halkyon/packages/halkyon_app/lib/src/testing/fake_simplelogin_gateway.dart

import 'dart:typed_data';

import 'package:halkyon_app/src/auth/data/auth_gateway.dart';
import 'package:halkyon_app/src/auth/model/auth_status.dart';
import 'package:halkyon_app/src/auth/model/session_grant.dart';
import 'package:halkyon_app/src/password/model/password_failed.dart';
import 'package:halkyon_app/src/password/model/unlocked_account_keys.dart';
import 'package:halkyon_app/src/simplelogin/data/simplelogin_gateway.dart';
import 'package:halkyon_app/src/simplelogin/model/simplelogin_arrival.dart';
import 'package:halkyon_app/src/simplelogin/model/simplelogin_failed.dart';
import 'package:halkyon_app/src/testing/fake_account_crypto.dart';
import 'package:halkyon_base_client/halkyon_base_client.dart' as protocol;
import 'package:halkyon_oidc_flutter/halkyon_oidc_flutter.dart' show OidcStart;

/// An account as [FakeSimpleLoginGateway] keeps it.
final class FakeSimpleLoginAccount({
  /// Its handle; null for an account of before, until its keys come.
  var String? handle,

  /// Its keys; null for an account of before, until they come.
  var protocol.KeysSetup? keys,
});

/// A [SimpleLoginGateway] without a server, as an instance's register
/// behaves in what an app sees (ADR 0020): SimpleLogin's people by the
/// subject a code names (`code for <subject>`, [codeFor]), accounts by the
/// person's ID ([accounts]), proofs checked by [FakeAccountCrypto]'s
/// fakes. The signed-in person is [_auth]'s. [failing] makes every call
/// fail.
class FakeSimpleLoginGateway(final AuthGateway _auth)
    implements SimpleLoginGateway {
  @override
  String get instanceUrl => 'https://halkyon.example/';

  /// Whether the instance offers SimpleLogin.
  bool isOffered = true;

  /// The accounts, by their person's ID.
  final accounts = <String, FakeSimpleLoginAccount>{};

  /// Whose each SimpleLogin subject is, by subject.
  final linked = <String, String>{};

  /// The calls made, by name, in order.
  final calls = <String>[];

  /// The ways back sign-ins began with, in order.
  final begunBack = <protocol.SimpleLoginReturn>[];

  /// Thrown by every call while set.
  Exception? failing;

  /// The handle suggested for someone new.
  String? suggestedHandle = 'anna_mueller';

  /// The code SimpleLogin hands back for [subject].
  static String codeFor(String subject) => 'code for $subject';

  final _begun = <protocol.UuidValue, ({bool link})>{};
  final _waiting = <protocol.UuidValue, String>{};
  final _signedIn = <protocol.UuidValue, String>{};
  final _challenges = <protocol.UuidValue, String>{};
  var _ids = 0;
  var _sessions = 0;

  /// Keys no phrase opens, as the register's decoy for a handle nobody has.
  static final _decoy = UnlockedAccountKeys(
    encryptionPublicKey: Uint8List(32),
    encryptionSecretKey: Uint8List(32),
    signingPublicKey: Uint8List(32),
    signingSecretKey: Uint8List(64),
  );

  /// Adds an account for [person] with [handle] and [keys], which
  /// SimpleLogin's [subject] signs in to.
  void addAccount(
    String person, {
    required String subject,
    String? handle,
    protocol.KeysSetup? keys,
  }) {
    accounts[person] = FakeSimpleLoginAccount(handle: handle, keys: keys);
    linked[subject] = person;
  }

  protocol.UuidValue _newId() => protocol.UuidValue.fromString(
    '00000000-0000-4000-8000-${(++_ids).toString().padLeft(12, '0')}',
  );

  Future<void> _call(String name) async {
    calls.add(name);
    if (failing case final error?) {
      throw error;
    }
  }

  String? get _person => switch (_auth.status) {
    SignedIn(:final authUserId) => authUserId,
    SignedOut() => null,
  };

  SessionGrant _grantFor(String person) =>
      SessionGrant(person, 'session-${++_sessions}');

