CallbackAction.h

// Copyright 2022 Stream.IO, Inc. All Rights Reserved.
#pragma once
 
#include "CoreMinimal.h"
#include "Engine/Engine.h"
#include "Engine/LatentActionManager.h"
#include "LatentActions.h"
#include "UObject/WeakObjectPtr.h"
 
template <class T, class Arg = const T&>
class TCallbackAction final : public FPendingLatentAction
{
public:
    TCallbackAction(T& Result, const FLatentActionInfo& LatentInfo)
        : ExecutionFunction(LatentInfo.ExecutionFunction), OutputLink(LatentInfo.Linkage), CallbackTarget(LatentInfo.CallbackTarget), Result(Result)
    {
    }
    TCallbackAction(const TCallbackAction&) = delete;
    TCallbackAction& operator=(const TCallbackAction&) = delete;
 
    static void CreateLatentAction(
        const UObject* WorldContextObject,
        const FLatentActionInfo LatentInfo,
        T& Output,
        TFunctionRef<void(TFunction<void(Arg)> Callback)> Action)
    {
        if (UWorld* World = GEngine->GetWorldFromContextObject(WorldContextObject, EGetWorldErrorMode::LogAndReturnNull))
        {
            FLatentActionManager& LatentActionManager = World->GetLatentActionManager();
            if (LatentActionManager.FindExistingAction<TCallbackAction<T, Arg>>(LatentInfo.CallbackTarget, LatentInfo.UUID))
            {
                return;
            }
 
            TCallbackAction<T, Arg>* DelegateAction = new TCallbackAction(Output, LatentInfo);
            Action(
                [DelegateAction](Arg InResult)
                {
                    DelegateAction->Result = InResult;
                    DelegateAction->bDone = true;
                });
            LatentActionManager.AddNewAction(LatentInfo.CallbackTarget, LatentInfo.UUID, DelegateAction);
        }
    }
 
private:
    virtual void UpdateOperation(FLatentResponse& Response) override
    {
        Response.FinishAndTriggerIf(bDone, ExecutionFunction, OutputLink, CallbackTarget);
    }
 
    FName ExecutionFunction;
    int32 OutputLink;
    FWeakObjectPtr CallbackTarget;
    T& Result;
    bool bDone = false;
};