glib/glib/gtimezone.c

/*
 * Copyright © 2010 Codethink Limited
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the licence, or (at your option) any later version.
 *
 * This library 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
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, see <http://www.gnu.org/licenses/>.
 *
 * Author: Ryan Lortie <desrt@desrt.ca>
 */

/* Prologue {{{1 */

#include "config.h"

#include "gtimezone.h"

#include <string.h>
#include <stdlib.h>
#include <signal.h>

#include "gmappedfile.h"
#include "gtestutils.h"
#include "gfileutils.h"
#include "gstrfuncs.h"
#include "ghash.h"
#include "gthread.h"
#include "gbytes.h"
#include "gslice.h"
#include "gdatetime.h"
#include "gdate.h"

#ifdef G_OS_WIN32
#define STRICT
#include <windows.h>
#endif

/**
 * SECTION:timezone
 * @title: GTimeZone
 * @short_description: a structure representing a time zone
 * @see_also: #GDateTime
 *
 * #GTimeZone is a structure that represents a time zone, at no
 * particular point in time.  It is refcounted and immutable.
 *
 * A time zone contains a number of intervals.  Each interval has
 * an abbreviation to describe it, an offet to UTC and a flag indicating
 * if the daylight savings time is in effect during that interval.  A
 * time zone always has at least one interval -- interval 0.
 *
 * Every UTC time is contained within exactly one interval, but a given
 * local time may be contained within zero, one or two intervals (due to
 * incontinuities associated with daylight savings time).
 *
 * An interval may refer to a specific period of time (eg: the duration
 * of daylight savings time during 2010) or it may refer to many periods
 * of time that share the same properties (eg: all periods of daylight
 * savings time).  It is also possible (usually for political reasons)
 * that some properties (like the abbreviation) change between intervals
 * without other properties changing.
 *
 * #GTimeZone is available since GLib 2.26.
 */

/**
 * GTimeZone:
 *
 * #GTimeZone is an opaque structure whose members cannot be accessed
 * directly.
 *
 * Since: 2.26
 **/

/* IANA zoneinfo file format {{{1 */

/* unaligned */
typedef struct { gchar bytes[8]; } gint64_be;
typedef struct { gchar bytes[4]; } gint32_be;
typedef struct { gchar bytes[4]; } guint32_be;

static inline gint64 gint64_from_be (const gint64_be be) {
  gint64 tmp; memcpy (&tmp, &be, sizeof tmp); return GINT64_FROM_BE (tmp);
}

static inline gint32 gint32_from_be (const gint32_be be) {
  gint32 tmp; memcpy (&tmp, &be, sizeof tmp); return GINT32_FROM_BE (tmp);
}

static inline guint32 guint32_from_be (const guint32_be be) {
  guint32 tmp; memcpy (&tmp, &be, sizeof tmp); return GUINT32_FROM_BE (tmp);
}

/* The layout of an IANA timezone file header */
struct tzhead
{
  gchar      tzh_magic[4];
  gchar      tzh_version;
  guchar     tzh_reserved[15];

  guint32_be tzh_ttisgmtcnt;
  guint32_be tzh_ttisstdcnt;
  guint32_be tzh_leapcnt;
  guint32_be tzh_timecnt;
  guint32_be tzh_typecnt;
  guint32_be tzh_charcnt;
};

struct ttinfo
{
  gint32_be tt_gmtoff;
  guint8    tt_isdst;
  guint8    tt_abbrind;
};

/* A Transition Date structure for TZ Rules, an intermediate structure
   for parsing MSWindows and Environment-variable time zones. It
   Generalizes MSWindows's SYSTEMTIME struct.
 */
typedef struct
{
  gint     year;
  gint     mon;
  gint     mday;
  gint     wday;
  gint     week;
  gint     hour;
  gint     min;
  gint     sec;
} TimeZoneDate;

/* POSIX Timezone abbreviations are typically 3 or 4 characters, but
   Microsoft uses 32-character names. We'll use one larger to ensure
   we have room for the terminating \0.
 */
#define NAME_SIZE 33

/* A MSWindows-style time zone transition rule. Generalizes the
   MSWindows TIME_ZONE_INFORMATION struct. Also used to compose time
   zones from tzset-style identifiers.
 */
typedef struct
{
  gint         start_year;
  gint32       std_offset;
  gint32       dlt_offset;
  TimeZoneDate dlt_start;
  TimeZoneDate dlt_end;
  gchar std_name[NAME_SIZE];
  gchar dlt_name[NAME_SIZE];
} TimeZoneRule;

/* GTimeZone's internal representation of a Daylight Savings (Summer)
   time interval.
 */
typedef struct
{
  gint32     gmt_offset;
  gboolean   is_dst;
  gchar     *abbrev;
} TransitionInfo;

/* GTimeZone's representation of a transition time to or from Daylight
   Savings (Summer) time and Standard time for the zone. */
typedef struct
{
  gint64 time;
  gint   info_index;
} Transition;

/* GTimeZone structure */
struct _GTimeZone
{
  gchar   *name;
  GArray  *t_info;         /* Array of TransitionInfo */
  GArray  *transitions;    /* Array of Transition */
  gint     ref_count;
};

G_LOCK_DEFINE_STATIC (time_zones);
static GHashTable/*<string?, GTimeZone>*/ *time_zones;

#define MIN_TZYEAR 1916 /* Daylight Savings started in WWI */
#define MAX_TZYEAR 2999 /* And it's not likely ever to go away, but
                           there's no point in getting carried
                           away. */

/**
 * g_time_zone_unref:
 * @tz: a #GTimeZone
 *
 * Decreases the reference count on @tz.
 *
 * Since: 2.26
 **/
void
g_time_zone_unref (GTimeZone *tz)
{
  int ref_count;

again:
  ref_count = g_atomic_int_get (&tz->ref_count);

  g_assert (ref_count > 0);

  if (ref_count == 1)
    {
      if (tz->name != NULL)
        {
          G_LOCK(time_zones);

          /* someone else might have grabbed a ref in the meantime */
          if G_UNLIKELY (g_atomic_int_get (&tz->ref_count) != 1)
            {
              G_UNLOCK(time_zones);
              goto again;
            }

          g_hash_table_remove (time_zones, tz->name);
          G_UNLOCK(time_zones);
        }

      if (tz->t_info != NULL)
        {
          gint idx;
          for (idx = 0; idx < tz->t_info->len; idx++)
            {
              TransitionInfo *info = &g_array_index (tz->t_info, TransitionInfo, idx);
              g_free (info->abbrev);
            }
          g_array_free (tz->t_info, TRUE);
        }
      if (tz->transitions != NULL)
        g_array_free (tz->transitions, TRUE);
      g_free (tz->name);

      g_slice_free (GTimeZone, tz);
    }

  else if G_UNLIKELY (!g_atomic_int_compare_and_exchange (&tz->ref_count,
                                                          ref_count,
                                                          ref_count - 1))
    goto again;
}

