/****************************************************************************
 * libc/time/lib_calendar2utc.c
 *
 *   Copyright (C) 2007, 2009, 2011 Gregory Nutt. All rights reserved.
 *   Author: Gregory Nutt <gnutt@nuttx.org>
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 * 3. Neither the name NuttX nor the names of its contributors may be
 *    used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 *
 ****************************************************************************/

/****************************************************************************
 * Included Files
 ****************************************************************************/

#include <nuttx/config.h>

#include <stdbool.h>
#include <time.h>
#include <debug.h>

#include <nuttx/time.h>

/****************************************************************************
 * Private Functions
 ****************************************************************************/

/****************************************************************************
 * Function:  clock_gregorian2utc, clock_julian2utc
 *
 * Description:
 *    UTC conversion routines.  These conversions are based
 *    on algorithms from p. 604 of Seidelman, P. K. 1992.
 *    Explanatory Supplement to the Astronomical Almanac.
 *    University Science Books, Mill Valley.
 *
 ****************************************************************************/

#ifdef CONFIG_GREGORIAN_TIME
static time_t clock_gregorian2utc(int year, int month, int day)
{
  int temp;

  /* temp = (month - 14)/12; */

  temp = (month <= 2 ? -1:0);

  return (1461*(year + 4800 + temp))/4
    + (367*(month - 2 - 12*temp))/12
    - (3*((year + 4900 + temp)/100))/4 + day - 32075;
}

#ifdef CONFIG_JULIAN_TIME
static time_t clock_julian2utc(int year, int month, int day)
{
  return 367*year
    - (7*(year + 5001 + (month-9)/7))/4
    + (275*month)/9
    + day + 1729777;
}
#endif /* CONFIG_JULIAN_TIME */
#endif /* CONFIG_GREGORIAN_TIME */

/****************************************************************************
 * Public Functions
 ****************************************************************************/

/****************************************************************************
 * Function:  clock_calendar2utc
 *
 * Description:
 *    Calendar/UTC conversion based on algorithms from p. 604
 *    of Seidelman, P. K. 1992.  Explanatory Supplement to
 *    the Astronomical Almanac.  University Science Books,
 *    Mill Valley.
 *
 ****************************************************************************/

#ifdef CONFIG_GREGORIAN_TIME
time_t clock_calendar2utc(int year, int month, int day)
{
  int dyear;
#ifdef CONFIG_JULIAN_TIME
  bool isgreg;
#endif /* CONFIG_JULIAN_TIME */

  /* Correct year & month ranges.  Shift month into range 1-12 */

  dyear = (month-1) / 12;	
  month -= 12 * dyear;
  year += dyear;

  if (month < 1)
    {
      month += 12;
      year -= 1;
    }

#ifdef CONFIG_JULIAN_TIME
  /* Determine which calendar to use */

  if (year > GREG_YEAR)
    {
      isgreg = true;
    }
  else if (year < GREG_YEAR)
    {
      isgreg = false;
    }
  else if (month > GREG_MONTH)
    {
      isgreg = true;
    }
  else if (month < GREG_MONTH)
    {
      isgreg = false;
    }
  else
    {
      isgreg = (day >= GREG_DAY);
    }

  /* Calculate and return date */

  if (isgreg)
    {
      return clock_gregorian2utc(year, month, day) - JD_OF_EPOCH;
    }
  else
    {
      return clock_julian2utc (year, month, day) - JD_OF_EPOCH;
    }

#else /* CONFIG_JULIAN_TIME */

  return clock_gregorian2utc(year, month, day) - JD_OF_EPOCH;

#endif /* CONFIG_JULIAN_TIME */
}
#else

/* A highly simplified version that only handles days in the time
 * since Jan 1, 1970.
 */

time_t clock_calendar2utc(int year, int month, int day)
{
  time_t days;

  /* Years since epoch in units of days (ignoring leap years). */

  days = (year - 1970) * 365;

  /* Add in the extra days for the leap years prior to the current year. */

  days += (year - 1969) >> 2;

  /* Add in the days up to the beginning of this month. */

  days += (time_t)clock_daysbeforemonth(month, clock_isleapyear(year));

  /* Add in the days since the beginning of this month (days are 1-based). */

  days += day - 1;

  /* Then convert the seconds and add in hours, minutes, and seconds */

  return days;
}
#endif /* CONFIG_GREGORIAN_TIME */