/*

  time.c (03.02.12)

  exFAT file system implementation library.

  Free exFAT implementation.

  Copyright (C) 2010-2023  Andrew Nayenko

  This program is free software; you can redistribute it and/or modify

  it under the terms of the GNU General Public License as published by

  the Free Software Foundation, either version 2 of the License, or

  (at your option) any later version.

  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.  See the

  GNU General Public License for more details.

  You should have received a copy of the GNU General Public License along

  with this program; if not, write to the Free Software Foundation, Inc.,

  51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.

*/

#include "exfat.h"

/* timezone offset from UTC in seconds; positive for western timezones,

   negative for eastern ones */

static long exfat_timezone;

#define SEC_IN_MIN 60ll

#define SEC_IN_HOUR (60 * SEC_IN_MIN)

#define SEC_IN_DAY (24 * SEC_IN_HOUR)

#define SEC_IN_YEAR (365 * SEC_IN_DAY) /* not leap year */

/* Unix epoch started at 0:00:00 UTC 1 January 1970 */

#define UNIX_EPOCH_YEAR 1970

/* exFAT epoch started at 0:00:00 UTC 1 January 1980 */

#define EXFAT_EPOCH_YEAR 1980

/* number of years from Unix epoch to exFAT epoch */

#define EPOCH_DIFF_YEAR (EXFAT_EPOCH_YEAR - UNIX_EPOCH_YEAR)

/* number of days from Unix epoch to exFAT epoch (considering leap days) */

#define EPOCH_DIFF_DAYS (EPOCH_DIFF_YEAR * 365 + EPOCH_DIFF_YEAR / 4)

/* number of seconds from Unix epoch to exFAT epoch (considering leap days) */

#define EPOCH_DIFF_SEC (EPOCH_DIFF_DAYS * SEC_IN_DAY)

/* number of leap years passed from exFAT epoch to the specified year

   (excluding the specified year itself) */

#define LEAP_YEARS(year) ((EXFAT_EPOCH_YEAR + (year) - 1) / 4 \

    - (EXFAT_EPOCH_YEAR - 1) / 4)

/* checks whether the specified year is leap */

#define IS_LEAP_YEAR(year) ((EXFAT_EPOCH_YEAR + (year)) % 4 == 0)

static const time_t days_in_year[] =

{

  /* Jan  Feb  Mar  Apr  May  Jun  Jul  Aug  Sep  Oct  Nov  Dec */

  0,   0,  31,  59,  90, 120, 151, 181, 212, 243, 273, 304, 334

};

time_t exfat_exfat2unix(le16_t date, le16_t time, uint8_t centisec,

    uint8_t tzoffset)

{

  time_t unix_time = EPOCH_DIFF_SEC;

  uint16_t ndate = le16_to_cpu(date);

  uint16_t ntime = le16_to_cpu(time);

  uint16_t day    = ndate & 0x1f;      /* 5 bits, 1-31 */

  uint16_t month  = ndate >> 5 & 0xf;  /* 4 bits, 1-12 */

  uint16_t year   = ndate >> 9;        /* 7 bits, 1-127 (+1980) */

  uint16_t twosec = ntime & 0x1f;      /* 5 bits, 0-29 (2 sec granularity) */

  uint16_t min    = ntime >> 5 & 0x3f; /* 6 bits, 0-59 */

  uint16_t hour   = ntime >> 11;       /* 5 bits, 0-23 */

  if (day == 0 || month == 0 || month > 12)

  {

    exfat_error("bad date %u-%02hu-%02hu",

        year + EXFAT_EPOCH_YEAR, month, day);

    return 0;

  }

  if (hour > 23 || min > 59 || twosec > 29)

  {

    exfat_error("bad time %hu:%02hu:%02u",

        hour, min, twosec * 2);

    return 0;

  }

  if (centisec > 199)

  {

    exfat_error("bad centiseconds count %hhu", centisec);

    return 0;

  }

  /* every 4th year between 1904 and 2096 is leap */

  unix_time += year * SEC_IN_YEAR + LEAP_YEARS(year) * SEC_IN_DAY;

  unix_time += days_in_year[month] * SEC_IN_DAY;

  /* if it's leap year and February has passed we should add 1 day */

  if ((EXFAT_EPOCH_YEAR + year) % 4 == 0 && month > 2)

    unix_time += SEC_IN_DAY;

  unix_time += (day - 1) * SEC_IN_DAY;

  unix_time += hour * SEC_IN_HOUR;

  unix_time += min * SEC_IN_MIN;

  /* exFAT represents time with 2 sec granularity */

  unix_time += twosec * 2;

  unix_time += centisec / 100;

  /* exFAT stores timestamps in local time, so we correct it to UTC */

  if (tzoffset & 0x80)

    /* lower 7 bits are signed timezone offset in 15 minute increments */

    unix_time -= (int8_t)(tzoffset << 1) * 15 * 60 / 2;

  else

    /* timezone offset not present, assume our local timezone */

    unix_time += exfat_timezone;

  return unix_time;

}

void exfat_unix2exfat(time_t unix_time, le16_t* date, le16_t* time,

    uint8_t* centisec, uint8_t* tzoffset)

{

  time_t shift = EPOCH_DIFF_SEC + exfat_timezone;

  uint16_t day, month, year;

  uint16_t twosec, min, hour;

  int days;

  int i;

  /* time before exFAT epoch cannot be represented */

  if (unix_time < shift)

    unix_time = shift;

  unix_time -= shift;

  days = unix_time / SEC_IN_DAY;

  year = (4 * days) / (4 * 365 + 1);

  days -= year * 365 + LEAP_YEARS(year);

  month = 0;

  for (i = 1; i <= 12; i++)

  {

    int leap_day = (IS_LEAP_YEAR(year) && i == 2);

    int leap_sub = (IS_LEAP_YEAR(year) && i >= 3);

    if (i == 12 || days - leap_sub < days_in_year[i + 1] + leap_day)

    {

      month = i;

      days -= days_in_year[i] + leap_sub;

      break;

    }

  }

  day = days + 1;

  hour = (unix_time % SEC_IN_DAY) / SEC_IN_HOUR;

  min = (unix_time % SEC_IN_HOUR) / SEC_IN_MIN;

  twosec = (unix_time % SEC_IN_MIN) / 2;

  *date = cpu_to_le16(day | (month << 5) | (year << 9));

  *time = cpu_to_le16(twosec | (min << 5) | (hour << 11));

  if (centisec)

    *centisec = (unix_time % 2) * 100;

  /* record our local timezone offset in exFAT (15 minute increment) format */

  *tzoffset = (uint8_t)(-exfat_timezone / 60 / 15) | 0x80;

}

void exfat_tzset(void)

{

#ifndef __UBOOT__

  time_t now;

  struct tm* utc;

  tzset();

  now = time(NULL);

  utc = gmtime(&now);

  /* gmtime() always sets tm_isdst to 0 because daylight savings never

     affect UTC. Setting tm_isdst to -1 makes mktime() to determine whether

     summer time is in effect. */

  utc->tm_isdst = -1;

  exfat_timezone = mktime(utc) - now;

#endif

}