/**
 * g_time_zone_ref:
 * @tz: a #GTimeZone
 *
 * Increases the reference count on @tz.
 *
 * Returns: a new reference to @tz.
 *
 * Since: 2.26
 **/
GTimeZone *
g_time_zone_ref (GTimeZone *tz)
{
  g_assert (tz->ref_count > 0);

  g_atomic_int_inc (&tz->ref_count);

  return tz;
}

/* fake zoneinfo creation (for RFC3339/ISO 8601 timezones) {{{1 */
/*
 * parses strings of the form h or hh[[:]mm[[[:]ss]]] where:
 *  - h[h] is 0 to 23
 *  - mm is 00 to 59
 *  - ss is 00 to 59
 */
static gboolean
parse_time (const gchar *time_,
            gint32      *offset)
{
  if (*time_ < '0' || '9' < *time_)
    return FALSE;

  *offset = 60 * 60 * (*time_++ - '0');

  if (*time_ == '\0')
    return TRUE;

  if (*time_ != ':')
    {
      if (*time_ < '0' || '9' < *time_)
        return FALSE;

      *offset *= 10;
      *offset += 60 * 60 * (*time_++ - '0');

      if (*offset > 23 * 60 * 60)
        return FALSE;

      if (*time_ == '\0')
        return TRUE;
    }

  if (*time_ == ':')
    time_++;

  if (*time_ < '0' || '5' < *time_)
    return FALSE;

  *offset += 10 * 60 * (*time_++ - '0');

  if (*time_ < '0' || '9' < *time_)
    return FALSE;

  *offset += 60 * (*time_++ - '0');

  if (*time_ == '\0')
    return TRUE;

  if (*time_ == ':')
    time_++;

  if (*time_ < '0' || '5' < *time_)
    return FALSE;

  *offset += 10 * (*time_++ - '0');

  if (*time_ < '0' || '9' < *time_)
    return FALSE;

  *offset += *time_++ - '0';

  return *time_ == '\0';
}

static gboolean
parse_constant_offset (const gchar *name,
                       gint32      *offset)
{
  if (g_strcmp0 (name, "UTC") == 0)
    {
      *offset = 0;
      return TRUE;
    }

  if (*name >= '0' && '9' >= *name)
    return parse_time (name, offset);

  switch (*name++)
    {
    case 'Z':
      *offset = 0;
      return !*name;

    case '+':
      return parse_time (name, offset);

    case '-':
      if (parse_time (name, offset))
        {
          *offset = -*offset;
          return TRUE;
        }

    default:
      return FALSE;
    }
}

static void
zone_for_constant_offset (GTimeZone *gtz, const gchar *name)
{
  gint32 offset;
  TransitionInfo info;

  if (name == NULL || !parse_constant_offset (name, &offset))
    return;

  info.gmt_offset = offset;
  info.is_dst = FALSE;
  info.abbrev =  g_strdup (name);


  gtz->t_info = g_array_sized_new (FALSE, TRUE, sizeof (TransitionInfo), 1);
  g_array_append_val (gtz->t_info, info);

  /* Constant offset, no transitions */
  gtz->transitions = NULL;
}

#ifdef G_OS_UNIX
static GBytes*
zone_info_unix (const gchar *identifier)
{
  gchar *filename;
  GMappedFile *file = NULL;
  GBytes *zoneinfo = NULL;

  /* identifier can be a relative or absolute path name;
     if relative, it is interpreted starting from /usr/share/zoneinfo
     while the POSIX standard says it should start with :,
     glibc allows both syntaxes, so we should too */
  if (identifier != NULL)
    {
      const gchar *tzdir;

      tzdir = getenv ("TZDIR");
      if (tzdir == NULL)
        tzdir = "/usr/share/zoneinfo";

      if (*identifier == ':')
        identifier ++;

      if (g_path_is_absolute (identifier))
        filename = g_strdup (identifier);
      else
        filename = g_build_filename (tzdir, identifier, NULL);
    }
  else
    filename = g_strdup ("/etc/localtime");

  file = g_mapped_file_new (filename, FALSE, NULL);
  if (file != NULL)
    {
      zoneinfo = g_bytes_new_with_free_func (g_mapped_file_get_contents (file),
                                             g_mapped_file_get_length (file),
                                             (GDestroyNotify)g_mapped_file_unref,
                                             g_mapped_file_ref (file));
      g_mapped_file_unref (file);
    }
  g_free (filename);
  return zoneinfo;
}

static void
init_zone_from_iana_info (GTimeZone *gtz, GBytes *zoneinfo)
{
  gsize size;
  guint index;
  guint32 time_count, type_count;
  guint8 *tz_transitions, *tz_type_index, *tz_ttinfo;
  guint8 *tz_abbrs;
  gsize timesize = sizeof (gint32);
  const struct tzhead *header = g_bytes_get_data (zoneinfo, &size);

  g_return_if_fail (size >= sizeof (struct tzhead) &&
                    memcmp (header, "TZif", 4) == 0);

  if (header->tzh_version == '2')
      {
        /* Skip ahead to the newer 64-bit data if it's available. */
        header = (const struct tzhead *)
          (((const gchar *) (header + 1)) +
           guint32_from_be(header->tzh_ttisgmtcnt) +
           guint32_from_be(header->tzh_ttisstdcnt) +
           8 * guint32_from_be(header->tzh_leapcnt) +
           5 * guint32_from_be(header->tzh_timecnt) +
           6 * guint32_from_be(header->tzh_typecnt) +
           guint32_from_be(header->tzh_charcnt));
        timesize = sizeof (gint64);
      }
  time_count = guint32_from_be(header->tzh_timecnt);
  type_count = guint32_from_be(header->tzh_typecnt);

  tz_transitions = ((guint8 *) (header) + sizeof (*header));
  tz_type_index = tz_transitions + timesize * time_count;
  tz_ttinfo = tz_type_index + time_count;
  tz_abbrs = tz_ttinfo + sizeof (struct ttinfo) * type_count;

  gtz->t_info = g_array_sized_new (FALSE, TRUE, sizeof (TransitionInfo),
                                   type_count);
  gtz->transitions = g_array_sized_new (FALSE, TRUE, sizeof (Transition),
                                        time_count);

  for (index = 0; index < type_count; index++)
    {
      TransitionInfo t_info;
      struct ttinfo info = ((struct ttinfo*)tz_ttinfo)[index];
      t_info.gmt_offset = gint32_from_be (info.tt_gmtoff);
      t_info.is_dst = info.tt_isdst ? TRUE : FALSE;
      t_info.abbrev = g_strdup ((gchar *) &tz_abbrs[info.tt_abbrind]);
      g_array_append_val (gtz->t_info, t_info);
    }

  for (index = 0; index < time_count; index++)
    {
      Transition trans;
      if (header->tzh_version == '2')
        trans.time = gint64_from_be (((gint64_be*)tz_transitions)[index]);
      else
        trans.time = gint32_from_be (((gint32_be*)tz_transitions)[index]);
      trans.info_index = tz_type_index[index];
      g_assert (trans.info_index >= 0);
      g_assert (trans.info_index < gtz->t_info->len);
      g_array_append_val (gtz->transitions, trans);
    }
}

