/*
 * Copyright (c) 2019 TAOS Data, Inc. <jhtao@taosdata.com>
 *
 * This program is free software: you can use, redistribute, and/or modify
 * it under the terms of the GNU Affero General Public License, version 3
 * or later ("AGPL"), as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program. If not, see <http://www.gnu.org/licenses/>.
 */

#ifdef DARWIN
#define _XOPEN_SOURCE
#else
#define _XOPEN_SOURCE 500
#endif

#define _BSD_SOURCE
#define _DEFAULT_SOURCE
#include "ttime.h"

/*
 * mktime64 - Converts date to seconds.
 * Converts Gregorian date to seconds since 1970-01-01 00:00:00.
 * Assumes input in normal date format, i.e. 1980-12-31 23:59:59
 * => year=1980, mon=12, day=31, hour=23, min=59, sec=59.
 *
 * [For the Julian calendar (which was used in Russia before 1917,
 * Britain & colonies before 1752, anywhere else before 1582,
 * and is still in use by some communities) leave out the
 * -year/100+year/400 terms, and add 10.]
 *
 * This algorithm was first published by Gauss (I think).
 *
 * A leap second can be indicated by calling this function with sec as
 * 60 (allowable under ISO 8601).  The leap second is treated the same
 * as the following second since they don't exist in UNIX time.
 *
 * An encoding of midnight at the end of the day as 24:00:00 - ie. midnight
 * tomorrow - (allowable under ISO 8601) is supported.
 */
static int64_t user_mktime64(const uint32_t year0, const uint32_t mon0, const uint32_t day, const uint32_t hour,
                             const uint32_t min, const uint32_t sec, int64_t time_zone) {
  uint32_t mon = mon0, year = year0;

  /* 1..12 -> 11,12,1..10 */
  if (0 >= (int32_t)(mon -= 2)) {
    mon += 12; /* Puts Feb last since it has leap day */
    year -= 1;
  }

  // int64_t res = (((((int64_t) (year/4 - year/100 + year/400 + 367*mon/12 + day) +
  //                year*365 - 719499)*24 + hour)*60 + min)*60 + sec);
  int64_t res;
  res = 367 * ((int64_t)mon) / 12;
  res += year / 4 - year / 100 + year / 400 + day + ((int64_t)year) * 365 - 719499;
  res = res * 24;
  res = ((res + hour) * 60 + min) * 60 + sec;

  return (res + time_zone);
}

// ==== mktime() kernel code =================//
static int64_t m_deltaUtc = 0;
void           deltaToUtcInitOnce() {
  struct tm tm = {0};

  (void)taosStrpTime("1970-01-01 00:00:00", (const char*)("%Y-%m-%d %H:%M:%S"), &tm);
  m_deltaUtc = (int64_t)taosMktime(&tm);
  // printf("====delta:%lld\n\n", seconds);
}

static int64_t parseFraction(char* str, char** end, int32_t timePrec);
static int32_t parseTimeWithTz(const char* timestr, int64_t* time, int32_t timePrec, char delim);
static int32_t parseLocaltime(char* timestr, int64_t* time, int32_t timePrec);
static int32_t parseLocaltimeDst(char* timestr, int64_t* time, int32_t timePrec);
static char*   forwardToTimeStringEnd(char* str);
static bool    checkTzPresent(const char* str, int32_t len);

static int32_t (*parseLocaltimeFp[])(char* timestr, int64_t* time, int32_t timePrec) = {parseLocaltime,
                                                                                        parseLocaltimeDst};

int32_t taosParseTime(const char* timestr, int64_t* time, int32_t len, int32_t timePrec, int8_t day_light) {
  /* parse datatime string in with tz */
  if (strnchr(timestr, 'T', len, false) != NULL) {
    return parseTimeWithTz(timestr, time, timePrec, 'T');
  } else if (checkTzPresent(timestr, len)) {
    return parseTimeWithTz(timestr, time, timePrec, 0);
  } else {
    return (*parseLocaltimeFp[day_light])((char*)timestr, time, timePrec);
  }
}

