route.hpp

/*
 * This file is part of libtcspc
 * Copyright 2019-2026 Board of Regents of the University of Wisconsin System
 * SPDX-License-Identifier: MIT
 */
 
#pragma once
 
#include "common.hpp"
#include "errors.hpp"
#include "int_arith.hpp"
#include "introspect.hpp"
#include "numeric_traits.hpp"
#include "processor.hpp"
#include "type_erased_processor.hpp"
#include "type_list.hpp"
 
#include <algorithm>
#include <array>
#include <concepts>
#include <cstddef>
#include <exception>
#include <functional>
#include <limits>
#include <numeric>
#include <type_traits>
#include <utility>
 
namespace tcspc {

template <typename R, typename... Events>
concept router_for = std::move_constructible<R> &&
                     (... && requires(R const &r, Events const &e) {
                         { r(e) } -> std::same_as<std::size_t>;
                     });
 
namespace internal {
 
// Design note: Currently the router produces a single downstream index per
// event. We could generalize this so that the router produces a boolean mask
// of the downstreams, such that a single event can be routed to multiple
// downstreams. But let's keep it simple. If necessary, a "multiroute"
// processor can be added.
 
template <typename Router, typename EventList> struct router_for_each_event;
 
template <typename Router, typename... Events>
struct router_for_each_event<Router, type_list<Events...>>
    : std::bool_constant<router_for<Router, Events...>> {};
 
// We do not require Downstream to handle all of RoutedEventList.
template <typename RoutedEventList, typename Router, std::size_t N,
          typename Downstream>
    requires type_list_like<RoutedEventList> && processor<Downstream> &&
             router_for_each_event<Router, RoutedEventList>::value
class route_homogeneous {
    Router router;
    std::array<Downstream, N> downstreams;
 
    LIBTCSPC_NOINLINE void flush_all_but(Downstream &excluded) {
        for (auto &d : downstreams) {
            if (&d != &excluded) {
                try {
                    d.flush();
                } catch (end_of_processing const &) {
                    ;
                }
            }
        }
    }
 
  public:
    explicit route_homogeneous(Router router,
                               std::array<Downstream, N> downstreams)
        : router(std::move(router)), downstreams(std::move(downstreams)) {}
 
    [[nodiscard]] auto introspect_node() const -> processor_info {
        return processor_info(this, "route_homogeneous");
    }
 
    [[nodiscard]] auto introspect_graph() const -> processor_graph {
        return std::transform_reduce(
            downstreams.begin(), downstreams.end(), processor_graph(),
            merge_processor_graphs, [this](auto const &d) {
                return d.introspect_graph().push_entry_point(this);
            });
    }
 
    template <typename Event>
        requires(convertible_to_type_list_member<std::remove_cvref_t<Event>,
                                                 RoutedEventList> and
                 handler_for<Downstream, std::remove_cvref_t<Event>>)
    void handle(Event &&event) {
        std::size_t index = router(std::as_const(event));
        if (index >= N)
            return;
        try {
            downstreams[index].handle(std::forward<Event>(event));
        } catch (end_of_processing const &) {
            flush_all_but(downstreams[index]);
            throw;
        }
    }
 
    template <typename Event>
        requires(not convertible_to_type_list_member<
                     std::remove_cvref_t<Event>, RoutedEventList> and
                 handler_for<Downstream, std::remove_cvref_t<Event>>)
    void handle(Event &&event) {
        for (auto &d : downstreams) {
            try {
                d.handle(std::as_const(event));
            } catch (end_of_processing const &) {
                flush_all_but(d);
                throw;
            }
        }
    }
 
    void flush() {
        std::exception_ptr end;
        for (auto &d : downstreams) {
            try {
                d.flush();
            } catch (end_of_processing const &) {
                if (not end)
                    end = std::current_exception();
            }
        }
        if (end)
            std::rethrow_exception(end);
    }
};
 
