refactor: Projektstruktur in app/ und backend/ aufgeteilt

app/lib/models/chat.dart

@@ -0,0 +1,162 @@
+import 'chat_message.dart';
+
+enum ChatType { general, jobSpecific }
+
+class Chat {
+  final String id;
+  final String title;
+  final String? receiver;
+  final ChatType type;
+  final String? jobId; // only for job-specific chats
+  final String? jobNumber; // only for job-specific chats
+  final List<ChatMessage> messages;
+  final DateTime lastMessageTime;
+  final String lastMessagePreview;
+
+  Chat({
+    required this.id,
+    required this.title,
+    this.receiver,
+    required this.type,
+    this.jobId,
+    this.jobNumber,
+    required this.messages,
+    required this.lastMessageTime,
+    required this.lastMessagePreview,
+  });
+
+  factory Chat.fromJson(Map<String, dynamic> json) {
+    final messagesList = json['messages'] as List? ?? [];
+    final messages =
+        messagesList
+            .map(
+              (messageJson) =>
+                  ChatMessage.fromJson(messageJson as Map<String, dynamic>),
+            )
+            .toList();
+
+    return Chat(
+      id: json['id']?.toString() ?? '',
+      title: json['title']?.toString() ?? '',
+      receiver: json['receiver']?.toString(),
+      type:
+          json['type'] == 'jobSpecific'
+              ? ChatType.jobSpecific
+              : ChatType.general,
+      jobId: json['jobId']?.toString(),
+      jobNumber: json['jobNumber']?.toString(),
+      messages: messages,
+      lastMessageTime: _resolveLastMessageTime(json, messages),
+      lastMessagePreview: _resolveLastMessagePreview(json, messages),
+    );
+  }
+
+  Map<String, dynamic> toJson() {
+    return {
+      'id': id,
+      'title': title,
+      'receiver': receiver,
+      'type': type == ChatType.jobSpecific ? 'jobSpecific' : 'general',
+      'jobId': jobId,
+      'jobNumber': jobNumber,
+      'messages': messages.map((message) => message.toJson()).toList(),
+      'lastMessageTime': lastMessageTime.toIso8601String(),
+      'lastMessagePreview': lastMessagePreview,
+    };
+  }
+
+  // Factory constructor for general chat
+  factory Chat.general({
+    required String id,
+    required String title,
+    String? receiver,
+    required List<ChatMessage> messages,
+  }) {
+    final lastMessage = messages.isNotEmpty ? messages.last : null;
+    return Chat(
+      id: id,
+      title: title,
+      receiver: receiver,
+      type: ChatType.general,
+      messages: messages,
+      lastMessageTime: lastMessage?.createdAt ?? DateTime.now(),
+      lastMessagePreview:
+          lastMessage != null
+              ? _previewForMessage(lastMessage)
+              : 'Noch keine Nachrichten',
+    );
+  }
+
+  // Factory constructor for job-specific chat
+  factory Chat.jobSpecific({
+    required String id,
+    required String jobId,
+    required String jobNumber,
+    String? receiver,
+    required List<ChatMessage> messages,
+  }) {
+    final lastMessage = messages.isNotEmpty ? messages.last : null;
+    return Chat(
+      id: id,
+      title: 'Job $jobNumber',
+      receiver: receiver,
+      type: ChatType.jobSpecific,
+      jobId: jobId,
+      jobNumber: jobNumber,
+      messages: messages,
+      lastMessageTime: lastMessage?.createdAt ?? DateTime.now(),
+      lastMessagePreview:
+          lastMessage != null
+              ? _previewForMessage(lastMessage)
+              : 'Noch keine Nachrichten',
+    );
+  }
+
+  static DateTime _resolveLastMessageTime(
+    Map<String, dynamic> json,
+    List<ChatMessage> messages,
+  ) {
+    if (messages.isNotEmpty) {
+      return messages.last.createdAt;
+    }
+    final raw = json['lastMessageTime']?.toString();
+    if (raw != null) {
+      final parsed = DateTime.tryParse(raw);
+      if (parsed != null) {
+        return parsed;
+      }
+    }
+    return DateTime.now();
+  }
+
+  static String _resolveLastMessagePreview(
+    Map<String, dynamic> json,
+    List<ChatMessage> messages,
+  ) {
+    if (messages.isNotEmpty) {
+      return _previewForMessage(messages.last);
+    }
+    return json['lastMessagePreview']?.toString() ?? 'Noch keine Nachrichten';
+  }
+
+  static String _previewForMessage(ChatMessage message) {
+    if (message.contentType == ChatContentType.image) {
+      return '[Bild]';
+    }
+    return message.content;
+  }
+
+  @override
+  String toString() {
+    return 'Chat(id: $id, title: $title, type: $type, jobId: $jobId, messagesCount: ${messages.length})';
+  }
+
+  @override
+  bool operator ==(Object other) {
+    if (identical(this, other)) return true;
+    return other is Chat && other.id == id;
+  }
+
+  @override
+  int get hashCode => id.hashCode;
+}