/*
 * Copyright (c) 2002-2018 Balabit
 * Copyright (c) 1998-2018 Balázs Scheidler
 *
 * 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 2.1 of the License, 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, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 *
 * As an additional exemption you are allowed to compile & link against the
 * OpenSSL libraries as published by the OpenSSL project. See the file
 * COPYING for details.
 *
 */
/*  $NetBSD: strptime.c,v 1.49 2015/10/09 17:21:45 christos Exp $ */

/*-
 * Copyright (c) 1997, 1998, 2005, 2008 The NetBSD Foundation, Inc.
 * All rights reserved.
 *
 * This code was contributed to The NetBSD Foundation by Klaus Klein.
 * Heavily optimised by David Laight
 *
 * 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.
 *
 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. 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 FOUNDATION 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.
 */

/*
 * MIT: musl http://git.musl-libc.org/cgit/musl/tree/src/time/strftime.c?id=6ad514e4e278f0c3b18eb2db1d45638c9af1c07f#n19
 * The license below only applies for the ISO8601 week calculation in this file.
 *
 */
/*
 *
 *  Copyright © 2005-2019 Rich Felker, et al.
 *
 *  Permission is hereby granted, free of charge, to any person obtaining
 *  a copy of this software and associated documentation files (the
 *  "Software"), to deal in the Software without restriction, including
 *  without limitation the rights to use, copy, modify, merge, publish,
 *  distribute, sublicense, and/or sell copies of the Software, and to
 *  permit persons to whom the Software is furnished to do so, subject to
 *  the following conditions:
 *
 *  The above copyright notice and this permission notice shall be
 *  included in all copies or substantial portions of the Software.
 *
 *  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 *  EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 *  MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
 *  IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
 *  CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
 *  TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
 *  SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */


#include "timeutils/wallclocktime.h"
#include "timeutils/unixtime.h"
#include "timeutils/cache.h"
#include "timeutils/misc.h"

#include <ctype.h>
#include <stdint.h>
#include <string.h>


void
wall_clock_time_unset(WallClockTime *self)
{
  WallClockTime val = WALL_CLOCK_TIME_INIT;
  *self = val;
}

#define __UNCONST(a)    ((void *)(unsigned long)(const void *)(a))

#define TM_YEAR_BASE 1900
#define TM_SUNDAY     0
#define TM_MONDAY     1
#define TM_TUESDAY    2
#define TM_WEDNESDAY  3
#define TM_THURSDAY   4
#define TM_FRIDAY     5
#define TM_SATURDAY   6

#define TM_JANUARY   0
#define TM_FEBRUARY  1
#define TM_MARCH     2
#define TM_APRIL     3
#define TM_MAY       4
#define TM_JUNE      5
#define TM_JULY      6
#define TM_AUGUST    7
#define TM_SEPTEMBER 8
#define TM_OCTOBER   9
#define TM_NOVEMBER  10
#define TM_DECEMBER  11

#define isleap(y) ((((y) % 4) == 0 && ((y) % 100) != 0) || ((y) % 400) == 0)
#define isleap_sum(a, b)  isleap((a) % 400 + (b) % 400)

static gboolean
_is_jan1_3_days_past_monday(WallClockTime *wct)
{
  return ((wct->wct_wday + 371 - wct->wct_yday - 2) % 7 <= 2);
}

static gint
_get_dec31_day_of_week(WallClockTime *wct)
{
  return (wct->wct_wday + 7 - wct->wct_yday - 1) % 7;
}

static gint
_get_jan1_day_of_week(WallClockTime *wct)
{
  return (wct->wct_wday + 371 - wct->wct_yday) % 7;
}

guint32
wall_clock_time_iso_week_number(WallClockTime *wct)
{
  gint week_number = (wct->wct_yday - (wct->wct_wday - 1 + 7) % 7 + 7 ) / 7;

  if (_is_jan1_3_days_past_monday(wct))
    week_number++;

