retry_when.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/observables/fwd.hpp>
#include <rpp/operators/fwd.hpp>
 
#include <rpp/defs.hpp>
#include <rpp/operators/details/strategy.hpp>
#include <rpp/utils/constraints.hpp>
#include <rpp/utils/utils.hpp>
 
namespace rpp::operators::details
{
    template<rpp::constraint::observer TObserver,
             typename TObservable,
             typename TNotifier>
    struct retry_when_state final : public rpp::composite_disposable
    {
        retry_when_state(TObserver&& observer, const TObservable& observable, const TNotifier& notifier)
            : observer(std::move(observer))
            , observable(observable)
            , notifier(notifier)
        {
        }
 
        std::atomic_bool is_inside_drain{};
 
        RPP_NO_UNIQUE_ADDRESS TObserver   observer;
        RPP_NO_UNIQUE_ADDRESS TObservable observable;
        RPP_NO_UNIQUE_ADDRESS TNotifier   notifier;
    };
 
    template<rpp::constraint::observer TObserver, typename TObservable, typename TNotifier>
    void drain(const std::shared_ptr<retry_when_state<TObserver, TObservable, TNotifier>>& state);
 
    template<rpp::constraint::observer TObserver,
             typename TObservable,
             typename TNotifier>
    struct retry_when_impl_inner_strategy
    {
        static constexpr auto preferred_disposables_mode = rpp::details::observers::disposables_mode::None;
 
        std::shared_ptr<retry_when_state<TObserver, TObservable, TNotifier>> state;
        mutable bool                                                         locally_disposed{};
 
        template<typename T>
        void on_next(T&&) const
        {
            locally_disposed = true;
            state->clear();
 
            if (state->is_inside_drain.exchange(false, std::memory_order::seq_cst))
                return;
 
            drain<TObserver, TObservable, TNotifier>(state);
        }
 
        void on_error(const std::exception_ptr& err) const
        {
            locally_disposed = true;
            state->observer.on_error(err);
        }
 
        void on_completed() const
        {
            locally_disposed = true;
            state->observer.on_completed();
        }
 
        void set_upstream(const disposable_wrapper& d) const { state->add(d); }
 
        bool is_disposed() const { return locally_disposed || state->is_disposed(); }
    };
 
    template<rpp::constraint::observer TObserver,
             typename TObservable,
             typename TNotifier>
    struct retry_when_impl_strategy
    {
        static constexpr auto preferred_disposables_mode = rpp::details::observers::disposables_mode::None;
 
        std::shared_ptr<retry_when_state<TObserver, TObservable, TNotifier>> 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
        {
            try
            {
                state->notifier(err).subscribe(retry_when_impl_inner_strategy<TObserver, TObservable, TNotifier>{state});
            }
            catch (...)
            {
                state->observer.on_error(std::current_exception());
            }
        }
 
        void on_completed() const
        {
            state->observer.on_completed();
        }
 
        void set_upstream(const disposable_wrapper& d) { state->add(d); }
 
        bool is_disposed() const { return state->is_disposed(); }
    };
 
    template<rpp::constraint::observer TObserver, typename TObservable, typename TNotifier>
    void drain(const std::shared_ptr<retry_when_state<TObserver, TObservable, TNotifier>>& state)
    {
        while (!state->is_disposed())
        {
            state->is_inside_drain.store(true, std::memory_order::seq_cst);
            try
            {
                using value_type = rpp::utils::extract_observer_type_t<TObserver>;
                state->observable.subscribe(rpp::observer<value_type, retry_when_impl_strategy<TObserver, TObservable, TNotifier>>{state});
 
                if (state->is_inside_drain.exchange(false, std::memory_order::seq_cst))
                    return;
            }
            catch (...)
            {
                state->observer.on_error(std::current_exception());
                return;
            }
        }
    }
 
    template<rpp::constraint::decayed_type TNotifier>
    struct retry_when_t
    {
        RPP_NO_UNIQUE_ADDRESS TNotifier notifier;
 
        template<rpp::constraint::decayed_type T>
        struct operator_traits
        {
            using result_type = T;
        };
 
        template<rpp::details::observables::constraint::disposables_strategy Prev>
        using updated_optimal_disposables_strategy = rpp::details::observables::fixed_disposables_strategy<1>;
 
        template<rpp::constraint::observer TObserver, typename TObservable>
        void subscribe(TObserver&& observer, TObservable&& observable) const
        {
            const auto d   = disposable_wrapper_impl<retry_when_state<std::decay_t<TObserver>, std::decay_t<TObservable>, std::decay_t<TNotifier>>>::make(std::forward<TObserver>(observer), std::forward<TObservable>(observable), notifier);
            auto       ptr = d.lock();
 
            ptr->observer.set_upstream(d.as_weak());
            drain(ptr);
        }
    };
} // namespace rpp::operators::details
 
namespace rpp::operators
{
    template<typename TNotifier>
        requires rpp::constraint::observable<std::invoke_result_t<TNotifier, std::exception_ptr>>
    auto retry_when(TNotifier&& notifier)
    {
        return details::retry_when_t<std::decay_t<TNotifier>>{std::forward<TNotifier>(notifier)};
    }
} // namespace rpp::operators