#elif defined (G_OS_WIN32)

static void
copy_windows_systemtime (SYSTEMTIME *s_time, TimeZoneDate *tzdate)
{
  tzdate->sec = s_time->wSecond;
  tzdate->min = s_time->wMinute;
  tzdate->hour = s_time->wHour;
  tzdate->mon = s_time->wMonth;
  tzdate->year = s_time->wYear;
  tzdate->wday = s_time->wDayOfWeek ? s_time->wDayOfWeek : 7;

  if (s_time->wYear)
    {
      tzdate->mday = s_time->wDay;
      tzdate->wday = 0;
    }
  else
    tzdate->week = s_time->wDay;
}

/* UTC = local time + bias while local time = UTC + offset */
static void
rule_from_windows_time_zone_info (TimeZoneRule *rule,
                                  TIME_ZONE_INFORMATION *tzi)
{
  /* Set offset */
  if (tzi->StandardDate.wMonth)
    {
      rule->std_offset = -(tzi->Bias + tzi->StandardBias) * 60;
      rule->dlt_offset = -(tzi->Bias + tzi->DaylightBias) * 60;
      copy_windows_systemtime (&(tzi->DaylightDate), &(rule->dlt_start));

      copy_windows_systemtime (&(tzi->StandardDate), &(rule->dlt_end));

    }

  else
    {
      rule->std_offset = -tzi->Bias * 60;
      rule->dlt_start.mon = 0;
    }
  strncpy (rule->std_name, (gchar*)tzi->StandardName, NAME_SIZE - 1);
  strncpy (rule->dlt_name, (gchar*)tzi->DaylightName, NAME_SIZE - 1);
}

static gchar*
windows_default_tzname (void)
{
  const gchar *subkey =
    "SYSTEM\\CurrentControlSet\\Control\\TimeZoneInformation";
  HKEY key;
  gchar *key_name = NULL;
  if (RegOpenKeyExA (HKEY_LOCAL_MACHINE, subkey, 0,
                     KEY_QUERY_VALUE, &key) == ERROR_SUCCESS)
    {
      DWORD size = 0;
      if (RegQueryValueExA (key, "TimeZoneKeyName", NULL, NULL,
                            NULL, &size) == ERROR_SUCCESS)
        {
          key_name = g_malloc ((gint)size);
          if (RegQueryValueExA (key, "TimeZoneKeyName", NULL, NULL,
                                (LPBYTE)key_name, &size) != ERROR_SUCCESS)
            {
              g_free (key_name);
              key_name = NULL;
            }
        }
      RegCloseKey (key);
    }
  return key_name;
}

typedef   struct
{
  LONG Bias;
  LONG StandardBias;
  LONG DaylightBias;
  SYSTEMTIME StandardDate;
  SYSTEMTIME DaylightDate;
} RegTZI;

static void
system_time_copy (SYSTEMTIME *orig, SYSTEMTIME *target)
{
  g_return_if_fail (orig != NULL);
  g_return_if_fail (target != NULL);

  target->wYear = orig->wYear;
  target->wMonth = orig->wMonth;
  target->wDayOfWeek = orig->wDayOfWeek;
  target->wDay = orig->wDay;
  target->wHour = orig->wHour;
  target->wMinute = orig->wMinute;
  target->wSecond = orig->wSecond;
  target->wMilliseconds = orig->wMilliseconds;
}

static void
register_tzi_to_tzi (RegTZI *reg, TIME_ZONE_INFORMATION *tzi)
{
  g_return_if_fail (reg != NULL);
  g_return_if_fail (tzi != NULL);
  tzi->Bias = reg->Bias;
  system_time_copy (&(reg->StandardDate), &(tzi->StandardDate));
  tzi->StandardBias = reg->StandardBias;
  system_time_copy (&(reg->DaylightDate), &(tzi->DaylightDate));
  tzi->DaylightBias = reg->DaylightBias;
}

static gint
rules_from_windows_time_zone (const gchar *identifier, TimeZoneRule **rules)
{
  HKEY key;
  gchar *subkey, *subkey_dynamic;
  gchar *key_name = NULL;
  const gchar *reg_key =
    "SOFTWARE\\Microsoft\\Windows NT\\CurrentVersion\\Time Zones\\";
  TIME_ZONE_INFORMATION tzi;
  DWORD size;
  gint rules_num = 0;
  RegTZI regtzi, regtzi_prev;

  *rules = NULL;
  key_name = NULL;

  if (!identifier)
    key_name = windows_default_tzname ();
  else
    key_name = g_strdup (identifier);

  if (!key_name)
    return 0;

  subkey = g_strconcat (reg_key, key_name, NULL);
  subkey_dynamic = g_strconcat (subkey, "\\Dynamic DST", NULL);

  if (RegOpenKeyExA (HKEY_LOCAL_MACHINE, subkey, 0,
                     KEY_QUERY_VALUE, &key) != ERROR_SUCCESS)
      return 0;
  size = sizeof tzi.StandardName;
  if (RegQueryValueExA (key, "Std", NULL, NULL,
                        (LPBYTE)&(tzi.StandardName), &size) != ERROR_SUCCESS)
    goto failed;

  size = sizeof tzi.DaylightName;

  if (RegQueryValueExA (key, "Dlt", NULL, NULL,
                        (LPBYTE)&(tzi.DaylightName), &size) != ERROR_SUCCESS)
    goto failed;

  RegCloseKey (key);
  if (RegOpenKeyExA (HKEY_LOCAL_MACHINE, subkey_dynamic, 0,
                     KEY_QUERY_VALUE, &key) == ERROR_SUCCESS)
    {
      DWORD first, last;
      int year, i;
      gchar *s;

      size = sizeof first;
      if (RegQueryValueExA (key, "FirstEntry", NULL, NULL,
                            (LPBYTE) &first, &size) != ERROR_SUCCESS)
        goto failed;

      size = sizeof last;
      if (RegQueryValueExA (key, "LastEntry", NULL, NULL,
                            (LPBYTE) &last, &size) != ERROR_SUCCESS)
        goto failed;

      rules_num = last - first + 2;
      *rules = g_new0 (TimeZoneRule, rules_num);

      for (year = first, i = 0; year <= last; year++)
        {
          s = g_strdup_printf ("%d", year);

          size = sizeof regtzi;
          if (RegQueryValueExA (key, s, NULL, NULL,
                            (LPBYTE) &regtzi, &size) != ERROR_SUCCESS)
            {
              g_free (*rules);
              *rules = NULL;
              break;
            }

          g_free (s);

          if (year > first && memcmp (&regtzi_prev, &regtzi, sizeof regtzi) == 0)
              continue;
          else
            memcpy (&regtzi_prev, &regtzi, sizeof regtzi);

          register_tzi_to_tzi (&regtzi, &tzi);
          rule_from_windows_time_zone_info (&(*rules)[i], &tzi);
          (*rules)[i++].start_year = year;
        }

      rules_num = i + 1;

failed:
      RegCloseKey (key);
    }
  else if (RegOpenKeyExA (HKEY_LOCAL_MACHINE, subkey, 0,
                          KEY_QUERY_VALUE, &key) == ERROR_SUCCESS)
    {
      size = sizeof regtzi;
      if (RegQueryValueExA (key, "TZI", NULL, NULL,
                            (LPBYTE) &regtzi, &size) == ERROR_SUCCESS)
        {
          rules_num = 2;
          *rules = g_new0 (TimeZoneRule, 2);
          register_tzi_to_tzi (&regtzi, &tzi);
          rule_from_windows_time_zone_info (&(*rules)[0], &tzi);
        }