  if (week_number == 0)
    {
      gint last_dec31 = _get_dec31_day_of_week(wct);
      if (last_dec31 == 4 || (last_dec31 == 5 && isleap(wct->wct_year-1)))
        return 53;
      return 52;
    }

  if (week_number == 53)
    {
      int jan1 = _get_jan1_day_of_week(wct);
      if (jan1 != 4 && (jan1 != 3 || !isleap(wct->wct_year)))
        return 1;
    }

  return week_number;
}

typedef struct
{
  const char *abday[7];
  const char *day[7];
  const char *abmon[12];
  const char *mon[12];
  const char *am_pm[2];
  const char *d_t_fmt;
  const char *d_fmt;
  const char *t_fmt;
  const char *t_fmt_ampm;
} _TimeLocale;

static const _TimeLocale _DefaultTimeLocale =
{
  /* abbreviated day */
  {
    "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat",
  },
  /* days */
  {
    "Sunday", "Monday", "Tuesday", "Wednesday", "Thursday",
    "Friday", "Saturday"
  },
  /* abbreviated month */
  {
    "Jan", "Feb", "Mar", "Apr", "May", "Jun",
    "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"
  },
  /* month */
  {
    "January", "February", "March", "April", "May", "June", "July",
    "August", "September", "October", "November", "December"
  },
  /* ampm */
  {
    "AM", "PM"
  },
  "%a %b %e %H:%M:%S %Y",
  "%m/%d/%y",
  "%H:%M:%S",
  "%I:%M:%S %p"
};

#define _TIME_LOCALE(loc) \
  (&_DefaultTimeLocale)

static const unsigned char *conv_num(const unsigned char *, int *, unsigned int, unsigned int);
static const unsigned char *find_string(const unsigned char *, int *, const char *const *,
                                        const char *const *, int);
static int first_wday_of(int yr);


/*
 * We do not implement alternate representations. However, we always
 * check whether a given modifier is allowed for a certain conversion.
 */
#define ALT_E     0x01
#define ALT_O     0x02
#define LEGAL_ALT(x)    { if (alt_format & ~(x)) return NULL; }

#define S_YEAR      (1 << 0)
#define S_MON       (1 << 1)
#define S_YDAY      (1 << 2)
#define S_MDAY      (1 << 3)
#define S_WDAY      (1 << 4)
#define S_HOUR      (1 << 5)
#define S_USEC      (1 << 6)

#define HAVE_MDAY(s)    (s & S_MDAY)
#define HAVE_MON(s)     (s & S_MON)
#define HAVE_WDAY(s)    (s & S_WDAY)
#define HAVE_YDAY(s)    (s & S_YDAY)
#define HAVE_YEAR(s)    (s & S_YEAR)
#define HAVE_HOUR(s)    (s & S_HOUR)
#define HAVE_USEC(s)    (s & S_USEC)

static char utc[] = { "UTC" };
/* RFC-822/RFC-2822 */
static const char *const nast[5] =
{
  "EST",    "CST",    "MST",    "PST",    "\0\0\0"
};
static const char *const nadt[5] =
{
  "EDT",    "CDT",    "MDT",    "PDT",    "\0\0\0"
};

/*
 * Table to determine the ordinal date for the start of a month.
 * Ref: http://en.wikipedia.org/wiki/ISO_week_date
 */
static const int start_of_month[2][13] =
{
  /* non-leap year */
  { 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365 },
  /* leap year */
  { 0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335, 366 }
};

static inline gboolean
_is_str_empty(const gchar *str)
{
  return !str || strcmp(str, "") == 0;
}

gchar *
wall_clock_time_strptime(WallClockTime *wct, const gchar *format, const gchar *input)
{
  unsigned char c;
  const unsigned char *bp, *ep, *zname;
  int alt_format, i, split_year = 0, neg = 0, state = 0,
                     day_offset = -1, week_offset = 0, offs, mandatory;
  const char *new_fmt;
  const char *const *system_tznames;
  int system_tznames_len;

  bp = (const unsigned char *)input;

  while (bp != NULL && (c = *format++) != '\0')
    {
      /* Clear `alternate' modifier prior to new conversion. */
      alt_format = 0;
      i = 0;