} // namespace internal

template <typename RoutedEventList, typename Router, std::size_t N,
          typename Downstream>
auto route_homogeneous(Router router, std::array<Downstream, N> downstreams) {
    return internal::route_homogeneous<RoutedEventList, Router, N, Downstream>(
        std::move(router), std::move(downstreams));
}

template <typename RoutedEventList, typename Router, typename... Downstreams>
auto route_homogeneous(Router router, Downstreams... downstreams) {
    return route_homogeneous<RoutedEventList, Router>(
        std::move(router), std::array{std::move(downstreams)...});
}

template <typename RoutedEventList, typename BroadcastEventList = type_list<>,
          typename Router, typename... Downstreams>
auto route(Router router, Downstreams... downstreams) {
    static_assert(type_list_like<RoutedEventList>);
    static_assert(type_list_like<BroadcastEventList>);
    static_assert(
        type_list_size_v<
            type_list_intersection_t<RoutedEventList, BroadcastEventList>> ==
            0,
        "routed event list and broadcast event list must not overlap");
    using type_erased_downstream = type_erased_processor<
        type_list_union_t<RoutedEventList, BroadcastEventList>>;
    return route_homogeneous<RoutedEventList, Router, sizeof...(Downstreams),
                             type_erased_downstream>(
        std::move(router),
        std::array<type_erased_downstream, sizeof...(Downstreams)>{
            type_erased_downstream(std::move(downstreams))...});
}

class null_router {
  public:
    template <typename Event>
    auto operator()(Event const & /* event */) const -> std::size_t {
        return std::size_t(-1);
    }
};

template <std::size_t N, typename NumericTraits = default_numeric_traits>
class channel_router {
    std::array<typename NumericTraits::channel_type, N> channels;
    std::array<std::size_t, N> indices;
 
  public:
    template <typename ChannelIndexPair>
    explicit channel_router(
        std::array<ChannelIndexPair, N> const &channel_indices)
        : channels(std::invoke([&] {
              std::array<typename NumericTraits::channel_type, N> ret{};
              std::transform(channel_indices.begin(), channel_indices.end(),
                             ret.begin(),
                             [](auto p) { return std::get<0>(p); });
              return ret;
          })),
          indices(std::invoke([&] {
              std::array<std::size_t, N> ret{};
              std::transform(channel_indices.begin(), channel_indices.end(),
                             ret.begin(),
                             [](auto p) { return std::get<1>(p); });
              return ret;
          })) {
 
        static_assert(
            std::is_convertible_v<decltype(std::get<0>(channel_indices[0])),
                                  typename NumericTraits::channel_type> &&
                std::is_convertible_v<
                    decltype(std::get<1>(channel_indices[0])), std::size_t>,
            "channel_indices must be an array of pair-like convertible to (channel, std::size_t)");
    }

    template <typename Event>
    auto operator()(Event const &event) const -> std::size_t {
        static_assert(std::is_same_v<decltype(event.channel),
                                     typename NumericTraits::channel_type>);
        auto it = std::find(channels.begin(), channels.end(), event.channel);
        if (it == channels.end())
            return std::numeric_limits<std::size_t>::max();
        return indices[internal::as_unsigned(
            std::distance(channels.begin(), it))];
    }
};

template <std::size_t N, typename Downstream>
auto broadcast_homogeneous(std::array<Downstream, N> downstreams) {
    return route_homogeneous<type_list<>, null_router, N, Downstream>(
        null_router(), std::move(downstreams));
}

template <typename... Downstreams>
auto broadcast_homogeneous(Downstreams... downstreams) {
    auto arr = std::array{std::move(downstreams)...};
    return broadcast_homogeneous(std::move(arr));
}

template <typename BroadcastEventList, typename... Downstreams>
auto broadcast(Downstreams... downstreams) {
    return route<type_list<>, BroadcastEventList, null_router, Downstreams...>(
        null_router(), std::move(downstreams)...);
}
 
} // namespace tcspc