  /// Whose [grant] is, or the device's person's.
  String _owner(SessionGrant? grant) =>
      grant?.authUserId ??
      _person ??
      (throw const SimpleLoginFailed(SimpleLoginProblem.failed));

  @override
  Future<bool> offered() async {
    await _call('offered');
    return isOffered;
  }

  @override
  Future<OidcStart> begin(
    protocol.SimpleLoginReturn back, {
    bool link = false,
  }) async {
    await _call('begin');
    if (!isOffered) {
      throw const SimpleLoginFailed(SimpleLoginProblem.unavailable);
    }
    begunBack.add(back);
    final attempt = _newId();
    _begun[attempt] = (link: link);
    final state = 'test-${back.name}.$attempt';
    return OidcStart(
      attempt: attempt,
      authorizationUrl: Uri.parse(
        'https://app.simplelogin.io/oauth2/authorize?state=$state',
      ),
      state: state,
    );
  }

  @override
  Future<SimpleLoginArrival> complete(
    protocol.UuidValue attempt,
    String code, {
    bool link = false,
  }) async {
    await _call('complete');
    final begun = _begun.remove(attempt);
    if (begun == null) {
      throw const SimpleLoginFailed(SimpleLoginProblem.startAgain);
    }
    if (begun.link != link) {
      throw const SimpleLoginFailed(SimpleLoginProblem.startAgain);
    }
    if (!code.startsWith('code for ')) {
      throw const SimpleLoginFailed(SimpleLoginProblem.rejected);
    }
    final subject = code.substring('code for '.length);
    final owner = linked[subject];
    if (link) {
      final person = _owner(null);
      if (owner != null && owner != person) {
        throw const SimpleLoginFailed(SimpleLoginProblem.takenByAnotherPerson);
      }
      if (owner == null && linked.containsValue(person)) {
        throw const SimpleLoginFailed(SimpleLoginProblem.otherIdentityLinked);
      }
      linked[subject] = person;
      final account = accounts.putIfAbsent(person, FakeSimpleLoginAccount.new);
      _signedIn[attempt] = person;
      return SimpleLoginAccount(
        attempt: attempt,
        grant: null,
        hasKeys: account.keys != null,
        handle: account.handle,
      );
    }
    if (owner == null) {
      _waiting[attempt] = subject;
      return SimpleLoginNewcomer(
        attempt: attempt,
        suggestedHandle: suggestedHandle,
      );
    }
    final account = accounts[owner]!;
    _signedIn[attempt] = owner;
    return SimpleLoginAccount(
      attempt: attempt,
      grant: _grantFor(owner),
      hasKeys: account.keys != null,
      handle: account.handle,
    );
  }

  SimpleLoginProblem? _handleProblem(String handle) {
    if (!RegExp(r'^[a-z0-9_]{3,30}$').hasMatch(handle)) {
      return SimpleLoginProblem.handleInvalid;
    }
    if (handle == 'admin') {
      return SimpleLoginProblem.handleReserved;
    }
    if (accounts.values.any((account) => account.handle == handle)) {
      return SimpleLoginProblem.handleTaken;
    }
    return null;
  }

  @override
  Future<SimpleLoginProblem?> checkHandle(
    protocol.UuidValue attempt,
    String handle,
  ) async {
    await _call('checkHandle');
    if (!_waiting.containsKey(attempt)) {
      throw const SimpleLoginFailed(SimpleLoginProblem.startAgain);
    }
    return _handleProblem(handle);
  }

  @override
  Future<SessionGrant> signUp(
    protocol.UuidValue attempt,
    String handle,
    protocol.KeysSetup setup,
  ) async {
    await _call('signUp');
    final subject = _waiting[attempt];
    if (subject == null || _person != null) {
      throw const SimpleLoginFailed(SimpleLoginProblem.startAgain);
    }
    if (_handleProblem(handle) case final problem?) {
      throw SimpleLoginFailed(problem);
    }
    _waiting.remove(attempt);
    final person = 'person-${accounts.length + 1}';
    addAccount(person, subject: subject, handle: handle, keys: setup);
    return _grantFor(person);
  }

