limen/include/dispatch.h

#pragma once
#include <cstdint>
#include <cstdio>
#include <optional>
#include <span>
#include "wire.h"
#include "timer_queue.h"
#include "net.h"
#include "prepend_buffer.h"
#include "udp.h"

uint16_t dispatch_listen_port_be();

struct responder {
    uint32_t message_id;
    udp::address reply_to;

    template <typename T>
    void respond(const T& msg) const {
        const auto& ns = net::get_state();
        prepend_buffer<4096> buf;
        span_writer out(buf.payload_ptr(), 2048);
        auto r = encode_response_into(out, message_id, msg);
        if (!r) {
            return;
        }
        buf.append(*r);
        udp::prepend(buf, reply_to.mac, ns.mac, ns.ip, reply_to.ip,
                     dispatch_listen_port_be(), reply_to.port, *r);
        net::send_raw(buf.span());
    }
};

using handler_fn = void (*)(const responder& resp, std::span<const uint8_t> payload);

struct handler_entry {
    int8_t type_id;
    handler_fn handle;
};

template <typename Req, auto Fn>
void typed_handler(const responder& resp, std::span<const uint8_t> payload) {
    msgpack::parser p(payload.data(), static_cast<int>(payload.size()));
    Req req;
    auto tup = req.as_tuple();
    auto r = msgpack::unpack(p, tup);
    if (!r) {
        char err[64];
        snprintf(err, sizeof(err), "decode request ext_id=%d: msgpack error %d",
                 Req::ext_id, static_cast<int>(r.error()));
        resp.respond(DeviceError{1, err});
        return;
    }
    auto result = Fn(resp, req);
    if (result)
        resp.respond(*result);
}

void dispatch_init(uint16_t listen_port_be);
timer_handle dispatch_schedule_ms(uint32_t ms, void (*fn)());
bool dispatch_cancel_timer(timer_handle h);
[[noreturn]] void dispatch_run(std::span<const handler_entry> handlers);