metamethod.h

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/**********************************************************************
 * LeechCraft - modular cross-platform feature rich internet client.
 * Copyright (C) 2006-2014  Georg Rudoy
 *
 * Distributed under the Boost Software License, Version 1.0.
 * (See accompanying file LICENSE or copy at https://www.boost.org/LICENSE_1_0.txt)
 **********************************************************************/

#pragma once

#include <coroutine>
#include <QMetaObject>
#include <util/sll/void.h>

namespace LC::Util::detail
{
    template<typename Ctx, typename F, typename... Args>
    struct MethodAwaiter
    {
        Ctx& Ctx_;
        std::decay_t<F> Method_;
        std::tuple<Ctx&, std::decay_t<Args>...> Args_;

        using R = std::invoke_result_t<std::decay_t<F>, Ctx&, std::decay_t<Args>...>;
        constexpr static bool IsVoid = std::is_same_v<R, void>;

        std::conditional_t<IsVoid, Void, std::optional<R>> Result_ {};

        std::exception_ptr Exception_ {};

        std::atomic_bool Ready_ { false };

        bool await_ready () const noexcept
        {
            return false;
        }

        void await_suspend (std::coroutine_handle<> handle) noexcept
        {
            const auto thread = QThread::currentThread ();
            QMetaObject::invokeMethod (&Ctx_,
                    [=, this]
                    {
                        try
                        {
                            if constexpr (IsVoid)
                                std::apply (Method_, Args_);
                            else
                                Result_ = std::apply (Method_, Args_);
                        }
                        catch (...)
                        {
                            Exception_ = std::current_exception ();
                        }

                        Ready_.store (true, std::memory_order_release);

                        QMetaObject::invokeMethod (thread, handle, Qt::QueuedConnection);
                    },
                    Qt::QueuedConnection);
        }

        R await_resume () const
        {
            while (!Ready_.load (std::memory_order_acquire))
                ;

            if (Exception_)
                std::rethrow_exception (Exception_);

            if constexpr (!IsVoid)
                return *Result_;
        }
    };
}

namespace LC::Util
{
    template<typename Ctx, typename F, typename... Args>
    auto MetaMethod (Ctx& ctx, F&& method, Args&&... args)
    {
        return detail::MethodAwaiter<Ctx, F, Args...> { ctx, std::forward<F> (method), { ctx, std::forward<Args> (args)... } };
    }
}