import 'dart:async';

void main() async {
  // First we'll look at basic rate limiting. Suppose
  // we want to limit our handling of incoming requests.
  // We'll serve these requests off a Stream.
  final requests = Stream.fromIterable(List.generate(5, (i) => i + 1));

  // This Timer will fire every 200 milliseconds. This is the regulator in
  // our rate limiting scheme.
  final limiter = Timer.periodic(Duration(milliseconds: 200), (_) {});

  // By awaiting the limiter before processing each request, we limit ourselves to
  // 1 request every 200 milliseconds.
  await for (var req in requests) {
    await limiter.tick;
    print('request $req ${DateTime.now()}');
  }

  // Cancel the limiter timer
  limiter.cancel();

  // We may want to allow short bursts of requests in
  // our rate limiting scheme while preserving the
  // overall rate limit. We can accomplish this by
  // using a bursty limiter.
  final burstyLimiter = StreamController<DateTime>();

  // Fill up the controller to represent allowed bursting.
  for (var i = 0; i < 3; i++) {
    burstyLimiter.add(DateTime.now());
  }

  // Every 200 milliseconds we'll try to add a new
  // value to burstyLimiter, up to its limit of 3.
  Timer.periodic(Duration(milliseconds: 200), (timer) {
    if (burstyLimiter.hasListener && !burstyLimiter.isClosed) {
      burstyLimiter.add(DateTime.now());
    } else {
      timer.cancel();
    }
  });

  // Now simulate 5 more incoming requests. The first
  // 3 of these will benefit from the burst capability
  // of burstyLimiter.
  final burstyRequests = Stream.fromIterable(List.generate(5, (i) => i + 1));

  await for (var req in burstyRequests) {
    await burstyLimiter.stream.first;
    print('request $req ${DateTime.now()}');
  }

  // Close the bursty limiter
  await burstyLimiter.close();
}