import 'package:flutter/foundation.dart';

import '../services/pin_lock_service.dart';

class PinLockViewModel extends ChangeNotifier {
  final PinLockService pinLockService;

  PinLockViewModel({required this.pinLockService});

  bool _isPinSet = false;
  bool _isUnlocked = false;
  bool _isLoading = false;
  bool _hasLoaded = false;
  String? _errorMessage;

  bool get isPinSet => _isPinSet;

  bool get isUnlocked => _isUnlocked;

  bool get isLoading => _isLoading;

  bool get hasLoaded => _hasLoaded;

  String? get errorMessage => _errorMessage;

  Future<void> ensureLoaded() async {
    if (_hasLoaded || _isLoading) return;

    await load();
  }

  /// Checks whether a PIN has already been configured on this device.
  Future<void> load() async {
    if (_isLoading) return;

    _isLoading = true;
    _errorMessage = null;
    notifyListeners();

    try {
      _isPinSet = await pinLockService.hasPin();
    } catch (_) {
      _errorMessage = 'Could not check PIN status.';
    } finally {
      _hasLoaded = true;
      _isLoading = false;
      notifyListeners();
    }
  }

  /// Creates a new PIN (first-time setup, or after disabling an old one).
  /// Unlocks the app immediately on success, since the person just proved
  /// they know it by typing it.
  Future<bool> setPin(String pin) async {
    _errorMessage = null;

    try {
      await pinLockService.setPin(pin);
      _isPinSet = true;
      _isUnlocked = true;
      notifyListeners();
      return true;
    } catch (_) {
      _errorMessage = 'Could not save PIN.';
      notifyListeners();
      return false;
    }
  }

  /// Checks an entered PIN against the stored one, unlocking on match.
  Future<bool> verify(String pin) async {
    _errorMessage = null;

    try {
      final matches = await pinLockService.verifyPin(pin);

      if (matches) {
        _isUnlocked = true;
        notifyListeners();
        return true;
      }

      _errorMessage = 'Incorrect PIN.';
      notifyListeners();
      return false;
    } catch (_) {
      _errorMessage = 'Could not verify PIN.';
      notifyListeners();
      return false;
    }
  }

  /// Replaces the current PIN. Requires the current PIN to match first.
  Future<bool> changePin({
    required String currentPin,
    required String newPin,
  }) async {
    final currentMatches = await pinLockService.verifyPin(currentPin);

    if (!currentMatches) {
      _errorMessage = 'Current PIN is incorrect.';
      notifyListeners();
      return false;
    }

    return setPin(newPin);
  }

  /// Removes the PIN entirely. Requires the current PIN to confirm.
  Future<bool> disablePin(String currentPin) async {
    final matches = await pinLockService.verifyPin(currentPin);

    if (!matches) {
      _errorMessage = 'Current PIN is incorrect.';
      notifyListeners();
      return false;
    }

    await pinLockService.clearPin();
    _isPinSet = false;
    notifyListeners();
    return true;
  }

  /// Re-locks the app. Call this on app backgrounding (e.g. from a
  /// WidgetsBindingObserver on AppLifecycleState.paused) if you want the
  /// PIN required again after the app is put away, not just on cold start.
  void lock() {
    if (!_isUnlocked) return;

    _isUnlocked = false;
    notifyListeners();
  }
}