Add awaiter for UnityEvent and generic version

BetterExtensions.asmdef

@@ -1,6 +1,6 @@
 {
     "name": "BetterExtensions",
-    "rootNamespace": "BetterExtensions",
+    "rootNamespace": "",
     "references": [],
     "includePlatforms": [],
     "excludePlatforms": [],

Runtime/Extension/ActionExtensions/ActionAwaiter.cs

@@ -0,0 +1,34 @@
+using System;
+using System.Threading;
+using System.Threading.Tasks;
+using UnityEngine.Events;
+
+namespace BetterExtensions.Runtime.Extension.ActionExtensions
+{
+    public static class ActionAwaiter
+    {
+        public static Task Await(this UnityEvent action, CancellationToken cancellationToken = default)
+        {
+            var taskCompletionSource = new TaskCompletionSource<bool>();
+            var buffer = new UnityEventWrapper(taskCompletionSource, ref action);
+            if (!cancellationToken.Equals(default))
+            {
+                cancellationToken.Register(() => buffer.Cancel());
+            }
+
+            return buffer.Initialize();
+        }
+
+        public static Task Await<T>(this UnityEvent<T> action, CancellationToken cancellationToken = default)
+        {
+            var taskCompletionSource = new TaskCompletionSource<T>();
+            var buffer = new UnityEventWrapper<T>(taskCompletionSource, ref action);
+            if (!cancellationToken.Equals(default))
+            {
+                cancellationToken.Register(() => buffer.Cancel());
+            }
+
+            return buffer.Initialize();
+        }
+    }
+}

Runtime/Extension/ActionExtensions/BaseActionWrapper.cs

@@ -0,0 +1,19 @@
+using System.Threading.Tasks;
+
+namespace BetterExtensions.Runtime.Extension.ActionExtensions
+{
+    internal abstract class BaseActionWrapper<T>
+    {
+        private protected TaskCompletionSource<T> _taskCompletionSource;
+
+        public BaseActionWrapper(TaskCompletionSource<T> taskCompletionSource)
+        {
+            _taskCompletionSource = taskCompletionSource;
+        }
+
+        public abstract Task<T> Initialize();
+
+
+        public abstract void Cancel();
+    }
+}

Runtime/Extension/ActionExtensions/UnityEventWrapper.cs

@@ -0,0 +1,63 @@
+using System.Threading.Tasks;
+using UnityEngine.Events;
+
+namespace BetterExtensions.Runtime.Extension.ActionExtensions
+{
+    internal class UnityEventWrapper<T> : BaseActionWrapper<T>
+    {
+        private UnityEvent<T> _action;
+
+        public UnityEventWrapper(TaskCompletionSource<T> taskCompletionSource, ref UnityEvent<T> action) : base(
+            taskCompletionSource)
+        {
+            _action = action;
+        }
+
+        public override Task<T> Initialize()
+        {
+            _action.AddListener(SetResult);
+            return _taskCompletionSource.Task;
+        }
+
+        public override void Cancel()
+        {
+            _action.RemoveListener(SetResult);
+            _taskCompletionSource.TrySetCanceled();
+        }
+
+        private void SetResult(T result)
+        {
+            _action.RemoveListener(SetResult);
+            _taskCompletionSource.TrySetResult(result);
+        }
+    }
+
+    internal class UnityEventWrapper : BaseActionWrapper<bool>
+    {
+        private UnityEvent _action;
+
+        public UnityEventWrapper(TaskCompletionSource<bool> taskCompletionSource, ref UnityEvent action) : base(
+            taskCompletionSource)
+        {
+            _action = action;
+        }
+
+        public override Task<bool> Initialize()
+        {
+            _action.AddListener(SetResult);
+            return _taskCompletionSource.Task;
+        }
+
+        private void SetResult()
+        {
+            _action.RemoveListener(SetResult);
+            _taskCompletionSource.TrySetResult(true);
+        }
+
+        public override void Cancel()
+        {
+            _action.RemoveListener(SetResult);
+            _taskCompletionSource.TrySetCanceled();
+        }
+    }
+}