Add reverse geocoder

app/lib/mobile/db_util.dart

@@ -2,9 +2,11 @@ import 'dart:io' as dart;
 
 import 'package:drift/drift.dart';
 import 'package:drift/native.dart';
+import 'package:flutter/services.dart' show rootBundle;
 import 'package:path/path.dart' as path_lib;
 import 'package:path_provider/path_provider.dart';
-import 'package:sqlite3_flutter_libs/sqlite3_flutter_libs.dart' as sqlite3;
+import 'package:sqlite3/sqlite3.dart';
+import 'package:sqlite3_flutter_libs/sqlite3_flutter_libs.dart' as sql;
 
 Future<Map<String, dynamic>> getSqliteConnectionArgs() async {
   // put the database file, called db.sqlite here, into the documents folder
@@ -32,5 +34,27 @@ QueryExecutor openSqliteConnection() {
 }
 
 Future<void> applyWorkaroundToOpenSqlite3OnOldAndroidVersions() {
-  return sqlite3.applyWorkaroundToOpenSqlite3OnOldAndroidVersions();
+  return sql.applyWorkaroundToOpenSqlite3OnOldAndroidVersions();
+}
+
+Future<Database> openRawSqliteDbFromAsset(
+  String assetRelativePath,
+  String outputFilename, {
+  bool isReadOnly = false,
+}) async {
+  final dbFolder = await getApplicationDocumentsDirectory();
+  final file = dart.File(path_lib.join(dbFolder.path, outputFilename));
+  if (!await file.exists()) {
+    // copy file from assets
+    final blob = await rootBundle.load("assets/$assetRelativePath");
+    final buffer = blob.buffer;
+    await file.writeAsBytes(
+      buffer.asUint8List(blob.offsetInBytes, blob.lengthInBytes),
+      flush: true,
+    );
+  }
+  return sqlite3.open(
+    file.path,
+    mode: isReadOnly ? OpenMode.readOnly : OpenMode.readWriteCreate,
+  );
 }