bool checkTzPresent(const char* str, int32_t len) {
  char*   seg = forwardToTimeStringEnd((char*)str);
  int32_t seg_len = len - (int32_t)(seg - str);

  char* c = &seg[seg_len - 1];
  for (int32_t i = 0; i < seg_len; ++i) {
    if (*c == 'Z' || *c == 'z' || *c == '+' || *c == '-') {
      return true;
    }
    c--;
  }

  return false;
}

char* forwardToTimeStringEnd(char* str) {
  int32_t i = 0;
  int32_t numOfSep = 0;

  while (str[i] != 0 && numOfSep < 2) {
    if (str[i++] == ':') {
      numOfSep++;
    }
  }

  while (str[i] >= '0' && str[i] <= '9') {
    i++;
  }

  return &str[i];
}

int64_t parseFraction(char* str, char** end, int32_t timePrec) {
  int32_t i = 0;
  int64_t fraction = 0;

  const int32_t MILLI_SEC_FRACTION_LEN = 3;
  const int32_t MICRO_SEC_FRACTION_LEN = 6;
  const int32_t NANO_SEC_FRACTION_LEN = 9;

  int32_t factor[9] = {1, 10, 100, 1000, 10000, 100000, 1000000, 10000000, 100000000};
  int32_t times = 1;

  while (str[i] >= '0' && str[i] <= '9') {
    i++;
  }

  int32_t totalLen = i;
  if (totalLen <= 0) {
    return -1;
  }

  /* parse the fraction */
  if (timePrec == TSDB_TIME_PRECISION_MILLI) {
    /* only use the initial 3 bits */
    if (i >= MILLI_SEC_FRACTION_LEN) {
      i = MILLI_SEC_FRACTION_LEN;
    }

    times = MILLI_SEC_FRACTION_LEN - i;
  } else if (timePrec == TSDB_TIME_PRECISION_MICRO) {
    if (i >= MICRO_SEC_FRACTION_LEN) {
      i = MICRO_SEC_FRACTION_LEN;
    }
    times = MICRO_SEC_FRACTION_LEN - i;
  } else {
    assert(timePrec == TSDB_TIME_PRECISION_NANO);
    if (i >= NANO_SEC_FRACTION_LEN) {
      i = NANO_SEC_FRACTION_LEN;
    }
    times = NANO_SEC_FRACTION_LEN - i;
  }

  fraction = strnatoi(str, i) * factor[times];
  *end = str + totalLen;

  return fraction;
}

int32_t parseTimezone(char* str, int64_t* tzOffset) {
  int64_t hour = 0;

  int32_t i = 0;
  if (str[i] != '+' && str[i] != '-') {
    return -1;
  }

  i++;

  char* sep = strchr(&str[i], ':');
  if (sep != NULL) {
    int32_t len = (int32_t)(sep - &str[i]);

    hour = strnatoi(&str[i], len);
    i += len + 1;
  } else {
    hour = strnatoi(&str[i], 2);
    i += 2;
  }

  // return error if there're illegal charaters after min(2 Digits)
  char* minStr = &str[i];
  if (minStr[1] != '\0' && minStr[2] != '\0') {
    return -1;
  }

  int64_t minute = strnatoi(&str[i], 2);
  if (minute > 59) {
    return -1;
  }

  if (str[0] == '+') {
    *tzOffset = -(hour * 3600 + minute * 60);
  } else {
    *tzOffset = hour * 3600 + minute * 60;
  }

