refactor: Projektstruktur in app/ und backend/ aufgeteilt

app/lib/services/ack_tracker.dart

@@ -0,0 +1,143 @@
+import 'package:flutter/foundation.dart';
+
+/// Represents a message awaiting acknowledgment
+class PendingMessage {
+  /// Unique message identifier
+  final String messageId;
+
+  /// Target topic
+  final String topic;
+
+  /// The JSON payload to retry sending
+  final String jsonPayload;
+
+  /// When the message was originally sent
+  final DateTime sentAt;
+
+  /// Number of retry attempts so far
+  int retryCount;
+
+  PendingMessage({
+    required this.messageId,
+    required this.topic,
+    required this.jsonPayload,
+    required this.sentAt,
+    this.retryCount = 0,
+  });
+}
+
+/// Tracks pending messages awaiting acknowledgment and handles retries.
+///
+/// This class is extracted from WebSocketService for testability.
+/// It manages:
+/// - Tracking sent messages that require ACK
+/// - Removing messages when ACK is received
+/// - Retrying unacknowledged messages
+/// - Timing out messages after max retries
+class AckTracker {
+  final Map<String, PendingMessage> _pendingMessages = {};
+
+  /// Maximum number of retry attempts before timeout
+  final int maxRetries;
+
+  /// Callback to retry sending a message.
+  /// Returns true if send was successful.
+  final Future<bool> Function(String topic, String payload)? onRetry;
+
+  /// Callback when a message times out (max retries exceeded)
+  final void Function(String messageId, String topic)? onTimeout;
+
+  AckTracker({
+    this.maxRetries = 4,
+    this.onRetry,
+    this.onTimeout,
+  });
+
+  /// Track a sent message that requires acknowledgment
+  void track(String messageId, String topic, String payload) {
+    _pendingMessages[messageId] = PendingMessage(
+      messageId: messageId,
+      topic: topic,
+      jsonPayload: payload,
+      sentAt: DateTime.now(),
+    );
+  }
+
+  /// Remove a message from tracking (ACK received)
+  void acknowledge(String messageId) {
+    _pendingMessages.remove(messageId);
+  }
+
+  /// Check if a message is pending acknowledgment
+  bool isPending(String messageId) =>
+      _pendingMessages.containsKey(messageId);
+
+  /// Get the number of pending messages
+  int get pendingCount => _pendingMessages.length;
+
+  /// Get all pending message IDs
+  List<String> get pendingMessageIds =>
+      List.unmodifiable(_pendingMessages.keys);
+
+  /// Get a pending message by ID (for testing)
+  @visibleForTesting
+  PendingMessage? getPendingMessage(String messageId) =>
+      _pendingMessages[messageId];
+
+  /// Process all pending messages and retry if needed.
+  ///
+  /// This should be called periodically (e.g., every 5 seconds).
+  /// Messages that exceed maxRetries will be timed out and removed.
+  ///
+  /// Set [isConnected] to false to skip retry attempts while disconnected.
+  Future<void> processRetries({bool isConnected = true}) async {
+    if (_pendingMessages.isEmpty) {
+      return;
+    }
+
+    final messagesToRemove = <String>[];
+
+    for (final entry in _pendingMessages.entries) {
+      final messageId = entry.key;
+      final pending = entry.value;
+
+      if (pending.retryCount >= maxRetries) {
+        // Max retries exceeded - timeout
+        onTimeout?.call(messageId, pending.topic);
+        messagesToRemove.add(messageId);
+      } else if (isConnected) {
+        // Increment retry count and attempt resend
+        pending.retryCount++;
+
+        if (onRetry != null) {
+          await onRetry!(pending.topic, pending.jsonPayload);
+        }
+      }
+    }
+
+    // Remove timed out messages
+    for (final messageId in messagesToRemove) {
+      _pendingMessages.remove(messageId);
+    }
+  }
+
+  /// Clear all pending messages.
+  ///
+  /// Primarily for testing purposes.
+  @visibleForTesting
+  void clearAll() => _pendingMessages.clear();
+
+  /// Clear pending messages for a specific topic pattern.
+  ///
+  /// Useful for clearing login messages when auth response is received.
+  void clearForTopic(String topicPattern) {
+    final toRemove = _pendingMessages.entries
+        .where((e) => e.value.topic == topicPattern)
+        .map((e) => e.key)
+        .toList();
+
+    for (final messageId in toRemove) {
+      _pendingMessages.remove(messageId);
+    }
+  }
+}