reduce.hpp

//                  ReactivePlusPlus library
//
//          Copyright Aleksey Loginov 2022 - 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/details/member_overload.hpp>
 
namespace rpp::details
{
struct reduce_tag;
}
 
namespace rpp::details
{
// accepts Result and Type and returns Result
template<typename Fn, typename Result, typename Type>
concept reduce_accumulator = std::is_invocable_r_v<std::decay_t<Result>, Fn, std::decay_t<Result>, std::decay_t<Type>>;
 
template<typename T>
concept is_can_be_summed = requires(T t)
{
    { t + t } -> std::convertible_to<T>;
};
 
template<typename T, typename CastBeforeDrop>
concept is_can_be_averaged = is_can_be_summed<T> && requires(CastBeforeDrop nt)
{
    { nt / size_t{} };
};
 
template<constraint::decayed_type Type, constraint::decayed_type Seed, reduce_accumulator<Seed, Type> AccumulatorFn, std::invocable<Seed&&> ResultSelectorFn>
struct reduce_impl;
 
template<constraint::decayed_type CastBeforeDivide, constraint::observable TObs>
auto average_impl(TObs&& observable);
 
template<constraint::observable TObs>
auto sum_impl(TObs&& observable);
 
template<constraint::observable TObs>
auto count_impl(TObs&& observable);
 
template<constraint::observable TObs, typename Comparator>
auto min_impl(TObs&& observable, Comparator&& comparator);
 
template<constraint::observable TObs, typename Comparator>
auto max_impl(TObs&& observable, Comparator&& comparator);
 
template<constraint::decayed_type Type, typename SpecificObservable>
struct member_overload<Type, SpecificObservable, reduce_tag>
{
    template<typename Seed, reduce_accumulator<Seed, Type> AccumulatorFn, std::invocable<Seed&&> ResultSelectorFn = std::identity>
    auto reduce(Seed&& initial_seed, AccumulatorFn&& accumulator, ResultSelectorFn&& result_selector = {}) const & requires is_header_included<reduce_tag, Seed, AccumulatorFn, ResultSelectorFn>
    {
        return static_cast<const SpecificObservable*>(this)->template lift<utils::decayed_invoke_result_t<ResultSelectorFn, std::decay_t<Seed>>>(
            reduce_impl<Type, std::decay_t<Seed>, std::decay_t<AccumulatorFn>, std::decay_t<ResultSelectorFn>>{
                                         std::forward<Seed>(initial_seed),
                                         std::forward<AccumulatorFn>(accumulator),
                                         std::forward<ResultSelectorFn>(result_selector)});
    }
 
    template<typename Seed, reduce_accumulator<Seed, Type> AccumulatorFn, std::invocable<Seed&&> ResultSelectorFn = std::identity>
    auto reduce(Seed&& initial_seed, AccumulatorFn&& accumulator, ResultSelectorFn&& result_selector = {}) && requires is_header_included<reduce_tag, Seed, AccumulatorFn, ResultSelectorFn>
    {
        return std::move(*static_cast<SpecificObservable*>(this)).template lift<utils::decayed_invoke_result_t<ResultSelectorFn, std::decay_t<Seed>>>(
            reduce_impl<Type, std::decay_t<Seed>, std::decay_t<AccumulatorFn>, std::decay_t<ResultSelectorFn>>{
                                         std::forward<Seed>(initial_seed),
                                         std::forward<AccumulatorFn>(accumulator),
                                         std::forward<ResultSelectorFn>(result_selector)});
    }
 
    template<typename CastBeforeDivide = Type, typename ...Args>
    auto average() const & requires (is_header_included<reduce_tag, CastBeforeDivide, Args...> && is_can_be_averaged<Type, CastBeforeDivide>)
    {
        return average_impl<CastBeforeDivide>(*static_cast<const SpecificObservable*>(this));
    }
 
    template<typename CastBeforeDivide = Type, typename ...Args>
    auto average() && requires (is_header_included<reduce_tag, CastBeforeDivide, Args...> && is_can_be_averaged<Type, CastBeforeDivide>)
    {
        return average_impl<CastBeforeDivide>(std::move(*static_cast<SpecificObservable*>(this)));
    }
 
    
    template<typename ...Args>
    auto sum() const & requires (is_header_included<reduce_tag, Args...> && is_can_be_summed<Type>)
    {
        return sum_impl(*static_cast<const SpecificObservable*>(this));
    }
 
    template<typename ...Args>
    auto sum() && requires (is_header_included<reduce_tag, Args...> && is_can_be_summed<Type>)
    {
        return sum_impl(std::move(*static_cast<SpecificObservable*>(this)));
    }
 
    template<typename ...Args>
    auto count() const & requires is_header_included<reduce_tag, Args...>
    {
        return count_impl(*static_cast<const SpecificObservable*>(this));
    }
 
    template<typename ...Args>
    auto count() && requires is_header_included<reduce_tag, Args...>
    {
        return count_impl(std::move(*static_cast<SpecificObservable*>(this)));
    }
 
    template<std::strict_weak_order<Type, Type> Comparator = std::less<Type>, typename ...Args>
    auto min(Comparator&& comparator = {}) const & requires is_header_included<reduce_tag, Comparator, Args...>
    {
        return min_impl(*static_cast<const SpecificObservable*>(this), std::forward<Comparator>(comparator));
    }
 
    template<std::strict_weak_order<Type, Type> Comparator = std::less<Type>, typename ...Args>
    auto min(Comparator&& comparator = {}) && requires is_header_included<reduce_tag, Comparator, Args...>
    {
        return min_impl(std::move(*static_cast<SpecificObservable*>(this)), std::forward<Comparator>(comparator));
    }
 
    template<std::strict_weak_order<Type, Type> Comparator = std::less<Type>, typename ...Args>
    auto max(Comparator&& comparator = {}) const & requires is_header_included<reduce_tag, Comparator, Args...>
    {
        return max_impl(*static_cast<const SpecificObservable*>(this), std::forward<Comparator>(comparator));
    }
 
    template<std::strict_weak_order<Type, Type> Comparator = std::less<Type>, typename ...Args>
    auto max(Comparator&& comparator = {}) && requires is_header_included<reduce_tag, Comparator, Args...>
    {
        return max_impl(std::move(*static_cast<SpecificObservable*>(this)), std::forward<Comparator>(comparator));
    }
};
} // namespace rpp::details