = {};
          }
          final scriptHash = cryptoCurrency.addressToScriptHash(
            address: allAddresses[i].value,
          );

          batches[batchNumber]!.addAll({
            scriptHash: [scriptHash]
          });
          if (i % batchSizeMax == batchSizeMax - 1) {
            batchNumber++;
          }
        }

        for (int i = 0; i < batches.length; i++) {
          final response =
              await electrumXClient.getBatchUTXOs(args: batches[i]!);
          for (final entry in response.entries) {
            if (entry.value.isNotEmpty) {
              fetchedUtxoList.add(entry.value);
            }
          }
        }
      } else {
        for (int i = 0; i < allAddresses.length; i++) {
          final scriptHash = cryptoCurrency.addressToScriptHash(
            address: allAddresses[i].value,
          );

          final utxos = await electrumXClient.getUTXOs(scripthash: scriptHash);
          if (utxos.isNotEmpty) {
            fetchedUtxoList.add(utxos);
          }
        }
      }

      final List<UTXO> outputArray = [];

      for (int i = 0; i < fetchedUtxoList.length; i++) {
        for (int j = 0; j < fetchedUtxoList[i].length; j++) {
          final utxo = await parseUTXO(
            jsonUTXO: fetchedUtxoList[i][j],
          );

          outputArray.add(utxo);
        }
      }

      await mainDB.updateUTXOs(walletId, outputArray);
    } catch (e, s) {
      Logging.instance.log(
        "Output fetch unsuccessful: $e\n$s",
        level: LogLevel.Error,
      );
    }
  }

  @override
  Future<TxData> confirmSend({required TxData txData}) async {
    try {
      Logging.instance.log("confirmSend txData: $txData", level: LogLevel.Info);

      final txHash = await electrumXClient.broadcastTransaction(
        rawTx: txData.raw!,
      );
      Logging.instance.log("Sent txHash: $txHash", level: LogLevel.Info);

      txData = txData.copyWith(
        usedUTXOs:
            txData.usedUTXOs!.map((e) => e.copyWith(used: true)).toList(),

        // TODO revisit setting these both
        txHash: txHash,
        txid: txHash,
      );
      // mark utxos as used
      await mainDB.putUTXOs(txData.usedUTXOs!);

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

  @override
  Future<TxData> prepareSend({required TxData txData}) async {
    try {
      final feeRateType = txData.feeRateType;
      final customSatsPerVByte = txData.satsPerVByte;
      final feeRateAmount = txData.feeRateAmount;
      final utxos = txData.utxos;

      if (customSatsPerVByte != null) {
        // check for send all
        bool isSendAll = false;
        if (txData.amount == info.cachedBalance.spendable) {
          isSendAll = true;
        }

        final bool coinControl = utxos != null;

        final result = await coinSelection(
          txData: txData.copyWith(feeRateAmount: -1),
          isSendAll: isSendAll,
          utxos: utxos?.toList(),
          coinControl: coinControl,
        );

        Logging.instance
            .log("PREPARE SEND RESULT: $result", level: LogLevel.Info);

        if (txData.fee!.raw.toInt() < txData.vSize!) {
          throw Exception(
              "Error in fee calculation: Transaction fee cannot be less than vSize");
        }

        return result;
      } else if (feeRateType is FeeRateType || feeRateAmount is int) {
        late final int rate;
        if (feeRateType is FeeRateType) {
          int fee = 0;
          final feeObject = await fees;
          switch (feeRateType) {
            case FeeRateType.fast:
              fee = feeObject.fast;
              break;
            case FeeRateType.average:
              fee = feeObject.medium;
              break;
            case FeeRateType.slow:
              fee = feeObject.slow;
              break;
            default:
              throw ArgumentError("Invalid use of custom fee");
          }
          rate = fee;
        } else {
          rate = feeRateAmount as int;
        }

        // check for send all
        bool isSendAll = false;
        if (txData.amount == info.cachedBalance.spendable) {
          isSendAll = true;
        }

        final bool coinControl = utxos != null;

        final result = await coinSelection(
          txData: txData.copyWith(
            feeRateAmount: rate,
          ),
          isSendAll: isSendAll,
          utxos: utxos?.toList(),
          coinControl: coinControl,
        );

        Logging.instance.log("prepare send: $result", level: LogLevel.Info);
        if (result.fee!.raw.toInt() < result.vSize!) {
          throw Exception(
              "Error in fee calculation: Transaction fee cannot be less than vSize");
        }

        return result;
      } else {
        throw ArgumentError("Invalid fee rate argument provided!");
      }
    } catch (e, s) {
      Logging.instance.log("Exception rethrown from prepareSend(): $e\n$s",
          level: LogLevel.Error);
      rethrow;
    }
  }

  @override
  Future<void> init() async {
    try {
      final features = await electrumXClient
          .getServerFeatures()
          .timeout(const Duration(seconds: 3));

      Logging.instance.log("features: $features", level: LogLevel.Info);

      _serverVersion =
          _parseServerVersion(features["server_version"] as String);

      if (cryptoCurrency.genesisHash != features['genesis_hash']) {
        throw Exception("genesis hash does not match!");
      }
    } catch (e, s) {
      Logging.instance.log("$e/n$s", level: LogLevel.Info);
    }

    await super.init();
  }

  // ===========================================================================
  // ========== Interface functions ============================================

  int estimateTxFee({required int vSize, required int feeRatePerKB});
  Amount roughFeeEstimate(int inputCount, int outputCount, int feeRatePerKB);

  Future<List<Address>> fetchAddressesForElectrumXScan();

  /// Certain coins need to check if the utxo should be marked
  /// as blocked as well as give a reason.
  ({String? blockedReason, bool blocked}) checkBlockUTXO(
    Map<String, dynamic> jsonUTXO,
    String? scriptPubKeyHex,
    Map<String, dynamic> jsonTX,
  );

  // ===========================================================================
  // ========== private helpers ================================================

  List<UTXO> _spendableUTXOs(List<UTXO> utxos) {
    return utxos
        .where(
          (e) =>
              !e.isBlocked &&
              e.isConfirmed(
                info.cachedChainHeight,
                cryptoCurrency.minConfirms,
              ),
        )
        .toList();
  }

  Future<Amount> _sweepAllEstimate(int feeRate, List<UTXO> usableUTXOs) async {
    final available = usableUTXOs
        .map((e) => BigInt.from(e.value))
        .fold(BigInt.zero, (p, e) => p + e);
    final inputCount = usableUTXOs.length;

    // transaction will only have 1 output minus the fee
    final estimatedFee = roughFeeEstimate(inputCount, 1, feeRate);

    return Amount(
          rawValue: available,
          fractionDigits: info.coin.decimals,
        ) -
        estimatedFee;
  }

  // stupid + fragile
  double? _parseServerVersion(String version) {
    double? result;
    try {
      final list = version.split(" ");
      if (list.isNotEmpty) {
        final numberStrings = list.last.split(".");
        final major = numberStrings.removeAt(0);

        result = double.tryParse("$major.${numberStrings.join("")}");
      }
    } catch (_) {}

    Logging.instance.log(
      "${info.name} _parseServerVersion($version) => $result",
      level: LogLevel.Info,
    );
    return result;
  }

  // ===========================================================================
}