app/lib/reverse_geocoder.dart

@@ -0,0 +1,172 @@
+import 'dart:math' as math;
+
+import 'package:collection/collection.dart';
+import 'package:kdtree/kdtree.dart';
+import 'package:logging/logging.dart';
+import 'package:nc_photos/entity/file.dart';
+import 'package:nc_photos/math_util.dart' as math_util;
+import 'package:nc_photos/mobile/platform.dart'
+    if (dart.library.html) 'package:nc_photos/web/platform.dart' as platform;
+import 'package:sqlite3/common.dart';
+
+class ReverseGeocoderLocation {
+  const ReverseGeocoderLocation(this.name, this.latitude, this.longitude,
+      this.countryCode, this.admin1, this.admin2);
+
+  @override
+  toString() => "$runtimeType {"
+      "name: $name, "
+      "latitude: $latitude, "
+      "longitude: $longitude, "
+      "countryCode: $countryCode, "
+      "admin1: $admin1, "
+      "admin2: $admin2, "
+      "}";
+
+  final String name;
+  final double latitude;
+  final double longitude;
+  final String countryCode;
+  final String? admin1;
+  final String? admin2;
+}
+
+class ReverseGeocoder {
+  Future<void> init() async {
+    final s = Stopwatch()..start();
+    _db = await _openDatabase();
+    _searchTree = _buildSearchTree(_db);
+    _log.info("[init] Elapsed time: ${s.elapsedMilliseconds}ms");
+  }
+
+  /// Convert a geographic coordinate (in degree) into a location
+  Future<ReverseGeocoderLocation?> call(
+      double latitude, double longitude) async {
+    _log.info(
+        "[call] latitude: ${latitude.toStringAsFixed(3)}, longitude: ${longitude.toStringAsFixed(3)}");
+    final latitudeInt = (latitude * 10000).round();
+    final longitudeInt = (longitude * 10000).round();
+    final nearest = _searchTree
+        .nearest({"t": latitudeInt, "g": longitudeInt}, 1).firstOrNull;
+    if (nearest == null) {
+      _log.info("[call] Nearest point not found");
+      return null;
+    }
+    final nearestLat = nearest[0]["t"];
+    final nearestLatF = nearestLat / 10000;
+    final nearestLng = nearest[0]["g"];
+    final nearestLngF = nearestLng / 10000;
+    _log.info("[call] Nearest point, (lat: $nearestLatF, lng: $nearestLngF)");
+    try {
+      final distance = _distanceInKm(
+        math_util.degToRad(latitude),
+        math_util.degToRad(longitude),
+        math_util.degToRad(nearestLatF),
+        math_util.degToRad(nearestLngF),
+      );
+      _log.info(
+          "[call] (lat: ${latitude.toStringAsFixed(3)}, lng: ${longitude.toStringAsFixed(3)}) <-> (lat: $nearestLatF, lng: $nearestLngF) = ${distance.toStringAsFixed(3)}km");
+      // a completely arbitrary threshold :)
+      if (distance > 10) {
+        _log.info("[call] Nearest point is too far away");
+        return null;
+      }
+    } catch (e, stackTrace) {
+      _log.severe("[call] Uncaught exception", e, stackTrace);
+    }
+
+    final data = _queryPoint(nearestLat, nearestLng);
+    if (data == null) {
+      _log.severe(
+          "[call] Row not found for point: latitude: $nearestLat, longitude: $nearestLng");
+      return null;
+    }
+    final result = ReverseGeocoderLocation(data.name, data.latitude / 10000,
+        data.longitude / 10000, data.countryCode, data.admin1, data.admin2);
+    _log.info("[call] Found: $result");
+    return result;
+  }
+
+  _DatabaseRow? _queryPoint(int latitudeInt, int longitudeInt) {
+    final result = _db.select(
+      "SELECT * FROM cities WHERE latitude = ? AND longitude = ? LIMIT 1;",
+      [latitudeInt, longitudeInt],
+    );
+    if (result.isEmpty) {
+      return null;
+    } else {
+      return _DatabaseRow(
+        result.first.columnAt(1),
+        result.first.columnAt(2),
+        result.first.columnAt(3),
+        result.first.columnAt(4),
+        result.first.columnAt(5),
+        result.first.columnAt(6),
+      );
+    }
+  }
+
+  late final CommonDatabase _db;
+  late final KDTree _searchTree;
+
+  static final _log = Logger("reverse_geocoder.ReverseGeocoder");
+}
+
+extension ReverseGeocoderExtension on ReverseGeocoderLocation {
+  ImageLocation toImageLocation() {
+    return ImageLocation(
+      name: name,
+      latitude: latitude,
+      longitude: longitude,
+      countryCode: countryCode,
+      admin1: admin1,
+      admin2: admin2,
+    );
+  }
+}
+
+class _DatabaseRow {
+  const _DatabaseRow(this.name, this.latitude, this.longitude, this.countryCode,
+      this.admin1, this.admin2);
+
+  final String name;
+  final int latitude;
+  final int longitude;
+  final String countryCode;
+  final String? admin1;
+  final String? admin2;
+}
+
+Future<CommonDatabase> _openDatabase() async {
+  return platform.openRawSqliteDbFromAsset("cities.sqlite", "cities.sqlite");
+}
+
+KDTree _buildSearchTree(CommonDatabase db) {
+  final results = db.select("SELECT latitude, longitude FROM cities;");
+  return KDTree(
+    results.map((e) => {"t": e.columnAt(0), "g": e.columnAt(1)}).toList(),
+    _kdTreeDistance,
+    ["t", "g"],
+  );
+}
+
+int _kdTreeDistance(Map a, Map b) {
+  return (math.pow((a["t"] as int) - (b["t"] as int), 2) +
+      math.pow((a["g"] as int) - (b["g"] as int), 2)) as int;
+}
+
+/// Calculate the distance in KM between two point
+///
+/// Both latitude and longitude are expected to be in radian
+double _distanceInKm(
+    double latitude1, double longitude1, double latitude2, double longitude2) {
+  final dLat = latitude2 - latitude1;
+  final dLon = longitude2 - longitude1;
+  final a = math.pow(math.sin(dLat / 2), 2) +
+      math.cos(latitude1) *
+          math.cos(latitude2) *
+          math.pow(math.sin(dLon / 2), 2);
+  final c = 2 * math.atan2(math.sqrt(a), math.sqrt(1 - a));
+  // 6371 = earth radius
+  return 6371 * c;
+}

app/pubspec.lock

@@ -679,6 +679,13 @@ packages:
       url: "https://pub.dartlang.org"
     source: hosted
     version: "4.6.0"
+  kdtree:
+    dependency: "direct main"
+    description:
+      name: kdtree
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "0.2.0"
   kiwi:
     dependency: "direct main"
     description:
@@ -1161,7 +1168,7 @@ packages:
     source: hosted
     version: "2.2.1+1"
   sqlite3:
-    dependency: transitive
+    dependency: "direct main"
     description:
       name: sqlite3
       url: "https://pub.dartlang.org"

app/pubspec.yaml

@@ -76,6 +76,7 @@ dependencies:
       ref: 1.0.0-nc-photos-2
       path: library
   intl: ^0.17.0
+  kdtree: ^0.2.0
   kiwi: ^4.0.1
   logging: ^1.0.1
   memory_info: ^0.0.2
@@ -90,6 +91,7 @@ dependencies:
   quiver: ^3.1.0
   screen_brightness:  ^0.2.1
   shared_preferences: ^2.0.8
+  sqlite3: any
   sqlite3_flutter_libs: ^0.5.8
   synchronized: ^3.0.0
   tuple: ^2.0.0