Add optional KYC flow and service-backed account limits

frontend/packages/sxchnge_kyc/lib/src/services/dummy.dart

@@ -0,0 +1,93 @@
+import '../models/identity.dart';
+import '../models/limits.dart';
+import '../transport/contracts.dart';
+import 'contracts.dart';
+
+/// Process-local backend stand-in. It never stores or sends document bytes.
+class DummyIdentityService implements IdentityService {
+  DummyIdentityService({this.delay = const Duration(milliseconds: 450)});
+  final Duration delay;
+  IdentityDTO _record = const IdentityDTO('unverified');
+  String? _lastKey;
+  KycError? nextError;
+  @override
+  bool get isSimulated => true;
+  Future<void> _wait() async {
+    await Future<void>.delayed(delay);
+    final error = nextError;
+    nextError = null;
+    if (error != null) throw KycException(error);
+  }
+
+  @override
+  Future<Identity> fetch() async {
+    await _wait();
+    return IdentityMapper.fromDTO(_record);
+  }
+
+  @override
+  Future<Identity> submit({
+    required Photo passport,
+    required Photo selfie,
+    required String idempotencyKey,
+  }) async {
+    await _wait();
+    if (_lastKey == idempotencyKey) return IdentityMapper.fromDTO(_record);
+    if (!IdentityMapper.fromDTO(_record).canSubmit)
+      throw const KycException(KycError.conflict);
+    if (passport.bytes.isEmpty || selfie.bytes.isEmpty)
+      throw const KycException(KycError.incomplete);
+    _lastKey = idempotencyKey;
+    _record = IdentityDTO('pending', id: idempotencyKey);
+    return IdentityMapper.fromDTO(_record);
+  }
+
+  /// Explicit demo-only human decision stand-in; unavailable in real adapters.
+  void review(IdentityStatus status, {ReviewReason? reason}) {
+    if (_record.status != 'pending')
+      throw const KycException(KycError.conflict);
+    if (![
+      IdentityStatus.approved,
+      IdentityStatus.changesRequested,
+      IdentityStatus.denied,
+    ].contains(status))
+      throw const KycException(KycError.conflict);
+    _record = IdentityDTO(status.name, id: _record.id, reason: reason?.name);
+  }
+}
+
+/// Mimics backend policy evaluation. Widgets/providers never compute active caps.
+/// Values are illustrative fixtures, not the product's real limits policy.
+class DummyLimitsService implements LimitsService {
+  DummyLimitsService(this.identity);
+  final IdentityService identity;
+  @override
+  Future<Limits> fetch() async {
+    final record = await identity.fetch();
+    final approved = record.status == IdentityStatus.approved;
+    return LimitsMapper.fromDTO(
+      LimitsDTO(
+        tier: approved ? 'verified' : 'basic',
+        simulated: true,
+        rows: [
+          LimitDTO(
+            'day',
+            'EUR',
+            10000,
+            250000,
+            approved ? 250000 : 10000,
+            approved ? 250000 : 10000,
+          ),
+          LimitDTO(
+            'month',
+            'EUR',
+            50000,
+            1000000,
+            approved ? 1000000 : 50000,
+            approved ? 1000000 : 50000,
+          ),
+        ],
+      ),
+    );
+  }
+}