Add optional KYC flow and service-backed account limits

frontend/packages/sxchnge_kyc/lib/src/models/identity.dart

@@ -0,0 +1,54 @@
+import 'dart:typed_data';
+
+enum IdentityStatus { unverified, pending, approved, changesRequested, denied }
+
+enum ReviewReason {
+  passportUnreadable,
+  selfieUnreadable,
+  passportExpired,
+  unableToVerify,
+}
+
+enum PhotoKind { passport, selfie }
+
+enum KycError {
+  unavailable,
+  internal,
+  permission,
+  format,
+  tooLarge,
+  unreadable,
+  tooSmall,
+  incomplete,
+  sessionExpired,
+  rateLimited,
+  conflict,
+}
+
+class KycException implements Exception {
+  const KycException(this.code);
+  final KycError code;
+}
+
+class Identity {
+  const Identity({
+    required this.status,
+    this.reason,
+    this.submissionId,
+    this.simulated = false,
+  });
+  final IdentityStatus status;
+  final ReviewReason? reason;
+  final String? submissionId;
+  final bool simulated;
+  bool get canSubmit =>
+      status == IdentityStatus.unverified ||
+      status == IdentityStatus.changesRequested;
+}
+
+/// Ephemeral image data only. Never serialize this model into storage or telemetry.
+class Photo {
+  Photo(Uint8List bytes)
+    : bytes = Uint8List.fromList(bytes).asUnmodifiableView();
+  final Uint8List bytes;
+}

frontend/packages/sxchnge_kyc/lib/src/models/limits.dart

@@ -0,0 +1,31 @@
+enum AccountTier { basic, verified }
+
+enum LimitPeriod { day, month }
+
+class VisibleLimit {
+  const VisibleLimit({
+    required this.period,
+    required this.currency,
+    required this.basicMinor,
+    required this.verifiedMinor,
+    required this.currentMinor,
+    required this.remainingMinor,
+  });
+  final LimitPeriod period;
+  final String currency;
+  final int basicMinor;
+  final int verifiedMinor;
+  final int currentMinor;
+  final int remainingMinor;
+}
+
+class Limits {
+  Limits({
+    required this.tier,
+    required List<VisibleLimit> rows,
+    required this.simulated,
+  }) : rows = List.unmodifiable(rows);
+  final AccountTier tier;
+  final List<VisibleLimit> rows;
+  final bool simulated;
+}

