public/lib/settings/lib/setting_store_legacy.dart

// Copyright 2018 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

import 'dart:async';

import 'package:fidl_fuchsia_devicesettings/fidl.dart';
import 'package:lib.app.dart/logging.dart';
import 'package:protobuf/protobuf.dart';

/// A store for settings expressed as protobufs. The settings are persisted
/// in the device setting service as JSON.
class SettingStoreLegacy<T extends GeneratedMessage>
    extends DeviceSettingsWatcher {
  /// The device settings key where the proto is stored.
  final String _settingsKey;

  /// Binding to watch changes in device settings.
  final DeviceSettingsWatcherBinding _deviceSettingsWatcherBinding =
      DeviceSettingsWatcherBinding();

  /// Connection to the device settings service.
  final DeviceSettingsManagerProxy _deviceSettingsManagerService;

  /// Used to publish changes to the setting.
  final StreamController<T> _updateStreamController =
      StreamController.broadcast();

  /// Since we do not have access to constructors with generics, an instance is
  /// provided at construction and used to operations. Note that protobufs
  /// (via [GeneratedMessage]) can spawn new instances and therefore this is
  /// only needed to seed.
  T _tmpSetting;

  SettingStoreLegacy(
      this._deviceSettingsManagerService, this._settingsKey, this._tmpSetting);

  /// Adds a listener to be informed when the setting changes from the device
  /// settings service perspective.
  void addlistener(void onEvent(T value)) {
    _updateStreamController.stream.listen(onEvent);
  }

  /// Connects to the device settings service and fetches the initial value.
  /// This is separate from the constructor to allow clients to add a listener
  /// beforehand.
  void connect() {
    _deviceSettingsManagerService.watch(
        _settingsKey, _deviceSettingsWatcherBinding.wrap(this), null);

    _fetch();
  }

  void _fetch() {
    _deviceSettingsManagerService.getString(_settingsKey,
        (String val, Status status) {
      if (status == Status.ok) {
        _tmpSetting.clear();
        _tmpSetting.mergeFromJson(val);
        _updateStreamController.add(_tmpSetting.clone());
      }
    });
  }

  /// Persists the provided setting's values to device settings.
  void commit(T setting) {
    _deviceSettingsManagerService.setString(_settingsKey, setting.writeToJson(),
        (bool result) {
      if (result) {
        return;
      }

      log.warning('Could not persist value at key: $_settingsKey');
    });
  }

  /// Upon a setting change, refetch value.
  @override
  void onChangeSettings(ValueType type) {
    _fetch();
  }
}