rx-combine_latest.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_COMBINE_LATEST_HPP)
#define RXCPP_OPERATORS_RX_COMBINE_LATEST_HPP

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

namespace rxcpp {

namespace operators {

namespace detail {

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

template<class... AN>
struct combine_latest_invalid : public rxo::operator_base<combine_latest_invalid_arguments<AN...>> {
    using type = observable<combine_latest_invalid_arguments<AN...>, combine_latest_invalid<AN...>>;
};
template<class... AN>
using combine_latest_invalid_t = typename combine_latest_invalid<AN...>::type;

template<class Selector, class... ObservableN>
struct is_combine_latest_selector_check {
    typedef rxu::decay_t<Selector> selector_type;

    struct tag_not_valid;
    template<class CS, class... CON>
    static auto check(int) -> decltype((*(CS*)nullptr)((*(typename CON::value_type*)nullptr)...));
    template<class CS, class... CON>
    static tag_not_valid check(...);

    using type = decltype(check<selector_type, rxu::decay_t<ObservableN>...>(0));

    static const bool value = !std::is_same<type, tag_not_valid>::value;
};

template<class Selector, class... ObservableN>
struct invalid_combine_latest_selector {
    static const bool value = false;
};

template<class Selector, class... ObservableN>
struct is_combine_latest_selector : public std::conditional<
    is_combine_latest_selector_check<Selector, ObservableN...>::value, 
    is_combine_latest_selector_check<Selector, ObservableN...>, 
    invalid_combine_latest_selector<Selector, ObservableN...>>::type {
};

template<class Selector, class... ON>
using result_combine_latest_selector_t = typename is_combine_latest_selector<Selector, ON...>::type;

template<class Coordination, class Selector, class... ObservableN>
struct combine_latest_traits {

    typedef std::tuple<ObservableN...> tuple_source_type;
    typedef std::tuple<rxu::detail::maybe<typename ObservableN::value_type>...> tuple_source_value_type;

    typedef rxu::decay_t<Selector> selector_type;
    typedef rxu::decay_t<Coordination> coordination_type;

    typedef typename is_combine_latest_selector<selector_type, ObservableN...>::type value_type;
};

template<class Coordination, class Selector, class... ObservableN>
struct combine_latest : public operator_base<rxu::value_type_t<combine_latest_traits<Coordination, Selector, ObservableN...>>>
{
    typedef combine_latest<Coordination, Selector, ObservableN...> this_type;

    typedef combine_latest_traits<Coordination, Selector, ObservableN...> traits;

    typedef typename traits::tuple_source_type tuple_source_type;
    typedef typename traits::tuple_source_value_type tuple_source_value_type;

    typedef typename traits::selector_type selector_type;

    typedef typename traits::coordination_type coordination_type;
    typedef typename coordination_type::coordinator_type coordinator_type;

    struct values
    {
        values(tuple_source_type o, selector_type s, coordination_type sf)
            : source(std::move(o))
            , selector(std::move(s))
            , coordination(std::move(sf))
        {
        }
        tuple_source_type source;
        selector_type selector;
        coordination_type coordination;
    };
    values initial;

    combine_latest(coordination_type sf, selector_type s, tuple_source_type ts)
        : initial(std::move(ts), std::move(s), std::move(sf))
    {
    }

    template<int Index, class State>
    void subscribe_one(std::shared_ptr<State> state) const {

        typedef typename std::tuple_element<Index, tuple_source_type>::type::value_type source_value_type;

        composite_subscription innercs;

        // when the out observer is unsubscribed all the
        // inner subscriptions are unsubscribed as well
        state->out.add(innercs);

        auto source = on_exception(
            [&](){return state->coordinator.in(std::get<Index>(state->source));},
            state->out);
        if (source.empty()) {
            return;
        }

        // this subscribe does not share the observer subscription
        // so that when it is unsubscribed the observer can be called
        // until the inner subscriptions have finished
        auto sink = make_subscriber<source_value_type>(
            state->out,
            innercs,
        // on_next
            [state](source_value_type st) {
                auto& value = std::get<Index>(state->latest);

                if (value.empty()) {
                    ++state->valuesSet;
                }

                value.reset(st);

                if (state->valuesSet == sizeof... (ObservableN)) {
                    auto values = rxu::surely(state->latest);
                    auto selectedResult = rxu::apply(values, state->selector);
                    state->out.on_next(selectedResult);
                }
            },
        // on_error
            [state](std::exception_ptr e) {
                state->out.on_error(e);
            },
        // on_completed
            [state]() {
                if (--state->pendingCompletions == 0) {
                    state->out.on_completed();
                }
            }
        );
        auto selectedSink = on_exception(
            [&](){return state->coordinator.out(sink);},
            state->out);
        if (selectedSink.empty()) {
            return;
        }
        source->subscribe(std::move(selectedSink.get()));
    }
    template<class State, int... IndexN>
    void subscribe_all(std::shared_ptr<State> state, rxu::values<int, IndexN...>) const {
        bool subscribed[] = {(subscribe_one<IndexN>(state), true)...};
        subscribed[0] = (*subscribed); // silence warning
    }

    template<class Subscriber>
    void on_subscribe(Subscriber scbr) const {
        static_assert(is_subscriber<Subscriber>::value, "subscribe must be passed a subscriber");

        typedef Subscriber output_type;

        struct combine_latest_state_type
            : public std::enable_shared_from_this<combine_latest_state_type>
            , public values
        {
            combine_latest_state_type(values i, coordinator_type coor, output_type oarg)
                : values(std::move(i))
                , pendingCompletions(sizeof... (ObservableN))
                , valuesSet(0)
                , coordinator(std::move(coor))
                , out(std::move(oarg))
            {
            }

