/* Provide tzset for systems that don't have it or for which it's broken.

   Copyright (C) 2001-2003, 2005-2007, 2009-2020 Free Software Foundation, Inc.

   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 3, 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, see <https://www.gnu.org/licenses/>.  */

/* written by Jim Meyering */

#include <config.h>

/* Specification.  */

#include <time.h>

#include "localtime-buffer.h"

/* This is a wrapper for tzset, for systems on which tzset may clobber

   the static buffer used for localtime's result.

   Work around the bug in some systems whereby tzset clobbers the

   static buffer that localtime uses for its return value.  The

   tzset function from Solaris 2.5, 2.5.1, and 2.6 has this problem.  */

void

tzset (void)

#undef tzset

{

#if TZSET_CLOBBERS_LOCALTIME

  /* Save and restore the contents of the buffer used for localtime's

     result around the call to tzset.  */

  struct tm save = *localtime_buffer_addr;

#endif

#if defined _WIN32 && ! defined __CYGWIN__

  /* Rectify the value of the environment variable TZ.

     There are four possible kinds of such values:

       - Traditional US time zone names, e.g. "PST8PDT".  Syntax: see

         <https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/tzset>

       - Time zone names based on geography, that contain one or more

         slashes, e.g. "Europe/Moscow".

       - Time zone names based on geography, without slashes, e.g.

         "Singapore".

       - Time zone names that contain explicit DST rules.  Syntax: see

         <https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap08.html#tag_08_03>

     The Microsoft CRT understands only the first kind.  It produces incorrect

     results if the value of TZ is of the other kinds.

     But in a Cygwin environment, /etc/profile.d/tzset.sh sets TZ to a value

     of the second kind for most geographies, or of the first kind in a few

     other geographies.  If it is of the second kind, neutralize it.  For the

     Microsoft CRT, an absent or empty TZ means the time zone that the user

     has set in the Windows Control Panel.

     If the value of TZ is of the third or fourth kind -- Cygwin programs

     understand these syntaxes as well --, it does not matter whether we

     neutralize it or not, since these values occur only when a Cygwin user

     has set TZ explicitly; this case is 1. rare and 2. under the user's

     responsibility.  */

  const char *tz = getenv ("TZ");

  if (tz != NULL && strchr (tz, '/') != NULL)

    _putenv ("TZ=");

  /* On native Windows, tzset() is deprecated.  Use _tzset() instead.  See

     <https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/posix-tzset>

     <https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/tzset>  */

  _tzset ();

#elif HAVE_TZSET

  tzset ();

#else

  /* Do nothing.  Avoid infinite recursion.  */

#endif

#if TZSET_CLOBBERS_LOCALTIME

  *localtime_buffer_addr = save;

#endif

}