      /* Eat up white-space. */
      if (isspace(c))
        {
          while (isspace(*bp))
            bp++;
          continue;
        }

      if (c != '%')
        goto literal;


again:
      switch (c = *format++)
        {
        case '%': /* "%%" is converted to "%". */
literal:
          if (c != *bp++)
            return NULL;
          LEGAL_ALT(0);
          continue;

        /*
         * "Alternative" modifiers. Just set the appropriate flag
         * and start over again.
         */
        case 'E': /* "%E?" alternative conversion modifier. */
          LEGAL_ALT(0);
          alt_format |= ALT_E;
          goto again;

        case 'O': /* "%O?" alternative conversion modifier. */
          LEGAL_ALT(0);
          alt_format |= ALT_O;
          goto again;

        /*
         * "Complex" conversion rules, implemented through recursion.
         */
        case 'c': /* Date and time, using the locale's format. */
          new_fmt = _TIME_LOCALE(loc)->d_t_fmt;
          state |= S_WDAY | S_MON | S_MDAY | S_YEAR;
          goto recurse;

        case 'D': /* The date as "%m/%d/%y". */
          new_fmt = "%m/%d/%y";
          LEGAL_ALT(0);
          state |= S_MON | S_MDAY | S_YEAR;
          goto recurse;

        case 'F': /* The date as "%Y-%m-%d". */
          new_fmt = "%Y-%m-%d";
          LEGAL_ALT(0);
          state |= S_MON | S_MDAY | S_YEAR;
          goto recurse;

        case 'R': /* The time as "%H:%M". */
          new_fmt = "%H:%M";
          LEGAL_ALT(0);
          goto recurse;

        case 'r': /* The time in 12-hour clock representation. */
          new_fmt = _TIME_LOCALE(loc)->t_fmt_ampm;
          LEGAL_ALT(0);
          goto recurse;

        case 'T': /* The time as "%H:%M:%S". */
          new_fmt = "%H:%M:%S";
          LEGAL_ALT(0);
          goto recurse;

        case 'X': /* The time, using the locale's format. */
          new_fmt = _TIME_LOCALE(loc)->t_fmt;
          goto recurse;

        case 'x': /* The date, using the locale's format. */
          new_fmt = _TIME_LOCALE(loc)->d_fmt;
          state |= S_MON | S_MDAY | S_YEAR;
recurse:
          bp = (const unsigned char *)wall_clock_time_strptime(wct, new_fmt, (const char *)bp);
          LEGAL_ALT(ALT_E);
          continue;

        /*
         * "Elementary" conversion rules.
         */
        case 'A': /* The day of week, using the locale's form. */
        case 'a':
          bp = find_string(bp, &wct->tm.tm_wday,
                           _TIME_LOCALE(loc)->day, _TIME_LOCALE(loc)->abday, 7);
          LEGAL_ALT(0);
          state |= S_WDAY;
          continue;

        case 'B': /* The month, using the locale's form. */
        case 'b':
        case 'h':
          bp = find_string(bp, &wct->tm.tm_mon,
                           _TIME_LOCALE(loc)->mon, _TIME_LOCALE(loc)->abmon,
                           12);
          LEGAL_ALT(0);
          state |= S_MON;
          continue;

        case 'C': /* The century number. */
          i = 20;
          bp = conv_num(bp, &i, 0, 99);

          i = i * 100 - TM_YEAR_BASE;
          if (split_year)
            i += wct->tm.tm_year % 100;
          split_year = 1;
          wct->tm.tm_year = i;
          LEGAL_ALT(ALT_E);
          state |= S_YEAR;
          continue;

        case 'd': /* The day of month. */
        case 'e':
          bp = conv_num(bp, &wct->tm.tm_mday, 1, 31);
          LEGAL_ALT(ALT_O);
          state |= S_MDAY;
          continue;

        case 'f':
        {
          const unsigned char *end = conv_num(bp, &wct->wct_usec, 0, 999999);
          if (!end)
            return NULL;
          int digits = end - bp;

