final2

lib/vendor/countdown/countdown.dart

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+// Copyright (c) 2015, Benjamin NGUYEN. All rights reserved. Use of this source code
+// is governed by a BSD-style license that can be found in the LICENSE file.
+
+/// The countdown library.
+library countdown;
+
+export 'src/countdown_base.dart';

lib/vendor/countdown/src/countdown_base.dart

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+// Copyright (c) 2015, Benjamin NGUYEN. All rights reserved. Use of this source code
+// is governed by a BSD-style license that can be found in the LICENSE file.
+
+library countdown.base;
+
+import "dart:async";
+
+class CountDown {
+  /// reference point for start and resume
+  DateTime? _begin;
+  Timer? _timer;
+  Duration? _duration;
+  Duration? remainingTime;
+  bool isPaused = false;
+  StreamController<Duration>? _controller;
+  Duration? _refresh;
+
+  /// provide a way to send less data to the client but keep the data of the timer up to date
+  int _everyTick = 0;
+  int counter = 0;
+
+  /// once you instantiate the CountDown you need to register to receive information
+  CountDown(Duration duration,
+      {Duration refresh = const Duration(milliseconds: 10), int everyTick = 1}) {
+    _refresh = refresh;
+    _everyTick = everyTick;
+
+    this._duration = duration;
+    _controller = StreamController<Duration>(
+        onListen: _onListen,
+        onPause: _onPause,
+        onResume: _onResume,
+        onCancel: _onCancel);
+  }
+
+  Stream<Duration> get stream => _controller!.stream;
+
+  /// _onListen
+  /// invoke when the first subscriber has subscribe and not before to avoid leak of memory
+  _onListen() {
+    // reference point
+    _begin = DateTime.now();
+    _timer = Timer.periodic(_refresh!, _tick);
+  }
+
+  /// the remaining time is set at '_refresh' ms accurate
+  _onPause() {
+    isPaused = true;
+    _timer?.cancel();
+    _timer = null;
+  }
+
+  /// ...restart the timer with the duration
+  _onResume() {
+    _begin = DateTime.now();
+
+    _duration = this.remainingTime;
+    isPaused = false;
+
+    //  lance le timer
+    _timer = Timer.periodic(_refresh!, _tick);
+  }
+
+  _onCancel() {
+    // on pause we already cancel the _timer
+    if (!isPaused) {
+      _timer?.cancel();
+      _timer = null;
+    }
+    // _controller.close(); // close automatically the "pipe" when the sub close it by sub.cancel()
+  }
+
+  void _tick(Timer? timer) {
+    counter++;
+    Duration alreadyConsumed = DateTime.now().difference(_begin!);
+    this.remainingTime = this._duration! - alreadyConsumed;
+    if (this.remainingTime!.isNegative) {
+      timer?.cancel();
+      timer = null;
+      // tell the onDone's subscriber that it's finish
+      _controller?.close();
+    } else {
+      // here we can control the frequency of sending data
+      if (counter % _everyTick == 0) {
+        _controller?.add(this.remainingTime!);
+        counter = 0;
+      }
+    }
+  }
+}