continuable/fluent/Continuable.h

/*
 *  Copyright (C) 2015 Naios <naios-dev@live.de>
 *
 *  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
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#ifndef _CONTINUABLE_H_
#define _CONTINUABLE_H_

#include "Callback.h"

namespace detail
{
    /// The internal state of the continuable
    /// which is used to save certain internal types.
    template<typename... Args>
    struct ContinuableState;

    template<typename... _Cain, typename _Proxy>
    struct ContinuableState<std::tuple<_Cain...>, _Proxy>
    {
    };

    typedef ContinuableState<std::tuple<>, void> DefaultContinuableState;

    /// The unwrap which is used to extract continuable parameter types.
    template<typename... Args>
    struct continuable_unwrap;

    // First parameter is the state.
    template<typename... _SArgs, typename... _CArgs>
    struct continuable_unwrap<ContinuableState<_SArgs...>, _CArgs...>
    {
        typedef ContinuableState<_SArgs...> state_t;

        typedef Callback<_CArgs...> callback_t;
    };

    // No state is given use an empty one.
    template<typename... _CArgs>
    struct continuable_unwrap<_CArgs...>
        : public continuable_unwrap<DefaultContinuableState, _CArgs...> { };

    /// Corrects void return types from functional types which should be Continuable<Callback<>>
    /*
    template<typename _RTy>
    struct convert_void_to_continuable;

    template<>
    struct convert_void_to_continuable<void>
    {
        typedef Continuable<Callback<>> type;
    };

    template<typename... _CArgs>
    struct convert_void_to_continuable<Continuable<_CArgs...>>
    {
        typedef Continuable<_CArgs...> type;
    };
    */

    // ContinuableImpl Forward definition
    template<typename _STy, typename _CTy>
    class _ContinuableImpl;

    template<typename... _STy, typename... _ATy>
    class _ContinuableImpl<ContinuableState<_STy...>, std::function<void(_ATy...)>>
    {
        // Make all instances of _ContinuableImpl to a friend.
        template<typename, typename>
        friend class _ContinuableImpl;

        typedef ContinuableState<_STy...> MyState;
        typedef Callback<_ATy...> MyCallback;

    public:
        typedef std::function<void(Callback<_ATy...>&&)> ForwardFunction;

    private:
        /// Functional which expects a callback that is inserted from the Continuable
        /// to chain everything together
        ForwardFunction _callback_insert;

        bool _released;

        void Dispatch()
        {
        }

    public:
        /// Deleted copy construct
        template<typename _RState, typename _RCTy>
        _ContinuableImpl(_ContinuableImpl<_RState, _RCTy> const&) = delete;

        /// Move construct
        template<typename _RState, typename _RCTy>
        _ContinuableImpl(_ContinuableImpl<_RState, _RCTy>&& right)
            : _released(right._released)
        {
            right._released = true;
        }

        // Construct through a ForwardFunction
        template<typename _FTy>
        _ContinuableImpl(_FTy&& callback_insert)
            : _callback_insert(std::forward<_FTy>(callback_insert)), _released(false) { }

        /// Destructor which calls the dispatch chain if needed.
        ~_ContinuableImpl()
        {
            if (!_released)
            {
                _released = true;
                Dispatch();
            }
        }

        /// Deleted copy assign
        template<typename _RState, typename _RCTy>
        _ContinuableImpl& operator= (_ContinuableImpl<_RState, _RCTy> const&) = delete;

        /// Move construct assign
        template<typename _RState, typename _RCTy>
        _ContinuableImpl& operator= (_ContinuableImpl<_RState, _RCTy>&& right)
        {
            _released = right._released;
            right._released = true;
            return *this;
        }

        // TODO Accept only correct callbacks
        template<typename _CTy>
        _ContinuableImpl<DefaultContinuableState, Callback<_ATy...>> then(_CTy&&)
        {
            // TODO Transmute the returned callback here.
            return _ContinuableImpl<DefaultContinuableState, Callback<_ATy...>>(std::move(*this));
        }

        /*
        // TODO Accept only correct callbacks
        template<typename... _CTy>
        Continuable<Callback<_ATy...>> all(_CTy&&...)
        {
            // TODO Transmute the returned callback here.
            return Continuable<Callback<_ATy...>>(std::move(*this));
        }
        */

        /// Invalidates the Continuable
        _ContinuableImpl& invalidate()
        {
            _released = true;
            return *this;
        }
    };
}

/// A continuable provides useful methods to react on the result of callbacks
/// and allows to chain multiple callback calls to a chain.
template<typename... Args>
using Continuable = detail::_ContinuableImpl<
    detail::DefaultContinuableState,
    Callback<Args...>>;

namespace detail
{
    template<typename _FTy, typename _RTy, typename... _ATy>
    struct ContinuableFactory;

    template<typename _FTy, typename _RTy, typename... _ATy>
    struct ContinuableFactory<_FTy, _RTy, ::fu::identity<std::function<void(_ATy...)>&&>>
    {
        static auto CreateFrom(_FTy&& functional)
            -> Continuable<_ATy...>
        {
            return Continuable<_ATy...>(
                typename Continuable<_ATy...>::ForwardFunction(std::forward<_FTy>(functional)));
        }
    };

    template<typename _FTy>
    using continuable_factory_t = ContinuableFactory<
        _FTy, ::fu::return_type_of_t<_FTy>, ::fu::argument_type_of_t<_FTy>>;

} // detail

/// Wraps a functional object which expects a r-value callback as argument into a continuable.
/// The callable is invoked when the continuable shall continue.
/// For example:
/// make_continuable([](Callback<int>&& callback)
/// {
///     /* Continue here */
///     callback(5);
/// });
template<typename _FTy>
inline auto make_continuable(_FTy&& functional)
    -> decltype(detail::continuable_factory_t<_FTy>::CreateFrom(std::declval<_FTy>()))
{
    return detail::continuable_factory_t<_FTy>::CreateFrom(std::forward<_FTy>(functional));
}

#endif // _CONTINUABLE_H_