retry.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/operators/fwd.hpp>
 
#include <rpp/defs.hpp>
#include <rpp/operators/details/strategy.hpp>
 
namespace rpp::operators::details
{
    template<rpp::constraint::observer TObserver, constraint::decayed_type Observable>
    struct retry_state_t final : public rpp::composite_disposable
    {
        retry_state_t(TObserver&& in_observer, const Observable& observable, std::optional<size_t> count)
            : count{count}
            , observer(std::move(in_observer))
            , observable(observable)
 
        {
        }
 
        std::optional<size_t> count;
        std::atomic<bool>     is_inside_drain{};
 
        RPP_NO_UNIQUE_ADDRESS TObserver  observer;
        RPP_NO_UNIQUE_ADDRESS Observable observable;
    };
 
    template<rpp::constraint::observer TObserver, typename TObservable>
    void drain(const std::shared_ptr<retry_state_t<TObserver, TObservable>>& state);
 
    template<rpp::constraint::observer TObserver, typename TObservable>
    struct retry_observer_strategy
    {
        static constexpr auto preferred_disposables_mode = rpp::details::observers::disposables_mode::None;
 
        std::shared_ptr<retry_state_t<TObserver, TObservable>> state;
        mutable bool                                           locally_disposed{};
 
        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
        {
            locally_disposed = true;
            if (state->count == 0)
            {
                state->observer.on_error(err);
                return;
            }
 
            state->clear();
 
            if (state->is_inside_drain.exchange(false, std::memory_order::seq_cst))
                return;
 
            drain(state);
        }
 
        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>
    void drain(const std::shared_ptr<retry_state_t<TObserver, TObservable>>& state)
    {
        while (!state->is_disposed())
        {
            if (state->count)
                --state->count.value();
            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(observer<value_type, retry_observer_strategy<TObserver, TObservable>>{state});
 
                if (state->is_inside_drain.exchange(false, std::memory_order::seq_cst))
                    return;
            }
            catch (...)
            {
                state->observer.on_error(std::current_exception());
                return;
            }
        }
    }
 
    struct retry_t
    {
        const std::optional<size_t> count{};
 
        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&& observble) const
        {
            const auto d   = disposable_wrapper_impl<retry_state_t<std::decay_t<TObserver>, std::decay_t<TObservable>>>::make(std::forward<TObserver>(observer), std::forward<TObservable>(observble), count ? count.value() + 1 : count);
            auto       ptr = d.lock();
 
            ptr->observer.set_upstream(d.as_weak());
            drain(ptr);
        }
    };
} // namespace rpp::operators::details
 
namespace rpp::operators
{
    inline auto retry(size_t count)
    {
        return details::retry_t{count};
    }
 
    inline auto retry()
    {
        return details::retry_t{};
    }
} // namespace rpp::operators