          /*
           * We have read up to 6 digits, but if the message has
           * sub-microsecond precision, eat-up the digits we cannot handle.
           */
          while (isdigit(*end))
            {
              end++;
            }

          /*
           * If we read less than 6 digits, we need to adjust the value:
           * "012" was parsed as 12 but is 12000 us.
           */
          while (digits++ < 6)
            {
              wct->wct_usec *= 10;
            }

          bp = end;
          LEGAL_ALT(0);
          state |= S_USEC;
          continue;
        }

        case 'k': /* The hour (24-hour clock representation). */
          LEGAL_ALT(0);
        /* FALLTHROUGH */
        case 'H':
          bp = conv_num(bp, &wct->tm.tm_hour, 0, 23);
          LEGAL_ALT(ALT_O);
          state |= S_HOUR;
          continue;

        case 'l': /* The hour (12-hour clock representation). */
          LEGAL_ALT(0);
        /* FALLTHROUGH */
        case 'I':
          bp = conv_num(bp, &wct->tm.tm_hour, 1, 12);
          if (wct->tm.tm_hour == 12)
            wct->tm.tm_hour = 0;
          LEGAL_ALT(ALT_O);
          state |= S_HOUR;
          continue;

        case 'j': /* The day of year. */
          i = 1;
          bp = conv_num(bp, &i, 1, 366);
          wct->tm.tm_yday = i - 1;
          LEGAL_ALT(0);
          state |= S_YDAY;
          continue;

        case 'M': /* The minute. */
          bp = conv_num(bp, &wct->tm.tm_min, 0, 59);
          LEGAL_ALT(ALT_O);
          continue;

        case 'm': /* The month. */
          i = 1;
          bp = conv_num(bp, &i, 1, 12);
          wct->tm.tm_mon = i - 1;
          LEGAL_ALT(ALT_O);
          state |= S_MON;
          continue;

        case 'p': /* The locale's equivalent of AM/PM. */
          bp = find_string(bp, &i, _TIME_LOCALE(loc)->am_pm,
                           NULL, 2);
          if (HAVE_HOUR(state) && wct->tm.tm_hour > 11)
            return NULL;
          wct->tm.tm_hour += i * 12;
          LEGAL_ALT(0);
          continue;

        case 'S': /* The seconds. */
          bp = conv_num(bp, &wct->tm.tm_sec, 0, 61);
          LEGAL_ALT(ALT_O);
          continue;

#ifndef TIME_MAX
#define TIME_MAX  INT64_MAX
#endif
        case 's': /* seconds since the epoch */
        {
          time_t sse = 0;
          uint64_t rulim = TIME_MAX;

          if (*bp < '0' || *bp > '9')
            {
              bp = NULL;
              continue;
            }

          do
            {
              sse *= 10;
              sse += *bp++ - '0';
              rulim /= 10;
            }
          while ((sse * 10 <= TIME_MAX) &&
                 rulim && *bp >= '0' && *bp <= '9');

          if (sse < 0 || (uint64_t)sse > TIME_MAX)
            {
              bp = NULL;
              continue;
            }

          cached_localtime(&sse, &wct->tm);
          state |= S_YDAY | S_WDAY |
                   S_MON | S_MDAY | S_YEAR;
        }
        continue;