  return 0;
}

/*
 * rfc3339 format:
 * 2013-04-12T15:52:01+08:00
 * 2013-04-12T15:52:01.123+08:00
 *
 * 2013-04-12T15:52:01Z
 * 2013-04-12T15:52:01.123Z
 *
 * iso-8601 format:
 * 2013-04-12T15:52:01+0800
 * 2013-04-12T15:52:01.123+0800
 */
int32_t parseTimeWithTz(const char* timestr, int64_t* time, int32_t timePrec, char delim) {
  int64_t factor =
      (timePrec == TSDB_TIME_PRECISION_MILLI) ? 1000 : (timePrec == TSDB_TIME_PRECISION_MICRO ? 1000000 : 1000000000);
  int64_t tzOffset = 0;

  struct tm tm = {0};

  char* str;
  if (delim == 'T') {
    str = taosStrpTime(timestr, "%Y-%m-%dT%H:%M:%S", &tm);
  } else if (delim == 0) {
    str = taosStrpTime(timestr, "%Y-%m-%d %H:%M:%S", &tm);
  } else {
    str = NULL;
  }

  if (str == NULL) {
    return -1;
  }

/* mktime will be affected by TZ, set by using taos_options */
#ifdef WINDOWS
  int64_t seconds = user_mktime64(tm.tm_year + 1900, tm.tm_mon + 1, tm.tm_mday, tm.tm_hour, tm.tm_min, tm.tm_sec, 0);
  // int64_t seconds = gmtime(&tm);
#else
  int64_t seconds = timegm(&tm);
#endif

  int64_t fraction = 0;
  str = forwardToTimeStringEnd((char*)timestr);

  if ((str[0] == 'Z' || str[0] == 'z') && str[1] == '\0') {
    /* utc time, no millisecond, return directly*/
    *time = seconds * factor;
  } else if (str[0] == '.') {
    str += 1;
    if ((fraction = parseFraction(str, &str, timePrec)) < 0) {
      return -1;
    }

    *time = seconds * factor + fraction;

    char seg = str[0];
    if (seg != 'Z' && seg != 'z' && seg != '+' && seg != '-') {
      return -1;
    } else if ((seg == 'Z' || seg == 'z') && str[1] != '\0') {
      return -1;
    } else if (seg == '+' || seg == '-') {
      // parse the timezone
      if (parseTimezone(str, &tzOffset) == -1) {
        return -1;
      }

      *time += tzOffset * factor;
    }

  } else if (str[0] == '+' || str[0] == '-') {
    *time = seconds * factor + fraction;

    // parse the timezone
    if (parseTimezone(str, &tzOffset) == -1) {
      return -1;
    }

    *time += tzOffset * factor;
  } else {
    return -1;
  }

  return 0;
}

int32_t parseLocaltime(char* timestr, int64_t* time, int32_t timePrec) {
  *time = 0;
  struct tm tm = {0};

  char* str = taosStrpTime(timestr, "%Y-%m-%d %H:%M:%S", &tm);
  if (str == NULL) {
    return -1;
  }

#ifdef _MSC_VER
#if _MSC_VER >= 1900
  int64_t timezone = _timezone;
#endif
#endif

  int64_t seconds =
      user_mktime64(tm.tm_year + 1900, tm.tm_mon + 1, tm.tm_mday, tm.tm_hour, tm.tm_min, tm.tm_sec, timezone);

  int64_t fraction = 0;

  if (*str == '.') {
    /* parse the second fraction part */
    if ((fraction = parseFraction(str + 1, &str, timePrec)) < 0) {
      return -1;
    }
  }

  int64_t factor =
      (timePrec == TSDB_TIME_PRECISION_MILLI) ? 1000 : (timePrec == TSDB_TIME_PRECISION_MICRO ? 1000000 : 1000000000);
  *time = factor * seconds + fraction;

  return 0;
}

int32_t parseLocaltimeDst(char* timestr, int64_t* time, int32_t timePrec) {
  *time = 0;
  struct tm tm = {0};
  tm.tm_isdst = -1;

  char* str = taosStrpTime(timestr, "%Y-%m-%d %H:%M:%S", &tm);
  if (str == NULL) {
    return -1;
  }

