clean up coin selection somewhat

lib/wallets/wallet/wallet_mixin_interfaces/electrumx_interface.dart

@@ -4,6 +4,7 @@ import 'dart:typed_data';
 
 import 'package:coinlib_flutter/coinlib_flutter.dart' as coinlib;
 import 'package:isar/isar.dart';
+
 import '../../../electrumx_rpc/cached_electrumx_client.dart';
 import '../../../electrumx_rpc/client_manager.dart';
 import '../../../electrumx_rpc/electrumx_client.dart';
@@ -64,7 +65,10 @@ mixin ElectrumXInterface<T extends ElectrumXCurrencyInterface>
   }
 
   Future<List<({String address, Amount amount, bool isChange})>>
-      _helperRecipientsConvert(List<String> addrs, List<int> satValues) async {
+      _helperRecipientsConvert(
+    List<String> addrs,
+    List<BigInt> satValues,
+  ) async {
     final List<({String address, Amount amount, bool isChange})> results = [];
 
     for (int i = 0; i < addrs.length; i++) {
@@ -72,7 +76,7 @@ mixin ElectrumXInterface<T extends ElectrumXCurrencyInterface>
         (
           address: addrs[i],
           amount: Amount(
-            rawValue: BigInt.from(satValues[i]),
+            rawValue: satValues[i],
             fractionDigits: cryptoCurrency.fractionDigits,
           ),
           isChange: (await mainDB.isar.addresses
@@ -105,44 +109,47 @@ mixin ElectrumXInterface<T extends ElectrumXCurrencyInterface>
     // TODO: multiple recipients one day
     assert(txData.recipients!.length == 1);
 
+    if (coinControl && utxos == null) {
+      throw Exception("Coin control used where utxos is null!");
+    }
+
     final recipientAddress = txData.recipients!.first.address;
-    final satoshiAmountToSend = txData.amount!.raw.toInt();
+    final satoshiAmountToSend = txData.amount!.raw;
     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;
-      }
+    final spendableOutputs = availableOutputs
+        .where(
+          (e) =>
+              !e.isBlocked &&
+              (e.used != true) &&
+              e.isConfirmed(currentChainHeight, cryptoCurrency.minConfirms),
+        )
+        .toList();
+    final spendableSatoshiValue =
+        spendableOutputs.fold(BigInt.zero, (p, e) => p + BigInt.from(e.value));
+
+    if (spendableSatoshiValue < satoshiAmountToSend) {
+      throw Exception("Insufficient balance");
+    } else if (spendableSatoshiValue == satoshiAmountToSend && !isSendAll) {
+      throw Exception("Insufficient balance to pay transaction fee");
     }
 
     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) {
+      // don't care about sorting if using all utxos
+    } else {
       // sort spendable by age (oldest first)
       spendableOutputs.sort(
         (a, b) => (b.blockTime ?? currentChainHeight)
             .compareTo((a.blockTime ?? currentChainHeight)),
       );
-      // Null check operator changed to null assignment in order to resolve a
-      // `Null check operator used on a null value` error.  currentChainHeight
-      // used in order to sort these unconfirmed outputs as the youngest, but we
-      // could just as well use currentChainHeight + 1.
     }
 
     Logging.instance.log(
@@ -161,26 +168,10 @@ mixin ElectrumXInterface<T extends ElectrumXCurrencyInterface>
     );
     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;
+    BigInt satoshisBeingUsed = BigInt.zero;
     int inputsBeingConsumed = 0;
-    List<UTXO> utxoObjectsToUse = [];
+    final List<UTXO> utxoObjectsToUse = [];
 
     if (!coinControl) {
       for (var i = 0;
@@ -188,7 +179,7 @@ mixin ElectrumXInterface<T extends ElectrumXCurrencyInterface>
               i < spendableOutputs.length;
           i++) {
         utxoObjectsToUse.add(spendableOutputs[i]);
-        satoshisBeingUsed += spendableOutputs[i].value;
+        satoshisBeingUsed += BigInt.from(spendableOutputs[i].value);
         inputsBeingConsumed += 1;
       }
       for (int i = 0;
@@ -196,12 +187,13 @@ mixin ElectrumXInterface<T extends ElectrumXCurrencyInterface>
               inputsBeingConsumed < spendableOutputs.length;
           i++) {
         utxoObjectsToUse.add(spendableOutputs[inputsBeingConsumed]);
-        satoshisBeingUsed += spendableOutputs[inputsBeingConsumed].value;
+        satoshisBeingUsed +=
+            BigInt.from(spendableOutputs[inputsBeingConsumed].value);
         inputsBeingConsumed += 1;
       }
     } else {
       satoshisBeingUsed = spendableSatoshiValue;
-      utxoObjectsToUse = spendableOutputs;
+      utxoObjectsToUse.addAll(spendableOutputs);
       inputsBeingConsumed = spendableOutputs.length;
     }
 