      RegCloseKey (key);
    }

  g_free (subkey_dynamic);
  g_free (subkey);
  g_free (key_name);

  if (*rules)
    {
      (*rules)[0].start_year = MIN_TZYEAR;
      if ((*rules)[rules_num - 2].start_year < MAX_TZYEAR)
        (*rules)[rules_num - 1].start_year = MAX_TZYEAR;
      else
        (*rules)[rules_num - 1].start_year = (*rules)[rules_num - 2].start_year + 1;

      return rules_num;
    }
  else
    return 0;
}

#endif

static void
find_relative_date (TimeZoneDate *buffer)
{
  gint wday;
  GDate date;
  g_date_clear (&date, 1);
  wday = buffer->wday;

  /* Get last day if last is needed, first day otherwise */
  if (buffer->mon == 13 || buffer->mon == 14) /* Julian Date */
    {
      g_date_set_dmy (&date, 1, 1, buffer->year);
      if (wday >= 59 && buffer->mon == 13 && g_date_is_leap_year (buffer->year))
        g_date_add_days (&date, wday);
      else
        g_date_add_days (&date, wday - 1);
      buffer->mon = (int) g_date_get_month (&date);
      buffer->mday = (int) g_date_get_day (&date);
      buffer->wday = 0;
    }
  else /* M.W.D */
    {
      guint days;
      guint days_in_month = g_date_days_in_month (buffer->mon, buffer->year);
      GDateWeekday first_wday;

      g_date_set_dmy (&date, 1, buffer->mon, buffer->year);
      first_wday = g_date_get_weekday (&date);

      if (first_wday > wday)
        ++(buffer->week);
      /* week is 1 <= w <= 5, we need 0-based */
      days = 7 * (buffer->week - 1) + wday - first_wday;

      while (days > days_in_month)
        days -= 7;

      g_date_add_days (&date, days);

      buffer->mday = g_date_get_day (&date);
    }
}

/* Offset is previous offset of local time. Returns 0 if month is 0 */
static gint64
boundary_for_year (TimeZoneDate *boundary,
                   gint          year,
                   gint32        offset)
{
  TimeZoneDate buffer;
  GDate date;
  const guint64 unix_epoch_start = 719163L;
  const guint64 seconds_per_day = 86400L;

  if (!boundary->mon)
    return 0;
  buffer = *boundary;

  if (boundary->year == 0)
    {
      buffer.year = year;

      if (buffer.wday)
        find_relative_date (&buffer);
    }

  g_assert (buffer.year == year);
  g_date_clear (&date, 1);
  g_date_set_dmy (&date, buffer.mday, buffer.mon, buffer.year);
  return ((g_date_get_julian (&date) - unix_epoch_start) * seconds_per_day +
          buffer.hour * 3600 + buffer.min * 60 + buffer.sec - offset);
}

static void
fill_transition_info_from_rule (TransitionInfo *info,
                                TimeZoneRule   *rule,
                                gboolean        is_dst)
{
  gint offset = is_dst ? rule->dlt_offset : rule->std_offset;
  gchar *name = is_dst ? rule->dlt_name : rule->std_name;

  info->gmt_offset = offset;
  info->is_dst = is_dst;

  if (name)
    info->abbrev = g_strdup (name);

  else
    info->abbrev = g_strdup_printf ("%+03d%02d",
                                      (int) offset / 3600,
                                      (int) abs (offset / 60) % 60);
}

static void
init_zone_from_rules (GTimeZone    *gtz,
                      TimeZoneRule *rules,
                      gint          rules_num)
{
  guint type_count = 0, trans_count = 0, info_index = 0;
  guint ri; /* rule index */
  gboolean skip_first_std_trans = TRUE;
  gint32 last_offset;

  type_count = 0;
  trans_count = 0;

  /* Last rule only contains max year */
  for (ri = 0; ri < rules_num - 1; ri++)
    {
      if (rules[ri].dlt_start.mon || rules[ri].dlt_end.mon)
        {
          guint rulespan = (rules[ri + 1].start_year - rules[ri].start_year);
          guint transitions = rules[ri].dlt_start.mon > 0 ? 1 : 0;
          transitions += rules[ri].dlt_end.mon > 0 ? 1 : 0;
          type_count += rules[ri].dlt_start.mon > 0 ? 2 : 1;
          trans_count += transitions * rulespan;
        }
      else
        type_count++;
    }

  gtz->t_info = g_array_sized_new (FALSE, TRUE, sizeof (TransitionInfo), type_count);
  gtz->transitions = g_array_sized_new (FALSE, TRUE, sizeof (Transition), trans_count);

  last_offset = rules[0].std_offset;

  for (ri = 0; ri < rules_num - 1; ri++)
    {
      if ((rules[ri].std_offset || rules[ri].dlt_offset) &&
          rules[ri].dlt_start.mon == 0 && rules[ri].dlt_end.mon == 0)
        {
          TransitionInfo std_info;
          /* Standard */
          fill_transition_info_from_rule (&std_info, &(rules[ri]), FALSE);
          g_array_append_val (gtz->t_info, std_info);

          if (ri > 0 &&
              ((rules[ri - 1].dlt_start.mon > 12 &&
                rules[ri - 1].dlt_start.wday > rules[ri - 1].dlt_end.wday) ||
                rules[ri - 1].dlt_start.mon > rules[ri - 1].dlt_end.mon))
            {
              /* The previous rule was a southern hemisphere rule that
                 starts the year with DST, so we need to add a
                 transition to return to standard time */
              guint year = rules[ri].start_year;
              gint64 std_time =  boundary_for_year (&rules[ri].dlt_end,
                                                    year, last_offset);
              Transition std_trans = {std_time, info_index};
              g_array_append_val (gtz->transitions, std_trans);

            }
          last_offset = rules[ri].std_offset;
          ++info_index;
          skip_first_std_trans = TRUE;
         }
      else
        {
          const guint start_year = rules[ri].start_year;
          const guint end_year = rules[ri + 1].start_year;
          gboolean dlt_first;
          guint year;
          TransitionInfo std_info, dlt_info;
          if (rules[ri].dlt_start.mon > 12)
            dlt_first = rules[ri].dlt_start.wday > rules[ri].dlt_end.wday;
          else
            dlt_first = rules[ri].dlt_start.mon > rules[ri].dlt_end.mon;
          /* Standard rules are always even, because before the first
             transition is always standard time, and 0 is even. */
          fill_transition_info_from_rule (&std_info, &(rules[ri]), FALSE);
          fill_transition_info_from_rule (&dlt_info, &(rules[ri]), TRUE);

          g_array_append_val (gtz->t_info, std_info);
          g_array_append_val (gtz->t_info, dlt_info);