  /* mktime will be affected by TZ, set by using taos_options */
  int64_t seconds = taosMktime(&tm);

  int64_t fraction = 0;

  if (*str == '.') {
    /* parse the second fraction part */
    if ((fraction = parseFraction(str + 1, &str, timePrec)) < 0) {
      return -1;
    }
  }

  int64_t factor =
      (timePrec == TSDB_TIME_PRECISION_MILLI) ? 1000 : (timePrec == TSDB_TIME_PRECISION_MICRO ? 1000000 : 1000000000);
  *time = factor * seconds + fraction;
  return 0;
}

char getPrecisionUnit(int32_t precision) {
  static char units[3] = {TIME_UNIT_MILLISECOND, TIME_UNIT_MICROSECOND, TIME_UNIT_NANOSECOND};
  switch (precision) {
    case TSDB_TIME_PRECISION_MILLI:
    case TSDB_TIME_PRECISION_MICRO:
    case TSDB_TIME_PRECISION_NANO:
      return units[precision];
    default:
      return 0;
  }
}

int64_t convertTimePrecision(int64_t time, int32_t fromPrecision, int32_t toPrecision) {
  assert(fromPrecision == TSDB_TIME_PRECISION_MILLI ||
         fromPrecision == TSDB_TIME_PRECISION_MICRO ||
         fromPrecision == TSDB_TIME_PRECISION_NANO);
  assert(toPrecision == TSDB_TIME_PRECISION_MILLI ||
         toPrecision == TSDB_TIME_PRECISION_MICRO ||
         toPrecision == TSDB_TIME_PRECISION_NANO);
  double tempResult = (double)time;
  switch(fromPrecision) {
    case TSDB_TIME_PRECISION_MILLI: {
      switch (toPrecision) {
        case TSDB_TIME_PRECISION_MILLI:
          return time;
        case TSDB_TIME_PRECISION_MICRO:
          tempResult *= 1000;
          time *= 1000;
          goto end_;
        case TSDB_TIME_PRECISION_NANO:
          tempResult *= 1000000;
          time *= 1000000;
          goto end_;
      }
    } // end from milli
    case TSDB_TIME_PRECISION_MICRO: {
      switch (toPrecision) {
        case TSDB_TIME_PRECISION_MILLI:
          return time / 1000;
        case TSDB_TIME_PRECISION_MICRO:
          return time;
        case TSDB_TIME_PRECISION_NANO:
          tempResult *= 1000;
          time *= 1000;
          goto end_;
      }
    } //end from micro
    case TSDB_TIME_PRECISION_NANO: {
      switch (toPrecision) {
        case TSDB_TIME_PRECISION_MILLI:
          return time / 1000000;
        case TSDB_TIME_PRECISION_MICRO:
          return time / 1000;
        case TSDB_TIME_PRECISION_NANO:
          return time;
      }
    } //end from nano
    default: {
      assert(0);
      return time;  // only to pass windows compilation
    }
  } //end switch fromPrecision
end_:
  if (tempResult >= (double)INT64_MAX) return INT64_MAX;
  if (tempResult <= (double)INT64_MIN) return INT64_MIN;  // INT64_MIN means NULL
  return time;
}

// !!!!notice:there are precision problems, double lose precison if time is too large, for example: 1626006833631000000*1.0 = double = 1626006833631000064
//int64_t convertTimePrecision(int64_t time, int32_t fromPrecision, int32_t toPrecision) {
//  assert(fromPrecision == TSDB_TIME_PRECISION_MILLI || fromPrecision == TSDB_TIME_PRECISION_MICRO ||
//         fromPrecision == TSDB_TIME_PRECISION_NANO);
//  assert(toPrecision == TSDB_TIME_PRECISION_MILLI || toPrecision == TSDB_TIME_PRECISION_MICRO ||
//         toPrecision == TSDB_TIME_PRECISION_NANO);
//  static double factors[3][3] = {{1., 1000., 1000000.}, {1.0 / 1000, 1., 1000.}, {1.0 / 1000000, 1.0 / 1000, 1.}};
//  ((double)time * factors[fromPrecision][toPrecision]);
//}


