#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <sys/epoll.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <fcntl.h>

#define PORT 50550
#define MAX_EVENTS 64

static int make_nonblocking(int fd) {
    int flags = fcntl(fd, F_GETFL, 0);
    fcntl(fd, F_SETFL, flags | O_NONBLOCK);
    return fd;
}

int main(void) {
    int listen_fd = socket(AF_INET, SOCK_STREAM, 0);
    struct sockaddr_in addr = {
        .sin_family = AF_INET,
        .sin_addr.s_addr = INADDR_ANY,
        .sin_port = htons(PORT)
    };

    bind(listen_fd, (struct sockaddr*)&addr, sizeof(addr));
    listen(listen_fd, SOMAXCONN);
    make_nonblocking(listen_fd);

    int epfd = epoll_create1(0);
    struct epoll_event ev = {.events = EPOLLIN, .data.fd = listen_fd};
    epoll_ctl(epfd, EPOLL_CTL_ADD, listen_fd, &ev);

    struct epoll_event events[MAX_EVENTS];
    printf("Listening on port %d...\n", PORT);

    for (;;) {
        int n = epoll_wait(epfd, events, MAX_EVENTS, -1);
        for (int i = 0; i < n; i++) {
            int fd = events[i].data.fd;

            if (fd == listen_fd) {
                // New connection
                int client_fd = accept(listen_fd, NULL, NULL);
                make_nonblocking(client_fd);
                ev.events = EPOLLIN;
                ev.data.fd = client_fd;
                epoll_ctl(epfd, EPOLL_CTL_ADD, client_fd, &ev);
                printf("New client %d connected.\n", client_fd);
            } else if (events[i].events & EPOLLIN) {
                // Data ready to read
                char buf[512];
                ssize_t len = read(fd, buf, sizeof(buf));
                if (len <= 0) {
                    close(fd);
                    printf("Client %d disconnected.\n", fd);
                } else {
                    write(fd, buf, len);  // echo back
                }
            }
        }
    }
}