            // on_completed on the output must wait until all the
            // subscriptions have received on_completed
            mutable int pendingCompletions;
            mutable int valuesSet;
            mutable tuple_source_value_type latest;
            coordinator_type coordinator;
            output_type out;
        };

        auto coordinator = initial.coordination.create_coordinator(scbr.get_subscription());

        // take a copy of the values for each subscription
        auto state = std::make_shared<combine_latest_state_type>(initial, std::move(coordinator), std::move(scbr));

        subscribe_all(state, typename rxu::values_from<int, sizeof...(ObservableN)>::type());
    }
};

}

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

}

template<> 
struct member_overload<combine_latest_tag>
{
    template<class Observable, class... ObservableN, 
        class Enabled = rxu::enable_if_all_true_type_t<
            all_observables<Observable, ObservableN...>>,
        class combine_latest = rxo::detail::combine_latest<identity_one_worker, rxu::detail::pack, rxu::decay_t<Observable>, rxu::decay_t<ObservableN>...>,
        class Value = rxu::value_type_t<combine_latest>,
        class Result = observable<Value, combine_latest>>
    static Result member(Observable&& o, ObservableN&&... on)
    {
        return Result(combine_latest(identity_current_thread(), rxu::pack(), std::make_tuple(std::forward<Observable>(o), std::forward<ObservableN>(on)...)));
    }

    template<class Observable, class Selector, class... ObservableN,
        class Enabled = rxu::enable_if_all_true_type_t<
            operators::detail::is_combine_latest_selector<Selector, Observable, ObservableN...>,
            all_observables<Observable, ObservableN...>>,
        class ResolvedSelector = rxu::decay_t<Selector>,
        class combine_latest = rxo::detail::combine_latest<identity_one_worker, ResolvedSelector, rxu::decay_t<Observable>, rxu::decay_t<ObservableN>...>,
        class Value = rxu::value_type_t<combine_latest>,
        class Result = observable<Value, combine_latest>>
    static Result member(Observable&& o, Selector&& s, ObservableN&&... on)
    {
        return Result(combine_latest(identity_current_thread(), std::forward<Selector>(s), std::make_tuple(std::forward<Observable>(o), std::forward<ObservableN>(on)...)));
    }

    template<class Coordination, class Observable, class... ObservableN, 
        class Enabled = rxu::enable_if_all_true_type_t<
            is_coordination<Coordination>,
            all_observables<Observable, ObservableN...>>,
        class combine_latest = rxo::detail::combine_latest<Coordination, rxu::detail::pack, rxu::decay_t<Observable>, rxu::decay_t<ObservableN>...>,
        class Value = rxu::value_type_t<combine_latest>,
        class Result = observable<Value, combine_latest>>
    static Result member(Observable&& o, Coordination&& cn, ObservableN&&... on)
    {
        return Result(combine_latest(std::forward<Coordination>(cn), rxu::pack(), std::make_tuple(std::forward<Observable>(o), std::forward<ObservableN>(on)...)));
    }

    template<class Coordination, class Selector, class Observable, class... ObservableN,
        class Enabled = rxu::enable_if_all_true_type_t<
            is_coordination<Coordination>,
            operators::detail::is_combine_latest_selector<Selector, Observable, ObservableN...>,
            all_observables<Observable, ObservableN...>>,
        class ResolvedSelector = rxu::decay_t<Selector>,
        class combine_latest = rxo::detail::combine_latest<Coordination, ResolvedSelector, rxu::decay_t<Observable>, rxu::decay_t<ObservableN>...>,
        class Value = rxu::value_type_t<combine_latest>,
        class Result = observable<Value, combine_latest>>
    static Result member(Observable&& o, Coordination&& cn, Selector&& s, ObservableN&&... on)
    {
        return Result(combine_latest(std::forward<Coordination>(cn), std::forward<Selector>(s), std::make_tuple(std::forward<Observable>(o), std::forward<ObservableN>(on)...)));
    }

    template<class... AN>
    static operators::detail::combine_latest_invalid_t<AN...> member(const AN&...) {
        std::terminate();
        return {};
        static_assert(sizeof...(AN) == 10000, "combine_latest takes (optional Coordination, optional Selector, required Observable, optional Observable...), Selector takes (Observable::value_type...)");
    } 
};

}

#endif