hsOptionalCall.h

/*==LICENSE==*

CyanWorlds.com Engine - MMOG client, server and tools
Copyright (C) 2011  Cyan Worlds, Inc.

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
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Additional permissions under GNU GPL version 3 section 7

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combining it with any of RAD Game Tools Bink SDK, Autodesk 3ds Max SDK,
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*==LICENSE==*/

#ifndef _hsOptionalCall_h
#define _hsOptionalCall_h

#include <memory>
#include <optional>
#include <type_traits>
#include <unordered_map>

#include "HeadSpin.h"

#ifdef HS_BUILD_FOR_WIN32
#   include "hsWindows.h"
#else
#   include <dlfcn.h>
#endif

namespace hsOptionalCallImpl
{
#ifdef HS_BUILD_FOR_WIN32
    using LibraryT = std::remove_pointer<HMODULE>::type;
    using LibNameT = const wchar_t*;
#else
    typedef void LibraryT;
    typedef const char* LibNameT;
#endif
    typedef std::unordered_map<LibNameT, std::weak_ptr<LibraryT>> LibraryMapT;

    static std::shared_ptr<LibraryT> TryLoadLibrary(LibNameT lib)
    {
        static LibraryMapT fLoadedLibraries;

        LibraryMapT::const_iterator it = fLoadedLibraries.find(lib);
        if (it != fLoadedLibraries.end() && !it->second.expired()) {
            return std::shared_ptr(it->second);
        } else {
#ifdef HS_BUILD_FOR_WIN32
            std::shared_ptr<LibraryT> p(LoadLibraryW(lib), [](LibraryT* ptr){
                FreeLibrary(ptr);
            });
#else
            std::shared_ptr<LibraryT> p(dlopen(lib, RTLD_LAZY | RTLD_LOCAL), [](LibraryT* ptr){
                dlclose(ptr);
            });
#endif
            fLoadedLibraries[lib] = std::weak_ptr(p);
            return p;
        }
    }

    static void* TryGetFunction(const std::shared_ptr<LibraryT>& lib, const char* func)
    {
#ifdef HS_BUILD_FOR_WIN32
        return GetProcAddress(lib.get(), func);
#else
        return dlsym(lib.get(), func);
#endif
    }
};

template<class, class...> class hsOptionalCall;

template<class _ReturnT, class... _ArgsT>
class hsOptionalCall<_ReturnT(_ArgsT...)>
{
    using _FuncPtrT = _ReturnT(*)(_ArgsT...);
    using _ResultT = typename std::conditional<std::is_void<_ReturnT>::value, std::nullptr_t, _ReturnT>::type;

    std::shared_ptr<hsOptionalCallImpl::LibraryT> fLibrary;
    _FuncPtrT fProc;

public:
    hsOptionalCall(hsOptionalCallImpl::LibNameT lib, const char* func)
        : fLibrary(), fProc()
    {
        fLibrary = hsOptionalCallImpl::TryLoadLibrary(lib);
        if (fLibrary) {
            fProc = (_FuncPtrT)hsOptionalCallImpl::TryGetFunction(fLibrary, func);
            if (!fProc) {
                fLibrary = nullptr;
            }
        }
    }

    ~hsOptionalCall()
    {
        fLibrary = nullptr;
    }

    std::optional<_ResultT> operator()(_ArgsT... args) const
    {
        if (fProc) {
            if constexpr (std::is_void<_ReturnT>::value) {
                return fProc(std::forward<_ArgsT>(args)...), nullptr;
            } else {
                return (_ResultT)fProc(std::forward<_ArgsT>(args)...);
            }
        }
        return std::nullopt;
    }

    operator bool() const
    {
        return fProc != nullptr;
    }

    _FuncPtrT Get() const { return fProc; }
};

template<class _ValueT>
class hsOptionalCall<_ValueT>
{
    std::shared_ptr<hsOptionalCallImpl::LibraryT> fLibrary;
    _ValueT* fValue;

public:
    hsOptionalCall(hsOptionalCallImpl::LibNameT lib, const char* func)
        : fLibrary(), fValue()
    {
        fLibrary = hsOptionalCallImpl::TryLoadLibrary(lib);
        if (fLibrary) {
            fValue = (_ValueT*)hsOptionalCallImpl::TryGetFunction(fLibrary, func);
            if (!fValue) {
                fLibrary = nullptr;
            }
        }
    }

    ~hsOptionalCall()
    {
        fLibrary = nullptr;
    }

    _ValueT operator *() const {
        return *fValue;
    }

    operator bool() const
    {
        return fValue != nullptr;
    }

    _ValueT Get() const { return *fValue; }
};

#define hsOptionalCallDecl(lib, func) \
    hsOptionalCall<decltype(func)> __##func(lib, #func);

#endif // _hsOptionalCall_h