Refactor ForexRateApiService to remove API key dependency and update README and launch configurations

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

lib/state/rent_controller.dart

@@ -41,35 +41,17 @@ class RentController extends ChangeNotifier {
 
   RentController({
     StorageService? storageService,
-    ForexRateApiService? exchangeService,
+    FrankfurterApiService? exchangeService,
     NotificationService? notificationService,
   }) : _storageService = storageService ?? StorageService(),
        _exchangeService =
-           exchangeService ??
-           ForexRateApiService(
-             httpClient: http.Client(),
-             apiKey: _exchangeRateApiKeyFromEnv(),
-           ) {
+           exchangeService ?? FrankfurterApiService(httpClient: http.Client()) {
     _notificationService =
         notificationService ?? NotificationService(_onNotificationAction);
   }
 
-  static String _exchangeRateApiKeyFromEnv() {
-    const key = String.fromEnvironment('FOREX_RATE_API_KEY');
-    final trimmed = key.trim();
-    if (trimmed.isEmpty) {
-      if (kDebugMode) {
-        debugPrint(
-          '[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 trimmed;
-  }
-
   final StorageService _storageService;
-  final ForexRateApiService _exchangeService;
+  final FrankfurterApiService _exchangeService;
   late NotificationService _notificationService;
 
   AppSettings _settings = AppSettings.defaults();
@@ -79,6 +61,33 @@ class RentController extends ChangeNotifier {
   String? _errorMessage;
   int _selectedYear = DateTime.now().year;
 
+  double? _lookupRateOnOrBefore(
+    Map<String, double> rates,
+    DateTime targetDate,
+  ) {
+    final target = DateTime(targetDate.year, targetDate.month, targetDate.day);
+    DateTime? nearestDate;
+    double? nearestRate;
+
+    for (final entry in rates.entries) {
+      final parsed = DateTime.tryParse(entry.key);
+      if (parsed == null) {
+        continue;
+      }
+      final day = DateTime(parsed.year, parsed.month, parsed.day);
+      if (day.isAfter(target)) {
+        continue;
+      }
+
+      if (nearestDate == null || day.isAfter(nearestDate)) {
+        nearestDate = day;
+        nearestRate = entry.value;
+      }
+    }
+
+    return nearestRate;
+  }
+
   AppSettings get settings => _settings;
   bool get isLoading => _isLoading;
   String? get errorMessage => _errorMessage;
@@ -334,27 +343,25 @@ class RentController extends ChangeNotifier {
           final usd = _settings.rentUsd;
           final estDate = DateTime(year, month, 1);
 
-          final ForexConversionResult conversion;
+          final ConversionResult conversion;
           if (batchRates != null) {
-            final dateStr = DateFormat('yyyy-MM-dd').format(estDate);
-            final quote = batchRates[dateStr];
+            final quote = _lookupRateOnOrBefore(batchRates, estDate);
             if (quote == null) {
-              throw StateError('Batch rates missing entry for $dateStr.');
+              throw StateError(
+                'Batch rates missing entry on or before ${DateFormat('yyyy-MM-dd').format(estDate)}.',
+              );
             }
-            conversion = ForexConversionResult(
-              quote: quote,
-              result: quote * usd,
-            );
+            conversion = ConversionResult(quote: quote, result: quote * usd);
           } else {
             // Pace individual requests to avoid triggering the rate limit.
             if (!isFirstIndividualFetch) {
               await Future.delayed(const Duration(milliseconds: 700));
             }
             isFirstIndividualFetch = false;
-            conversion = await _exchangeService.convertUsdToSek(
+            final quote = await _exchangeService.fetchUsdToSekRate(
               estDate: estDate,
-              amount: usd,
             );
+            conversion = ConversionResult(quote: quote, result: quote * usd);
           }
 
           if (kDebugMode) {
@@ -385,9 +392,7 @@ class RentController extends ChangeNotifier {
           savedMonths++;
         } catch (err) {
           final errorText = err.toString();
-          if (errorText.contains('429') ||
-              errorText.contains('104') ||
-              errorText.toLowerCase().contains('rate_limit_reached')) {
+          if (errorText.contains('429')) {
             pausedByRateLimit = true;
             _errorMessage =
                 'Backfill paused by API rate limits after $savedMonths new month(s). Run backfill again in a minute to continue.';