// !!!!notice: double lose precison if time is too large, for example: 1626006833631000000*1.0 = double = 1626006833631000064
int64_t convertTimeFromPrecisionToUnit(int64_t time, int32_t fromPrecision, char toUnit) {
  assert(fromPrecision == TSDB_TIME_PRECISION_MILLI || fromPrecision == TSDB_TIME_PRECISION_MICRO ||
         fromPrecision == TSDB_TIME_PRECISION_NANO);
  int64_t factors[3] = {NANOSECOND_PER_MSEC, NANOSECOND_PER_USEC, 1};
  double tmp = time;
  switch (toUnit) {
    case 's':{
      tmp /= (NANOSECOND_PER_SEC/factors[fromPrecision]);     // the result of division is an integer
      time /= (NANOSECOND_PER_SEC/factors[fromPrecision]);
      break;
    }
    case 'm':
      tmp /= (NANOSECOND_PER_MINUTE/factors[fromPrecision]);  // the result of division is an integer
      time /= (NANOSECOND_PER_MINUTE/factors[fromPrecision]);
      break;
    case 'h':
      tmp /= (NANOSECOND_PER_HOUR/factors[fromPrecision]);    // the result of division is an integer
      time /= (NANOSECOND_PER_HOUR/factors[fromPrecision]);
      break;
    case 'd':
      tmp /= (NANOSECOND_PER_DAY/factors[fromPrecision]);     // the result of division is an integer
      time /= (NANOSECOND_PER_DAY/factors[fromPrecision]);
      break;
    case 'w':
      tmp /= (NANOSECOND_PER_WEEK/factors[fromPrecision]);    // the result of division is an integer
      time /= (NANOSECOND_PER_WEEK/factors[fromPrecision]);
      break;
    case 'a':
      tmp /= (NANOSECOND_PER_MSEC/factors[fromPrecision]);    // the result of division is an integer
      time /= (NANOSECOND_PER_MSEC/factors[fromPrecision]);
      break;
    case 'u':
      // the result of (NANOSECOND_PER_USEC/(double)factors[fromPrecision]) maybe a double
      switch (fromPrecision) {
        case TSDB_TIME_PRECISION_MILLI:{
          tmp /= 1000;
          time /= 1000;
          break;
        }
        case TSDB_TIME_PRECISION_MICRO:{
          tmp /= 1;
          time /= 1;
          break;
        }
        case TSDB_TIME_PRECISION_NANO:{
          tmp *= 1000;
          time *= 1000;
          break;
        }
      }
      break;
    case 'b':
      tmp *= factors[fromPrecision];
      time *= factors[fromPrecision];
      break;
    default: {
      return -1;
    }
  }
  if (tmp >= (double)INT64_MAX) return INT64_MAX;
  if (tmp <= (double)INT64_MIN) return INT64_MIN;
  return time;
}

int32_t convertStringToTimestamp(int16_t type, char *inputData, int64_t timePrec, int64_t *timeVal) {
  int32_t charLen = varDataLen(inputData);
  char *newColData;
  if (type == TSDB_DATA_TYPE_BINARY || type == TSDB_DATA_TYPE_VARBINARY) {
    newColData = taosMemoryCalloc(1,  charLen + 1);
    memcpy(newColData, varDataVal(inputData), charLen);
    bool ret = taosParseTime(newColData, timeVal, charLen, (int32_t)timePrec, tsDaylight);
    if (ret != TSDB_CODE_SUCCESS) {
      taosMemoryFree(newColData);
      return ret;
    }
    taosMemoryFree(newColData);
  } else if (type == TSDB_DATA_TYPE_NCHAR) {
    newColData = taosMemoryCalloc(1,  charLen / TSDB_NCHAR_SIZE + 1);
    int len = taosUcs4ToMbs((TdUcs4 *)varDataVal(inputData), charLen, newColData);
    if (len < 0){
      taosMemoryFree(newColData);
      return TSDB_CODE_FAILED;
    }
    newColData[len] = 0;
    bool ret = taosParseTime(newColData, timeVal, len + 1, (int32_t)timePrec, tsDaylight);
    if (ret != TSDB_CODE_SUCCESS) {
      taosMemoryFree(newColData);
      return ret;
    }
    taosMemoryFree(newColData);
  } else {
    return TSDB_CODE_FAILED;
  }
  return TSDB_CODE_SUCCESS;
}

