/*
FUNCTION
<<tzset>>---set timezone characteristics from <[TZ]> environment variable

INDEX
	tzset

SYNOPSIS
	#include <time.h>
	void tzset(void);

DESCRIPTION
<<tzset>> examines the <[TZ]> environment variable and sets up the three
external variables: <<_timezone>>, <<_daylight>>, and <<tzname>>.
The value of <<_timezone>> shall be the offset from the current time
to Universal Time.
The value of <<_daylight>> shall be 0 if there is no daylight savings
time for the current time zone, otherwise it will be non-zero.
The <<tzname>> array has two entries: the first is the designation of the
standard time period, the second is the designation of the alternate time
period.

The <[TZ]> environment variable is expected to be in the following POSIX
format (spaces inserted for clarity):

    <[std]> <[offset1]> [<[dst]> [<[offset2]>] [,<[start]> [/<[time1]>], <[end]> [/<[time2]>]]]

where:

<[std]> is the designation for the standard time period (minimum 3,
maximum <<TZNAME_MAX>> bytes) in one of two forms:

*- quoted within angle bracket '<' '>' characters: portable numeric
sign or alphanumeric characters in the current locale; the
quoting characters are not included in the designation

*- unquoted: portable alphabetic characters in the current locale

<[offset1]> is the value to add to local standard time to get Universal Time;
it has the format:

    [<[S]>]<[hh]>[:<[mm]>[:<[ss]>]]

    where:

    <[S]> is an optional numeric sign character; if negative '-', the
    time zone is East of the International Reference
    Meridian; else it is positive and West, and '+' may be used

    <[hh]> is the required numeric hour between 0 and 24

    <[mm]> is the optional numeric minute between 0 and 59

    <[ss]> is the optional numeric second between 0 and 59

<[dst]> is the designation of the alternate (daylight saving or
summer) time period, with the same limits and forms as
the standard time period designation

<[offset2]> is the value to add to local alternate time to get
Universal Time; it has the same format as <[offset1]>

<[start]> is the date in the year that alternate time starts;
the form may be one of:
(quotes "'" around characters below are used only to distinguish literals)

    <[n]>	zero based Julian day (0-365), counting February 29 Leap days

    'J'<[n]>	one based Julian day (1-365), not counting February 29 Leap
    days; in all years day 59 is February 28 and day 60 is March 1

    'M'<[m]>'.'<[w]>'.'<[d]>
    month <[m]> (1-12) week <[w]> (1-5) day <[d]> (0-6) where week 1 is
    the first week in month <[m]> with day <[d]>; week 5 is the last
    week in the month; day 0 is Sunday

<[time1]> is the optional local time that alternate time starts, in
the same format as <[offset1]> without any sign, and defaults
to 02:00:00

<[end]> is the date in the year that alternate time ends, in the same
forms as <[start]>

<[time2]> is the optional local time that alternate time ends, in
the same format as <[offset1]> without any sign, and
defaults to 02:00:00

Note that there is no white-space padding between fields. Also note that
if <[TZ]> is null, the default is Universal Time which has no daylight saving
time. If <[TZ]> is empty, the default EST5EDT is used.

RETURNS
There is no return value.

PORTABILITY
<<tzset>> is part of the POSIX standard.

Supporting OS subroutine required: None
*/

#define _DEFAULT_SOURCE
#include <_ansi.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <time.h>
#include "local.h"

#define TZNAME_MIN	3	/* POSIX min TZ abbr size local def */
#define TZNAME_MAX	10	/* POSIX max TZ abbr size local def */

static char __tzname_std[TZNAME_MAX + 2];
static char __tzname_dst[TZNAME_MAX + 2];
static char *prev_tzenv = NULL;

void
_tzset_unlocked (void)
{
  char *tzenv;
  unsigned short hh, mm, ss, m, w, d;
  int sign, n;
  int i, ch;
  long offset0, offset1;
  __tzinfo_type *tz = __gettzinfo ();
  static const struct __tzrule_struct default_tzrule = {'J', 0, 0, 0, 0, (time_t)0, 0L };

  if ((tzenv = getenv ("TZ")) == NULL)
      {
	_timezone = 0;
	_daylight = 0;
	_tzname[0] = "GMT";
	_tzname[1] = "GMT";
	tz->__tzrule[0] = default_tzrule;
	tz->__tzrule[1] = default_tzrule;
	free(prev_tzenv);
	prev_tzenv = NULL;
	return;
      }

  if (prev_tzenv != NULL && strcmp(tzenv, prev_tzenv) == 0)
    return;

  free(prev_tzenv);
  prev_tzenv = malloc (strlen(tzenv) + 1);
  if (prev_tzenv != NULL)
    strcpy (prev_tzenv, tzenv);

  /* default to unnamed UTC in case of error */
  _timezone = 0;
  _daylight = 0;
  _tzname[0] = "";
  _tzname[1] = "";
  tz->__tzrule[0] = default_tzrule;
  tz->__tzrule[1] = default_tzrule;

  /* ignore implementation-specific format specifier */
  if (*tzenv == ':')
    ++tzenv;  

  /* allow POSIX angle bracket < > quoted signed alphanumeric tz abbr e.g. <MESZ+0330> */
  if (*tzenv == '<')
    {
      ++tzenv;

      /* quit if no items, too few or too many chars, or no close quote '>' */
      if (sscanf (tzenv, "%11[-+0-9A-Za-z]%n", __tzname_std, &n) <= 0
		|| n < TZNAME_MIN || TZNAME_MAX < n || '>' != tzenv[n])
        return;