          /* Transition dates. We hope that a year which ends daylight
             time in a southern-hemisphere country (i.e., one that
             begins the year in daylight time) will include a rule
             which has only a dlt_end. */
          for (year = start_year; year < end_year; year++)
            {
              gint32 dlt_offset = (dlt_first ? last_offset :
                                   rules[ri].dlt_offset);
              gint32 std_offset = (dlt_first ? rules[ri].std_offset :
                                   last_offset);
              /* NB: boundary_for_year returns 0 if mon == 0 */
              gint64 std_time =  boundary_for_year (&rules[ri].dlt_end,
                                                    year, dlt_offset);
              gint64 dlt_time = boundary_for_year (&rules[ri].dlt_start,
                                                   year, std_offset);
              Transition std_trans = {std_time, info_index};
              Transition dlt_trans = {dlt_time, info_index + 1};
              last_offset = (dlt_first ? rules[ri].dlt_offset :
                             rules[ri].std_offset);
              if (dlt_first)
                {
                  if (skip_first_std_trans)
                    skip_first_std_trans = FALSE;
                  else if (std_time)
                    g_array_append_val (gtz->transitions, std_trans);
                  if (dlt_time)
                    g_array_append_val (gtz->transitions, dlt_trans);
                }
              else
                {
                  if (dlt_time)
                    g_array_append_val (gtz->transitions, dlt_trans);
                  if (std_time)
                    g_array_append_val (gtz->transitions, std_trans);
                }
            }

          info_index += 2;
        }
    }
  if (ri > 0 &&
      ((rules[ri - 1].dlt_start.mon > 12 &&
        rules[ri - 1].dlt_start.wday > rules[ri - 1].dlt_end.wday) ||
       rules[ri - 1].dlt_start.mon > rules[ri - 1].dlt_end.mon))
    {
      /* The previous rule was a southern hemisphere rule that
         starts the year with DST, so we need to add a
         transition to return to standard time */
      TransitionInfo info;
      guint year = rules[ri].start_year;
      Transition trans;
      fill_transition_info_from_rule (&info, &(rules[ri - 1]), FALSE);
      g_array_append_val (gtz->t_info, info);
      trans.time = boundary_for_year (&rules[ri - 1].dlt_end,
                                      year, last_offset);
      trans.info_index = info_index;
      g_array_append_val (gtz->transitions, trans);
     }
}

/*
 * parses date[/time] for parsing TZ environment variable
 *
 * date is either Mm.w.d, Jn or N
 * - m is 1 to 12
 * - w is 1 to 5
 * - d is 0 to 6
 * - n is 1 to 365
 * - N is 0 to 365
 *
 * time is either h or hh[[:]mm[[[:]ss]]]
 *  - h[h] is 0 to 23
 *  - mm is 00 to 59
 *  - ss is 00 to 59
 */
static gboolean
parse_mwd_boundary (gchar **pos, TimeZoneDate *boundary)
{
  gint month, week, day;

  if (**pos == '\0' || **pos < '0' || '9' < **pos)
    return FALSE;

  month = *(*pos)++ - '0';

  if ((month == 1 && **pos >= '0' && '2' >= **pos) ||
      (month == 0 && **pos >= '0' && '9' >= **pos))
    {
      month *= 10;
      month += *(*pos)++ - '0';
    }

  if (*(*pos)++ != '.' || month == 0)
    return FALSE;

  if (**pos == '\0' || **pos < '1' || '5' < **pos)
    return FALSE;

  week = *(*pos)++ - '0';

  if (*(*pos)++ != '.')
    return FALSE;

  if (**pos == '\0' || **pos < '0' || '6' < **pos)
    return FALSE;

  day = *(*pos)++ - '0';

  if (!day)
    day += 7;

  boundary->year = 0;
  boundary->mon = month;
  boundary->week = week;
  boundary->wday = day;
  return TRUE;
}

/* Different implementations of tzset interpret the Julian day field
   differently. For example, Linux specifies that it should be 1-based
   (1 Jan is JD 1) for both Jn and n formats, while zOS and BSD
   specify that a Jn JD is 1-based while an n JD is 0-based. Rather
   than trying to follow different specs, we will follow GDate's
   practice thatIn order to keep it simple, we will follow Linux's
   practice. */

static gboolean
parse_julian_boundary (gchar** pos, TimeZoneDate *boundary,
                       gboolean ignore_leap)
{
  gint day = 0;
  GDate date;

  while (**pos >= '0' && '9' >= **pos)
    {
      day *= 10;
      day += *(*pos)++ - '0';
    }

  if (day < 1 || 365 < day)
    return FALSE;

  g_date_clear (&date, 1);
  g_date_set_julian (&date, day);
  boundary->year = 0;
  boundary->mon = (int) g_date_get_month (&date);
  boundary->mday = (int) g_date_get_day (&date);
  boundary->wday = 0;

  if (!ignore_leap && day >= 59)
    boundary->mday++;

  return TRUE;
}

static gboolean
parse_tz_boundary (const gchar  *identifier,
                   TimeZoneDate *boundary)
{
  gchar *pos;

  pos = (gchar*)identifier;
  /* Month-week-weekday */
  if (*pos == 'M')
    {
      ++pos;
      if (!parse_mwd_boundary (&pos, boundary))
        return FALSE;
    }
  /* Julian date which ignores Feb 29 in leap years */
  else if (*pos == 'J')
    {
      ++pos;
      if (!parse_julian_boundary (&pos, boundary, FALSE))
        return FALSE ;
    }
  /* Julian date which counts Feb 29 in leap years */
  else if (*pos >= '0' && '9' >= *pos)
    {
      if (!parse_julian_boundary (&pos, boundary, TRUE))
        return FALSE;
    }
  else
    return FALSE;

  /* Time */

  if (*pos == '/')
    {
      gint32 offset;

      if (!parse_time (++pos, &offset))
        return FALSE;

      boundary->hour = offset / 3600;
      boundary->min = (offset / 60) % 60;
      boundary->sec = offset % 3600;

      return TRUE;
    }

  else
    {
      boundary->hour = 2;
      boundary->min = 0;
      boundary->sec = 0;

      return *pos == '\0';
    }
}

static gint
create_ruleset_from_rule (TimeZoneRule **rules, TimeZoneRule *rule)
{
  *rules = g_new0 (TimeZoneRule, 2);

  (*rules)[0].start_year = MIN_TZYEAR;
  (*rules)[1].start_year = MAX_TZYEAR;