frontend/packages/sxchnge_kyc/lib/src/providers/identity.dart

@@ -0,0 +1,235 @@
+import 'dart:math';
+
+import 'package:flutter/foundation.dart';
+
+import 'package:sxchnge_analytics/sxchnge_analytics.dart';
+
+import '../models/identity.dart';
+import '../services/contracts.dart';
+import '../services/dummy.dart';
+
+class IdentityProvider extends ChangeNotifier {
+  IdentityProvider(
+    this.service,
+    this.photos,
+    this.journeys, {
+    this.onStatusChanged,
+  });
+  final Future<void> Function()? onStatusChanged;
+  final IdentityService service;
+  final PhotoService photos;
+  final JourneyRecorder journeys;
+  Identity? record;
+  Photo? passport;
+  Photo? selfie;
+  KycError? error;
+  PhotoKind? photoError;
+  bool busy = false;
+  bool stale = false;
+  bool editing = false;
+  bool confirmed = false;
+  int step = 0;
+  bool _disposed = false;
+  String? _key;
+  bool get hasDraft => passport != null || selfie != null;
+  bool get canSubmit =>
+      !busy &&
+      !stale &&
+      confirmed &&
+      passport != null &&
+      selfie != null &&
+      (record?.canSubmit ?? false);
+  bool get isDemo => service.isSimulated;
+  void _notify() {
+    if (!_disposed) notifyListeners();
+  }
+
+  JourneyOperation _begin(JourneyStep step) =>
+      journeys.begin(JourneyKind.kyc, step, simulated: isDemo);
+  Future<void> refresh() async {
+    if (busy) return;
+    busy = true;
+    error = null;
+    photoError = null;
+    _notify();
+    final op = _begin(JourneyStep.kycStatus);
+    try {
+      final result = await service.fetch();
+      if (_disposed) return;
+      record = result;
+      stale = false;
+      await onStatusChanged?.call();
+      if (_disposed) return;
+      if (!result.canSubmit) {
+        _clear();
+        editing = false;
+      }
+      journeys.finish(op, simulated: isDemo, terminal: true);
+    } catch (e) {
+      if (_disposed) return;
+      stale = true;
+      error = _error(e);
+      journeys.finish(op, failure: JourneyFailure.unavailable, terminal: false);
+    }
+    busy = false;
+    _notify();
+  }
+
+  void start() {
+    if (busy || stale || !(record?.canSubmit ?? false)) return;
+    editing = true;
+    error = null;
+    if (!hasDraft) {
+      step = 0;
+      confirmed = false;
+    }
+    final op = _begin(JourneyStep.kycPreparation);
+    journeys.finish(op, simulated: isDemo);
+    _notify();
+  }
+
+  Future<void> pick(PhotoKind kind) async {
+    if (busy || !editing) return;
+    busy = true;
+    error = null;
+    photoError = null;
+    _notify();
+    final op = _begin(
+      kind == PhotoKind.passport
+          ? JourneyStep.kycPassport
+          : JourneyStep.kycSelfie,
+    );
+    try {
+      final photo = await photos.pick();
+      if (_disposed) return;
+      if (photo != null) {
+        if (kind == PhotoKind.passport) {
+          passport = photo;
+        } else {
+          selfie = photo;
+        }
+        confirmed = false;
+        _key = null;
+      }
+      journeys.finish(op, simulated: isDemo, cancelled: photo == null);
+    } catch (e) {
+      if (_disposed) return;
+      error = _error(e);
+      photoError = kind;
+      journeys.finish(op, failure: JourneyFailure.document);
+    }
+    busy = false;
+    _notify();
+  }
+
+  void remove(PhotoKind kind) {
+    if (busy) return;
+    if (kind == PhotoKind.passport) {
+      passport = null;
+    } else {
+      selfie = null;
+    }
+    confirmed = false;
+    _key = null;
+    _notify();
+  }
+
+  void back() {
+    if (!busy && step > 0) {
+      step--;
+      error = null;
+      _notify();
+    }
+  }
+
+  void next() {
+    if (busy ||
+        (step == 0 && passport == null) ||
+        (step == 1 && selfie == null))
+      return;
+    if (step < 2) step++;
+    error = null;
+    _notify();
+  }
+
+  void confirm(bool value) {
+    if (!busy) {
+      confirmed = value;
+      _notify();
+    }
+  }
+
+  Future<void> submit() async {
+    if (!canSubmit) return;
+    busy = true;
+    error = null;
+    photoError = null;
+    _notify();
+    _key ??= List.generate(
+      16,
+      (_) => Random.secure().nextInt(256).toRadixString(16).padLeft(2, '0'),
+    ).join();
+    final op = _begin(JourneyStep.kycSubmission);
+    try {
+      final result = await service.submit(
+        passport: passport!,
+        selfie: selfie!,
+        idempotencyKey: _key!,
+      );
+      if (_disposed) return;
+      if (result.canSubmit) throw const KycException(KycError.conflict);
+      record = result;
+      editing = false;
+      _clear();
+      await onStatusChanged?.call();
+      if (_disposed) return;
+      journeys.finish(op, simulated: isDemo, terminal: true);
+    } catch (e) {
+      if (_disposed) return;
+      error = _error(e);
+      if (error == KycError.conflict || error == KycError.sessionExpired)
+        stale = true;
+      journeys.finish(op, failure: JourneyFailure.unavailable);
+    }
+    busy = false;
+    _notify();
+  }
+
+  Future<void> demoReview(IdentityStatus status, {ReviewReason? reason}) async {
+    if (busy || service is! DummyIdentityService) return;
+    try {
+      (service as DummyIdentityService).review(status, reason: reason);
+    } on KycException catch (e) {
+      error = e.code;
+      _notify();
+      return;
+    }
+    await refresh();
+  }
+
+  void exit() {
+    if (busy) return;
+    journeys.abandon(JourneyExit.navigation);
+    _clear();
+    editing = false;
+    error = null;
+    _notify();
+  }
+
+  void _clear() {
+    passport = null;
+    selfie = null;
+    confirmed = false;
+    _key = null;
+    step = 0;
+  }
+
+  KycError _error(Object e) => e is KycException ? e.code : KycError.internal;
+  @override
+  void dispose() {
+    _disposed = true;
+    _clear();
+    journeys.dispose();
+    super.dispose();
+  }
+}

