import 'dart:io';
import 'package:path_provider/path_provider.dart';

class FileCacheService {
  Future<String> get _localPath async {
    // Use getTemporaryDirectory() for system-cleared cache
    // Use getApplicationDocumentsDirectory() for persistent data
    final directory = await getApplicationDocumentsDirectory();
    return directory.path;
  }

  Future<File> get _localFile async {
    final path = await _localPath;
    return File('$path/cached_data.json');
  }

  Future<File> writeData(String data) async {
    final file = await _localFile;
    return file.writeAsString(data);
  }

  Future<String?> readData() async {
    try {
      final file = await _localFile;
      return await file.readAsString();
    } catch (e) {
      return null; // Cache miss
    }
  }
}

import 'package:path/path.dart';
import 'package:sqflite/sqflite.dart';

class DatabaseService {
  late Database _database;

  Future<void> initDB() async {
    _database = await openDatabase(
      join(await getDatabasesPath(), 'app_cache.db'),
      onCreate: (db, version) {
        return db.execute(
          'CREATE TABLE cache_data(id INTEGER PRIMARY KEY, key TEXT, payload TEXT)',
        );
      },
      version: 1,
    );
  }

  Future<void> insertCache(String key, String payload) async {
    await _database.insert(
      'cache_data',
      {'key': key, 'payload': payload},
      conflictAlgorithm: ConflictAlgorithm.replace,
    );
  }

  Future<String?> getCache(String key) async {
    final List<Map<String, Object?>> maps = await _database.query(
      'cache_data',
      where: 'key = ?',
      whereArgs: [key], // MUST use whereArgs to prevent SQL injection
    );
    if (maps.isNotEmpty) {
      return maps.first['payload'] as String;
    }
    return null;
  }
}

Stream<UserProfile> getUserProfile() async* {
  // 1. Check local cache
  final localData = await _databaseService.getCache('user_profile');
  if (localData != null) {
    yield UserProfile.fromJson(localData);
  }

  // 2. Fetch remote data
  try {
    final remoteData = await _apiClient.fetchUserProfile();
    // 3. Update cache
    await _databaseService.insertCache('user_profile', remoteData.toJson());
    // 4. Yield fresh data
    yield remoteData;
  } catch (e) {
    // Handle network failure; local data has already been yielded
  }
}

class MyApplication : Application() {
  lateinit var flutterEngine : FlutterEngine
  override fun onCreate() {
    super.onCreate()
    flutterEngine = FlutterEngine(this)
    // Optional: Configure initial route before executing entrypoint
    flutterEngine.navigationChannel.setInitialRoute("/cached_route");
    flutterEngine.dartExecutor.executeDartEntrypoint(
      DartExecutor.DartEntrypoint.createDefault()
    )
    FlutterEngineCache.getInstance().put("my_engine_id", flutterEngine)
  }
}

// For Activity
startActivity(
  FlutterActivity
    .withCachedEngine("my_engine_id")
    .backgroundMode(FlutterActivityLaunchConfigs.BackgroundMode.transparent)
    .build(this)
)

// For Fragment
val flutterFragment = FlutterFragment.withCachedEngine("my_engine_id")
    .renderMode(FlutterView.RenderMode.texture)
    .shouldAttachEngineToActivity(false)
    .build()

class CustomImageCache extends ImageCache {
  @override
  bool containsKey(Object key) {
    // Check if cache is tracking this key
    return super.containsKey(key); 
  }
}

ListView(
  // Use ScrollCacheExtent.pixels for pixel-based caching
  scrollCacheExtent: const ScrollCacheExtent.pixels(500.0),
  children: [ ... ],
)

Viewport(
  // Use ScrollCacheExtent.viewport for fraction-based caching
  scrollCacheExtent: const ScrollCacheExtent.viewport(0.5),
  slivers: [ ... ],
)