Build exchange workspace and shared transaction services (#28)
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import 'dart:math';
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import 'package:sxchnge_kyc/limits_transport.dart';
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import 'package:sxchnge_kyc/sxchnge_kyc.dart';
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import '../models/wallet.dart';
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import '../transport/wallet.dart';
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import 'contracts.dart';
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/// Coherent, account-scoped backend stand-in. No network or persistence.
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class DummyWalletService implements WalletService {
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DummyWalletService(
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this.identity, {
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this.delay = const Duration(milliseconds: 350),
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this.settlement = const Duration(seconds: 2),
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DateTime Function()? now,
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String initialLocale = 'en',
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}) : now = now ?? DateTime.now,
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_locale = initialLocale;
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final IdentityService identity;
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final Duration delay, settlement;
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final DateTime Function() now;
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final _accounts = [
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AccountDTO('eur', 'EUR', 2, 7500),
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AccountDTO('usd', 'USD', 2, 0),
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AccountDTO('gbp', 'GBP', 2, 0),
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];
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final Map<String, QuoteDTO> _quotes = {};
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final _usedQuotes = <String>{};
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final Map<String, OperationDTO> _submissions = {};
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String _locale;
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int _serial = 0;
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WalletError? nextError;
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bool failNextOperation = false;
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bool loseNextResponse = false;
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@override
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bool get isSimulated => true;
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Future<void> _wait() async {
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await Future<void>.delayed(delay);
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final error = nextError;
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nextError = null;
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if (error != null) throw WalletException(error);
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}
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AccountDTO _account(String id) => _accounts.firstWhere(
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(a) => a.id == id,
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orElse: () => throw const WalletException(WalletError.notFound),
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);
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// Fixed demo ratios to EUR; never marketed as live rates.
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int _weight(String id) => switch (id) {
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'eur' => 1100,
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'usd' => 1000,
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'gbp' => 1300,
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_ => throw const WalletException(WalletError.unsupported),
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};
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int _eur(int minor, String id) => (minor * _weight(id) + 1099) ~/ 1100;
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void _settle() {
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for (final o in _submissions.values) {
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if (o.status != 'pending' || now().isBefore(o.ready)) continue;
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o.status = o.fail ? 'failed' : 'completed';
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final q = o.quote;
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if (o.fail) {
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if (q.request.kind != 'topUp')
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_account(q.request.source).available += q.debit;
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} else if (q.request.kind == 'topUp') {
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_account(q.request.source).available += q.credit;
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} else if (q.request.kind == 'exchange') {
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_account(q.request.destination!).available += q.credit;
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}
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}
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}
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int _usage({required bool monthly, required bool pending}) {
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final current = now();
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return _submissions.values
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.where(
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(o) =>
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o.quote.request.kind != 'topUp' &&
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o.status == (pending ? 'pending' : 'completed') &&
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o.created.year == current.year &&
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o.created.month == current.month &&
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(monthly || o.created.day == current.day),
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)
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.fold(
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0,
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(total, o) => total + _eur(o.quote.debit, o.quote.request.source),
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);
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}
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Future<bool> _verified() async =>
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(await identity.fetch()).status == IdentityStatus.approved;
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void _check(QuoteDTO q, bool verified) {
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if (q.request.kind == 'topUp') return;
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if (_account(q.request.source).available < q.debit)
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throw const WalletException(WalletError.insufficientFunds);
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final charge = _eur(q.debit, q.request.source);
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if (charge +
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_usage(monthly: false, pending: false) +
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_usage(monthly: false, pending: true) >
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(verified ? 250000 : 10000) ||
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charge +
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_usage(monthly: true, pending: false) +
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_usage(monthly: true, pending: true) >
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(verified ? 1000000 : 50000))
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throw const WalletException(WalletError.limitExceeded);
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}
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@override
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Future<WalletSnapshot> fetch() async {
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await _wait();
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_settle();
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return WalletSnapshot(
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accounts: _accounts.map(WalletMapper.account).toList(),
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operations: _submissions.values
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.toList()
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.reversed
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.map(WalletMapper.operation)
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.toList(),
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);
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}
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@override
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Future<Quote> quote(TransferRequest r) async {
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await _wait();
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_settle();
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_account(r.source);
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if (r.amount <= 0 || r.amount > 100000000)
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throw const WalletException(WalletError.invalidAmount);
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if (r.kind == TransferKind.exchange &&