static int32_t getDuration(int64_t val, char unit, int64_t* result, int32_t timePrecision) {
  switch (unit) {
    case 's':
      (*result) = convertTimePrecision(val * MILLISECOND_PER_SECOND, TSDB_TIME_PRECISION_MILLI, timePrecision);
      break;
    case 'm':
      (*result) = convertTimePrecision(val * MILLISECOND_PER_MINUTE, TSDB_TIME_PRECISION_MILLI, timePrecision);
      break;
    case 'h':
      (*result) = convertTimePrecision(val * MILLISECOND_PER_HOUR, TSDB_TIME_PRECISION_MILLI, timePrecision);
      break;
    case 'd':
      (*result) = convertTimePrecision(val * MILLISECOND_PER_DAY, TSDB_TIME_PRECISION_MILLI, timePrecision);
      break;
    case 'w':
      (*result) = convertTimePrecision(val * MILLISECOND_PER_WEEK, TSDB_TIME_PRECISION_MILLI, timePrecision);
      break;
    case 'a':
      (*result) = convertTimePrecision(val, TSDB_TIME_PRECISION_MILLI, timePrecision);
      break;
    case 'u':
      (*result) = convertTimePrecision(val, TSDB_TIME_PRECISION_MICRO, timePrecision);
      break;
    case 'b':
      (*result) = convertTimePrecision(val, TSDB_TIME_PRECISION_NANO, timePrecision);
      break;
    default: {
      return -1;
    }
  }
  return 0;
}

/*
 * n - months
 * y - Years
 * is not allowed, since the duration of month or year are both variable.
 *
 * b - nanoseconds;
 * u - microseconds;
 * a - Millionseconds
 * s - Seconds
 * m - Minutes
 * h - Hours
 * d - Days (24 hours)
 * w - Weeks (7 days)
 */
int32_t parseAbsoluteDuration(const char* token, int32_t tokenlen, int64_t* duration, char* unit,
                              int32_t timePrecision) {
  errno = 0;
  char* endPtr = NULL;

  /* get the basic numeric value */
  int64_t timestamp = strtoll(token, &endPtr, 10);
  if (errno != 0) {
    return -1;
  }

  /* natual month/year are not allowed in absolute duration */
  *unit = token[tokenlen - 1];
  if (*unit == 'n' || *unit == 'y') {
    return -1;
  }

  return getDuration(timestamp, *unit, duration, timePrecision);
}

int32_t parseNatualDuration(const char* token, int32_t tokenLen, int64_t* duration, char* unit, int32_t timePrecision) {
  errno = 0;

  /* get the basic numeric value */
  *duration = strtoll(token, NULL, 10);
  if (errno != 0) {
    return -1;
  }

  *unit = token[tokenLen - 1];
  if (*unit == 'n' || *unit == 'y') {
    return 0;
  }

  return getDuration(*duration, *unit, duration, timePrecision);
}

int64_t taosTimeAdd(int64_t t, int64_t duration, char unit, int32_t precision) {
  if (duration == 0) {
    return t;
  }

  if (unit != 'n' && unit != 'y') {
    return t + duration;
  }

  // The following code handles the y/n time duration
  int64_t numOfMonth = duration;
  if (unit == 'y') {
    numOfMonth *= 12;
  }

