// Auto dark/bright from the tablet's light sensor. The Redmi Pad SE has no separate one:
// Xiaomi derives it from the front camera ("camera_light_Sensor") and offers it as
// Android's ordinary light sensor, the one auto-brightness reads. No camera permission.

import 'package:flutter/services.dart';

/// Light levels in lux, about once a second, from MainActivity. Ends at once (an error,
/// which [Themes.followLight] ignores) where there is no sensor or no Android side.
Stream<double> lightLevels() =>
    const EventChannel('yukart/light')
        .receiveBroadcastStream()
        .map((e) => (e as num).toDouble());

/// Dark or bright from light levels, with a gap and a hold so dusk, shade and
/// passing lights do not flicker it.
class LightSwitch {
  /// Dark at or below this.
  static const darkAt = 15.0;

  /// Bright at or above this; in between, whatever it was.
  static const brightAt = 60.0;

  /// How long a level must last before it switches.
  static const hold = Duration(seconds: 5);

  bool? _dark;
  DateTime? _since;

  bool? get isDark => _dark;

  /// A change is waiting out its hold.
  bool get pending => _since != null;

  /// The hold has passed with no reading against it (a sensor that reports only on
  /// change goes quiet): make the waiting change.
  void settle() {
    if (_since == null) return;
    _dark = !_dark!;
    _since = null;
  }

  /// Feed one reading; returns the verdict (null until a reading outside the gap).
  bool? feed(double lux, DateTime now) {
    final want = lux <= darkAt
        ? true
        : lux >= brightAt
        ? false
        : _dark;
    if (_dark == null) {
      // The first clear reading decides at once; one in the gap leaves it open.
      _dark = want;
    } else if (want == _dark) {
      _since = null;
    } else {
      _since ??= now;
      if (now.difference(_since!) >= hold) {
        _dark = want;
        _since = null;
      }
    }
    return _dark;
  }
}