extern "C" {
#include <stdio.h>
#include <arpa/inet.h>
}

#include <format>
#include <expected>
#include <string>
#include <ostream>
#include <iostream>

std::expected<std::string, std::string> nethost6(std::string network, int prefix, uint32_t num) {
        struct in6_addr addr;
        unsigned char mask[16] = {0};
        if (inet_pton(AF_INET6, network.data(), &addr) != 1) {
                return std::unexpected(std::format("Invalid network address {}", network));
        }
        for (int i = 0; i < prefix; i++) {
                mask[i / 8] |= (1 << (7 - (i % 8)));
        }
        for (int i = 0; i < 16; i++) {
                addr.s6_addr[i] &= mask[i];
        }

        uint64_t *host_part = (uint64_t *)&addr.s6_addr[8];
        uint64_t hostnum = be64toh(*host_part);
        hostnum += num;
        *host_part = htobe64(hostnum);

        char buffer[INET6_ADDRSTRLEN] = {'\0'};
        inet_ntop(AF_INET6, &addr, buffer, INET6_ADDRSTRLEN);

        return std::string(buffer);
}


std::expected<std::string, std::string> nethost4(std::string network, int prefix, uint32_t num) {
        struct in_addr inaddr;
        if (inet_pton(AF_INET, network.data(), &inaddr) != 1) {
                return std::unexpected(std::format("Invalid network address {}", network));
        }
        uint32_t ip = ntohl(inaddr.s_addr);
        uint32_t mask = (prefix == 0) ? 0 : (~0U << (32 - prefix));
        uint32_t fip = (ip & mask) + num;
        struct in_addr ip_addr;
        ip_addr.s_addr = htonl(fip);
        return std::string(inet_ntoa(ip_addr));
}

std::expected<std::string, std::string> nethost(std::string network, int prefix, uint32_t num) {
        struct sockaddr_in sa;
        if (inet_pton(AF_INET, network.data(), &(sa.sin_addr)) == 1) {
                return nethost4(network, prefix, num);
        } else if (inet_pton(AF_INET6, network.data(), &(sa.sin_addr)) == 1) {
                return nethost6(network, prefix, num);
        }
        return std::unexpected(std::format("Unknown network address {}", network));
}

int main() {
        auto net4Res = nethost4("192.168.1.151", 24, 1);
        if (!net4Res) {
                std::cerr << net4Res.error() << std::endl;
                return 1;
        }
        std::cout << net4Res.value() << std::endl;

        auto net6Res = nethost6("2001:db8:abcd:1234::0", 64, 1);
        if (!net6Res) {
                std::cerr << net6Res.error() << std::endl;
                return 1;
        }
        std::cout << net6Res.value() << std::endl;


        return 0;
}