      ++tzenv;	/* bump for close quote '>' */
    }
  else
    {
      /* allow POSIX unquoted alphabetic tz abbr e.g. MESZ */
      if (sscanf (tzenv, "%11[A-Za-z]%n", __tzname_std, &n) <= 0
				|| n < TZNAME_MIN || TZNAME_MAX < n)
        return;
    }
 
  tzenv += n;

  sign = 1;
  if (*tzenv == '-')
    {
      sign = -1;
      ++tzenv;
    }
  else if (*tzenv == '+')
    ++tzenv;

  mm = 0;
  ss = 0;
 
  if (sscanf (tzenv, "%hu%n:%hu%n:%hu%n", &hh, &n, &mm, &n, &ss, &n) < 1)
    return;
  
  offset0 = sign * (ss + SECSPERMIN * mm + SECSPERHOUR * hh);
  tzenv += n;

  /* allow POSIX angle bracket < > quoted signed alphanumeric tz abbr e.g. <MESZ+0330> */
  if (*tzenv == '<')
    {
      ++tzenv;

      /* quit if no items, too few or too many chars, or no close quote '>' */
      if (sscanf (tzenv, "%11[-+0-9A-Za-z]%n", __tzname_dst, &n) <= 0 && tzenv[0] == '>')
	{ /* No dst */
          _tzname[0] = __tzname_std;
          _tzname[1] = _tzname[0];
          tz->__tzrule[0].offset = offset0;
          _timezone = offset0;
	  return;
        }
      else if (n < TZNAME_MIN || TZNAME_MAX < n || '>' != tzenv[n])
	{ /* error */
	  return;
	}

      ++tzenv;	/* bump for close quote '>' */
    }
  else
    {
      /* allow POSIX unquoted alphabetic tz abbr e.g. MESZ */
      if (sscanf (tzenv, "%11[A-Za-z]%n", __tzname_dst, &n) <= 0)
	{ /* No dst */
          _tzname[0] = __tzname_std;
          _tzname[1] = _tzname[0];
          tz->__tzrule[0].offset = offset0;
          _timezone = offset0;
	  return;
        }
      else if (n < TZNAME_MIN || TZNAME_MAX < n)
	{ /* error */
	  return;
	}
    }

  tzenv += n;

  /* otherwise we have a dst name, look for the offset */
  sign = 1;
  if (*tzenv == '-')
    {
      sign = -1;
      ++tzenv;
    }
  else if (*tzenv == '+')
    ++tzenv;

  hh = 0;  
  mm = 0;
  ss = 0;
  
  n  = 0;
  if (sscanf (tzenv, "%hu%n:%hu%n:%hu%n", &hh, &n, &mm, &n, &ss, &n) <= 0)
    offset1 = offset0 - 3600;
  else
    offset1 = sign * (ss + SECSPERMIN * mm + SECSPERHOUR * hh);

  tzenv += n;

  for (i = 0; i < 2; ++i)
    {
      if (*tzenv == ',')
        ++tzenv;

      if (*tzenv == 'M')
	{
	  if (sscanf (tzenv, "M%hu%n.%hu%n.%hu%n", &m, &n, &w, &n, &d, &n) != 3 ||
	      m < 1 || m > 12 || w < 1 || w > 5 || d > 6)
	    return;
	  
	  tz->__tzrule[i].ch = 'M';
	  tz->__tzrule[i].m = m;
	  tz->__tzrule[i].n = w;
	  tz->__tzrule[i].d = d;
	  
	  tzenv += n;
	}
      else 
	{
	  char *end;
	  if (*tzenv == 'J')
	    {
	      ch = 'J';
	      ++tzenv;
	    }
	  else
	    ch = 'D';
	  
	  d = strtoul (tzenv, &end, 10);
	  
	  /* if unspecified, default to US settings */
	  /* From 1987-2006, US was M4.1.0,M10.5.0, but starting in 2007 is
	   * M3.2.0,M11.1.0 (2nd Sunday March through 1st Sunday November)  */
	  if (end == tzenv)
	    {
	      if (i == 0)
		{
		  tz->__tzrule[0].ch = 'M';
		  tz->__tzrule[0].m = 3;
		  tz->__tzrule[0].n = 2;
		  tz->__tzrule[0].d = 0;
		}
	      else
		{
		  tz->__tzrule[1].ch = 'M';
		  tz->__tzrule[1].m = 11;
		  tz->__tzrule[1].n = 1;
		  tz->__tzrule[1].d = 0;
		}
	    }
	  else
	    {
	      tz->__tzrule[i].ch = ch;
	      tz->__tzrule[i].d = d;
	    }
	  
	  tzenv = end;
	}
      
      /* default time is 02:00:00 am */
      hh = 2;
      mm = 0;
      ss = 0;
      n = 0;
      
      if (*tzenv == '/')
	if (sscanf (tzenv, "/%hu%n:%hu%n:%hu%n", &hh, &n, &mm, &n, &ss, &n) <= 0)
	  {
	    /* error in time format, restore tz rules to default and return */
	    tz->__tzrule[0] = default_tzrule;
	    tz->__tzrule[1] = default_tzrule;
            return;
          }

      tz->__tzrule[i].s = ss + SECSPERMIN * mm + SECSPERHOUR  * hh;
      
      tzenv += n;
    }

  tz->__tzrule[0].offset = offset0;
  tz->__tzrule[1].offset = offset1;
  _tzname[0] = __tzname_std;
  _tzname[1] = __tzname_dst;
  __tzcalc_limits (tz->__tzyear);
  _timezone = tz->__tzrule[0].offset;  
  _daylight = tz->__tzrule[0].offset != tz->__tzrule[1].offset;
}

void
tzset (void)
{
  TZ_LOCK;
  _tzset_unlocked ();
  TZ_UNLOCK;
}