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

/// Opaque binary records too large for the keychain, such as encrypted
/// editor drafts. Callers encrypt before writing; nothing here is secret.
abstract interface class BlobStore {
  Future<Uint8List?> read(String name);
  Future<void> write(String name, Uint8List bytes);
  Future<void> delete(String name);
}

class MemoryBlobStore implements BlobStore {
  final values = <String, Uint8List>{};
  @override
  Future<Uint8List?> read(String name) async => values[name];
  @override
  Future<void> write(String name, Uint8List bytes) async =>
      values[name] = Uint8List.fromList(bytes);
  @override
  Future<void> delete(String name) async => values.remove(name);
}

/// Files in the app's private support directory, written atomically
/// (temporary file, flush, rename) so a crash never leaves half a record.
class FileBlobStore implements BlobStore {
  Future<Directory>? _root;
  Future<Directory> get root => _root ??= () async {
    final base = await getApplicationSupportDirectory();
    return Directory('${base.path}/sm-blobs').create(recursive: true);
  }();

  static String _check(String name) {
    if (!RegExp(r'^[A-Za-z0-9_-]{1,80}$').hasMatch(name)) {
      throw ArgumentError.value(name, 'name');
    }
    return name;
  }

  @override
  Future<Uint8List?> read(String name) async {
    final file = File('${(await root).path}/${_check(name)}');
    return await file.exists() ? file.readAsBytes() : null;
  }

  @override
  Future<void> write(String name, Uint8List bytes) async {
    final dir = await root;
    final target = File('${dir.path}/${_check(name)}');
    final temp = File('${dir.path}/.${_check(name)}.tmp');
    await temp.writeAsBytes(bytes, flush: true);
    await temp.rename(target.path);
  }

  @override
  Future<void> delete(String name) async {
    final file = File('${(await root).path}/${_check(name)}');
    if (await file.exists()) await file.delete();
  }
}