winrt: implement await async operation helper

async.go

@@ -0,0 +1,48 @@
+package winrt
+
+import (
+	"fmt"
+
+	"github.com/go-ole/go-ole"
+	"github.com/saltosystems/winrt-go/windows/foundation"
+)
+
+// AwaitAsyncOperation waits for the given IAsyncOperation to complete.
+// The genericParamSignature is the WinRT signature of the generic parameter type of the IAsyncOperation.
+//
+// For example, for `IAsyncOperation<Int32>`, the signature would simply be [SignatureInt32].
+//
+// To obtain the signature of more complex types, use [ParameterizedInstanceGUID].
+//
+// For example for `IAsyncOperation<IVectorView<GattClientNotificationResult>>`,
+// you would use:
+//
+//	```go
+//	winrt.ParameterizedInstanceGUID(collections.GUIDIVectorView, genericattributeprofile.SignatureGattClientNotificationResult)
+//	```
+func AwaitAsyncOperation(asyncOperation *foundation.IAsyncOperation, genericParamSignature string) error {
+	var status foundation.AsyncStatus
+
+	// We need to obtain the GUID of the AsyncOperationCompletedHandler, but its a generic delegate
+	// so we also need the generic parameter type's signature:
+	// AsyncOperationCompletedHandler<genericParamSignature>
+	iid := ParameterizedInstanceGUID(foundation.GUIDAsyncOperationCompletedHandler, genericParamSignature)
+
+	// Wait until the async operation completes.
+	waitChan := make(chan struct{})
+	handler := foundation.NewAsyncOperationCompletedHandler(ole.NewGUID(iid), func(instance *foundation.AsyncOperationCompletedHandler, asyncInfo *foundation.IAsyncOperation, asyncStatus foundation.AsyncStatus) {
+		status = asyncStatus
+		close(waitChan)
+	})
+	defer handler.Release()
+
+	asyncOperation.SetCompleted(handler)
+
+	// Wait until async operation has stopped, and finish.
+	<-waitChan
+
+	if status != foundation.AsyncStatusCompleted {
+		return fmt.Errorf("async operation failed with status %d", status)
+	}
+	return nil
+}