#include <sys/socket.h> // socket functions
#include <netinet/in.h> // sockaddr_in
#include <cstdlib> // exit() and EXIT_FAILURE
#include <iostream> // cout
#include <unistd.h> // read
#include <signal.h>

#include <ext/stdio_filebuf.h> // buffered stream

#include <thread>

using SOCKET_FD = int;
constexpr uint16_t LISTEN_PORT = 42069;
const int yes = 1;
SOCKET_FD listener = -1, connection = -1;

void handle_client(SOCKET_FD client_fd, bool (*handler)(std::istream&, std::ostream&, void*), void* ctx) {
    using Filebuf = __gnu_cxx::stdio_filebuf<char>;

    // setup input stream
    FILE* fin = fdopen(client_fd, "r");
    Filebuf in_buf(fin, std::ios::in);
    std::istream is(&in_buf);

    // setup output stream
    FILE* fout = fdopen(client_fd, "w");
    Filebuf out_buf(fout, std::ios::out);
    std::ostream os(&out_buf);

    signal(SIGPIPE, SIG_IGN); // ignore pipe signal

    if (handler(is, os, ctx)) {
        shutdown(listener, SHUT_RD);
    }

    fclose(fin);
    fclose(fout);
    close(client_fd);
}

void serve(bool (*handler)(std::istream&, std::ostream&, void*), void* ctx) {
    sockaddr_in addr{ .sin_family = AF_INET, .sin_port = htons(LISTEN_PORT), .sin_addr = in_addr{ .s_addr = INADDR_ANY } };

    if ((listener = socket(AF_INET, SOCK_STREAM, 0)) < 0 || 
                    setsockopt(listener, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(yes)) < 0 ||
                    bind(listener, (const sockaddr*) &addr, sizeof(addr)) < 0 ||
                    listen(listener, 10) < 0) {
        goto cleanup;
    }

    while ((connection = accept(listener, nullptr, nullptr)) > 0) {
        std::thread(handle_client, connection, handler, ctx).detach();
    }

    cleanup:
    std::cout << "Server shutting down..." << std::endl;
    if (connection != -1) close(connection); 
    if (listener != -1) close(listener);
}

bool h(std::istream& is, std::ostream& os, void* ctx) {
    std::string s;
    os << "hello from " << std::this_thread::get_id() <<"! are you there?" << std::endl;
    is >> s;
    os << s << " to you too!" << std::endl;
    return true;
}