frontend/packages/sxchnge_kyc/lib/src/providers/limits.dart

@@ -0,0 +1,37 @@
+import 'package:flutter/foundation.dart';
+
+import '../models/limits.dart';
+import '../services/contracts.dart';
+
+class LimitsProvider extends ChangeNotifier {
+  LimitsProvider(this.service);
+  final LimitsService service;
+  Limits? data;
+  bool loading = false;
+  bool failed = false;
+  int _revision = 0;
+  bool _disposed = false;
+  Future<void> refresh() async {
+    final revision = ++_revision;
+    loading = true;
+    failed = false;
+    notifyListeners();
+    try {
+      final result = await service.fetch();
+      if (_disposed || revision != _revision) return;
+      data = result;
+    } catch (_) {
+      if (_disposed || revision != _revision) return;
+      failed = true;
+    }
+    if (_disposed || revision != _revision) return;
+    loading = false;
+    notifyListeners();
+  }
+
+  @override
+  void dispose() {
+    _disposed = true;
+    super.dispose();
+  }
+}

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

@@ -0,0 +1,24 @@
+import '../models/identity.dart';
+import '../models/limits.dart';
+
+abstract interface class IdentityService {
+  bool get isSimulated;
+  Future<Identity> fetch();
+
+  /// Backend adapters must scope the key to the authenticated account and reject
+  /// stale/duplicate review transitions. Retrying the same key is idempotent.
+  Future<Identity> submit({
+    required Photo passport,
+    required Photo selfie,
+    required String idempotencyKey,
+  });
+}
+
+abstract interface class LimitsService {
+  /// Fetch server-owned visible limits. No client-selected KYC status or tier.
+  Future<Limits> fetch();
+}
+
+abstract interface class PhotoService {
+  Future<Photo?> pick();
+}

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,
+          ),
+        ],
+      ),
+    );
+  }
+}