  struct tm tm;
  time_t    tt = (time_t)(t / TSDB_TICK_PER_SECOND(precision));
  taosLocalTime(&tt, &tm);
  int32_t mon = tm.tm_year * 12 + tm.tm_mon + (int32_t)numOfMonth;
  tm.tm_year = mon / 12;
  tm.tm_mon = mon % 12;

  return (int64_t)(taosMktime(&tm) * TSDB_TICK_PER_SECOND(precision));
}

int32_t taosTimeCountInterval(int64_t skey, int64_t ekey, int64_t interval, char unit, int32_t precision) {
  if (ekey < skey) {
    int64_t tmp = ekey;
    ekey = skey;
    skey = tmp;
  }
  if (unit != 'n' && unit != 'y') {
    return (int32_t)((ekey - skey) / interval);
  }

  skey /= (int64_t)(TSDB_TICK_PER_SECOND(precision));
  ekey /= (int64_t)(TSDB_TICK_PER_SECOND(precision));

  struct tm tm;
  time_t    t = (time_t)skey;
  taosLocalTime(&t, &tm);
  int32_t smon = tm.tm_year * 12 + tm.tm_mon;

  t = (time_t)ekey;
  taosLocalTime(&t, &tm);
  int32_t emon = tm.tm_year * 12 + tm.tm_mon;

  if (unit == 'y') {
    interval *= 12;
  }

  return (emon - smon) / (int32_t)interval;
}

int64_t taosTimeTruncate(int64_t t, const SInterval* pInterval, int32_t precision) {
  if (pInterval->sliding == 0) {
    assert(pInterval->interval == 0);
    return t;
  }

  int64_t start = t;
  if (pInterval->slidingUnit == 'n' || pInterval->slidingUnit == 'y') {
    start /= (int64_t)(TSDB_TICK_PER_SECOND(precision));
    struct tm tm;
    time_t    tt = (time_t)start;
    taosLocalTime(&tt, &tm);
    tm.tm_sec = 0;
    tm.tm_min = 0;
    tm.tm_hour = 0;
    tm.tm_mday = 1;

    if (pInterval->slidingUnit == 'y') {
      tm.tm_mon = 0;
      tm.tm_year = (int32_t)(tm.tm_year / pInterval->sliding * pInterval->sliding);
    } else {
      int32_t mon = tm.tm_year * 12 + tm.tm_mon;
      mon = (int32_t)(mon / pInterval->sliding * pInterval->sliding);
      tm.tm_year = mon / 12;
      tm.tm_mon = mon % 12;
    }

    start = (int64_t)(taosMktime(&tm) * TSDB_TICK_PER_SECOND(precision));
  } else {
    int64_t delta = t - pInterval->interval;
    int32_t factor = (delta >= 0) ? 1 : -1;

    start = (delta / pInterval->sliding + factor) * pInterval->sliding;

    if (pInterval->intervalUnit == 'd' || pInterval->intervalUnit == 'w') {
      /*
       * here we revised the start time of day according to the local time zone,
       * but in case of DST, the start time of one day need to be dynamically decided.
       */
      // todo refactor to extract function that is available for Linux/Windows/Mac platform
#if defined(WINDOWS) && _MSC_VER >= 1900
      // see https://docs.microsoft.com/en-us/cpp/c-runtime-library/daylight-dstbias-timezone-and-tzname?view=vs-2019
      int64_t timezone = _timezone;
      int32_t daylight = _daylight;
      char**  tzname = _tzname;
#endif

      start += (int64_t)(timezone * TSDB_TICK_PER_SECOND(precision));
    }

    int64_t end = 0;

    // not enough time range
    if (start < 0 || INT64_MAX - start > pInterval->interval - 1) {
      end = taosTimeAdd(start, pInterval->interval, pInterval->intervalUnit, precision) - 1;
      while (end < t && ((start + pInterval->sliding) <= INT64_MAX)) {  // move forward to the correct time window
        start += pInterval->sliding;

        if (start < 0 || INT64_MAX - start > pInterval->interval - 1) {
          end = start + pInterval->interval - 1;
        } else {
          end = INT64_MAX;
          break;
        }
      }
    } else {
      end = INT64_MAX;
    }
  }

