Refactor environment variable handling and update build instructions

- Introduced a Makefile for building the release APK with `make build release`.
- Updated README to reflect new build command and usage of `--dart-define-from-file=.env`.
- Removed dotenv dependency and switched to using Dart's `--dart-define` for API key management.
- Adjusted ForexRateAPI key loading logic to improve error handling and clarity.

Signed-off-by: Hans Kokx <hans.d.kokx@gmail.com>

lib/main.dart

@@ -1,12 +1,10 @@
 import 'package:flutter/material.dart';
-import 'package:flutter_dotenv/flutter_dotenv.dart';
 import 'package:provider/provider.dart';
 import 'package:rental_income_tracker/screens/home_screen.dart';
 import 'package:rental_income_tracker/state/rent_controller.dart';
 
 Future<void> main() async {
   WidgetsFlutterBinding.ensureInitialized();
-  await dotenv.load(fileName: '.env');
   runApp(const RentalIncomeTrackerApp());
 }
 

lib/screens/settings_screen.dart

@@ -198,7 +198,7 @@ class _SettingsScreenState extends State<SettingsScreen> {
               ),
               const SizedBox(height: 16),
               const Text(
-                'ForexRateAPI key is loaded from .env (FOREX_RATE_API_KEY).',
+                'ForexRateAPI key is loaded from FOREX_RATE_API_KEY via --dart-define-from-file=.env.',
               ),
             ],
           ),

lib/services/open_exchange_service.dart

@@ -41,7 +41,7 @@ class ForexRateApiService {
       final parsed = jsonDecode(response.body) as Map<String, dynamic>;
       final error = parsed['error'] as Map<String, dynamic>?;
       final code = error?['code']?.toString().toLowerCase();
-      return code == 'rate_limit_reached';
+      return code == '104' || code == 'rate_limit_reached';
     } catch (_) {
       return false;
     }
@@ -136,6 +136,62 @@ class ForexRateApiService {
     if (apiKey == 'REPLACE_WITH_YOUR_FOREXRATE_API_KEY') {
       throw StateError('ForexRateAPI key is not configured.');
     }
-    return null;
+
+    final start = DateTime(year, 1, 1);
+    final end = DateTime(year, 12, 31);
+    final uri =
+        Uri.https('api.forexrateapi.com', '/v1/timeframe', <String, String>{
+          'api_key': apiKey,
+          'base': 'USD',
+          'currencies': 'SEK',
+          'start_date': DateFormat('yyyy-MM-dd').format(start),
+          'end_date': DateFormat('yyyy-MM-dd').format(end),
+        });
+
+    _log('Timeframe request: ${_redactedUri(uri)}');
+
+    final response = await _getWithRateLimitRetry(uri, operation: 'Timeframe');
+    if (response.statusCode != 200) {
+      _log(
+        'Timeframe endpoint unavailable for this account or request; falling back to per-day requests. status=${response.statusCode}',
+      );
+      return null;
+    }
+
+    final json = jsonDecode(response.body) as Map<String, dynamic>;
+    final success = json['success'] as bool? ?? false;
+    if (!success) {
+      _log(
+        'Timeframe success=false; falling back to per-day requests. error=${json['error']}',
+      );
+      return null;
+    }
+
+    final rates = json['rates'] as Map<String, dynamic>?;
+    if (rates == null) {
+      _log(
+        'Timeframe response missing rates; falling back to per-day requests.',
+      );
+      return null;
+    }
+
+    final results = <String, double>{};
+    for (final entry in rates.entries) {
+      final dayRates = entry.value as Map<String, dynamic>?;
+      final sek = dayRates?['SEK'];
+      if (sek is num) {
+        results[entry.key] = sek.toDouble();
+      }
+    }
+
+    if (results.isEmpty) {
+      _log(
+        'Timeframe parsed no SEK entries; falling back to per-day requests.',
+      );
+      return null;
+    }
+
+    _log('Timeframe parsed ${results.length} daily SEK quotes.');
+    return results;
   }
 }

lib/state/rent_controller.dart

@@ -2,7 +2,6 @@ import 'dart:convert';
 import 'dart:io';
 
 import 'package:flutter/foundation.dart';
-import 'package:flutter_dotenv/flutter_dotenv.dart';
 import 'package:http/http.dart' as http;
 import 'package:intl/intl.dart';
 import 'package:rental_income_tracker/models/app_settings.dart';
@@ -56,16 +55,17 @@ class RentController extends ChangeNotifier {
   }
 
   static String _exchangeRateApiKeyFromEnv() {
-    final key = dotenv.env['FOREX_RATE_API_KEY']?.trim() ?? '';
-    if (key.isEmpty) {
+    const key = String.fromEnvironment('FOREX_RATE_API_KEY');
+    final trimmed = key.trim();
+    if (trimmed.isEmpty) {
       if (kDebugMode) {
         debugPrint(
-          '[RentController] FOREX_RATE_API_KEY missing in .env, API calls will fail until set.',
+          '[RentController] FOREX_RATE_API_KEY missing from dart defines. Pass --dart-define-from-file=.env (or --dart-define) when building/running.',
         );
       }
       return 'REPLACE_WITH_YOUR_FOREXRATE_API_KEY';
     }
-    return key;
+    return trimmed;
   }
 
   final StorageService _storageService;