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#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <sys/types.h>
#include <arpa/inet.h>
#include <sys/select.h>

#define PORT 8080
#define MAX_CLIENTS  FD_SETSIZE
#define BUFFER_SIZE 1024

int main() {
    int listen_fd, new_fd, max_fd, activity, i, valread, sd;
    int client_socket[MAX_CLIENTS];
    struct sockaddr_in address;
    char buffer[BUFFER_SIZE];

    // Initialize all client_socket[] to 0
    for (i = 0; i < MAX_CLIENTS; i++)
        client_socket[i] = 0;

    // Create listening socket
    if ((listen_fd = socket(AF_INET, SOCK_STREAM, 0)) == 0) {
        perror("socket failed");
        exit(EXIT_FAILURE);
    }

    // Prepare address
    address.sin_family = AF_INET;
    address.sin_addr.s_addr = INADDR_ANY;
    address.sin_port = htons(PORT);

    // Bind
    if (bind(listen_fd, (struct sockaddr *)&address, sizeof(address)) < 0) {
        perror("bind failed");
        exit(EXIT_FAILURE);
    }

    // Listen
    if (listen(listen_fd, 5) < 0) {
        perror("listen");
        exit(EXIT_FAILURE);
    }

    printf("Server listening on port %d\n", PORT);

    fd_set readfds;

    while (1) {
        // Clear and set file descriptors
        FD_ZERO(&readfds);
        FD_SET(listen_fd, &readfds);
        max_fd = listen_fd;

        // Add client sockets to set
        for (i = 0; i < MAX_CLIENTS; i++) {
            sd = client_socket[i];
            if (sd > 0)
                FD_SET(sd, &readfds);
            if (sd > max_fd)
                max_fd = sd;
        }

        // Wait for activity
        activity = select(max_fd + 1, &readfds, NULL, NULL, NULL);

        if ((activity < 0) && (errno != EINTR)) {
            perror("select error");
        }

        // Incoming connection
        if (FD_ISSET(listen_fd, &readfds)) {
            socklen_t addrlen = sizeof(address);
            if ((new_fd = accept(listen_fd, (struct sockaddr *)&address, &addrlen)) < 0) {
                perror("accept");
                exit(EXIT_FAILURE);
            }
            printf("New connection: socket fd %d, IP: %s, port: %d\n",
                   new_fd, inet_ntoa(address.sin_addr), ntohs(address.sin_port));

            // Add new socket to array
            for (i = 0; i < MAX_CLIENTS; i++) {
                if (client_socket[i] == 0) {
                    client_socket[i] = new_fd;
                    break;
                }
            }
        }

        // IO on client sockets
        for (i = 0; i < MAX_CLIENTS; i++) {
            sd = client_socket[i];
            if (FD_ISSET(sd, &readfds)) {
                if ((valread = read(sd, buffer, BUFFER_SIZE)) == 0) {
                    // Client disconnected
                    getpeername(sd, (struct sockaddr *)&address, (socklen_t *)&addrlen);
                    printf("Host disconnected: IP %s, port %d\n",
                           inet_ntoa(address.sin_addr), ntohs(address.sin_port));
                    close(sd);
                    client_socket[i] = 0;
                } else {
                    buffer[valread] = '\0';
                    printf("Received from client %d: %s\n", sd, buffer);
                    send(sd, buffer, valread, 0); // Echo back
                }
            }
        }
    }

    return 0;
}