#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <unistd.h>
#include <sys/select.h>
#include <sys/time.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <endian.h>

#define VERSION_3           3
#define VERSION_4           4

#define MODE_CLIENT         3
#define MODE_SERVER         4

#define NTP_LI              0			//闰秒指示符
#define NTP_VN              VERSION_3   //版本号
#define NTP_MODE            MODE_CLIENT	//NTP模式
#define NTP_STRATUM         0			//本地时钟层级
#define NTP_POLL            4			//轮询间隔
#define NTP_PRECISION       -6			//本地时钟精度

#define NTP_HLEN            48

#define NTP_PORT            123
#define NTP_SERVER          "182.92.12.11"

#define TIMEOUT             10

#define BUFSIZE             1500

#define JAN_1970 2208988800 //自1900-1-1到1970-1-1经过的秒数

//用于64位时间戳,即小数部分为32位
//NTP_CONV_FRAC32(x)将x转换为NTP时间戳中的小数部分值
//NTP_REVE_FRAC32(x)将NTP时间戳中的小数部分值x解析成具体值
#define NTP_CONV_FRAC32(x)  (uint64_t) ((x) * ((uint64_t)1<<32))
#define NTP_REVE_FRAC32(x)  ((double) ((double) (x) / ((uint64_t)1<<32)))

//用于32位时间戳,即小数部分为16位
//NTP_CONV_FRAC16(x)将x转换为NTP时间戳中的小数部分值
//NTP_REVE_FRAC16(x)将NTP时间戳中的小数部分值x解析成具体值
#define NTP_CONV_FRAC16(x)  (uint32_t) ((x) * ((uint32_t)1<<16))
#define NTP_REVE_FRAC16(x)  ((double)((double) (x) / ((uint32_t)1<<16)))

//timeval结构中tv_usec字段和NTP时间戳小数部分互转
#define USEC2FRAC(x)        ((uint32_t) NTP_CONV_FRAC32( (x) / 1000000.0 ))
#define FRAC2USEC(x)        ((uint32_t) NTP_REVE_FRAC32( (x) * 1000000.0 ))


#define NTP_LFIXED2DOUBLE(x)    ((double) ( ntohl(((struct l_fixedpt *) (x))->intpart) - JAN_1970 + FRAC2USEC(ntohl(((struct l_fixedpt *) (x))->fracpart)) / 1000000.0 ))


typedef struct _uint64_time
{
    uint32_t int_part;
    uint32_t float_part;
} uint64_time;

typedef struct _NTP_time
{
    unsigned char leap_ver_mode;
    unsigned char stratum;
    char poll;
    char precision;
    int32_t root_delay;
    int32_t root_dispersion;
    int32_t reference_identifine;
    uint64_time reference_time;
    uint64_time original_time;
    uint64_time receive_time;
    uint64_time transmit_time;
} NTP_time, *NTP_time_Ptr;


struct s_fixedpt     //32位NTP时间戳
{	
  uint16_t    intpart;	//整数部分
  uint16_t    fracpart;	//小数部分
};

struct l_fixedpt //64位NTP时间戳
{	
  uint32_t    intpart;
  uint32_t    fracpart;
};

//此结构体按位定义字段,所以需要解决字节序问题
struct ntphdr 
{
#if __BYTE_ORDER == __BID_ENDIAN	//大端
  unsigned int    ntp_li : 2;
  unsigned int    ntp_vn : VERSION_3;
  unsigned int    ntp_mode : MODE_CLIENT;
#elif __BYTE_ORDER == __LITTLE_ENDIAN	//小端
  unsigned int    ntp_mode : MODE_CLIENT;
  unsigned int    ntp_vn : VERSION_3;
  unsigned int    ntp_li : 2;
#endif
  uint8_t         ntp_stratum;	//本地时钟层级
  uint8_t         ntp_poll;		//轮询间隔
  int8_t          ntp_precision;	//时钟精度
  struct s_fixedpt    ntp_rtdelay;
  struct s_fixedpt    ntp_rtdispersion;
  uint32_t            ntp_refid;
  struct l_fixedpt    ntp_refts;
  struct l_fixedpt    ntp_orits;	//客户端发送时间请求的时间
  struct l_fixedpt    ntp_recvts;	//服务器收到时间请求的时间
  struct l_fixedpt    ntp_transts;	//服务器发送时间回复的时间
};


