Adds requests for total flight time and flight in between timestamps

lib/config.dart

@@ -1,6 +1,12 @@
 // This file holds a class to represent the configuration/settings of the app
 
+import 'dart:io';
+
 import 'package:json_annotation/json_annotation.dart';
+import 'dart:convert';
+import 'package:path_provider/path_provider.dart';
+import 'package:path/path.dart' as path;
+
 part 'generated/config.g.dart';
 
 @JsonSerializable()
@@ -10,7 +16,24 @@ class RTimeConfig {
   RTimeConfig({required this.language});
 
   factory RTimeConfig.fromJson(Map<String, dynamic> json) =>
-      _$PersonFromJson(json);
+      _$RTimeConfigFromJson(json);
 
-  Map<String, dynamic> toJson() => _$PersonToJson(this);
+  Map<String, dynamic> toJson() => _$RTimeConfigToJson(this);
+
+  static Future<RTimeConfig?> readFromConfig() async {
+    final directory = await getApplicationDocumentsDirectory();
+    final configName = "rtime_config.json";
+    final configPath = path.join(directory.path, configName);
+
+    final string = jsonDecode(await File(configPath).readAsString());
+    return RTimeConfig.fromJson(string);
+  }
+
+  void writeConfig() async {
+    final directory = await getApplicationDocumentsDirectory();
+    final configName = "rtime_config.json";
+    final configPath = path.join(directory.path, configName);
+
+    await File(configPath).writeAsString(jsonEncode(toJson()));
+  }
 }

lib/db/db_helper.dart

@@ -160,6 +160,34 @@ class DbHelper {
     return maps.map((e) => Flight.fromMap(e)).toList();
   }
 
+  Future<List<Flight>> getFlightsBetween(
+    int startTimestamp,
+    int endTimestamp,
+  ) async {
+    final db = await database;
+    final maps = await db.rawQuery('''
+        SELECT * FROM flights AS F
+        WHERE F.start_timestamp >= $startTimestamp AND F.end_timestamp <= $endTimestamp
+    ''');
+    return maps.map((e) => Flight.fromMap(e)).toList();
+  }
+
+  Future<int?> getTotalFlightTime() async {
+    final db = await database;
+    final ft = await db.rawQuery('''
+        SELECT SUM(F.end_timestamp - F.startTimestamp) FROM flights AS F
+    ''');
+    final mapping = ft.firstOrNull;
+    if (mapping == null) {
+      return null;
+    }
+    final val = mapping["SUM(F.end_timestamp - F.startTimestamp)"];
+    if (val is! int) {
+      return null;
+    }
+    return val;
+  }
+
   Future closeDb() async {
     final db = await database;
     log.info("Closing database.");