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(r.source == r.destination || r.destination == null))
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throw const WalletException(WalletError.unsupported);
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if (r.kind == TransferKind.payout &&
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(r.recipient.trim().length < 6 || r.recipient.length > 140))
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throw const WalletException(WalletError.invalidRecipient);
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if (r.kind == TransferKind.exchange) _account(r.destination!);
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final fee = switch (r.kind) {
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TransferKind.topUp => 0,
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TransferKind.exchange => max(1, r.amount ~/ 200),
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TransferKind.payout => 100,
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};
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final n = r.kind == TransferKind.exchange ? _weight(r.source) : 1;
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final d = r.kind == TransferKind.exchange ? _weight(r.destination!) : 1;
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final q = QuoteDTO(
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'quote-${++_serial}',
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WalletMapper.request(r),
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fee,
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r.kind == TransferKind.topUp ? r.amount : r.amount + fee,
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r.amount * n ~/ d,
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now().add(const Duration(seconds: 60)),
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n,
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d,
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);
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if (q.credit <= 0) throw const WalletException(WalletError.invalidAmount);
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final verified = await _verified();
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_settle();
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_check(q, verified);
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_quotes[q.id] = q;
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return WalletMapper.quote(q);
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}
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@override
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Future<WalletOperation> submit(String quoteId, String idempotencyKey) async {
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await _wait();
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if (_submissions.containsKey(idempotencyKey))
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return WalletMapper.operation(_submissions[idempotencyKey]!);
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final q = _quotes[quoteId];
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if (q == null) throw const WalletException(WalletError.expiredQuote);
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final verified = await _verified();
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_settle();
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if (_submissions.containsKey(idempotencyKey))
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return WalletMapper.operation(_submissions[idempotencyKey]!);
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if (!now().isBefore(q.expires))
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throw const WalletException(WalletError.expiredQuote);
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if (_usedQuotes.contains(q.id))
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throw const WalletException(WalletError.expiredQuote);
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_check(q, verified);
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_usedQuotes.add(q.id);
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if (q.request.kind != 'topUp')
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_account(q.request.source).available -= q.debit;
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final o = OperationDTO(
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'op-${++_serial}',
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q,
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now(),
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now().add(settlement),
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fail: failNextOperation,
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);
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failNextOperation = false;
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_submissions[idempotencyKey] = o;
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if (loseNextResponse) {
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loseNextResponse = false;
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throw const WalletException(WalletError.uncertain);
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}
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return WalletMapper.operation(o);
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}
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@override
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Future<WalletOperation?> findSubmission(String key) async {
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await _wait();
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_settle();
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final o = _submissions[key];
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return o == null ? null : WalletMapper.operation(o);
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}
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@override
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Future<AccountProfile> profile() async {
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await _wait();
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return WalletMapper.profile(_locale);
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}
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@override
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Future<AccountProfile> saveLocale(String locale) async {
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await _wait();
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if (!['en', 'ru'].contains(locale))
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throw const WalletException(WalletError.unsupported);
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_locale = locale;
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return WalletMapper.profile(_locale);
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}
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// Kept separate from wallet fetch because LimitsService has a different result.
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Future<Limits> fetchLimits() async {
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await _wait();
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final verified = await _verified();
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_settle();
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final rows = <LimitDTO>[];
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for (final monthly in [false, true]) {
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final basic = monthly ? 50000 : 10000;
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final upgraded = monthly ? 1000000 : 250000;
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final current = verified ? upgraded : basic;
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final used = _usage(monthly: monthly, pending: false);
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final pending = _usage(monthly: monthly, pending: true);
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rows.add(
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LimitDTO(
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monthly ? 'month' : 'day',
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'EUR',
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basic,
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upgraded,
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current,
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max(0, current - used - pending),
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used,
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pending,
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),
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);
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}
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return LimitsMapper.fromDTO(
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LimitsDTO(
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tier: verified ? 'verified' : 'basic',
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rows: rows,
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simulated: true,
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),
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);
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}
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}
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class WalletLimitsService implements LimitsService {
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const WalletLimitsService(this.wallet);
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final DummyWalletService wallet;
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@override
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Future<Limits> fetch() => wallet.fetchLimits();
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}
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