simple working json import and export

lib/service/json_file_service.dart

@@ -0,0 +1,69 @@
+import 'dart:convert';
+import 'dart:io';
+
+import 'package:file_selector/file_selector.dart';
+import 'package:flutter/services.dart';
+
+import '../model/bookmark.dart';
+import '../model/collection.dart';
+import '../assets/constants.dart' as constants;
+
+class JsonFileService {
+  static Future<bool> exportToJson({
+    required List<Collection> collections,
+    required List<Bookmark> bookmarks,
+  }) async {
+    final dir = await _directoryPath;
+
+    final data = {
+      'collections': collections.map((c) => c.toJson()).toList(),
+      'bookmarks': bookmarks.map((b) => b.toJson()).toList(),
+    };
+    final json = jsonEncode(data).codeUnits;
+    final file = XFile.fromData(
+      Uint8List.fromList(json),
+      mimeType: 'application/json',
+      name: constants.jsonFileName,
+    );
+
+    file.saveTo('$dir/${constants.jsonFileName}');
+
+    return false;
+  }
+
+  static Future<({List<Collection> collections, List<Bookmark> bookmarks})>
+  importFromJson() async {
+    const typeGroup = XTypeGroup(label: 'json', extensions: <String>['json']);
+    final XFile? file = await openFile(
+      acceptedTypeGroups: <XTypeGroup>[typeGroup],
+    );
+
+    if (file == null) {
+      return (collections: <Collection>[], bookmarks: <Bookmark>[]);
+    }
+
+    final jsonString = await file.readAsString();
+
+    final data = jsonDecode(jsonString) as Map<String, dynamic>;
+
+    final collections = (data['collections'] as List<dynamic>? ?? [])
+        .map((json) => Collection.fromJson(json as Map<String, dynamic>))
+        .toList();
+
+    final bookmarks = (data['bookmarks'] as List<dynamic>? ?? [])
+        .map((json) => Bookmark.fromJson(json as Map<String, dynamic>))
+        .toList();
+
+    return (collections: collections, bookmarks: bookmarks);
+  }
+
+  static Future<String> get _directoryPath async {
+    if (Platform.isAndroid) {
+      return await getDirectoryPath(
+            initialDirectory: constants.defaultAndroidExportDirectory,
+          ) ??
+          '';
+    }
+    return await getDirectoryPath() ?? '';
+  }
+}