gps-speedo/lib/ui/features/speedometer/speedometer_view_model.dart

import 'dart:async';
import 'package:flutter/widgets.dart';
import 'package:shared_preferences/shared_preferences.dart';
import '../../../core/constants/speed_unit.dart';
import '../../../data/models/location_data.dart';
import '../../../data/repositories/location_repository.dart';

/// ViewModel for the speedometer UI.
///
/// Thin state manager — subscribes to [LocationRepository] and exposes
/// the current display state to the view. No data-layer logic here.
class SpeedometerViewModel extends ChangeNotifier {
  final LocationRepository _repository;
  final SharedPreferences _prefs;

  SpeedUnit _displayUnit = SpeedUnit.kmh;
  LocationData _displayData = LocationData(
    speed: 0.0,
    heading: -1.0,
    displaySpeed: '--',
    displayHeading: 'N/A',
    isSpeedValid: false,
    isHeadingValid: false,
    timestamp: DateTime.now(),
  );

  LocationData get displayData => _displayData;
  SpeedUnit get displayUnit => _displayUnit;

  SpeedometerViewModel({
    required LocationRepository repository,
    required SharedPreferences prefs,
  })  : _repository = repository,
        _prefs = prefs;

  void init() {
    _repository.locationStream.listen(_onLocationData);
    _loadSettings();
  }

  void _onLocationData(LocationData data) {
    _displayData = data;
    notifyListeners();
  }

  Future<void> _loadSettings() async {
    _displayUnit = _parseSpeedUnit(_prefs.getString('speed_unit') ?? 'km/h');
    notifyListeners();
  }

  static SpeedUnit _parseSpeedUnit(String unit) {
    switch (unit) {
      case 'mph':
        return SpeedUnit.mph;
      case 'kts':
        return SpeedUnit.knots;
      default:
        return SpeedUnit.kmh;
    }
  }

  double get displaySpeed {
    return _displayUnit.convert(_displayData.speed);
  }

  String get displaySpeedText {
    return _displayData.displaySpeed;
  }

  String get displayHeading {
    return _displayData.displayHeading;
  }

  bool get isSpeedValid {
    return _displayData.isSpeedValid;
  }

  bool get isHeadingValid {
    return _displayData.isHeadingValid;
  }
}