Adding OpenHaystack Mobile app

Co-Authored-By: Lukas Burg <lukas.burg@hemalu.de>

openhaystack-mobile/lib/location/location_model.dart

@@ -0,0 +1,131 @@
+import 'dart:async';
+
+import 'package:flutter/material.dart';
+import 'package:flutter/services.dart';
+import 'package:geocoding/geocoding.dart' as geocode;
+import 'package:latlong2/latlong.dart';
+import 'package:location/location.dart';
+
+class LocationModel extends ChangeNotifier {
+  LatLng? here;
+  geocode.Placemark? herePlace;
+  StreamSubscription<LocationData>? locationStream;
+  final Location _location = Location();
+  bool initialLocationSet = false;
+
+  /// Requests access to the device location from the user.
+  /// 
+  /// Initializes the location services and requests location
+  /// access from the user if not granged.
+  /// Returns if location access was granted.
+  Future<bool> requestLocationAccess() async {
+    // Enable location service
+    var serviceEnabled = await _location.serviceEnabled();
+    if (!serviceEnabled) {
+      serviceEnabled = await _location.requestService();
+      if (!serviceEnabled) {
+        print('Could not enable location service.');
+        return false;
+      }
+    }
+
+    // Request location access from user if not permanently denied or already granted
+    var permissionGranted = await _location.hasPermission();
+    if (permissionGranted == PermissionStatus.denied) {
+      permissionGranted = await _location.requestPermission();
+      
+    }
+
+    if (permissionGranted == PermissionStatus.granted) {
+      // Permission not granted
+      return true;
+    } else if (permissionGranted == PermissionStatus.grantedLimited) {
+      // Permission granted to access approximate location
+      return false;
+    } else {
+      // Permission not granted
+      return false;
+    }
+  }
+
+  /// Requests location updates from the platform.
+  /// 
+  /// Listeners will be notified about locaiton changes.
+  Future<void> requestLocationUpdates() async {
+    var permissionGranted = await requestLocationAccess();
+    if (permissionGranted) {
+
+      // Handle future location updates
+      locationStream ??= _location.onLocationChanged.listen(_updateLocation);
+
+      // Fetch the current location
+      var locationData = await _location.getLocation();
+      _updateLocation(locationData);
+    } else {
+      initialLocationSet = true;
+      if (locationStream != null) {
+        locationStream?.cancel();
+        locationStream = null;
+      }
+      _removeCurrentLocation();
+      notifyListeners();
+    }
+  }
+
+  /// Updates the current location if new location data is available.
+  /// 
+  /// Additionally updates the current address information to match
+  /// the new location.
+  void _updateLocation(LocationData locationData) {
+    if (locationData.latitude != null && locationData.longitude != null) {
+      // print('Locaiton here: ${locationData.latitude!}, ${locationData.longitude!}');
+      here = LatLng(locationData.latitude!, locationData.longitude!);
+      initialLocationSet = true;
+      getAddress(here!)
+        .then((value) {
+          herePlace = value;
+          notifyListeners();
+        });
+    } else {
+      print('Received invalid location data: $locationData');
+    }
+    notifyListeners();
+  }
+
+  /// Cancels the listening for location updates.
+  void cancelLocationUpdates() {
+    if (locationStream != null) {
+      locationStream?.cancel();
+      locationStream = null;
+    }
+    _removeCurrentLocation();
+    notifyListeners();
+  }
+
+  /// Resets the currently stored location and address information
+  void _removeCurrentLocation() {
+    here = null;
+    herePlace = null;
+  }
+
+  /// Returns the address for a given geolocation (latitude & longitude).
+  /// 
+  /// Only works on mobile platforms with their local APIs.
+  static Future<geocode.Placemark?> getAddress(LatLng? location) async {
+    if (location == null) {
+      return null;
+    }
+    double lat = location.latitude;
+    double lng = location.longitude;
+
+    try {
+      List<geocode.Placemark> placemarks = await geocode.placemarkFromCoordinates(lat, lng);
+      return placemarks.first;
+    } on MissingPluginException {
+      return null;
+    } on PlatformException {
+      return null; 
+    }
+  }
+
+}