  (*rules)[0].std_offset = -rule->std_offset;
  (*rules)[0].dlt_offset = -rule->dlt_offset;
  (*rules)[0].dlt_start  = rule->dlt_start;
  (*rules)[0].dlt_end = rule->dlt_end;
  strcpy ((*rules)[0].std_name, rule->std_name);
  strcpy ((*rules)[0].dlt_name, rule->dlt_name);
  return 2;
}

static gboolean
parse_offset (gchar **pos, gint32 *target)
{
  gchar *buffer;
  gchar *target_pos = *pos;
  gboolean ret;

  while (**pos == '+' || **pos == '-' || **pos == ':' ||
         (**pos >= '0' && '9' >= **pos))
    ++(*pos);

  buffer = g_strndup (target_pos, *pos - target_pos);
  ret = parse_constant_offset (buffer, target);
  g_free (buffer);

  return ret;
}

static gboolean
parse_identifier_boundary (gchar **pos, TimeZoneDate *target)
{
  gchar *buffer;
  gchar *target_pos = *pos;
  gboolean ret;

  while (**pos != ',' && **pos != '\0')
    ++(*pos);
  buffer = g_strndup (target_pos, *pos - target_pos);
  ret = parse_tz_boundary (buffer, target);
  g_free (buffer);

  return ret;
}

static gboolean
set_tz_name (gchar **pos, gchar *buffer, guint size)
{
  gchar *name_pos = *pos;
  guint len;

  /* Name is ASCII alpha (Is this necessarily true?) */
  while (g_ascii_isalpha (**pos))
    ++(*pos);

  /* Name should be three or more alphabetic characters */
  if (*pos - name_pos < 3)
    return FALSE;

  memset (buffer, 0, NAME_SIZE);
  /* name_pos isn't 0-terminated, so we have to limit the length expressly */
  len = *pos - name_pos > size - 1 ? size - 1 : *pos - name_pos;
  strncpy (buffer, name_pos, len);
  return TRUE;
}

static gboolean
parse_identifier_boundaries (gchar **pos, TimeZoneRule *tzr)
{
  if (*(*pos)++ != ',')
    return FALSE;

  /* Start date */
  if (!parse_identifier_boundary (pos, &(tzr->dlt_start)) || *(*pos)++ != ',')
    return FALSE;

  /* End date */
  if (!parse_identifier_boundary (pos, &(tzr->dlt_end)))
    return FALSE;
  return TRUE;
}

/*
 * Creates an array of TimeZoneRule from a TZ environment variable
 * type of identifier.  Should free rules afterwards
 */
static gint
rules_from_identifier (const gchar   *identifier,
                       TimeZoneRule **rules)
{
  gchar *pos;
  TimeZoneRule tzr;

  if (!identifier)
    return 0;

  pos = (gchar*)identifier;
  memset (&tzr, 0, sizeof (tzr));
  /* Standard offset */
  if (!(set_tz_name (&pos, tzr.std_name, NAME_SIZE)) ||
      !parse_offset (&pos, &(tzr.std_offset)))
    return 0;

  if (*pos == 0)
    return create_ruleset_from_rule (rules, &tzr);

  /* Format 2 */
  if (!(set_tz_name (&pos, tzr.dlt_name, NAME_SIZE)))
    return 0;
  parse_offset (&pos, &(tzr.dlt_offset));
  if (tzr.dlt_offset == 0) /* No daylight offset given, assume it's 1
                              hour earlier that standard */
    tzr.dlt_offset = tzr.std_offset - 3600;
  if (*pos == '\0')
#ifdef G_OS_WIN32
    /* Windows allows us to use the US DST boundaries if they're not given */
    {
      int i;
      guint rules_num = 0;

      /* Use US rules, Windows' default is Pacific Standard Time */
      if ((rules_num = rules_from_windows_time_zone ("Pacific Standard Time",
                                                     rules)))
        {
          for (i = 0; i < rules_num - 1; i++)
            {
              (*rules)[i].std_offset = - tzr.std_offset;
              (*rules)[i].dlt_offset = - tzr.dlt_offset;
              strcpy ((*rules)[i].std_name, tzr.std_name);
              strcpy ((*rules)[i].dlt_name, tzr.dlt_name);
            }

          return rules_num;
        }
      else
        return 0;
    }
#else
  return 0;
#endif
  /* Start and end required (format 2) */
  if (!parse_identifier_boundaries (&pos, &tzr))
    return 0;

  return create_ruleset_from_rule (rules, &tzr);
}

/* Construction {{{1 */
/**
 * g_time_zone_new:
 * @identifier: (nullable): a timezone identifier
 *
 * Creates a #GTimeZone corresponding to @identifier.
 *
 * @identifier can either be an RFC3339/ISO 8601 time offset or
 * something that would pass as a valid value for the `TZ` environment
 * variable (including %NULL).
 *
 * In Windows, @identifier can also be the unlocalized name of a time
 * zone for standard time, for example "Pacific Standard Time".
 *
 * Valid RFC3339 time offsets are `"Z"` (for UTC) or
 * `"±hh:mm"`.  ISO 8601 additionally specifies
 * `"±hhmm"` and `"±hh"`.  Offsets are
 * time values to be added to Coordinated Universal Time (UTC) to get
 * the local time.
 *
 * In UNIX, the `TZ` environment variable typically corresponds
 * to the name of a file in the zoneinfo database, or string in
 * "std offset [dst [offset],start[/time],end[/time]]" (POSIX) format.
 * There  are  no spaces in the specification. The name of standard
 * and daylight savings time zone must be three or more alphabetic
 * characters. Offsets are time values to be added to local time to
 * get Coordinated Universal Time (UTC) and should be
 * `"[±]hh[[:]mm[:ss]]"`.  Dates are either
 * `"Jn"` (Julian day with n between 1 and 365, leap
 * years not counted), `"n"` (zero-based Julian day
 * with n between 0 and 365) or `"Mm.w.d"` (day d
 * (0 <= d <= 6) of week w (1 <= w <= 5) of month m (1 <= m <= 12), day
 * 0 is a Sunday).  Times are in local wall clock time, the default is
 * 02:00:00.
 *
 * In Windows, the "tzn[+|–]hh[:mm[:ss]][dzn]" format is used, but also
 * accepts POSIX format.  The Windows format uses US rules for all time
 * zones; daylight savings time is 60 minutes behind the standard time
 * with date and time of change taken from Pacific Standard Time.
 * Offsets are time values to be added to the local time to get
 * Coordinated Universal Time (UTC).
 *
 * g_time_zone_new_local() calls this function with the value of the
 * `TZ` environment variable. This function itself is independent of
 * the value of `TZ`, but if @identifier is %NULL then `/etc/localtime`
 * will be consulted to discover the correct time zone on UNIX and the
 * registry will be consulted or GetTimeZoneInformation() will be used
 * to get the local time zone on Windows.
 *
 * If intervals are not available, only time zone rules from `TZ`
 * environment variable or other means, then they will be computed
 * from year 1900 to 2037.  If the maximum year for the rules is
 * available and it is greater than 2037, then it will followed
 * instead.
 *
 * See
 * [RFC3339 §5.6](http://tools.ietf.org/html/rfc3339#section-5.6)
 * for a precise definition of valid RFC3339 time offsets
 * (the `time-offset` expansion) and ISO 8601 for the
 * full list of valid time offsets.  See
 * [The GNU C Library manual](http://www.gnu.org/s/libc/manual/html_node/TZ-Variable.html)
 * for an explanation of the possible
 * values of the `TZ` environment variable. See
 * [Microsoft Time Zone Index Values](http://msdn.microsoft.com/en-us/library/ms912391%28v=winembedded.11%29.aspx)
 * for the list of time zones on Windows.
 *
 * You should release the return value by calling g_time_zone_unref()
 * when you are done with it.
 *
 * Returns: the requested timezone
 *
 * Since: 2.26
 **/
GTimeZone *
g_time_zone_new (const gchar *identifier)
{
  GTimeZone *tz = NULL;
  TimeZoneRule *rules;
  gint rules_num;

