// sntp_version_mismatch.c
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <time.h>

#define NTP_TIMESTAMP_DELTA 2208988800ull
#define NTP_PORT 123

typedef struct {
    uint8_t li_vn_mode;
    uint8_t stratum, poll;
    int8_t precision;
    uint32_t rootDelay, rootDispersion, refId;
    uint32_t refTm_s, refTm_f, origTm_s, origTm_f;
    uint32_t rxTm_s, rxTm_f, txTm_s, txTm_f;
} ntp_packet;

int main(int argc, char *argv[]) {
    if (argc != 2) {
        printf("Usage: %s <server_ip>\n", argv[0]);
        return 1;
    }

    int sockfd = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
    struct sockaddr_in server;
    ntp_packet pkt;

    memset(&pkt, 0, sizeof(pkt));
    pkt.li_vn_mode = (0 << 6) | (1 << 3) | 3; // Version 1, Mode 3 (client)

    struct timeval tv;
    gettimeofday(&tv, NULL);
    uint32_t txTm = htonl(tv.tv_sec + NTP_TIMESTAMP_DELTA);
    pkt.txTm_s = txTm;

    server.sin_family = AF_INET;
    server.sin_port = htons(NTP_PORT);
    inet_pton(AF_INET, argv[1], &server.sin_addr);

    sendto(sockfd, &pkt, sizeof(pkt), 0, (struct sockaddr *)&server, sizeof(server));
    printf("NTP packet with version 1 sent to %s\n", argv[1]);
    close(sockfd);
    return 0;
}