refactored data providers with centralized cache resolution, unified UI using custom dialogs and bottom sheets, and enhanced network error handling for Dio and TLS errors

lib/api/errors/error_mapper.dart

@@ -1,6 +1,7 @@
 import 'dart:async';
 import 'dart:io';
 
+import 'package:dio/dio.dart';
 import 'package:http/http.dart' as http;
 
 import '../api_error.dart';
@@ -9,10 +10,46 @@ import '../webuntis/webuntis_error.dart';
 import 'app_exception.dart';
 import 'network_exception.dart';
 import 'parse_exception.dart';
+import 'server_exception.dart';
 import 'talk_exception.dart';
 import 'webuntis_exception.dart';
 
 const String _defaultFallback = 'Etwas ist schiefgelaufen. Bitte versuche es erneut.';
+const String _tlsErrorMessage =
+    'Die sichere Verbindung zum Server wurde abgelehnt (Zertifikat oder TLS-Fehler). '
+    'Häufige Ursachen: falsche Geräte-Uhrzeit oder ein WLAN mit Anmeldeseite (z.B. Café/Hotel).';
+
+AppException? _dioToAppException(DioException error) {
+  switch (error.type) {
+    case DioExceptionType.connectionTimeout:
+    case DioExceptionType.sendTimeout:
+    case DioExceptionType.receiveTimeout:
+      return NetworkException.timeout(technicalDetails: error.message);
+    case DioExceptionType.connectionError:
+      return NetworkException(technicalDetails: error.message);
+    case DioExceptionType.badCertificate:
+      return const NetworkException(
+        userMessage: _tlsErrorMessage,
+      );
+    case DioExceptionType.badResponse:
+      final status = error.response?.statusCode;
+      return ServerException(
+        statusCode: status ?? -1,
+        technicalDetails: 'HTTP $status: ${error.message}',
+      );
+    case DioExceptionType.cancel:
+    case DioExceptionType.unknown:
+      final inner = error.error;
+      if (inner is SocketException) return NetworkException(technicalDetails: inner.message);
+      if (inner is HandshakeException) {
+        return const NetworkException(
+          userMessage: _tlsErrorMessage,
+        );
+      }
+      if (inner is FormatException) return ParseException(technicalDetails: inner.message);
+      return null;
+  }
+}
 
 String errorToUserMessage(Object? error, {String fallback = _defaultFallback}) {
   if (error == null) return fallback;
@@ -21,6 +58,11 @@ String errorToUserMessage(Object? error, {String fallback = _defaultFallback}) {
   if (error is TalkError) return TalkException(error).userMessage;
   if (error is WebuntisError) return WebuntisException(error).userMessage;
 
+  if (error is DioException) {
+    final mapped = _dioToAppException(error);
+    if (mapped != null) return mapped.userMessage;
+  }
+
   if (error is SocketException) {
     return const NetworkException().userMessage;
   }
@@ -31,7 +73,7 @@ String errorToUserMessage(Object? error, {String fallback = _defaultFallback}) {
     return const NetworkException().userMessage;
   }
   if (error is HandshakeException) {
-    return 'Sichere Verbindung konnte nicht hergestellt werden.';
+    return _tlsErrorMessage;
   }
   if (error is FormatException) {
     return const ParseException().userMessage;
@@ -48,12 +90,20 @@ String? errorToTechnicalDetails(Object? error) {
   if (error is AppException) return error.technicalDetails ?? error.toString();
   if (error is TalkError) return TalkException(error).technicalDetails;
   if (error is WebuntisError) return WebuntisException(error).technicalDetails;
+  if (error is DioException) {
+    final mapped = _dioToAppException(error);
+    if (mapped != null) return mapped.technicalDetails ?? mapped.toString();
+  }
   return error.toString();
 }
 
 bool errorAllowsRetry(Object? error) {
   if (error == null) return true;
   if (error is AppException) return error.allowRetry;
+  if (error is DioException) {
+    final mapped = _dioToAppException(error);
+    if (mapped != null) return mapped.allowRetry;
+  }
   return true;
 }