  G_LOCK (time_zones);
  if (time_zones == NULL)
    time_zones = g_hash_table_new (g_str_hash, g_str_equal);

  if (identifier)
    {
      tz = g_hash_table_lookup (time_zones, identifier);
      if (tz)
        {
          g_atomic_int_inc (&tz->ref_count);
          G_UNLOCK (time_zones);
          return tz;
        }
    }

  tz = g_slice_new0 (GTimeZone);
  tz->name = g_strdup (identifier);
  tz->ref_count = 0;

  zone_for_constant_offset (tz, identifier);

  if (tz->t_info == NULL &&
      (rules_num = rules_from_identifier (identifier, &rules)))
    {
      init_zone_from_rules (tz, rules, rules_num);
      g_free (rules);
    }

  if (tz->t_info == NULL)
    {
#ifdef G_OS_UNIX
      GBytes *zoneinfo = zone_info_unix (identifier);
      if (!zoneinfo)
        zone_for_constant_offset (tz, "UTC");
      else
        {
          init_zone_from_iana_info (tz, zoneinfo);
          g_bytes_unref (zoneinfo);
        }
#elif defined (G_OS_WIN32)
      if ((rules_num = rules_from_windows_time_zone (identifier, &rules)))
        {
          init_zone_from_rules (tz, rules, rules_num);
          g_free (rules);
        }
    }

  if (tz->t_info == NULL)
    {
      if (identifier)
        zone_for_constant_offset (tz, "UTC");
      else
        {
          TIME_ZONE_INFORMATION tzi;

          if (GetTimeZoneInformation (&tzi) != TIME_ZONE_ID_INVALID)
            {
              rules = g_new0 (TimeZoneRule, 2);

              rule_from_windows_time_zone_info (&rules[0], &tzi);

              memset (rules[0].std_name, 0, NAME_SIZE);
              memset (rules[0].dlt_name, 0, NAME_SIZE);

              rules[0].start_year = MIN_TZYEAR;
              rules[1].start_year = MAX_TZYEAR;

              init_zone_from_rules (tz, rules, 2);

              g_free (rules);
            }
        }
#endif
    }

  if (tz->t_info != NULL)
    {
      if (identifier)
        g_hash_table_insert (time_zones, tz->name, tz);
    }
  g_atomic_int_inc (&tz->ref_count);
  G_UNLOCK (time_zones);

  return tz;
}

/**
 * g_time_zone_new_utc:
 *
 * Creates a #GTimeZone corresponding to UTC.
 *
 * This is equivalent to calling g_time_zone_new() with a value like
 * "Z", "UTC", "+00", etc.
 *
 * You should release the return value by calling g_time_zone_unref()
 * when you are done with it.
 *
 * Returns: the universal timezone
 *
 * Since: 2.26
 **/
GTimeZone *
g_time_zone_new_utc (void)
{
  return g_time_zone_new ("UTC");
}

/**
 * g_time_zone_new_local:
 *
 * Creates a #GTimeZone corresponding to local time.  The local time
 * zone may change between invocations to this function; for example,
 * if the system administrator changes it.
 *
 * This is equivalent to calling g_time_zone_new() with the value of
 * the `TZ` environment variable (including the possibility of %NULL).
 *
 * You should release the return value by calling g_time_zone_unref()
 * when you are done with it.
 *
 * Returns: the local timezone
 *
 * Since: 2.26
 **/
GTimeZone *
g_time_zone_new_local (void)
{
  return g_time_zone_new (getenv ("TZ"));
}

#define TRANSITION(n)         g_array_index (tz->transitions, Transition, n)
#define TRANSITION_INFO(n)    g_array_index (tz->t_info, TransitionInfo, n)

/* Internal helpers {{{1 */
/* NB: Interval 0 is before the first transition, so there's no
 * transition structure to point to which TransitionInfo to
 * use. Rule-based zones are set up so that TI 0 is always standard
 * time (which is what's in effect before Daylight time got started
 * in the early 20th century), but IANA tzfiles don't follow that
 * convention. The tzfile documentation says to use the first
 * standard-time (i.e., non-DST) tinfo, so that's what we do.
 */
inline static const TransitionInfo*
interval_info (GTimeZone *tz,
               guint      interval)
{
  guint index;
  g_return_val_if_fail (tz->t_info != NULL, NULL);
  if (interval && tz->transitions && interval <= tz->transitions->len)
    index = (TRANSITION(interval - 1)).info_index;
  else
    {
      for (index = 0; index < tz->t_info->len; index++)
        {
          TransitionInfo *tzinfo = &(TRANSITION_INFO(index));
          if (!tzinfo->is_dst)
            return tzinfo;
        }
      index = 0;
    }

  return &(TRANSITION_INFO(index));
}

inline static gint64
interval_start (GTimeZone *tz,
                guint      interval)
{
  if (!interval || tz->transitions == NULL || tz->transitions->len == 0)
    return G_MININT64;
  if (interval > tz->transitions->len)
    interval = tz->transitions->len;
  return (TRANSITION(interval - 1)).time;
}

inline static gint64
interval_end (GTimeZone *tz,
              guint      interval)
{
  if (tz->transitions && interval < tz->transitions->len)
    return (TRANSITION(interval)).time - 1;
  return G_MAXINT64;
}

inline static gint32
interval_offset (GTimeZone *tz,
                 guint      interval)
{
  g_return_val_if_fail (tz->t_info != NULL, 0);
  return interval_info (tz, interval)->gmt_offset;
}

inline static gboolean
interval_isdst (GTimeZone *tz,
                guint      interval)
{
  g_return_val_if_fail (tz->t_info != NULL, 0);
  return interval_info (tz, interval)->is_dst;
}


inline static gchar*
interval_abbrev (GTimeZone *tz,
                  guint      interval)
{
  g_return_val_if_fail (tz->t_info != NULL, 0);
  return interval_info (tz, interval)->abbrev;
}

inline static gint64
interval_local_start (GTimeZone *tz,
                      guint      interval)
{
  if (interval)
    return interval_start (tz, interval) + interval_offset (tz, interval);

  return G_MININT64;
}

inline static gint64
interval_local_end (GTimeZone *tz,
                    guint      interval)
{
  if (tz->transitions && interval < tz->transitions->len)
    return interval_end (tz, interval) + interval_offset (tz, interval);

  return G_MAXINT64;
}

static gboolean
interval_valid (GTimeZone *tz,
                guint      interval)
{
  if ( tz->transitions == NULL)
    return interval == 0;
  return interval <= tz->transitions->len;
}

