49 lines
1.5 KiB
Dart
49 lines
1.5 KiB
Dart
import 'dart:async';
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extension StreamExtension on Stream {
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/// Returns a new Stream which outputs only `true` for every update of the original
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/// stream, ratelimited by the Duration t
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Stream<bool> rateLimit(Duration t) {
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final controller = StreamController<bool>();
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Timer? timer;
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var gotMessage = false;
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// as we call our inline-defined function recursively we need to make sure that the
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// variable exists prior of creating the function. Silly dart.
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Function? onMessage;
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// callback to determine if we should send out an update
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onMessage = () {
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// do nothing if it is already closed
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if (controller.isClosed) {
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return;
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}
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if (timer == null) {
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// if we don't have a timer yet, send out the update and start a timer
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gotMessage = false;
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controller.add(true);
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timer = Timer(t, () {
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// the timer has ended...delete it and, if we got a message, re-run the
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// method to send out an update!
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timer = null;
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if (gotMessage) {
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onMessage?.call();
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}
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});
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} else {
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// set that we got a message
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gotMessage = true;
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}
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};
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final subscription = listen(
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(_) => onMessage?.call(),
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onDone: () => controller.close(),
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onError: (e, s) => controller.addError(e, s),
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);
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// add proper cleanup to the subscription and the controller, to not memory leak
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controller.onCancel = () {
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subscription.cancel();
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controller.close();
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};
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return controller.stream;
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}
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}
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