implement queue to events emitter

lib/src/managers/event.dart

@@ -1,4 +1,5 @@
 import 'dart:async';
+import 'dart:collection';
 
 import 'package:meta/meta.dart';
 import 'package:synchronized/synchronized.dart' as sync;
@@ -22,9 +23,13 @@ class EventsEmitter<T> extends EventsListenable<T> {
   // suppport for multiple event listeners
   final streamCtrl = StreamController<T>.broadcast(sync: false);
 
+  bool _queueMode = false;
+  final _queue = Queue<T>();
+
   EventsEmitter({
     bool listenSynchronized = false,
   }) : super(synchronized: listenSynchronized) {
+    // clean up
     onDispose(() async => await streamCtrl.close());
   }
 
@@ -33,14 +38,40 @@ class EventsEmitter<T> extends EventsListenable<T> {
 
   @internal
   void emit(T event) {
-    // do nothing if already closed
-    if (streamCtrl.isClosed) {
+    // check if already disposed
+    if (isDisposed) {
       logger.warning('failed to emit event ${event} on a disposed emitter');
       return;
     }
+    // queue mode
+    if (_queueMode) {
+      _queue.add(event);
+      return;
+    }
     // emit the event
     streamCtrl.add(event);
   }
+
+  @internal
+  void updateQueueMode(bool newValue, {bool shouldEmitQueued = true}) {
+    // check if already disposed
+    if (isDisposed) {
+      logger.warning('failed to update queueMode on a disposed emitter');
+      return;
+    }
+    if (_queueMode == newValue) return;
+    _queueMode = newValue;
+    if (!_queueMode && shouldEmitQueued) emitQueued();
+  }
+
+  @internal
+  void emitQueued() {
+    while (_queue.isNotEmpty) {
+      final event = _queue.removeFirst();
+      // emit the event
+      streamCtrl.add(event);
+    }
+  }
 }
 
 // for listening only