import 'dart:async';

import 'package:flutter/scheduler.dart';
import 'package:get/src/state_manager/rx/rx_callbacks.dart';

abstract class RxInterface<T> {
  RxInterface([T initial]);

  /// add listener to stream
  void addListener(Stream<T> rxGetx);

  bool get canUpdate;

  /// close stream
  void close() {
    subject?.close();
  }

  StreamController<T> subject;

  /// Calls [callback] with current value, when the value changes.
  StreamSubscription<T> listen(ValueCallback<T> callback);
}

/// Unlike GetxController, which serves to control events on each of its pages,
/// GetxService is not automatically disposed. It is ideal for situations where,
/// once started, that service will remain in memory, such as Auth control for example.
abstract class GetxService extends DisposableInterface {}

/// Special callable class to keep the contract of a regular method, and avoid
/// overrides if you extend the class that uses it, as Dart has no final methods.
/// Used in [DisposableInterface] to avoid the danger of overriding onStart.
///
class _InternalFinalCallback<T> {
  T Function() callback;
  _InternalFinalCallback();
  T call() => callback.call();
}

abstract class DisposableInterface {
  /// Called at the exact moment the widget is allocated in memory.
  /// It uses an internal "callable" type, to avoid any @overrides in subclases.
  /// This method should be internal and is required to define the lifetime cycle
  /// of the subclass.
  final onStart = _InternalFinalCallback<void>();

  bool _initialized = false;

  /// Checks whether the controller has already been initialized.
  bool get initialized => _initialized;

  DisposableInterface() {
    onStart.callback = _onStart;
  }

  // Internal callback that starts the cycle of this controller.
  void _onStart() {
    onInit();
    _initialized = true;
    SchedulerBinding.instance?.addPostFrameCallback((_) => onReady());
  }

  /// Called Called immediately after the widget is allocated in memory.
  void onInit() async {}

  /// Called after rendering the screen. It is the perfect place to enter navigation events,
  /// be it snackbar, dialogs, or a new route.
  void onReady() async {}

  /// Called before the onDelete method. onClose is used to close events
  /// before the controller is destroyed, such as closing streams, for example.
  onClose() async {}
}