//
// Copyright (c) 2023-2025 Ivica Siladic, Bruno Iljazovic, Korina Simicevic
//
// Distributed under the Boost Software License, Version 1.0.
// (See accompanying file LICENSE or copy at http://www.boost.org/LICENSE_1_0.txt)
//

#ifndef BOOST_MQTT5_ENDPOINTS_HPP
#define BOOST_MQTT5_ENDPOINTS_HPP

#include <boost/mqtt5/types.hpp>

#include <boost/mqtt5/detail/log_invoke.hpp>

#include <boost/asio/append.hpp>
#include <boost/asio/associated_allocator.hpp>
#include <boost/asio/associated_cancellation_slot.hpp>
#include <boost/asio/associated_executor.hpp>
#include <boost/asio/async_result.hpp>
#include <boost/asio/deferred.hpp>
#include <boost/asio/error.hpp>
#include <boost/asio/experimental/parallel_group.hpp>
#include <boost/asio/ip/tcp.hpp>
#include <boost/asio/post.hpp>
#include <boost/asio/prepend.hpp>
#include <boost/spirit/home/x3.hpp>

#include <array>
#include <chrono>
#include <string>

namespace boost::mqtt5::detail {

namespace asio = boost::asio;

using epoints = asio::ip::tcp::resolver::results_type;

template <typename Owner, typename Handler>
class resolve_op {
    struct on_resolve {};

    Owner& _owner;

    using handler_type = Handler;
    handler_type _handler;

public:
    resolve_op(Owner& owner, Handler&& handler) :
        _owner(owner), _handler(std::move(handler))
    {}

    resolve_op(resolve_op&&) = default;
    resolve_op(const resolve_op&) = delete;

    resolve_op& operator=(resolve_op&&) = default;
    resolve_op& operator=(const resolve_op&) = delete;

    using allocator_type = asio::associated_allocator_t<handler_type>;
    allocator_type get_allocator() const noexcept {
        return asio::get_associated_allocator(_handler);
    }

    using cancellation_slot_type =
        asio::associated_cancellation_slot_t<handler_type>;
    cancellation_slot_type get_cancellation_slot() const noexcept {
        return asio::get_associated_cancellation_slot(_handler);
    }

    using executor_type = asio::associated_executor_t<handler_type>;
    executor_type get_executor() const noexcept {
        return asio::get_associated_executor(_handler);
    }

    void perform() {
        namespace asioex = boost::asio::experimental;

        if (_owner._servers.empty())
            return complete_post(asio::error::host_not_found, {}, {});

        _owner._current_host++;

        if (_owner._current_host + 1 > static_cast<int>(_owner._servers.size())) {
            _owner._current_host = -1;
            return complete_post(asio::error::try_again, {}, {});
        }

        authority_path ap = _owner._servers[_owner._current_host];

        _owner._connect_timer.expires_after(std::chrono::seconds(5));

        auto timed_resolve = asioex::make_parallel_group(
            _owner._resolver.async_resolve(ap.host, ap.port, asio::deferred),
            _owner._connect_timer.async_wait(asio::deferred)
        );

        timed_resolve.async_wait(
            asioex::wait_for_one(),
            asio::append(
                asio::prepend(std::move(*this), on_resolve {}),
                std::move(ap)
            )
        );
    }

    void operator()(
        on_resolve, std::array<std::size_t, 2> ord,
        error_code resolve_ec, epoints epts,
        error_code timer_ec, authority_path ap
    ) {
        if (
            (ord[0] == 0 && resolve_ec == asio::error::operation_aborted) ||
            (ord[0] == 1 && timer_ec == asio::error::operation_aborted)
        )
            return complete(asio::error::operation_aborted, {}, {});

        resolve_ec = timer_ec ? resolve_ec : asio::error::timed_out;
        _owner._log.at_resolve(resolve_ec, ap.host, ap.port, epts);
        if (!resolve_ec)
            return complete(error_code {}, std::move(epts), std::move(ap));

        perform();
    }

private:
    void complete(error_code ec, epoints eps, authority_path ap) {
        std::move(_handler)(ec, std::move(eps), std::move(ap));
    }

    void complete_post(error_code ec, epoints eps, authority_path ap) {
        asio::post(
            _owner.get_executor(),
            asio::prepend(
                std::move(_handler), ec,
                std::move(eps), std::move(ap)
            )
        );

    }
};


template <typename LoggerType>
class endpoints {
    using logger_type = LoggerType;

    asio::ip::tcp::resolver _resolver;
    asio::steady_timer& _connect_timer;

    std::vector<authority_path> _servers;

    int _current_host { -1 };

    log_invoke<logger_type>& _log;

    template <typename Owner, typename Handler>
    friend class resolve_op;

    template <typename T>
    static constexpr auto to_(T& arg) {
        return [&](auto& ctx) { arg = boost::spirit::x3::_attr(ctx); };
    }

    template <typename T, typename Parser>
    static constexpr auto as_(Parser&& p){
        return boost::spirit::x3::rule<struct _, T>{} = std::forward<Parser>(p);
    }

public:
    template <typename Executor>
    endpoints(
        Executor ex, asio::steady_timer& timer,
        log_invoke<logger_type>& log
    ) :
        _resolver(std::move(ex)), _connect_timer(timer),
        _log(log)
    {}

    endpoints(const endpoints&) = delete;
    endpoints& operator=(const endpoints&) = delete;

    void clone_servers(const endpoints& other) {
        _servers = other._servers;
    }

    using executor_type = asio::ip::tcp::resolver::executor_type;
    // NOTE: asio::ip::basic_resolver returns executor by value
    executor_type get_executor() noexcept {
        return _resolver.get_executor();
    }

    template <typename CompletionToken>
    decltype(auto) async_next_endpoint(CompletionToken&& token) {
        using Signature = void (error_code, epoints, authority_path);

        auto initiation = [](auto handler, endpoints& self) {
            resolve_op { self, std::move(handler) }.perform();
        };

        return asio::async_initiate<CompletionToken, Signature>(
            initiation, token, std::ref(*this)
        );
    }

    void brokers(std::string hosts, uint16_t default_port) {
        namespace x3 = boost::spirit::x3;

        _servers.clear();

        std::string host, port, path;

        // loosely based on RFC 3986
        auto unreserved_ = x3::char_("-a-zA-Z_0-9._~");
        auto digit_ = x3::char_("0-9");
        auto separator_ = x3::char_(',');

        auto host_ = as_<std::string>(+unreserved_)[to_(host)];
        auto port_ = as_<std::string>(':' >> +digit_)[to_(port)];
        auto path_ = as_<std::string>(+(x3::char_('/') >> *unreserved_))[to_(path)];
        auto uri_ = *x3::omit[x3::space] >> (host_ >> -port_ >> -path_) >>
            (*x3::omit[x3::space] >> x3::omit[separator_ | x3::eoi]);

        for (auto b = hosts.begin(); b != hosts.end(); ) {
            host.clear(); port.clear(); path.clear();
            if (phrase_parse(b, hosts.end(), uri_, x3::eps(false))) {
                _servers.push_back({
                    std::move(host),
                    port.empty()
                        ? std::to_string(default_port)
                        : std::move(port),
                    std::move(path)
                });
            }
            else b = hosts.end();
        }
    }

};


} // end namespace boost::mqtt5::detail

#endif // !BOOST_MQTT5_ENDPOINTS_HPP
