look ahead

lib/services/ing_csv_import.dart

@@ -47,15 +47,30 @@ bool isSameTransaction(BankTransaction a, BankTransaction b) {
 
 int _amountCents(double amount) => (amount * 100).round();
 
+/// Coarse bucket so fuzzy [isSameTransaction] only compares likely peers.
+String _dedupeBucket(BankTransaction tx) =>
+    '${tx.date}|${tx.currency.toUpperCase()}|${_amountCents(tx.amount)}';
+
 /// Merge [extra] into [existing], skipping duplicates. Newest date first.
 List<BankTransaction> mergeTransactions(
   List<BankTransaction> existing,
   List<BankTransaction> extra,
 ) {
+  if (extra.isEmpty) return existing;
+  final buckets = <String, List<BankTransaction>>{};
+  for (final tx in existing) {
+    buckets.putIfAbsent(_dedupeBucket(tx), () => []).add(tx);
+  }
+
   final out = List<BankTransaction>.of(existing);
   for (final tx in extra) {
-    if (out.any((e) => isSameTransaction(e, tx))) continue;
+    final key = _dedupeBucket(tx);
+    final peers = buckets[key];
+    if (peers != null && peers.any((e) => isSameTransaction(e, tx))) {
+      continue;
+    }
     out.add(tx);
+    buckets.putIfAbsent(key, () => []).add(tx);
   }
   out.sort((a, b) {
     final byDate = b.date.compareTo(a.date);
@@ -70,9 +85,20 @@ List<BankTransaction> filterNewTransactions(
   List<BankTransaction> existing,
   List<BankTransaction> candidates,
 ) {
+  if (candidates.isEmpty) return const [];
+  if (existing.isEmpty) return List<BankTransaction>.of(candidates);
+
+  final buckets = <String, List<BankTransaction>>{};
+  for (final tx in existing) {
+    buckets.putIfAbsent(_dedupeBucket(tx), () => []).add(tx);
+  }
+
   return [
     for (final tx in candidates)
-      if (!existing.any((e) => isSameTransaction(e, tx))) tx,
+      if (!(buckets[_dedupeBucket(tx)]
+              ?.any((e) => isSameTransaction(e, tx)) ??
+          false))
+        tx,
   ];
 }