rx-pairwise.hpp

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// Copyright (c) Microsoft Open Technologies, Inc. All rights reserved. See License.txt in the project root for license information.

#pragma once

#if !defined(RXCPP_OPERATORS_RX_PAIRWISE_HPP)
#define RXCPP_OPERATORS_RX_PAIRWISE_HPP

#include "../rx-includes.hpp"

namespace rxcpp {

namespace operators {

namespace detail {

template<class... AN>
struct pairwise_invalid_arguments {};

template<class... AN>
struct pairwise_invalid : public rxo::operator_base<pairwise_invalid_arguments<AN...>> {
    using type = observable<pairwise_invalid_arguments<AN...>, pairwise_invalid<AN...>>;
};
template<class... AN>
using pairwise_invalid_t = typename pairwise_invalid<AN...>::type;

template<class T>
struct pairwise
{
    typedef rxu::decay_t<T> source_value_type;
    typedef std::tuple<source_value_type, source_value_type> value_type;

    template<class Subscriber>
    struct pairwise_observer
    {
        typedef pairwise_observer<Subscriber> this_type;
        typedef std::tuple<source_value_type, source_value_type> value_type;
        typedef rxu::decay_t<Subscriber> dest_type;
        typedef observer<T, this_type> observer_type;
        dest_type dest;
        mutable rxu::detail::maybe<source_value_type> remembered;

        pairwise_observer(dest_type d)
            : dest(std::move(d))
        {
        }
        void on_next(source_value_type v) const {
            if (remembered.empty()) {
                remembered.reset(v);
                return;
            }

            dest.on_next(std::make_tuple(remembered.get(), v));
            remembered.reset(v);
        }
        void on_error(std::exception_ptr e) const {
            dest.on_error(e);
        }
        void on_completed() const {
            dest.on_completed();
        }

        static subscriber<T, observer_type> make(dest_type d) {
            auto cs = d.get_subscription();
            return make_subscriber<T>(std::move(cs), observer_type(this_type(std::move(d))));
        }
    };

    template<class Subscriber>
    auto operator()(Subscriber dest) const
        -> decltype(pairwise_observer<Subscriber>::make(std::move(dest))) {
        return      pairwise_observer<Subscriber>::make(std::move(dest));
    }
};

}

template<class... AN>
auto pairwise(AN&&... an)
    ->     operator_factory<pairwise_tag, AN...> {
    return operator_factory<pairwise_tag, AN...>(std::make_tuple(std::forward<AN>(an)...));
}

}

template<>
struct member_overload<pairwise_tag>
{
    template<class Observable,
        class Enabled = rxu::enable_if_all_true_type_t<
            is_observable<Observable>>,
        class SourceValue = rxu::value_type_t<Observable>,
        class Pairwise = rxo::detail::pairwise<SourceValue>,
        class Value = rxu::value_type_t<Pairwise>>
    static auto member(Observable&& o)
    -> decltype(o.template lift<Value>(Pairwise())) {
        return  o.template lift<Value>(Pairwise());
    }

    template<class... AN>
    static operators::detail::pairwise_invalid_t<AN...> member(AN...) {
        std::terminate();
        return {};
        static_assert(sizeof...(AN) == 10000, "pairwise takes no arguments");
    }
};

}

#endif