@@ -214,72 +206,20 @@ mixin ElectrumXInterface<T extends ElectrumXCurrencyInterface>
 
     // numberOfOutputs' length must always be equal to that of recipientsArray and recipientsAmtArray
     final List<String> recipientsArray = [recipientAddress];
-    final List<int> recipientsAmtArray = [satoshiAmountToSend];
+    final List<BigInt> recipientsAmtArray = [satoshiAmountToSend];
 
     // gather required signing data
     final utxoSigningData = await fetchBuildTxData(utxoObjectsToUse);
 
     if (isSendAll) {
-      Logging.instance
-          .log("Attempting to send all $cryptoCurrency", level: LogLevel.Info);
-      if (txData.recipients!.length != 1) {
-        throw Exception(
-          "Send all to more than one recipient not yet supported",
-        );
-      }
-
-      final int vSizeForOneOutput = (await buildTransaction(
+      return await _sendAllBuilder(
+        txData: txData,
+        recipientAddress: recipientAddress,
+        satoshiAmountToSend: satoshiAmountToSend,
+        satoshisBeingUsed: satoshisBeingUsed,
         utxoSigningData: utxoSigningData,
-        txData: txData.copyWith(
-          recipients: await _helperRecipientsConvert(
-            [recipientAddress],
-            [satoshisBeingUsed - 1],
-          ),
-        ),
-      ))
-          .vSize!;
-      int feeForOneOutput = satsPerVByte != null
-          ? (satsPerVByte * vSizeForOneOutput)
-          : estimateTxFee(
-              vSize: vSizeForOneOutput,
-              feeRatePerKB: selectedTxFeeRate,
-            );
-
-      if (satsPerVByte == null) {
-        final int roughEstimate = roughFeeEstimate(
-          spendableOutputs.length,
-          1,
-          selectedTxFeeRate,
-        ).raw.toInt();
-        if (feeForOneOutput < roughEstimate) {
-          feeForOneOutput = roughEstimate;
-        }
-      }
-
-      final int amount = satoshiAmountToSend - feeForOneOutput;
-
-      if (amount < 0) {
-        throw Exception(
-          "Estimated fee ($feeForOneOutput sats) is greater than balance!",
-        );
-      }
-
-      final data = await buildTransaction(
-        txData: txData.copyWith(
-          recipients: await _helperRecipientsConvert(
-            [recipientAddress],
-            [amount],
-          ),
-        ),
-        utxoSigningData: utxoSigningData,
-      );
-
-      return data.copyWith(
-        fee: Amount(
-          rawValue: BigInt.from(feeForOneOutput),
-          fractionDigits: cryptoCurrency.fractionDigits,
-        ),
-        usedUTXOs: utxoSigningData.map((e) => e.utxo).toList(),
+        satsPerVByte: satsPerVByte,
+        feeRatePerKB: selectedTxFeeRate,
       );
     }
 
@@ -290,7 +230,7 @@ mixin ElectrumXInterface<T extends ElectrumXCurrencyInterface>
         txData: txData.copyWith(
           recipients: await _helperRecipientsConvert(
             [recipientAddress],
-            [satoshisBeingUsed - 1],
+            [satoshisBeingUsed - BigInt.one],
           ),
         ),
       ))
@@ -301,6 +241,9 @@ mixin ElectrumXInterface<T extends ElectrumXCurrencyInterface>
     }
 
     final int vSizeForTwoOutPuts;
+
+    BigInt maxBI(BigInt a, BigInt b) => a > b ? a : b;
+
     try {
       vSizeForTwoOutPuts = (await buildTransaction(
         utxoSigningData: utxoSigningData,
@@ -309,7 +252,10 @@ mixin ElectrumXInterface<T extends ElectrumXCurrencyInterface>
             [recipientAddress, (await getCurrentChangeAddress())!.value],
             [
               satoshiAmountToSend,
-              max(0, satoshisBeingUsed - satoshiAmountToSend - 1),
+              maxBI(
+                BigInt.zero,
+                satoshisBeingUsed - (satoshiAmountToSend + BigInt.one),
+              ),
             ],
           ),
         ),
@@ -321,53 +267,112 @@ mixin ElectrumXInterface<T extends ElectrumXCurrencyInterface>
     }
 
