scan.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/AlexInLog/ReactivePlusPlus
//
 
#pragma once
 
#include <rpp/operators/fwd.hpp>
 
#include <rpp/defs.hpp>
#include <rpp/operators/details/strategy.hpp>
#include <rpp/utils/utils.hpp>
 
#include <optional>
 
namespace rpp::operators::details
{
    template<rpp::constraint::observer TObserver, rpp::constraint::decayed_type Seed, rpp::constraint::decayed_type Fn>
    struct scan_observer_strategy
    {
        static constexpr auto preferred_disposables_mode = rpp::details::observers::disposables_mode::None;
 
        RPP_NO_UNIQUE_ADDRESS TObserver    observer;
        RPP_NO_UNIQUE_ADDRESS mutable Seed seed;
        RPP_NO_UNIQUE_ADDRESS Fn           fn;
 
        RPP_CALL_DURING_CONSTRUCTION(
            observer.on_next(utils::as_const(seed)););
 
        template<typename T>
        void on_next(T&& v) const
        {
            seed = fn(std::move(seed), std::forward<T>(v));
            observer.on_next(utils::as_const(seed));
        }
 
        void on_error(const std::exception_ptr& err) const { observer.on_error(err); }
 
        void on_completed() const { observer.on_completed(); }
 
        void set_upstream(const disposable_wrapper& d) { observer.set_upstream(d); }
 
        bool is_disposed() const { return observer.is_disposed(); }
    };
 
    template<rpp::constraint::decayed_type InitialValue, rpp::constraint::decayed_type Fn>
    struct scan_t : lift_operator<scan_t<InitialValue, Fn>, InitialValue, Fn>
    {
        using operators::details::lift_operator<scan_t<InitialValue, Fn>, InitialValue, Fn>::lift_operator;
 
        template<rpp::constraint::decayed_type T>
        struct operator_traits
        {
            static_assert(std::is_invocable_r_v<InitialValue, Fn, InitialValue&&, T>, "Accumulator is not invocable with Seed&& abnd T returning Seed");
 
            using result_type = InitialValue;
 
            template<rpp::constraint::observer_of_type<result_type> TObserver>
            using observer_strategy = scan_observer_strategy<TObserver, InitialValue, Fn>;
        };
 
        template<rpp::details::observables::constraint::disposables_strategy Prev>
        using updated_optimal_disposables_strategy = Prev;
    };
 
    template<rpp::constraint::observer TObserver, rpp::constraint::decayed_type Fn>
    struct scan_no_seed_observer_strategy
    {
        static constexpr auto preferred_disposables_mode = rpp::details::observers::disposables_mode::None;
 
        using Seed = rpp::utils::extract_observer_type_t<TObserver>;
 
        RPP_NO_UNIQUE_ADDRESS TObserver observer;
        RPP_NO_UNIQUE_ADDRESS Fn        fn;
        mutable std::optional<Seed>     seed{};
 
        template<rpp::constraint::decayed_same_as<Seed> T>
        void on_next(T&& v) const
        {
            if (seed)
                seed = fn(std::move(seed).value(), std::forward<T>(v));
            else
                seed = std::forward<T>(v);
 
            observer.on_next(utils::as_const(seed.value()));
        }
 
        void on_error(const std::exception_ptr& err) const { observer.on_error(err); }
 
        void on_completed() const { observer.on_completed(); }
 
        void set_upstream(const disposable_wrapper& d) { observer.set_upstream(d); }
 
        bool is_disposed() const { return observer.is_disposed(); }
    };
 
    template<rpp::constraint::decayed_type Fn>
    struct scan_no_seed_t : lift_operator<scan_no_seed_t<Fn>, Fn>
    {
        using lift_operator<scan_no_seed_t<Fn>, Fn>::lift_operator;
 
        template<rpp::constraint::decayed_type T>
        struct operator_traits
        {
            static_assert(std::is_invocable_r_v<T, Fn, T&&, T>, "Accumulator is not invocable with T&& abnd T returning T");
 
            using result_type = T;
 
            template<rpp::constraint::observer_of_type<result_type> TObserver>
            using observer_strategy = scan_no_seed_observer_strategy<TObserver, Fn>;
        };
 
        template<rpp::details::observables::constraint::disposables_strategy Prev>
        using updated_optimal_disposables_strategy = Prev;
    };
} // namespace rpp::operators::details
 
namespace rpp::operators
{
     * @see https://reactivex.io/documentation/operators/scan.html
     */
    template<typename InitialValue, typename Fn>
        requires (!utils::is_not_template_callable<Fn> || std::same_as<std::decay_t<InitialValue>, std::invoke_result_t<Fn, std::decay_t<InitialValue> &&, rpp::utils::convertible_to_any>>)
    auto scan(InitialValue&& initial_value, Fn&& accumulator)
    {
        return details::scan_t<std::decay_t<InitialValue>, std::decay_t<Fn>>{std::forward<InitialValue>(initial_value), std::forward<Fn>(accumulator)};
    }

     *
     * @par Example
     * @snippet scan.cpp scan_no_seed
     *
     * @ingroup transforming_operators
     * @see https://reactivex.io/documentation/operators/scan.html
     */
    template<typename Fn>
    auto scan(Fn&& accumulator)
    {
        return details::scan_no_seed_t<std::decay_t<Fn>>{std::forward<Fn>(accumulator)};
    }
} // namespace rpp::operators