import 'dart:developer';

import 'package:flutter/foundation.dart';

import '../../api/demo/demo_mode.dart';
import '../../api/errors/error_mapper.dart';
import '../../api/marianumconnect/auth/device_token_name.dart';
import '../../api/marianumconnect/queries/auth_guardian/auth_guardian_request.dart';
import '../../api/marianumconnect/queries/auth_guardian/auth_guardian_verify.dart';
import '../../api/marianumconnect/queries/auth_guardian/guardian_login_exception.dart';
import '../../auth_link/device_binding.dart';
import '../../auth_link/guardian_login_link.dart';
import '../../auth_link/pending_guardian_request.dart';
import '../../session/session.dart';
import '../../session/session_manager.dart';
import '../../widget_data/widget_sync.dart';

enum GuardianLoginStep { enterEmail, enterCode }

/// Drives the passwordless guardian login: request a mail, then finish with
/// the mailed code or link. The running request is persisted so the flow
/// survives the app being killed while the user reads the mail.
class GuardianLoginController extends ChangeNotifier {
  final AuthGuardianRequest _request;
  final AuthGuardianVerify _verify;
  final PendingGuardianRequestStore _store;
  final Future<void> Function(Session session) _signIn;
  final Future<String> Function() _tokenName;
  final DateTime Function() _now;

  GuardianLoginController({
    AuthGuardianRequest? request,
    AuthGuardianVerify? verify,
    PendingGuardianRequestStore store = const PendingGuardianRequestStore(),
    Future<void> Function(Session session)? signIn,
    Future<String> Function()? tokenName,
    DateTime Function()? now,
  }) : _request = request ?? AuthGuardianRequest(),
       _verify = verify ?? AuthGuardianVerify(),
       _store = store,
       _signIn = signIn ?? _defaultSignIn,
       _tokenName = tokenName ?? DeviceTokenName.resolve,
       _now = now ?? DateTime.now;

  GuardianLoginStep _step = GuardianLoginStep.enterEmail;
  PendingGuardianRequest? _pending;
  bool _loading = false;
  String? _errorMessage;
  String? _errorDetails;

  GuardianLoginStep get step => _step;
  PendingGuardianRequest? get pending => _pending;
  bool get loading => _loading;
  String? get errorMessage => _errorMessage;
  String? get errorDetails => _errorDetails;

  bool canResend() => resendCooldown() == Duration.zero;

  /// Restzeit, bis [resend] wieder erlaubt ist.
  Duration resendCooldown() {
    final pending = _pending;
    if (pending == null) return Duration.zero;
    final remaining = pending.resendAvailableAt.difference(_now());
    return remaining.isNegative ? Duration.zero : remaining;
  }

  /// Picks up a request started before the app was closed.
  Future<void> restore() async {
    final stored = await _store.read();
    if (stored == null) return;
    if (stored.isExpired(_now())) {
      await _store.clear();
      return;
    }
    _pending = stored;
    _step = GuardianLoginStep.enterCode;
    notifyListeners();
  }

  /// Sends the login mail. Returns true when the user is already signed in
  /// (demo address), false when the code step follows or the request failed.
  Future<bool> requestCode(String email) async {
    final normalized = email.trim().toLowerCase();
    if (DemoMode.matchesGuardian(normalized)) {
      var signedIn = false;
      await _run(() async {
        await _signIn(GuardianSession(email: normalized, isDemo: true));
        signedIn = true;
      });
      return signedIn;
    }
    await _run(() async {
      final secret = DeviceBinding.generateSecret();
      final response = await _request.run(
        email: normalized,
        deviceChallenge: DeviceBinding.challengeFor(secret),
        tokenName: await _tokenName(),
      );
      final pending = PendingGuardianRequest(
        requestId: response.requestId,
        email: normalized,
        deviceSecret: secret,
        expiresAt: response.expiresAt,
        resendAvailableAt: response.resendAvailableAt,
        codeLength: response.codeLength,
      );
      await _store.write(pending);
      _pending = pending;
      _step = GuardianLoginStep.enterCode;
    });
    return false;
  }