/* g_time_zone_find_interval() {{{1 */

/**
 * g_time_zone_adjust_time:
 * @tz: a #GTimeZone
 * @type: the #GTimeType of @time_
 * @time_: a pointer to a number of seconds since January 1, 1970
 *
 * Finds an interval within @tz that corresponds to the given @time_,
 * possibly adjusting @time_ if required to fit into an interval.
 * The meaning of @time_ depends on @type.
 *
 * This function is similar to g_time_zone_find_interval(), with the
 * difference that it always succeeds (by making the adjustments
 * described below).
 *
 * In any of the cases where g_time_zone_find_interval() succeeds then
 * this function returns the same value, without modifying @time_.
 *
 * This function may, however, modify @time_ in order to deal with
 * non-existent times.  If the non-existent local @time_ of 02:30 were
 * requested on March 14th 2010 in Toronto then this function would
 * adjust @time_ to be 03:00 and return the interval containing the
 * adjusted time.
 *
 * Returns: the interval containing @time_, never -1
 *
 * Since: 2.26
 **/
gint
g_time_zone_adjust_time (GTimeZone *tz,
                         GTimeType  type,
                         gint64    *time_)
{
  gint i;
  guint intervals;

  if (tz->transitions == NULL)
    return 0;

  intervals = tz->transitions->len;

  /* find the interval containing *time UTC
   * TODO: this could be binary searched (or better) */
  for (i = 0; i <= intervals; i++)
    if (*time_ <= interval_end (tz, i))
      break;

  g_assert (interval_start (tz, i) <= *time_ && *time_ <= interval_end (tz, i));

  if (type != G_TIME_TYPE_UNIVERSAL)
    {
      if (*time_ < interval_local_start (tz, i))
        /* if time came before the start of this interval... */
        {
          i--;

          /* if it's not in the previous interval... */
          if (*time_ > interval_local_end (tz, i))
            {
              /* it doesn't exist.  fast-forward it. */
              i++;
              *time_ = interval_local_start (tz, i);
            }
        }

      else if (*time_ > interval_local_end (tz, i))
        /* if time came after the end of this interval... */
        {
          i++;

          /* if it's not in the next interval... */
          if (*time_ < interval_local_start (tz, i))
            /* it doesn't exist.  fast-forward it. */
            *time_ = interval_local_start (tz, i);
        }

      else if (interval_isdst (tz, i) != type)
        /* it's in this interval, but dst flag doesn't match.
         * check neighbours for a better fit. */
        {
          if (i && *time_ <= interval_local_end (tz, i - 1))
            i--;

          else if (i < intervals &&
                   *time_ >= interval_local_start (tz, i + 1))
            i++;
        }
    }

  return i;
}

/**
 * g_time_zone_find_interval:
 * @tz: a #GTimeZone
 * @type: the #GTimeType of @time_
 * @time_: a number of seconds since January 1, 1970
 *
 * Finds an the interval within @tz that corresponds to the given @time_.
 * The meaning of @time_ depends on @type.
 *
 * If @type is %G_TIME_TYPE_UNIVERSAL then this function will always
 * succeed (since universal time is monotonic and continuous).
 *
 * Otherwise @time_ is treated as local time.  The distinction between
 * %G_TIME_TYPE_STANDARD and %G_TIME_TYPE_DAYLIGHT is ignored except in
 * the case that the given @time_ is ambiguous.  In Toronto, for example,
 * 01:30 on November 7th 2010 occurred twice (once inside of daylight
 * savings time and the next, an hour later, outside of daylight savings
 * time).  In this case, the different value of @type would result in a
 * different interval being returned.
 *
 * It is still possible for this function to fail.  In Toronto, for
 * example, 02:00 on March 14th 2010 does not exist (due to the leap
 * forward to begin daylight savings time).  -1 is returned in that
 * case.
 *
 * Returns: the interval containing @time_, or -1 in case of failure
 *
 * Since: 2.26
 */
gint
g_time_zone_find_interval (GTimeZone *tz,
                           GTimeType  type,
                           gint64     time_)
{
  gint i;
  guint intervals;

  if (tz->transitions == NULL)
    return 0;
  intervals = tz->transitions->len;
  for (i = 0; i <= intervals; i++)
    if (time_ <= interval_end (tz, i))
      break;

  if (type == G_TIME_TYPE_UNIVERSAL)
    return i;

  if (time_ < interval_local_start (tz, i))
    {
      if (time_ > interval_local_end (tz, --i))
        return -1;
    }

  else if (time_ > interval_local_end (tz, i))
    {
      if (time_ < interval_local_start (tz, ++i))
        return -1;
    }

  else if (interval_isdst (tz, i) != type)
    {
      if (i && time_ <= interval_local_end (tz, i - 1))
        i--;

      else if (i < intervals && time_ >= interval_local_start (tz, i + 1))
        i++;
    }

  return i;
}

/* Public API accessors {{{1 */

/**
 * g_time_zone_get_abbreviation:
 * @tz: a #GTimeZone
 * @interval: an interval within the timezone
 *
 * Determines the time zone abbreviation to be used during a particular
 * @interval of time in the time zone @tz.
 *
 * For example, in Toronto this is currently "EST" during the winter
 * months and "EDT" during the summer months when daylight savings time
 * is in effect.
 *
 * Returns: the time zone abbreviation, which belongs to @tz
 *
 * Since: 2.26
 **/
const gchar *
g_time_zone_get_abbreviation (GTimeZone *tz,
                              gint       interval)
{
  g_return_val_if_fail (interval_valid (tz, (guint)interval), NULL);

  return interval_abbrev (tz, (guint)interval);
}

/**
 * g_time_zone_get_offset:
 * @tz: a #GTimeZone
 * @interval: an interval within the timezone
 *
 * Determines the offset to UTC in effect during a particular @interval
 * of time in the time zone @tz.
 *
 * The offset is the number of seconds that you add to UTC time to
 * arrive at local time for @tz (ie: negative numbers for time zones
 * west of GMT, positive numbers for east).
 *
 * Returns: the number of seconds that should be added to UTC to get the
 *          local time in @tz
 *
 * Since: 2.26
 **/
gint32
g_time_zone_get_offset (GTimeZone *tz,
                        gint       interval)
{
  g_return_val_if_fail (interval_valid (tz, (guint)interval), 0);

  return interval_offset (tz, (guint)interval);
}

/**
 * g_time_zone_is_dst:
 * @tz: a #GTimeZone
 * @interval: an interval within the timezone
 *
 * Determines if daylight savings time is in effect during a particular
 * @interval of time in the time zone @tz.
 *
 * Returns: %TRUE if daylight savings time is in effect
 *
 * Since: 2.26
 **/
gboolean
g_time_zone_is_dst (GTimeZone *tz,
                    gint       interval)
{
  g_return_val_if_fail (interval_valid (tz, interval), FALSE);

  if (tz->transitions == NULL)
    return FALSE;

  return interval_isdst (tz, (guint)interval);
}

/* Epilogue {{{1 */
/* vim:set foldmethod=marker: */