        case 'U': /* The week of year, beginning on sunday. */
        case 'W': /* The week of year, beginning on monday. */
          /*
           * XXX This is bogus, as we can not assume any valid
           * information present in the tm structure at this
           * point to calculate a real value, so just check the
           * range for now.
           */
          bp = conv_num(bp, &i, 0, 53);
          LEGAL_ALT(ALT_O);
          if (c == 'U')
            day_offset = TM_SUNDAY;
          else
            day_offset = TM_MONDAY;
          week_offset = i;
          continue;

        case 'w': /* The day of week, beginning on sunday. */
          bp = conv_num(bp, &wct->tm.tm_wday, 0, 6);
          LEGAL_ALT(ALT_O);
          state |= S_WDAY;
          continue;

        case 'u': /* The day of week, monday = 1. */
          bp = conv_num(bp, &i, 1, 7);
          wct->tm.tm_wday = i % 7;
          LEGAL_ALT(ALT_O);
          state |= S_WDAY;
          continue;

        case 'g': /* The year corresponding to the ISO week
         * number but without the century.
         */
          bp = conv_num(bp, &i, 0, 99);
          continue;

        case 'G': /* The year corresponding to the ISO week
         * number with century.
         */
          do
            bp++;
          while (isdigit(*bp));
          continue;

        case 'V': /* The ISO 8601:1988 week number as decimal */
          bp = conv_num(bp, &i, 0, 53);
          continue;

        case 'Y': /* The year. */
          i = TM_YEAR_BASE; /* just for data sanity... */
          bp = conv_num(bp, &i, 0, 9999);
          wct->tm.tm_year = i - TM_YEAR_BASE;
          LEGAL_ALT(ALT_E);
          state |= S_YEAR;
          continue;

        case 'y': /* The year within 100 years of the epoch. */
          /* LEGAL_ALT(ALT_E | ALT_O); */
          bp = conv_num(bp, &i, 0, 99);

          if (split_year)
            /* preserve century */
            i += (wct->tm.tm_year / 100) * 100;
          else
            {
              split_year = 1;
              if (i <= 68)
                i = i + 2000 - TM_YEAR_BASE;
              else
                i = i + 1900 - TM_YEAR_BASE;
            }
          wct->tm.tm_year = i;
          state |= S_YEAR;
          continue;

        case 'Z':
        case 'z':
          mandatory = c == 'z';
          /*
           * We recognize all ISO 8601 formats:
           * Z  = Zulu time/UTC
           * [+-]hhmm
           * [+-]hh:mm
           * [+-]hh
           * We recognize all RFC-822/RFC-2822 formats:
           * UT|GMT
           *          North American : UTC offsets
           * E[DS]T = Eastern : -4 | -5
           * C[DS]T = Central : -5 | -6
           * M[DS]T = Mountain: -6 | -7
           * P[DS]T = Pacific : -7 | -8
           *          Military
           * [A-IL-M] = -1 ... -9 (J not used)
           * [N-Y]  = +1 ... +12
           */
          if (mandatory)
            while (isspace(*bp))
              bp++;

          zname = bp;
          switch (*bp++)
            {
            case 'G':
              if (*bp++ != 'M')
                return NULL;
            /*FALLTHROUGH*/
            case 'U':
              if (*bp++ != 'T')
                return NULL;
            /*FALLTHROUGH*/
            case 'Z':
              wct->tm.tm_isdst = 0;
              wct->wct_gmtoff = 0;
              wct->wct_zone = utc;
              continue;
            case '+':
              neg = 0;
              break;
            case '-':
              neg = 1;
              break;
            default:
              --bp;
              ep = find_string(bp, &i, nast, NULL, 4);
              if (ep != NULL)
                {
                  wct->wct_gmtoff = (-5 - i) * 3600;
                  wct->wct_zone = __UNCONST(nast[i]);
                  bp = ep;
                  continue;
                }
              ep = find_string(bp, &i, nadt, NULL, 4);
              if (ep != NULL)
                {
                  wct->tm.tm_isdst = 1;
                  wct->wct_gmtoff = (-4 - i) * 3600;
                  wct->wct_zone = __UNCONST(nadt[i]);
                  bp = ep;
                  continue;
                }
              system_tznames = cached_get_system_tznames();
              system_tznames_len = _is_str_empty(system_tznames[1]) ? 1 : 2;
              ep = find_string(bp, &i, system_tznames, NULL, system_tznames_len);
              if (ep != NULL)
                {
                  wct->tm.tm_isdst = i;
                  wct->wct_gmtoff = -cached_get_system_tzofs() + wct->tm.tm_isdst*3600;
                  wct->wct_zone = system_tznames[i];
                  bp = ep;
                  continue;
                }


