context.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 <stdexcept>
#include <QMetaObject>
#include <QObject>
#include <QVector>
#include "../threadsconfig.h"

namespace LC::Util
{
    namespace detail
    {
        struct DeadObjectInfo
        {
            std::string ClassName_;
            QString ObjectName_;
        };
    }

    class UTIL_THREADS_API ContextDeadException : public std::runtime_error
    {
    public:
        explicit ContextDeadException (const detail::DeadObjectInfo& info);
    };

    namespace detail
    {
        template<typename T>
        decltype (auto) Awaiter (T&& obj)
        {
            if constexpr (requires { operator co_await (std::forward<T> (obj)); })
                return operator co_await (std::forward<T> (obj));
            else if constexpr (requires { std::forward<T> (obj).operator co_await (); })
                return std::forward<T> (obj).operator co_await ();
            else
                return std::forward<T> (obj);
        }

        UTIL_THREADS_API void CheckDeadObjects (const QVector<DeadObjectInfo>&);

        template<typename Promise, typename OrigAwaiter>
        struct AwaitableWrapper
        {
            Promise& Promise_;
            OrigAwaiter Orig_;

            bool await_ready ()
            {
                return Orig_.await_ready ();
            }

            decltype (auto) await_suspend (auto handle)
            {
                return Orig_.await_suspend (handle);
            }

            decltype (auto) await_resume ()
            {
                CheckDeadObjects (Promise_.DeadObjects_);
                return Orig_.await_resume ();
            }
        };
    }

    struct [[nodiscard]] AddContextObject
    {
        QObject& Context_;

        explicit AddContextObject (QObject& context)
        : Context_ { context }
        {
        }

        bool await_ready () const noexcept
        {
            return false;
        }

        template<typename Promise>
            requires requires { typename Promise::HasContextExtensions; }
        bool await_suspend (std::coroutine_handle<Promise> handle)
        {
            auto conn = QObject::connect (&Context_,
                    &QObject::destroyed,
                    [handle] (QObject *object)
                    {
                        auto className = object->metaObject ()->className ();
                        handle.promise ().DeadObjects_.push_back ({ className, object->objectName () });
                        handle.resume ();
                    });
            handle.promise ().ContextConnections_.push_back (conn);
            return false;
        }

        void await_resume ()
        {
        }
    };

    template<typename>
    struct ContextExtensions
    {
        using HasContextExtensions = void;

        QVector<QMetaObject::Connection> ContextConnections_;
        QVector<detail::DeadObjectInfo> DeadObjects_;

        void FinalSuspend () const noexcept
        {
            for (const auto& conn : ContextConnections_)
                QObject::disconnect (conn);
        }

        AddContextObject await_transform (AddContextObject awaitable) const
        {
            return awaitable;
        }

        template<typename T>
        auto await_transform (T&& awaitable)
        {
            using OrigAwaiter = decltype (detail::Awaiter (std::forward<T> (awaitable)));
            return detail::AwaitableWrapper<ContextExtensions, OrigAwaiter> { *this, detail::Awaiter (std::forward<T> (awaitable)) };
        }
    };
}