  @override
  Future<protocol.KeyProofChallenge> beginMend(
    protocol.UuidValue attempt,
    String handle,
  ) async {
    await _call('beginMend');
    if (!_waiting.containsKey(attempt) || _person != null) {
      throw const SimpleLoginFailed(SimpleLoginProblem.startAgain);
    }
    final challenge = _newId();
    final owner = accounts.entries
        .where((entry) => entry.value.handle == handle)
        .firstOrNull;
    // A handle nobody has gets a decoy alike.
    _challenges[challenge] = owner?.key ?? '';
    final keys = owner?.value.keys;
    return protocol.KeyProofChallenge(
      challenge: challenge,
      nonce: ByteData(32),
      encryptionPublicKey: keys?.encryptionPublicKey ?? ByteData(32),
      signingPublicKey: keys?.signingPublicKey ?? ByteData(32),
      recoveryKeys: keys?.recoveryKeys ?? FakeAccountCrypto.wrap('', _decoy),
    );
  }

  @override
  Future<SimpleLoginAccount> mend(
    protocol.UuidValue attempt,
    protocol.KeysProof proof,
  ) async {
    await _call('mend');
    final subject = _waiting[attempt];
    if (subject == null || _person != null) {
      throw const SimpleLoginFailed(SimpleLoginProblem.startAgain);
    }
    final owner = _challenges.remove(proof.challenge);
    final account = accounts[owner];
    if (owner == null ||
        account == null ||
        !FakeAccountCrypto.proves(
          proof.signature,
          account.keys?.recoveryProofKey,
        )) {
      throw const PasswordFailed(PasswordProblem.wrongCredentials);
    }
    _waiting.remove(attempt);
    linked
      ..removeWhere((_, person) => person == owner)
      ..[subject] = owner;
    _signedIn[attempt] = owner;
    return SimpleLoginAccount(
      attempt: attempt,
      grant: _grantFor(owner),
      hasKeys: account.keys != null,
      handle: account.handle,
    );
  }

  @override
  Future<protocol.KeysChallenge> beginUnlock({SessionGrant? as}) async {
    await _call('beginUnlock');
    final person = _owner(as);
    final keys = accounts[person]?.keys;
    if (keys == null) {
      throw const PasswordFailed(PasswordProblem.noPassword);
    }
    final challenge = _newId();
    _challenges[challenge] = person;
    return protocol.KeysChallenge(
      challenge: challenge,
      nonce: ByteData(32),
      salt: keys.salt,
      costs: keys.costs,
    );
  }

  @override
  Future<protocol.DeviceKeys> unlock(
    protocol.KeysProof proof, {
    SessionGrant? as,
  }) async {
    await _call('unlock');
    final person = _owner(as);
    if (_challenges.remove(proof.challenge) != person) {
      throw const PasswordFailed(PasswordProblem.challengeExpired);
    }
    final keys = accounts[person]!.keys!;
    if (!FakeAccountCrypto.provesPassword(proof, keys.passwordProofKey)) {
      throw const PasswordFailed(PasswordProblem.wrongCredentials);
    }
    return protocol.DeviceKeys(
      encryptionPublicKey: keys.encryptionPublicKey,
      signingPublicKey: keys.signingPublicKey,
      passwordKeys: keys.passwordKeys,
    );
  }

  @override
  Future<void> setKeys(
    protocol.UuidValue attempt,
    protocol.KeysSetup setup, {
    String? handle,
    SessionGrant? as,
  }) async {
    await _call('setKeys');
    final person = _owner(as);
    if (_signedIn[attempt] != person) {
      throw const SimpleLoginFailed(SimpleLoginProblem.startAgain);
    }
    final account = accounts[person]!;
    if (account.keys != null) {
      throw const PasswordFailed(PasswordProblem.passwordExists);
    }
    if ((account.handle == null) != (handle != null)) {
      throw const SimpleLoginFailed(SimpleLoginProblem.handleInvalid);
    }
    if (handle != null) {
      if (_handleProblem(handle) case final problem?) {
        throw SimpleLoginFailed(problem);
      }
      account.handle = handle;
    }
    _signedIn.remove(attempt);
    account.keys = setup;
  }
}