major refactor

lib/services/data_service/data_service_traction.dart

@@ -0,0 +1,118 @@
+part of 'data_service.dart';
+
+extension DataServiceTraction on DataService {
+  Future<void> fetchHadTraction({int offset = 0, int limit = 100}) async {
+    await fetchTraction(
+      hadOnly: true,
+      offset: offset,
+      limit: limit,
+      append: offset > 0,
+    );
+  }
+
+  Future<void> fetchTraction({
+    bool hadOnly = false,
+    int offset = 0,
+    int limit = 50,
+    String? locoClass,
+    String? locoNumber,
+    bool mileageFirst = true,
+    bool append = false,
+    Map<String, dynamic>? filters,
+  }) async {
+    _isTractionLoading = true;
+
+    try {
+      final params = StringBuffer('?limit=$limit&offset=$offset');
+      if (hadOnly) params.write('&had_only=true');
+      if (!mileageFirst) params.write('&mileage_first=false');
+
+      final payload = <String, dynamic>{};
+      if (locoClass != null && locoClass.isNotEmpty) {
+        payload['class'] = locoClass;
+      }
+      if (locoNumber != null && locoNumber.isNotEmpty) {
+        payload['number'] = locoNumber;
+      }
+      if (filters != null) {
+        filters.forEach((key, value) {
+          if (value == null) return;
+          if (value is String && value.trim().isEmpty) return;
+          payload[key] = value;
+        });
+      }
+
+      final json = await api.post(
+        '/locos/search/v2${params.toString()}',
+        payload.isEmpty ? null : payload,
+      );
+
+      if (json is List) {
+        final newItems = json.map((e) => LocoSummary.fromJson(e)).toList();
+        _traction = append ? [..._traction, ...newItems] : newItems;
+        _tractionHasMore = newItems.length >= limit - 1;
+      } else {
+        throw Exception('Unexpected traction response: $json');
+      }
+    } catch (e) {
+      debugPrint('Failed to fetch traction: $e');
+      if (!append) {
+        _traction = [];
+      }
+      _tractionHasMore = false;
+    } finally {
+      _isTractionLoading = false;
+      _notifyAsync();
+    }
+  }
+
+  Future<List<LocoAttrVersion>> fetchLocoTimeline(int locoId) async {
+    _isLocoTimelineLoading[locoId] = true;
+    _notifyAsync();
+    try {
+      final json = await api.get('/loco/get-timeline/$locoId');
+      final timeline = LocoAttrVersion.fromGroupedJson(json);
+      _locoTimelines[locoId] = timeline;
+      return timeline;
+    } catch (e) {
+      debugPrint('Failed to fetch loco timeline for $locoId: $e');
+      _locoTimelines[locoId] = [];
+      return [];
+    } finally {
+      _isLocoTimelineLoading[locoId] = false;
+      _notifyAsync();
+    }
+  }
+
+  Future<dynamic> createLoco(Map<String, dynamic> payload) async {
+    try {
+      final response = await api.put('/loco/new', payload);
+      final locoClass = payload['class']?.toString();
+      if (locoClass != null &&
+          locoClass.isNotEmpty &&
+          !_locoClasses.contains(locoClass)) {
+        _locoClasses = [..._locoClasses, locoClass];
+      }
+      _notifyAsync();
+      return response;
+    } catch (e) {
+      debugPrint('Failed to create loco: $e');
+      rethrow;
+    }
+  }
+
+  Future<List<String>> fetchClassList() async {
+    if (_locoClasses.isNotEmpty) return _locoClasses;
+    try {
+      final json = await api.get('/loco/classlist');
+      if (json is List) {
+        _locoClasses = json.map((e) => e.toString()).toList();
+        _notifyAsync();
+      }
+    } catch (e) {
+      debugPrint('Failed to fetch class list: $e');
+    }
+    return _locoClasses;
+  }
+}
+