opt: add event loop def

flutter/lib/utils/event_loop.dart

@@ -0,0 +1,79 @@
+import 'dart:async';
+
+import 'package:flutter/foundation.dart';
+
+typedef EventCallback<Data> = Future<dynamic> Function(Data data);
+
+abstract class BaseEvent<EventType, Data> {
+  EventType type;
+  Data data;
+
+  /// Constructor
+  BaseEvent(this.type, this.data);
+
+  /// Consume this event
+  @visibleForTesting
+  Future<dynamic> consume() async {
+    final cb = findCallback(type);
+    if (cb == null) {
+      return null;
+    } else {
+      return cb(data);
+    }
+  }
+
+  EventCallback<Data>? findCallback(EventType type);
+}
+
+abstract class BaseEventLoop<EventType, Data> {
+  final List<BaseEvent<EventType, Data>> _evts = [];
+  Timer? _timer;
+
+  List<BaseEvent<EventType, Data>> get evts => _evts;
+
+  Future<void> onReady() async {
+    // Poll every 100ms.
+    _timer = Timer.periodic(Duration(milliseconds: 100), _handleTimer);
+  }
+
+  /// An Event is about to be consumed.
+  Future<void> onPreConsume(BaseEvent<EventType, Data> evt) async {}
+  /// An Event was consumed.
+  Future<void> onPostConsume(BaseEvent<EventType, Data> evt) async {}
+  /// Events are all handled and cleared.
+  Future<void> onEventsClear() async {}
+  /// Events start to consume.
+  Future<void> onEventsStartConsuming() async {}
+
+  Future<void> _handleTimer(Timer timer) async {
+      if (_evts.isEmpty) {
+        return;
+      }
+      timer.cancel();
+      _timer = null;
+      // handle logic
+      await onEventsStartConsuming();
+      while (_evts.isNotEmpty) {
+        final evt = _evts.first;
+        _evts.remove(evt);
+        await onPreConsume(evt);
+        await evt.consume();
+        await onPostConsume(evt);
+      }
+      await onEventsClear();
+      // Now events are all processed
+      _timer = Timer.periodic(Duration(milliseconds: 100), _handleTimer);
+  }
+
+  Future<void> close() async {
+    _timer?.cancel();
+  }
+
+  void push_event(BaseEvent<EventType, Data> evt) {
+    _evts.add(evt);
+  }
+
+  void clear() {
+    _evts.clear();
+  }
+}