in_addr_t inet_host(const char *host)
{
  in_addr_t saddr;
  struct hostent *hostent;

  if ((saddr = inet_addr(host)) == INADDR_NONE) {
    if ((hostent = gethostbyname(host)) == NULL)
      return INADDR_NONE;

    memmove(&saddr, hostent->h_addr, hostent->h_length);
  }

  return saddr;
}


int get_ntp_packet(void *buf, size_t *size)  //构建并发送NTP请求报文
{
  struct ntphdr *ntp;
  struct timeval tv;

  if (!size || *size < NTP_HLEN)
    return -1;

  memset(buf, 0, *size);

  ntp = (struct ntphdr *) buf;
  ntp->ntp_li = NTP_LI;
  ntp->ntp_vn = NTP_VN;
  ntp->ntp_mode = NTP_MODE;
  ntp->ntp_stratum = NTP_STRATUM;
  ntp->ntp_poll = NTP_POLL;
  ntp->ntp_precision = NTP_PRECISION;

  gettimeofday(&tv, NULL);  //把目前的时间用tv 结构体返回
  printf("sec: %ld\n", tv.tv_sec);
  printf("usec: %ld\n", tv.tv_usec);
  ntp->ntp_transts.intpart = htonl(tv.tv_sec + JAN_1970);	//将UTC时间戳改为NTP时间戳
  ntp->ntp_transts.fracpart = htonl(USEC2FRAC(tv.tv_usec));
  printf("intpart: %u\n", ntp->ntp_orits.intpart);
  printf("fracpart: %u\n", ntp->ntp_orits.fracpart);

  *size = NTP_HLEN;

  return 0;
}



double get_rrt(const struct ntphdr *ntp, const struct timeval *recvtv)  //往返时延
{
  double t1, t2, t3, t4;

  t1 = NTP_LFIXED2DOUBLE(&ntp->ntp_orits);
  t2 = NTP_LFIXED2DOUBLE(&ntp->ntp_recvts);
  t3 = NTP_LFIXED2DOUBLE(&ntp->ntp_transts);
  t4 = recvtv->tv_sec + recvtv->tv_usec / 1000000.0;

  return (t4 - t1) - (t3 - t2);
}

double get_offset(const struct ntphdr *ntp, const struct timeval *recvtv)  //偏移量
{
  double t1, t2, t3, t4;

  t1 = NTP_LFIXED2DOUBLE(&ntp->ntp_orits);
  printf("t1 = %f\n", t1);
  t2 = NTP_LFIXED2DOUBLE(&ntp->ntp_recvts);
  printf("t2 = %f\n", t2);
  t3 = NTP_LFIXED2DOUBLE(&ntp->ntp_transts);
  printf("t3 = %f\n", t3);
  t4 = recvtv->tv_sec + recvtv->tv_usec / 1000000.0;
  printf("t4 = %f\n", t4);

  return ((t2 - t1) + (t3 - t4)) / 2;
}

void test_len()
{
  printf("sizeof(int8_t) = %ld\n", sizeof(int8_t));
  printf("sizeof(uint8_t) = %ld\n", sizeof(uint8_t));
  printf("sizeof(unsigned int) = %ld\n", sizeof(unsigned int));
  printf("sizeof(uint32_t) = %ld\n", sizeof(uint32_t));
  printf("sizeof(struct ntphdr) = %ld\n", sizeof(struct ntphdr));
  printf("sizeof(struct NTP_time) = %ld\n", sizeof(NTP_time));
}


int main(int argc, char *argv[])
{
  char dateBuf[64] = {0};
  char cmd[128] = {0};
  struct tm* local;
  char buf[BUFSIZE];
  size_t nbytes;
  int sockfd = 0;
  int maxfd1;
  struct sockaddr_in servaddr;
  fd_set readfds;
  struct timeval timeout;	//超时时间
  struct timeval recvtv;
  struct timeval tv;		//1970.1.1至今偏移秒数和微秒数
  double offset;

  test_len();
  // if (argc != 2) {
  // usage();
  // exit(-1);

