#include <fcntl.h>
#include <unistd.h>
#include <sys/epoll.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <stdlib.h>
#include <signal.h>
#include <arpa/inet.h>
#include <sys/signalfd.h>
#include <ctype.h>

const char HOST[] = "127.0.0.1";
const size_t MAXSIZE = 4096;

int main(int argc, char* argv[]) {
    int sockfd = socket(AF_INET, SOCK_STREAM, 0);
    sigset_t set;
    sigemptyset(&set);
    sigaddset(&set, SIGTERM);

    int epoll_fd = epoll_create1(0);
    int sigfd = signalfd(-1, &set, O_NONBLOCK);
    int flags = fcntl(sigfd, F_GETFL);
    fcntl(sigfd, F_SETFL, flags | O_NONBLOCK);

    struct epoll_event sig_event = {.data.fd = sigfd, .events = EPOLLIN};
    epoll_ctl(epoll_fd, EPOLL_CTL_ADD, sigfd, &sig_event);

    u_int16_t port = strtol(argv[1], NULL, 10);
    struct sockaddr_in addr = {.sin_family = AF_INET, .sin_port = htons(port)};
    inet_aton(HOST, &addr.sin_addr);
    bind(sockfd, (struct sockaddr*)&addr, sizeof(addr));
    listen(sockfd, SOMAXCONN);

    struct epoll_event sock_event = {.data.fd = sockfd, .events = EPOLLIN};

    flags = fcntl(sockfd, F_GETFL);
    fcntl(sockfd, F_SETFL, flags | O_NONBLOCK);

    epoll_ctl(epoll_fd, EPOLL_CTL_ADD, sockfd, &sock_event);

    struct epoll_event events[MAXSIZE];
    int open_fds[MAXSIZE];
    size_t open_fds_size = 0;

    while (1) {
        int event_num = epoll_wait(epoll_fd, events, MAXSIZE, -1);
        for (size_t i = 0; i < event_num; ++i) {
            if (events[i].data.fd == sigfd) {
                for (size_t j = 0; j < open_fds_size; ++j) {
                    shutdown(open_fds[j], SHUT_RDWR);
                    close(open_fds[j]);
                }
                close(sockfd);
                close(epoll_fd);
                _exit(0);
            }
        }
        for (size_t i = 0; i < event_num; ++i) {
            if (events[i].data.fd == sockfd) {
                int confd = accept(sockfd, NULL, NULL);
                struct epoll_event fd_event = {.events = EPOLLIN, .data.fd = confd};
                flags = fcntl(confd, F_GETFL);
                fcntl(confd, F_SETFL, flags | O_NONBLOCK);
                epoll_ctl(epoll_fd, EPOLL_CTL_ADD, confd, &fd_event);
                open_fds[open_fds_size] = confd;
                open_fds_size += 1;
            } else {
                int sz = 0;
                char buffer[MAXSIZE];
                while (1) {
                    sz = read(events[i].data.fd, buffer, sizeof(buffer));
                    if (sz == -1) {
                        break;
                    }
                    if (sz == 0) {
                        size_t it = 0;
                        for (; it < open_fds_size; ++it) {
                            if (open_fds[it] == events[i].data.fd) {
                                break;
                            }
                        }
                        close(open_fds[it]);
                        for (size_t j = it + 1; j < open_fds_size; ++j) {
                            open_fds[j - 1] = open_fds[j];
                        }
                        open_fds_size -= 1;
                        break;
                    }
                    char buffer_write[MAXSIZE];
                    for (size_t j = 0; j < sz; ++j) {
                        buffer_write[j] = toupper(buffer[j]);
                    }
                    write(events[i].data.fd, buffer_write, sz);
                }
            }
        }
    }
}