Stream POC

main.dart

import 'dart:async';
import 'package:rxdart/rxdart.dart';

void main() async {
  final fakeAdapter = FakeBluetoothAdapter();

  final sub = fakeAdapter
      .availableDevices()
      .listen(print);

  // scan needs to be called if not no readings will be emitted
  fakeAdapter.scan();

  await Future.delayed(const Duration(seconds: 6));
  print('Starting second scan');
  fakeAdapter.scan();
  // Does not drop the initial 500ms of readings

  await Future.delayed(const Duration(seconds: 6))
      .then((value) => sub.cancel());
}

// Simulates a bluetooth adapter.
class FakeBluetoothAdapter {
  final BehaviorSubject<List<int>> deviceIds = BehaviorSubject.seeded([]);

// Emits device id readings for the [duration] of the scan
  Future<void> scan({Duration duration = const Duration(seconds: 5)}) async {
    lastScanStartTime = DateTime.now();
    final timer = Timer.periodic(const Duration(milliseconds: 50), (timer) {
      final timePassedSinceScanStarted =
          DateTime.now().difference(lastScanStartTime).inMilliseconds;
      //simulate device readings
      final reading = switch (timePassedSinceScanStarted) {
        < 200 => [1],
        >= 200 && < 300 => [1, 12],
        >= 400 && < 500 => [1, 12, 8],
        _ => [1, 12, 8, 27],
      };
      deviceIds.add(reading);
    });

    //Stop emitting values
    await Future.delayed(duration).then((value) => timer.cancel());
    print('Scanning stopped');
  }

  var lastScanStartTime = DateTime.now();

  // amount of time we discard new readings on a new scan
  static const _newScanSkpTime = Duration(seconds: 1);

  Duration skipDuration() {
    var diff = DateTime.now().difference(lastScanStartTime);
    var hasEnoughTimePassed = diff > _newScanSkpTime;

    final ret = hasEnoughTimePassed ? Duration.zero : diff;

    return ret;
  }

  bool _afterSkipTime() {
    return skipDuration() > Duration.zero;
  }

  Stream<String> availableDevices() async* {
    final myDevicesStream = deviceIds.skipWhile((_) => _afterSkipTime()).map(
        (results) =>
            "${DateTime.now().difference(lastScanStartTime).inMilliseconds} ms => $results");

    scan();

    yield* myDevicesStream;
  }
}