     // Assume 1 output, only for recipient and no change
-    final feeForOneOutput = satsPerVByte != null
-        ? (satsPerVByte * vSizeForOneOutput)
-        : estimateTxFee(
-            vSize: vSizeForOneOutput,
-            feeRatePerKB: selectedTxFeeRate,
-          );
+    final feeForOneOutput = BigInt.from(
+      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,
-          );
+    final feeForTwoOutputs = BigInt.from(
+      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);
+    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.
-        final 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) {
+    final difference = satoshisBeingUsed - satoshiAmountToSend;
+
+    Future<TxData> singleOutputTxn() async {
+      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: $difference sats',
+        level: LogLevel.Info,
+      );
+      Logging.instance.log(
+        'Estimated fee: $feeForOneOutput',
+        level: LogLevel.Info,
+      );
+      final txnData = await buildTransaction(
+        utxoSigningData: utxoSigningData,
+        txData: txData.copyWith(
+          recipients: await _helperRecipientsConvert(
+            recipientsArray,
+            recipientsAmtArray,
+          ),
+        ),
+      );
+      return txnData.copyWith(
+        fee: Amount(
+          rawValue: feeForOneOutput,
+          fractionDigits: cryptoCurrency.fractionDigits,
+        ),
+        usedUTXOs: utxoSigningData.map((e) => e.utxo).toList(),
+      );
+    }
+
+    // no change output required
+    if (difference == feeForOneOutput) {
+      Logging.instance.log('1 output in tx', level: LogLevel.Info);
+      return await singleOutputTxn();
+    } else if (difference < feeForOneOutput) {
+      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");
+    } else {
+      if (difference > (feeForOneOutput + cryptoCurrency.dustLimit.raw)) {
+        final changeOutputSize = difference - feeForTwoOutputs;
+        // check if possible to add the change output
+        if (changeOutputSize > cryptoCurrency.dustLimit.raw &&
+            difference - 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;
+          BigInt feeBeingPaid = difference - changeOutputSize;
 
+          // add change output
           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(
+            'Input size: $satoshisBeingUsed',
+            level: LogLevel.Info,
+          );
           Logging.instance.log(
             'Recipient output size: $satoshiAmountToSend',
             level: LogLevel.Info,
@@ -380,10 +385,12 @@ mixin ElectrumXInterface<T extends ElectrumXCurrencyInterface>
             'Difference (fee being paid): $feeBeingPaid sats',
             level: LogLevel.Info,
           );
-          Logging.instance
-              .log('Estimated fee: $feeForTwoOutputs', level: LogLevel.Info);
+          Logging.instance.log(
+            'Estimated fee: $feeForTwoOutputs',
+            level: LogLevel.Info,
+          );
 
-          var txn = await buildTransaction(
+          TxData txnData = await buildTransaction(
             utxoSigningData: utxoSigningData,
             txData: txData.copyWith(
               recipients: await _helperRecipientsConvert(
@@ -394,13 +401,12 @@ mixin ElectrumXInterface<T extends ElectrumXCurrencyInterface>
           );
 
           // make sure minimum fee is accurate if that is being used
-          if (txn.vSize! - feeBeingPaid == 1) {
-            final int changeOutputSize =
-                satoshisBeingUsed - satoshiAmountToSend - txn.vSize!;
-            feeBeingPaid =
-                satoshisBeingUsed - satoshiAmountToSend - changeOutputSize;
+          if (BigInt.from(txnData.vSize!) - feeBeingPaid == BigInt.one) {
+            final changeOutputSize = difference - BigInt.from(txnData.vSize!);
+            feeBeingPaid = difference - changeOutputSize;
             recipientsAmtArray.removeLast();
             recipientsAmtArray.add(changeOutputSize);
+
             Logging.instance.log(
               'Adjusted Input size: $satoshisBeingUsed',
               level: LogLevel.Info,
@@ -421,7 +427,8 @@ mixin ElectrumXInterface<T extends ElectrumXCurrencyInterface>
               'Adjusted Estimated fee: $feeForTwoOutputs',
               level: LogLevel.Info,
             );
-            txn = await buildTransaction(
+
+            txnData = await buildTransaction(
               utxoSigningData: utxoSigningData,
               txData: txData.copyWith(
                 recipients: await _helperRecipientsConvert(
@@ -432,9 +439,9 @@ mixin ElectrumXInterface<T extends ElectrumXCurrencyInterface>
             );
           }
 
