// Copyright Epic Games, Inc. All Rights Reserved.

#pragma once

#include "CoreMinimal.h"
#include "UObject/Object.h"
#include "UObject/WeakObjectPtr.h"
#include "Templates/Casts.h"
#include "ScriptInterface.h"

/**
 * An alternative to TWeakObjectPtr that makes it easier to work through an interface.
 */
template <class T>
struct TWeakInterfacePtr
{
    /**
     * Construct a new default weak pointer, pointing to null object.
     */
    TWeakInterfacePtr()
        : InterfaceInstance(nullptr)
    {
    }

    /**
     * Construct from an object pointer
     * @param Object The object to create a weak pointer to. This object must implement interface T.
     */
    template <
        typename U,
        decltype(ImplicitConv<typename TCopyQualifiersFromTo<U, UObject>::Type*>((U*)nullptr))* = nullptr>
    TWeakInterfacePtr(U* Object)
    {
        InterfaceInstance = Cast<T>(Object);
        if (InterfaceInstance != nullptr)
        {
            ObjectInstance = Object;
        }
    }

    /**
     * Construct from an interface pointer
     * @param Interface The interface pointer to create a weak pointer to. There must be a UObject behind the interface.
     */
    TWeakInterfacePtr(T* Interface)
        : InterfaceInstance(nullptr)
    {
        ObjectInstance = Cast<UObject>(Interface);
        if (ObjectInstance != nullptr)
        {
            InterfaceInstance = Interface;
        }
    }

    UE_DEPRECATED(4.27, "Please use the constructor that takes a pointer")
    TWeakInterfacePtr(T& Interface)
        : InterfaceInstance(nullptr)
    {
        ObjectInstance = Cast<UObject>(&Interface);
        if (ObjectInstance != nullptr)
        {
            InterfaceInstance = &Interface;
        }
    }

    /**
     * Reset the weak pointer back to the null state.
     */
    FORCEINLINE void Reset()
    {
        InterfaceInstance = nullptr;
        ObjectInstance.Reset();
    }

    /**
     * Test if this points to a live object. Parameters are passed to the underlying TWeakObjectPtr.
     */
    FORCEINLINE bool IsValid(bool bEvenIfPendingKill, bool bThreadsafeTest = false) const
    {
        return InterfaceInstance != nullptr && ObjectInstance.IsValid(bEvenIfPendingKill, bThreadsafeTest);
    }

    /**
     * Test if this points to a live object. Calls the underlying TWeakObjectPtr's parameterless IsValid method.
     */
    FORCEINLINE bool IsValid() const
    {
        return InterfaceInstance != nullptr && ObjectInstance.IsValid();
    }

    /**
     * Test if this pointer is stale. Parameters are passed to the underlying TWeakObjectPtr.
     */
    FORCEINLINE bool IsStale(bool bEvenIfPendingKill = false, bool bThreadsafeTest = false) const
    {
        return InterfaceInstance != nullptr && ObjectInstance.IsStale(bEvenIfPendingKill, bThreadsafeTest);
    }

    /**
     * Dereference the weak pointer into an interface pointer.
     */
    FORCEINLINE T* Get() const
    {
        return IsValid() ? InterfaceInstance : nullptr;
    }

    /**
     * Dereference the weak pointer into a UObject pointer.
     */
    FORCEINLINE UObject* GetObject() const
    {
        return ObjectInstance.Get();
    }

    /**
     * Dereference the weak pointer.
     */
    FORCEINLINE T& operator*() const
    {
        check(IsValid());
        return *InterfaceInstance;
    }

    /**
     * Dereference the weak pointer.
     */
    FORCEINLINE T* operator->() const
    {
        check(IsValid());
        return InterfaceInstance;
    }

    /**
     * Assign from an interface pointer.
     */
    FORCEINLINE TWeakInterfacePtr<T>& operator=(T* Other)
    {
        *this = TWeakInterfacePtr<T>(Other);
        return *this;
    }

    /**
     * Assign from another weak pointer.
     */
    FORCEINLINE TWeakInterfacePtr<T>& operator=(const TWeakInterfacePtr<T>& Other)
    {
        ObjectInstance    = Other.ObjectInstance;
        InterfaceInstance = Other.InterfaceInstance;
        return *this;
    }

    /**
     * Assign from a script interface.
     */
    FORCEINLINE TWeakInterfacePtr<T>& operator=(const TScriptInterface<T>& Other)
    {
        ObjectInstance    = Other.GetObject();
        InterfaceInstance = (T*)Other.GetInterface();
        return *this;
    }

    FORCEINLINE bool operator==(const TWeakInterfacePtr<T>& Other) const
    {
        return InterfaceInstance == Other.InterfaceInstance;
    }

    FORCEINLINE bool operator!=(const TWeakInterfacePtr<T>& Other) const
    {
        return InterfaceInstance != Other.InterfaceInstance;
    }

    UE_DEPRECATED(4.27, "Implicit equality with a UObject pointer has been deprecated - use GetObject() and test equality on its return value")
    FORCEINLINE bool operator==(const UObject* Other) const
    {
        return Other == ObjectInstance.Get();
    }

    FORCEINLINE TScriptInterface<T> ToScriptInterface() const
    {
        UObject* Object = ObjectInstance.Get();
        if (Object)
        {
            return TScriptInterface<T>(Object);
        }

        return TScriptInterface<T>();
    }

private:
    TWeakObjectPtr<UObject> ObjectInstance;
    T* InterfaceInstance;
};