AuROXTL/Include/auROXTL/Objects/SafeDestroy.hpp

/***
    Copyright (C) 2022 J Reece Wilson (a/k/a "Reece"). All rights reserved.

    File: SafeDestroy.hpp
    Date: 2022-07-19
    Author: Reece
***/
#pragma once

namespace AuUtil
{
    namespace Detail
    {
        template <class T>
        struct AuHasDestroy
        {
            template <class C> static constexpr AuTrueType  Test(decltype(&C::DestroyPrivate));
            template <class C> static constexpr AuFalseType Test(...);
            using type = decltype(Test<T>(0));
        };

        template <class T>
        struct AuHasDeconstruct
        {
            template <class C> static constexpr AuTrueType  Test(decltype(&C::DeconstructPrivate));
            template <class C> static constexpr AuFalseType Test(...);
            using type = decltype(Test<T>(0));
        };

        template <class T>
        struct AuHasPreDeconstruct
        {
            template <class C> static constexpr AuTrueType  Test(decltype(&C::PreDeconstructPrivate));
            template <class C> static constexpr AuFalseType Test(...);
            using type = decltype(Test<T>(0));
        };

        template <class T>
        constexpr inline bool AuHasDestroy_v = AuHasDestroy<T>::type::value;

        template <class T>
        constexpr inline bool AuHasDesconstruct_v = AuHasDeconstruct<T>::type::value;

        template <class T>
        constexpr inline bool AuHasPreDesconstruct_v = AuHasPreDeconstruct<T>::type::value;
    }

#define AU_SAFE_DESTROY(type)                                                 \
public:                                                                       \
    virtual ~type()                                                           \
    {                                                                         \
        if (AuAtomicTestAndSet(&this->uCurrentState_, 2))                     \
        {                                                                     \
            return;                                                           \
        }                                                                     \
                                                                              \
        type :: _TryPreDeconstruct<type>(this);                               \
                                                                              \
        this->Destroy();                                                      \
                                                                              \
        type :: _TryDeconstruct<type>(this);                                  \
                                                                              \
    }                                                                         \
                                                                              \
    inline void Destroy()                                                     \
    {                                                                         \
        if (AuAtomicTestAndSet(&this->uCurrentState_, 1))                     \
        {                                                                     \
            return;                                                           \
        }                                                                     \
                                                                              \
        type ::  _TryDeconstructPrivate<type>(this);                          \
    }                                                                         \
                                                                              \
    friend AuUtil::Detail::AuHasDestroy<type>;                                \
    friend AuUtil::Detail::AuHasDeconstruct<type>;                            \
    friend AuUtil::Detail::AuHasPreDeconstruct<type>;                         \
                                                                              \
private:                                                                      \
    AuUInt32 uCurrentState_{};                                                \
                                                                              \
    template<typename T>                                                      \
    static void _TryPreDeconstruct(T *that)                                   \
    {                                                                         \
        if constexpr (AuUtil::Detail::AuHasPreDesconstruct_v<T>)              \
        {                                                                     \
            that->PreDeconstructPrivate();                                    \
        }                                                                     \
    }                                                                         \
                                                                              \
    template<typename T>                                                      \
    static void _TryDeconstruct(T *that)                                      \
    {                                                                         \
        if constexpr (AuUtil::Detail::AuHasDesconstruct_v<T>)                 \
        {                                                                     \
            that->DeconstructPrivate();                                       \
        }                                                                     \
    }                                                                         \
                                                                              \
    template<typename T>                                                      \
    static void _TryDeconstructPrivate(T *that)                               \
    {                                                                         \
        if constexpr (AuUtil::Detail::AuHasDestroy_v<T>)                      \
        {                                                                     \
            that->DestroyPrivate();                                           \
        }                                                                     \
    }                                                                         \
                                                                              \
public:
}

/**
    Safe destroy objects:   
          * implement a builtin ::Destroy function for objects whose ownership is expectantly shared instead of explicitly owned (eg: overlapped io resources over simplier utility class objects with explicit an release function)
          
          * allow the user to define ::DestroyPrivate, ::DeconstructPrivate, and ::*Pre*DeconstructPrivate methods in their class
          
          * forces virtual destruction to prevent hidden leaks
            note: The real reason we do this is bc "some projects" expect the destruction implementation itself to be a virtual destructor (an implicitly overloaded virtual, if it were a regular method).
                  That way API objects can call a `virtual ~IInterface()` and nuke safely nuke away the underlying safe-destroy object by using the builtin "everyone has this destruct method" destructor;
                  bypassing the need for a `virtual Destroy() = 0;` and alternative an AU_SAFE_DESTROY.
          
          * enable safe explicit double ~Type() support; however, some objects in your STL may not support this behaviour (eg: AuFunction)
            workaround: implement explicit ::Deconstruct() with AuResetMember calls to fixup the UB

          * allows for an arbitrary amount of Type::Destroy() and Type::~Type() calls across multiple threads
    
    Usage:
        Defines #define AU_SAFE_DESTROY(type)

        Simply add AU_SAFE_DESTROY to the types body add arbitrarily add the following callback methods as needed

        void DestroyPrivate(void) - Generic called once object destroy
        void DeconstructPrivate(void) - Object destruction hook. Called once. Called After DestroyPrivate.
        void PreDeconstructPrivate(void) - Object destruction hook. Called once. Called before DestroyPrivate.

        These user defined functions may be private and/or virtual, if implemented at all.
*/