-          return txn.copyWith(
+          return txnData.copyWith(
             fee: Amount(
-              rawValue: BigInt.from(feeBeingPaid),
+              rawValue: feeBeingPaid,
               fractionDigits: cryptoCurrency.fractionDigits,
             ),
             usedUTXOs: utxoSigningData.map((e) => e.utxo).toList(),
@@ -442,126 +449,91 @@ mixin ElectrumXInterface<T extends ElectrumXCurrencyInterface>
         } 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',
+            'Reverting to 1 output in tx',
             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 = await buildTransaction(
-            utxoSigningData: utxoSigningData,
-            txData: txData.copyWith(
-              recipients: await _helperRecipientsConvert(
-                recipientsArray,
-                recipientsAmtArray,
-              ),
-            ),
-          );
 
-          return txn.copyWith(
-            fee: Amount(
-              rawValue: BigInt.from(satoshisBeingUsed - satoshiAmountToSend),
-              fractionDigits: cryptoCurrency.fractionDigits,
-            ),
-            usedUTXOs: utxoSigningData.map((e) => e.utxo).toList(),
-          );
+          return await singleOutputTxn();
         }
-      } 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 = await buildTransaction(
-          utxoSigningData: utxoSigningData,
-          txData: txData.copyWith(
-            recipients: await _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 = await buildTransaction(
-        utxoSigningData: utxoSigningData,
-        txData: txData.copyWith(
-          recipients: await _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;
     }
+
+    return txData;
+  }
+
+  Future<TxData> _sendAllBuilder({
+    required TxData txData,
+    required String recipientAddress,
+    required BigInt satoshiAmountToSend,
+    required BigInt satoshisBeingUsed,
+    required List<SigningData> utxoSigningData,
+    required int? satsPerVByte,
+    required int feeRatePerKB,
+  }) async {
+    Logging.instance
+        .log("Attempting to send all $cryptoCurrency", level: LogLevel.Info);
+    if (txData.recipients!.length != 1) {
+      throw Exception(
+        "Send all to more than one recipient not yet supported",
+      );
+    }
+
+    final int vSizeForOneOutput = (await buildTransaction(
+      utxoSigningData: utxoSigningData,
+      txData: txData.copyWith(
+        recipients: await _helperRecipientsConvert(
+          [recipientAddress],
+          [satoshisBeingUsed - BigInt.one],
+        ),
+      ),
+    ))
+        .vSize!;
+    BigInt feeForOneOutput = BigInt.from(
+      satsPerVByte != null
+          ? (satsPerVByte * vSizeForOneOutput)
+          : estimateTxFee(
+              vSize: vSizeForOneOutput,
+              feeRatePerKB: feeRatePerKB,
+            ),
+    );
+
+    if (satsPerVByte == null) {
+      final roughEstimate = roughFeeEstimate(
+        utxoSigningData.length,
+        1,
+        feeRatePerKB,
+      ).raw;
+      if (feeForOneOutput < roughEstimate) {
+        feeForOneOutput = roughEstimate;
+      }
+    }
+
+    final amount = satoshiAmountToSend - feeForOneOutput;
+
+    if (amount.isNegative) {
+      throw Exception(
+        "Estimated fee ($feeForOneOutput sats) is greater than balance!",
+      );
+    }
+
+    final data = await buildTransaction(
+      txData: txData.copyWith(
+        recipients: await _helperRecipientsConvert(
+          [recipientAddress],
+          [amount],
+        ),
+      ),
+      utxoSigningData: utxoSigningData,
+    );
+
+    return data.copyWith(
+      fee: Amount(
+        rawValue: feeForOneOutput,
+        fractionDigits: cryptoCurrency.fractionDigits,
+      ),
+      usedUTXOs: utxoSigningData.map((e) => e.utxo).toList(),
+    );
   }
 
   Future<List<SigningData>> fetchBuildTxData(