feat(contacts): обмен контактами NFC→BLE

lib/core/nfc/nfc_exchange_service.dart

@@ -3,13 +3,14 @@ import 'dart:io';
 
 import 'package:flutter/services.dart';
 
-enum NfcEventType { received, cancelled }
+enum NfcEventType { received, cancelled, error }
 
 class NfcEvent {
   final NfcEventType type;
   final int? id;
+  final String? reason;
 
-  const NfcEvent(this.type, this.id);
+  const NfcEvent(this.type, this.id, {this.reason});
 }
 
 class NfcStatus {
@@ -59,9 +60,14 @@ class NfcExchangeService {
   NfcEvent _decodeEvent(dynamic raw) {
     final map = raw is Map ? raw : const {};
     final id = map['id'];
-    final type = map['event'] == 'received'
-        ? NfcEventType.received
-        : NfcEventType.cancelled;
-    return NfcEvent(type, id is int ? id : (id is num ? id.toInt() : null));
+    final parsedId = id is int ? id : (id is num ? id.toInt() : null);
+    switch (map['event']) {
+      case 'received':
+        return NfcEvent(NfcEventType.received, parsedId);
+      case 'error':
+        return NfcEvent(NfcEventType.error, null, reason: map['reason'] as String?);
+      default:
+        return const NfcEvent(NfcEventType.cancelled, null);
+    }
   }
 }

lib/frontend/screens/contacts/nfc_exchange_sheet.dart

@@ -12,7 +12,7 @@ import '../../../main.dart';
 import '../../widgets/custom_notification.dart';
 import '../../widgets/komet_avatar.dart';
 
-enum _Stage { checking, unsupported, disabled, scanning, found, adding, added }
+enum _Stage { checking, unsupported, disabled, failed, scanning, found, adding, added }
 
 class NfcExchangeSheet extends StatefulWidget {
   const NfcExchangeSheet({super.key});
@@ -30,6 +30,7 @@ class _NfcExchangeSheetState extends State<NfcExchangeSheet>
   _Stage _stage = _Stage.checking;
   int? _peerId;
   Map<String, dynamic>? _peerInfo;
+  String _failReason = '';
 
   @override
   void initState() {
@@ -78,6 +79,15 @@ class _NfcExchangeSheetState extends State<NfcExchangeSheet>
       }
       return;
     }
+    if (event.type == NfcEventType.error) {
+      if (mounted && _peerId == null) {
+        setState(() {
+          _failReason = _reasonText(event.reason);
+          _stage = _Stage.failed;
+        });
+      }
+      return;
+    }
     final id = event.id;
     if (id == null || _peerId != null) return;
     _peerId = id;
@@ -141,6 +151,17 @@ class _NfcExchangeSheetState extends State<NfcExchangeSheet>
     }
   }
 
+  String _reasonText(String? reason) {
+    switch (reason) {
+      case 'bluetooth_off':
+        return 'Включите Bluetooth и попробуйте снова';
+      case 'permission':
+        return 'Нужны разрешения Bluetooth для обмена';
+      default:
+        return 'Не удалось установить соединение';
+    }
+  }
+
   @override
   Widget build(BuildContext context) {
     final cs = Theme.of(context).colorScheme;
@@ -191,6 +212,8 @@ class _NfcExchangeSheetState extends State<NfcExchangeSheet>
           Symbols.nfc,
           'Включите NFC в настройках телефона и попробуйте снова',
         );
+      case _Stage.failed:
+        return _message(cs, Symbols.bluetooth_disabled, _failReason);
       case _Stage.scanning:
         return _scanning(cs);
       case _Stage.found: