#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/socket.h>
#include <stdlib.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <signal.h>
#include <limits.h>
#include <sys/epoll.h>
#include <fcntl.h>
#include <unistd.h>


volatile sig_atomic_t terminated = 0;

void handle(int signum) {
    terminated = 1;
}

int create_local_server(in_port_t port) {
    in_addr_t addr = inet_addr("127.0.0.1");

    struct sockaddr_in hints = {
        .sin_family = AF_INET,
        .sin_addr.s_addr = addr,
        .sin_port = port
    };

    int host_socket = socket(AF_INET, SOCK_STREAM, 0);

    bind(host_socket, (struct sockaddr*) &hints, sizeof(hints));

    return host_socket;
}

void add_user_fd(int epoll_fd, int user_fd) {
    struct epoll_event event = {
        .events = EPOLLIN,
        .data = {.fd = user_fd}
    };

    epoll_ctl(epoll_fd, EPOLL_CTL_ADD, user_fd, &event);
}

void change_data(char* recv, int size, char* send) {
    for (int i = 0; i < size; i ++) {
        if ((recv[i] <= 'z') && (recv[i] >= 'a')) {
            send[i] = recv[i] + 'A' - 'a';
        } else {
            send[i] = recv[i];
        }
    }
}

int main(int argc, char* argv[]) {

    struct sigaction handler = {
        .sa_handler = handle
    };

    sigaction(SIGTERM, &handler, NULL);

    in_port_t port = htons(atoi(argv[1]));

    int host_socket = create_local_server(port);
    fcntl(host_socket, F_SETFL, fcntl(host_socket, F_GETFL) | O_NONBLOCK);

    int epoll_fd = epoll_create1(0);

    int users_num = 0;

    if (listen(host_socket, 20) >= 0) {
        char recv_data[BUFSIZ];
        char send_data[BUFSIZ];
        while (!terminated) {
            int user_socket = 0;
            while ((user_socket = accept(host_socket, NULL, NULL)) > 0) {
                add_user_fd(epoll_fd, user_socket);
                users_num++;
            }

            if (users_num == 0) {
                continue;
            }

            struct epoll_event event;
            epoll_wait(epoll_fd, &event, 1, -1);

            int user_fd = event.data.fd;

            int size_of_recv = 0;
            if ((size_of_recv = read(user_fd, &recv_data, sizeof(recv_data))) == 0){
                shutdown(user_fd, SHUT_RDWR);
            } else {
                printf("%s", recv_data);
                change_data(recv_data, size_of_recv, send_data);
                write(user_fd, send_data, size_of_recv);
            }
        }
    }

    close(host_socket);

    return 0;
}