  ASSERT(pInterval->offset >= 0);

  if (pInterval->offset > 0) {
    start = taosTimeAdd(start, pInterval->offset, pInterval->offsetUnit, precision);
    if (start > t) {
      start = taosTimeAdd(start, -pInterval->interval, pInterval->intervalUnit, precision);
    } else {
      // try to move current window to the left-hande-side, due to the offset effect.
      int64_t end = taosTimeAdd(start, pInterval->interval, pInterval->intervalUnit, precision) - 1;
      ASSERT(end >= t);
      end = taosTimeAdd(end, -pInterval->sliding, pInterval->slidingUnit, precision);
      if (end >= t) {
        start = taosTimeAdd(start, -pInterval->sliding, pInterval->slidingUnit, precision);
      }
    }
  }

  return start;
}

// internal function, when program is paused in debugger,
// one can call this function from debugger to print a
// timestamp as human readable string, for example (gdb):
//     p fmtts(1593769722)
// outputs:
//     2020-07-03 17:48:42
// and the parameter can also be a variable.
const char* fmtts(int64_t ts) {
  static char buf[96];
  size_t      pos = 0;
  struct tm   tm;

  if (ts > -62135625943 && ts < 32503651200) {
    time_t t = (time_t)ts;
    taosLocalTime(&t, &tm);
    pos += strftime(buf + pos, sizeof(buf), "s=%Y-%m-%d %H:%M:%S", &tm);
  }

  if (ts > -62135625943000 && ts < 32503651200000) {
    time_t t = (time_t)(ts / 1000);
    taosLocalTime(&t, &tm);
    if (pos > 0) {
      buf[pos++] = ' ';
      buf[pos++] = '|';
      buf[pos++] = ' ';
    }
    pos += strftime(buf + pos, sizeof(buf), "ms=%Y-%m-%d %H:%M:%S", &tm);
    pos += sprintf(buf + pos, ".%03d", (int32_t)(ts % 1000));
  }

  {
    time_t t = (time_t)(ts / 1000000);
    taosLocalTime(&t, &tm);
    if (pos > 0) {
      buf[pos++] = ' ';
      buf[pos++] = '|';
      buf[pos++] = ' ';
    }
    pos += strftime(buf + pos, sizeof(buf), "us=%Y-%m-%d %H:%M:%S", &tm);
    pos += sprintf(buf + pos, ".%06d", (int32_t)(ts % 1000000));
  }

  return buf;
}

void taosFormatUtcTime(char* buf, int32_t bufLen, int64_t t, int32_t precision) {
  char       ts[40] = {0};
  struct tm* ptm;

  int32_t fractionLen;
  char*   format = NULL;
  time_t  quot = 0;
  long    mod = 0;

  switch (precision) {
    case TSDB_TIME_PRECISION_MILLI: {
      quot = t / 1000;
      fractionLen = 5;
      format = ".%03" PRId64;
      mod = t % 1000;
      break;
    }

    case TSDB_TIME_PRECISION_MICRO: {
      quot = t / 1000000;
      fractionLen = 8;
      format = ".%06" PRId64;
      mod = t % 1000000;
      break;
    }

    case TSDB_TIME_PRECISION_NANO: {
      quot = t / 1000000000;
      fractionLen = 11;
      format = ".%09" PRId64;
      mod = t % 1000000000;
      break;
    }

    default:
      fractionLen = 0;
      assert(false);
  }

  ptm = taosLocalTime(&quot, NULL);
  int32_t length = (int32_t)strftime(ts, 40, "%Y-%m-%dT%H:%M:%S", ptm);
  length += snprintf(ts + length, fractionLen, format, mod);
  length += (int32_t)strftime(ts + length, 40 - length, "%z", ptm);

  tstrncpy(buf, ts, bufLen);
}