  //构建服务器地址套接字结构
  servaddr.sin_family = AF_INET;
  servaddr.sin_port = htons(NTP_PORT);
  servaddr.sin_addr.s_addr = inet_host("119.28.183.184");

  if ((sockfd = socket(AF_INET, SOCK_DGRAM, 0)) < 0) {
    perror("socket error");
    exit(-1);
  }

  if (connect(sockfd, (struct sockaddr *) &servaddr, sizeof(struct sockaddr)) != 0) {
    perror("connect error");
    exit(-1);
  }

  //构建并发送NTP报文
  nbytes = BUFSIZE;
  if (get_ntp_packet(buf, &nbytes) != 0) {
    fprintf(stderr, "construct ntp request error \n");
    exit(-1);
  }
  send(sockfd, buf, nbytes, 0);

  FD_ZERO(&readfds);	//清空fd_set集合	
  FD_SET(sockfd, &readfds);	//将给定的文件描述符加入到集合中
  maxfd1 = sockfd + 1;

  //设置select超时时间
  timeout.tv_sec = TIMEOUT;
  timeout.tv_usec = 0;

  if (select(maxfd1, &readfds, NULL, NULL, &timeout) > 0) {
    if (FD_ISSET(sockfd, &readfds))
    {
      if ((nbytes = recv(sockfd, buf, BUFSIZE, 0)) < 0)
      {
        perror("recv error");
        exit(-1);
      }

      struct ntphdr *ndr = (struct ntphdr *)buf;
      printf("ntp mode: %u\n", ndr->ntp_mode);
      printf("ntp vn: %u\n", ndr->ntp_vn);
      printf("ntp li: %u\n", ndr->ntp_li);

      printf("ntp startum: %u\n", ndr->ntp_stratum);
      printf("ntp poll: %u\n", ndr->ntp_poll);
      printf("ntp precision: %u\n", ndr->ntp_precision);
      printf("ntp orits int: %u\n", ndr->ntp_orits.intpart);
      printf("ntp orits frac: %u\n", ndr->ntp_orits.fracpart);
      printf("ntp recvts int: %u\n", ndr->ntp_recvts.intpart);
      printf("ntp recvts frac: %u\n", ndr->ntp_recvts.fracpart);
      printf("ntp transts int: %u\n", ndr->ntp_transts.intpart);
      printf("ntp transts frac: %u\n", ndr->ntp_transts.fracpart);

      //接收到服务器数据后记录一次时间,用以计算C/S之间时间偏移量
      gettimeofday(&recvtv, NULL);
      offset = get_offset((struct ntphdr *) buf, &recvtv);
      printf("offset = %f\n", offset);
      //再次系统时间,用以进行校时
      gettimeofday(&tv, NULL);	//1970.1.1至今偏移时间的秒数和微秒数

      //针对tv.tv_usec向上溢出的处理,并进行校时
      tv.tv_sec += (int) offset + 28800;
      tv.tv_usec += offset - (int) offset;

      local = localtime((time_t*)&tv.tv_sec);	//1970.1.1到目前的偏移秒数和微秒数变为本地时间

      strftime(dateBuf, 64, "%Y-%m-%d %H:%M:%S", local);	//格式化本地时间
      sprintf(cmd, "system busybox date -s \"%s\"", dateBuf);
      printf("cmd: %s\n", cmd);

      printf("Now: %s \n", ctime((time_t *) &tv.tv_sec));


    }
  }

  close(sockfd);

  return 0;
}