feat: add payment card grouping and analysis

lib/providers/payment_card_provider.dart

@@ -0,0 +1,124 @@
+import 'package:flutter/material.dart';
+import 'package:hive/hive.dart';
+import 'package:uuid/uuid.dart';
+
+import '../models/payment_card_model.dart';
+
+class PaymentCardProvider extends ChangeNotifier {
+  late Box<PaymentCardModel> _cardBox;
+  final List<PaymentCardModel> _cards = [];
+
+  List<PaymentCardModel> get cards => List.unmodifiable(_cards);
+
+  PaymentCardModel? get defaultCard {
+    try {
+      return _cards.firstWhere((card) => card.isDefault);
+    } catch (_) {
+      return _cards.isNotEmpty ? _cards.first : null;
+    }
+  }
+
+  Future<void> init() async {
+    _cardBox = await Hive.openBox<PaymentCardModel>('payment_cards');
+    _cards
+      ..clear()
+      ..addAll(_cardBox.values);
+    _sortCards();
+    notifyListeners();
+  }
+
+  Future<PaymentCardModel> addCard({
+    required String issuerName,
+    required String last4,
+    required String colorHex,
+    required String iconName,
+    bool isDefault = false,
+  }) async {
+    if (isDefault) {
+      await _unsetDefaultCard();
+    }
+
+    final card = PaymentCardModel(
+      id: const Uuid().v4(),
+      issuerName: issuerName,
+      last4: last4,
+      colorHex: colorHex,
+      iconName: iconName,
+      isDefault: isDefault,
+    );
+
+    await _cardBox.put(card.id, card);
+    _cards.add(card);
+    _sortCards();
+    notifyListeners();
+    return card;
+  }
+
+  Future<void> updateCard(PaymentCardModel updated) async {
+    final index = _cards.indexWhere((card) => card.id == updated.id);
+    if (index == -1) return;
+
+    if (updated.isDefault) {
+      await _unsetDefaultCard(exceptId: updated.id);
+    }
+
+    _cards[index] = updated;
+    await _cardBox.put(updated.id, updated);
+    _sortCards();
+    notifyListeners();
+  }
+
+  Future<void> deleteCard(String id) async {
+    await _cardBox.delete(id);
+    _cards.removeWhere((card) => card.id == id);
+
+    if (!_cards.any((card) => card.isDefault) && _cards.isNotEmpty) {
+      _cards.first.isDefault = true;
+      await _cardBox.put(_cards.first.id, _cards.first);
+    }
+
+    _sortCards();
+    notifyListeners();
+  }
+
+  Future<void> setDefaultCard(String id) async {
+    final index = _cards.indexWhere((card) => card.id == id);
+    if (index == -1) return;
+
+    await _unsetDefaultCard(exceptId: id);
+    _cards[index].isDefault = true;
+    await _cardBox.put(id, _cards[index]);
+    _sortCards();
+    notifyListeners();
+  }
+
+  PaymentCardModel? getCardById(String? id) {
+    if (id == null) return null;
+    try {
+      return _cards.firstWhere((card) => card.id == id);
+    } catch (_) {
+      return null;
+    }
+  }
+
+  void _sortCards() {
+    _cards.sort((a, b) {
+      if (a.isDefault != b.isDefault) {
+        return a.isDefault ? -1 : 1;
+      }
+      final issuerCompare =
+          a.issuerName.toLowerCase().compareTo(b.issuerName.toLowerCase());
+      if (issuerCompare != 0) return issuerCompare;
+      return a.last4.compareTo(b.last4);
+    });
+  }
+
+  Future<void> _unsetDefaultCard({String? exceptId}) async {
+    for (final card in _cards) {
+      if (card.isDefault && card.id != exceptId) {
+        card.isDefault = false;
+        await _cardBox.put(card.id, card);
+      }
+    }
+  }
+}