concat.hpp

//                   ReactivePlusPlus library
//
//           Copyright Aleksey Loginov 2023 - present.
//  Distributed under the Boost Software License, Version 1.0.
//     (See accompanying file LICENSE_1_0.txt or copy at
//           https://www.boost.org/LICENSE_1_0.txt)
//
//  Project home: https://github.com/victimsnino/ReactivePlusPlus
 
#pragma once
 
#include <rpp/sources/fwd.hpp>
 
#include <rpp/memory_model.hpp>
#include <rpp/observables/observable.hpp>
#include <rpp/observables/variant_observable.hpp>
#include <rpp/operators/details/strategy.hpp>
#include <rpp/sources/from.hpp>
 
#include <exception>
 
namespace rpp::details
{
    template<rpp::constraint::observer TObserver, constraint::decayed_type PackedContainer>
    struct concat_state_t : public rpp::composite_disposable
    {
        concat_state_t(TObserver&& in_observer, const PackedContainer& in_container)
            : observer(std::move(in_observer))
            , container(in_container)
        {
            try
            {
                itr = std::cbegin(container);
            }
            catch (...)
            {
                this->observer.on_error(std::current_exception());
            }
        }
 
        RPP_NO_UNIQUE_ADDRESS TObserver                 observer;
        RPP_NO_UNIQUE_ADDRESS PackedContainer           container;
        std::optional<decltype(std::cbegin(container))> itr{};
        std::atomic<bool>                               is_inside_drain{};
    };
 
    template<rpp::constraint::observer TObserver, typename PackedContainer>
    void drain(TObserver&& observer, PackedContainer&& container, size_t index);
 
    template<rpp::constraint::observer TObserver, constraint::decayed_type PackedContainer>
    struct concat_source_observer_strategy
    {
        static constexpr auto preferred_disposables_mode = rpp::details::observers::disposables_mode::Boolean;
 
        std::shared_ptr<concat_state_t<TObserver, PackedContainer>> state{};
 
        template<typename T>
        void on_next(T&& v) const
        {
            state->observer.on_next(std::forward<T>(v));
        }
 
        void on_error(const std::exception_ptr& err) const
        {
            state->observer.on_error(err);
        }
 
        void set_upstream(const disposable_wrapper& d) { state->add(d); }
 
        bool is_disposed() const { return state->is_disposed(); }
 
        void on_completed() const
        {
            state->clear();
 
            if (state->is_inside_drain.exchange(false, std::memory_order::seq_cst))
                return;
 
            drain(state);
        }
    };
 
    template<rpp::constraint::observer TObserver, typename PackedContainer>
    void drain(const std::shared_ptr<concat_state_t<TObserver, PackedContainer>>& state)
    {
        while (!state->is_disposed())
        {
            if (state->itr.value() == std::cend(state->container))
            {
                state->observer.on_completed();
                return;
            }
 
            using value_type = rpp::utils::extract_observable_type_t<utils::iterable_value_t<PackedContainer>>;
            state->is_inside_drain.store(true, std::memory_order::seq_cst);
            try
            {
                (*(state->itr.value()++)).subscribe(observer<value_type, concat_source_observer_strategy<std::decay_t<TObserver>, std::decay_t<PackedContainer>>>{state});
 
                if (state->is_inside_drain.exchange(false, std::memory_order::seq_cst))
                    return;
            }
            catch (...)
            {
                state->observer.on_error(std::current_exception());
                return;
            }
        }
    }
 
    template<constraint::decayed_type PackedContainer>
    struct concat_strategy
    {
        template<typename... Args>
            requires (!constraint::variadic_decayed_same_as<concat_strategy<PackedContainer>, Args...>)
        concat_strategy(Args&&... args)
            : container{std::forward<Args>(args)...}
        {
        }
 
        RPP_NO_UNIQUE_ADDRESS PackedContainer container;
 
        using value_type = rpp::utils::extract_observable_type_t<utils::iterable_value_t<PackedContainer>>;
 
        using optimal_disposables_strategy = rpp::details::observables::default_disposables_strategy;
 
 
        template<constraint::observer_strategy<value_type> Strategy>
        void subscribe(observer<value_type, Strategy>&& obs) const
        {
            const auto d     = disposable_wrapper_impl<concat_state_t<observer<value_type, Strategy>, PackedContainer>>::make(std::move(obs), container);
            const auto state = d.lock();
            state->observer.set_upstream(d.as_weak());
            drain(state);
        }
    };
 
    template<typename PackedContainer, typename... Args>
    auto make_concat_from_iterable(Args&&... args)
    {
        return observable<utils::extract_observable_type_t<utils::iterable_value_t<std::decay_t<PackedContainer>>>, concat_strategy<std::decay_t<PackedContainer>>>{std::forward<Args>(args)...};
    }
} // namespace rpp::details
 
namespace rpp::source
{
     * @par Example
     * @snippet concat.cpp concat_as_source
     *
     * @ingroup creational_operators
     * @see https://reactivex.io/documentation/operators/concat.html
     */
    template<constraint::memory_model MemoryModel /*= memory_model::use_stack*/, rpp::constraint::observable TObservable, rpp::constraint::observable... TObservables>
        requires (std::same_as<rpp::utils::extract_observable_type_t<TObservable>, rpp::utils::extract_observable_type_t<TObservables>> && ...)
    auto concat(TObservable&& obs, TObservables&&... others)
    {
        if constexpr ((rpp::constraint::decayed_same_as<TObservable, TObservables> && ...))
        {
            using inner_container = std::array<std::decay_t<TObservable>, sizeof...(TObservables) + 1>;
            using container       = std::conditional_t<std::same_as<MemoryModel, rpp::memory_model::use_stack>, inner_container, details::shared_container<inner_container>>;
            return rpp::details::make_concat_from_iterable<container>(std::forward<TObservable>(obs), std::forward<TObservables>(others)...);
        }
        else
        {
            using variant_observable_t = rpp::variant_observable<rpp::utils::extract_observable_type_t<TObservable>, std::decay_t<TObservable>, std::decay_t<TObservables>...>;
            return concat<MemoryModel>(variant_observable_t{std::forward<TObservable>(obs)}, variant_observable_t{std::forward<TObservables>(others)}...);
        }
    }

     *
     * @details Actually it subscribes on first observable from emissions. When first observable completes, then it subscribes on second observable from emissions and etc...
     *
     * @param iterable is container with observables to subscribe on
     *
     * @tparam MemoryModel rpp::memory_model strategy used to handle provided observables
     * @note `#include <rpp/operators/concat.hpp>`
     *
     * @par Example
     * @snippet concat.cpp concat_as_source_vector
     *
     * @ingroup creational_operators
     * @see https://reactivex.io/documentation/operators/concat.html
     */
    template<constraint::memory_model MemoryModel /*= memory_model::use_stack*/, constraint::iterable Iterable>
        requires constraint::observable<utils::iterable_value_t<Iterable>>
    auto concat(Iterable&& iterable)
    {
        using Container = std::conditional_t<std::same_as<MemoryModel, rpp::memory_model::use_stack>, std::decay_t<Iterable>, details::shared_container<std::decay_t<Iterable>>>;
        return rpp::details::make_concat_from_iterable<Container>(std::forward<Iterable>(iterable));
    }
} // namespace rpp::source