fix: spark coin confirmations issue

lib/wallets/isar/models/spark_coin.dart

@@ -1,3 +1,5 @@
+import 'dart:math';
+
 import 'package:isar/isar.dart';
 
 part 'spark_coin.g.dart';
@@ -59,6 +61,19 @@ class SparkCoin {
   @ignore
   BigInt get diversifier => BigInt.parse(diversifierIntString);
 
+  int getConfirmations(int currentChainHeight) {
+    if (height == null || height! <= 0) return 0;
+    return max(0, currentChainHeight - (height! - 1));
+  }
+
+  bool isConfirmed(
+    int currentChainHeight,
+    int minimumConfirms,
+  ) {
+    final confirmations = getConfirmations(currentChainHeight);
+    return confirmations >= minimumConfirms;
+  }
+
   SparkCoin({
     required this.walletId,
     required this.type,

lib/wallets/wallet/wallet_mixin_interfaces/spark_interface.dart

@@ -1071,9 +1071,7 @@ mixin SparkInterface<T extends ElectrumXCurrencyInterface>
       final spendable = Amount(
         rawValue: unusedCoins
             .where(
-              (e) =>
+              (e) => e.isConfirmed(currentHeight, cryptoCurrency.minConfirms),
-                  e.height != null &&
-                  e.height! + cryptoCurrency.minConfirms <= currentHeight,
             )
             .map((e) => e.value)
             .fold(BigInt.zero, (prev, e) => prev + e),