  Future<void> resend() async {
    final pending = _pending;
    if (pending == null || !canResend()) return;
    await requestCode(pending.email);
  }

  /// Mail clients and autofill may insert spaces into the code.
  static String normalizeCode(String code) =>
      code.replaceAll(RegExp(r'\s'), '');

  Future<bool> submitCode(String code) => _complete(code: normalizeCode(code));

  /// Completes the login from a mail link. A link belonging to another
  /// request (other device, or an older mail) cannot be verified here.
  Future<bool> submitLink(GuardianLoginLink link) {
    if (_pending?.requestId != link.requestId) {
      _errorMessage = GuardianLoginException.messageFor(
        GuardianLoginError.deviceMismatch,
      );
      _errorDetails = null;
      notifyListeners();
      return Future.value(false);
    }
    return _complete(linkToken: link.linkToken);
  }

  /// A mail link that does not belong to the server the app talks to (a live
  /// link while the app points at beta). Without this the tap would do nothing
  /// at all.
  void rejectForeignLink() {
    _errorMessage =
        'Dieser Anmeldelink gehört zu einem anderen Server als dem, mit dem '
        'die App gerade verbunden ist. Bitte gib den Code aus der E-Mail ein.';
    _errorDetails = null;
    notifyListeners();
  }

  /// Abandons the running request, e.g. to correct a mistyped address.
  Future<void> changeEmail() async {
    await _store.clear();
    _pending = null;
    _step = GuardianLoginStep.enterEmail;
    _errorMessage = null;
    _errorDetails = null;
    notifyListeners();
  }

  Future<bool> _complete({String? code, String? linkToken}) async {
    final pending = _pending;
    if (pending == null) {
      _errorMessage = GuardianLoginException.messageFor(
        GuardianLoginError.requestExpired,
      );
      _errorDetails = null;
      _step = GuardianLoginStep.enterEmail;
      notifyListeners();
      return false;
    }
    var signedIn = false;
    await _run(() async {
      await _verify.run(
        requestId: pending.requestId,
        deviceVerifier: pending.deviceSecret,
        tokenName: await _tokenName(),
        code: code,
        linkToken: linkToken,
      );
      await _store.clear();
      await _signIn(GuardianSession(email: pending.email));
      signedIn = true;
    });
    return signedIn;
  }

  Future<void> _run(Future<void> Function() body) async {
    if (_loading) return;
    _loading = true;
    _errorMessage = null;
    _errorDetails = null;
    notifyListeners();
    try {
      await body();
    } on GuardianLoginException catch (e) {
      _errorMessage = e.userMessage;
      _errorDetails = e.technicalDetails;
      // These end the request for good; only a new mail helps.
      if (e.error
          case GuardianLoginError.requestExpired ||
              GuardianLoginError.requestConsumed ||
              GuardianLoginError.tooManyAttempts) {
        await _store.clear();
        _pending = null;
        _step = GuardianLoginStep.enterEmail;
      }
    } catch (e) {
      log('Guardian login failed: $e');
      _errorMessage = errorToUserMessage(e);
      _errorDetails = errorToTechnicalDetails(e);
    } finally {
      _loading = false;
      notifyListeners();
    }
  }

  static Future<void> _defaultSignIn(Session session) async {
    // Sign in first: the one-time code is already spent at this point, so a
    // failing widget reset must not cost the session (the user would have to
    // request a fresh mail for a login that actually succeeded).
    await SessionManager().signIn(session);
    // Drop any widget snapshot of a previous account.
    try {
      await WidgetSync.clear();
      await WidgetSync.triggerUpdate();
    } on Object catch (e) {
      log('Guardian login: widget reset failed: $e');
    }
  }
}