#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <netinet/tcp.h>   // For TCP_INFO

#define PORT 9090
#define BUFFER_SIZE 1024

void print_tcp_info(int sockfd) {
    struct tcp_info info;
    socklen_t len = sizeof(info);

    if (getsockopt(sockfd, IPPROTO_TCP, TCP_INFO, &info, &len) == 0) {
        printf("\n--- TCP_INFO (Server side) ---\n");
        printf("State: %u\n", info.tcpi_state);
        printf("RTT: %u µs\n", info.tcpi_rtt);
        printf("RTT Variance: %u µs\n", info.tcpi_rttvar);
        printf("Send CWND: %u\n", info.tcpi_snd_cwnd);
        printf("Re-transmits: %u\n", info.tcpi_retransmits);
        printf("Unacked: %u\n", info.tcpi_unacked);
        printf("Sacked: %u\n", info.tcpi_sacked);
        printf("Lost: %u\n", info.tcpi_lost);
        printf("Retrans: %u\n", info.tcpi_retrans);
    } else {
        perror("getsockopt TCP_INFO");
    }
}

int main() {
    int server_fd, client_fd;
    struct sockaddr_in server_addr, client_addr;
    socklen_t addr_len = sizeof(client_addr);
    char buffer[BUFFER_SIZE];

    server_fd = socket(AF_INET, SOCK_STREAM, 0);
    if (server_fd < 0) {
        perror("Socket creation failed");
        exit(EXIT_FAILURE);
    }

    server_addr.sin_family = AF_INET;
    server_addr.sin_addr.s_addr = INADDR_ANY;
    server_addr.sin_port = htons(PORT);

    if (bind(server_fd, (struct sockaddr *)&server_addr, sizeof(server_addr)) < 0) {
        perror("Bind failed");
        close(server_fd);
        exit(EXIT_FAILURE);
    }

    if (listen(server_fd, 3) < 0) {
        perror("Listen failed");
        close(server_fd);
        exit(EXIT_FAILURE);
    }

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

    client_fd = accept(server_fd, (struct sockaddr *)&client_addr, &addr_len);
    if (client_fd < 0) {
        perror("Accept failed");
        close(server_fd);
        exit(EXIT_FAILURE);
    }

    // Print TCP info after connection established
    print_tcp_info(client_fd);

    int n = read(client_fd, buffer, sizeof(buffer));
    buffer[n] = '\0';
    printf("Server received: %s\n", buffer);

    char *msg = "Hello from Server";
    send(client_fd, msg, strlen(msg), 0);

    // Print TCP info after data transfer
    print_tcp_info(client_fd);

    close(client_fd);
    close(server_fd);
    return 0;
}