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

@@ -0,0 +1,81 @@
+import 'dart:typed_data';
+import 'dart:ui' as ui;
+
+import 'package:file_selector/file_selector.dart';
+
+import 'package:image/image.dart' as metadata;
+
+import '../models/identity.dart';
+import 'contracts.dart';
+
+class FilePhotoService implements PhotoService {
+  const FilePhotoService();
+  static const maxBytes = 10 * 1024 * 1024;
+  @override
+  Future<Photo?> pick() async {
+    try {
+      final file = await openFile(
+        acceptedTypeGroups: const [
+          XTypeGroup(
+            label: 'JPEG / PNG',
+            extensions: ['jpg', 'jpeg', 'png'],
+            mimeTypes: ['image/jpeg', 'image/png'],
+            uniformTypeIdentifiers: ['public.jpeg', 'public.png'],
+          ),
+        ],
+      );
+      if (file == null) return null;
+      if (await file.length() > maxBytes)
+        throw const KycException(KycError.tooLarge);
+      final bytes = await file.readAsBytes();
+      return await validate(bytes);
+    } on KycException {
+      rethrow;
+    } catch (_) {
+      throw const KycException(KycError.permission);
+    }
+  }
+
+  static Future<Photo> validate(Uint8List bytes) async {
+    try {
+      if (bytes.length > maxBytes) throw const KycException(KycError.tooLarge);
+      final png =
+          bytes.length > 8 &&
+          bytes[0] == 137 &&
+          bytes[1] == 80 &&
+          bytes[2] == 78 &&
+          bytes[3] == 71;
+      final jpg =
+          bytes.length > 3 &&
+          bytes[0] == 255 &&
+          bytes[1] == 216 &&
+          bytes[2] == 255;
+      if (!png && !jpg) throw const KycException(KycError.format);
+      final metadata.Decoder decoder = png
+          ? metadata.PngDecoder()
+          : metadata.JpegDecoder();
+      final info = decoder.startDecode(bytes);
+      if (info == null) throw const KycException(KycError.unreadable);
+      if (info.width < 600 || info.height < 600)
+        throw const KycException(KycError.tooSmall);
+      if (info.width * info.height > 40000000)
+        throw const KycException(KycError.tooLarge);
+      final codec = await ui.instantiateImageCodec(
+        bytes,
+        targetWidth: 1000,
+        allowUpscaling: false,
+      );
+      try {
+        final frame = await codec.getNextFrame();
+        frame.image.dispose();
+      } finally {
+        codec.dispose();
+      }
+      return Photo(bytes);
+    } on KycException {
+      rethrow;
+    } catch (_) {
+      throw const KycException(KycError.unreadable);
+    }
+  }
+}

frontend/packages/sxchnge_kyc/lib/src/transport/contracts.dart

@@ -0,0 +1,64 @@
+import '../models/identity.dart';
+import '../models/limits.dart';
+
+// Transport contracts for the stub. Replace with generated backend DTOs later.
+class IdentityDTO {
+  const IdentityDTO(this.status, {this.reason, this.id, this.simulated = true});
+  final String status;
+  final String? reason;
+  final String? id;
+  final bool simulated;
+}
+
+class IdentityMapper {
+  static Identity fromDTO(IdentityDTO dto) => Identity(
+    status: IdentityStatus.values.byName(dto.status),
+    reason: dto.reason == null ? null : ReviewReason.values.byName(dto.reason!),
+    submissionId: dto.id,
+    simulated: dto.simulated,
+  );
+}
+
+class LimitsDTO {
+  const LimitsDTO({
+    required this.tier,
+    required this.rows,
+    required this.simulated,
+  });
+  final String tier;
+  final List<LimitDTO> rows;
+  final bool simulated;
+}
+
+class LimitDTO {
+  const LimitDTO(
+    this.period,
+    this.currency,
+    this.basic,
+    this.verified,
+    this.current,
+    this.remaining,
+  );
+  final String period;
+  final String currency;
+  final int basic, verified, current, remaining;
+}
+
+class LimitsMapper {
+  static Limits fromDTO(LimitsDTO dto) => Limits(
+    tier: AccountTier.values.byName(dto.tier),
+    simulated: dto.simulated,
+    rows: dto.rows
+        .map(
+          (r) => VisibleLimit(
+            period: LimitPeriod.values.byName(r.period),
+            currency: r.currency,
+            basicMinor: r.basic,
+            verifiedMinor: r.verified,
+            currentMinor: r.current,
+            remainingMinor: r.remaining,
+          ),
+        )
+        .toList(),
+  );
+}

frontend/packages/sxchnge_kyc/lib/sxchnge_kyc.dart

@@ -0,0 +1,7 @@
+export 'src/models/identity.dart';
+export 'src/models/limits.dart';
+export 'src/providers/identity.dart';
+export 'src/providers/limits.dart';
+export 'src/services/contracts.dart';
+export 'src/services/dummy.dart';
+export 'src/services/photos.dart';