              if ((*bp >= 'A' && *bp <= 'I') ||
                  (*bp >= 'L' && *bp <= 'Y'))
                {
                  /* Argh! No 'J'! */
                  if (*bp >= 'A' && *bp <= 'I')
                    wct->wct_gmtoff =
                      (('A' - 1) - (int)*bp) * 3600;
                  else if (*bp >= 'L' && *bp <= 'M')
                    wct->wct_gmtoff = ('A' - (int)*bp) * 3600;
                  else if (*bp >= 'N' && *bp <= 'Y')
                    wct->wct_gmtoff = ((int)*bp - 'M') * 3600;
                  wct->wct_zone = utc; /* XXX */
                  bp++;
                  continue;
                }
              if (mandatory)
                return NULL;

              bp = zname;
              continue;
            }
          offs = 0;
          for (i = 0; i < 4; )
            {
              if (isdigit(*bp))
                {
                  offs = offs * 10 + (*bp++ - '0');
                  i++;
                  continue;
                }
              if (i == 2 && *bp == ':')
                {
                  bp++;
                  continue;
                }
              break;
            }
          switch (i)
            {
            case 2:
              offs *= 3600;
              break;
            case 4:
              i = offs % 100;
              offs /= 100;
              if (i >= 60)
                goto out;
              /* Convert minutes into decimal */
              offs = offs * 3600 + i * 60;
              break;
            default:
out:
              if (mandatory)
                return NULL;
              bp = zname;
              continue;
            }
          if (neg)
            offs = -offs;
          wct->tm.tm_isdst = 0; /* XXX */
          wct->wct_gmtoff = offs;
          wct->wct_zone = utc; /* XXX */
          continue;

        /*
         * Miscellaneous conversions.
         */
        case 'n': /* Any kind of white-space. */
        case 't':
          while (isspace(*bp))
            bp++;
          LEGAL_ALT(0);
          continue;


        default:  /* Unknown/unsupported conversion. */
          return NULL;
        }
    }

  if (!HAVE_YDAY(state) && HAVE_YEAR(state))
    {
      if (HAVE_MON(state) && HAVE_MDAY(state))
        {
          /* calculate day of year (ordinal date) */
          wct->tm.tm_yday =  start_of_month[isleap_sum(wct->tm.tm_year,
                                                       TM_YEAR_BASE)][wct->tm.tm_mon] + (wct->tm.tm_mday - 1);
          state |= S_YDAY;
        }
      else if (day_offset != -1)
        {
          /*
           * Set the date to the first Sunday (or Monday)
           * of the specified week of the year.
           */
          if (!HAVE_WDAY(state))
            {
              wct->tm.tm_wday = day_offset;
              state |= S_WDAY;
            }
          wct->tm.tm_yday = (7 -
                             first_wday_of(wct->tm.tm_year + TM_YEAR_BASE) +
                             day_offset) % 7 + (week_offset - 1) * 7 +
                            wct->tm.tm_wday  - day_offset;
          state |= S_YDAY;
        }
    }

  if (HAVE_YDAY(state) && HAVE_YEAR(state))
    {
      int isleap;

      if (!HAVE_MON(state))
        {
          /* calculate month of day of year */
          i = 0;
          isleap = isleap_sum(wct->tm.tm_year, TM_YEAR_BASE);
          while (wct->tm.tm_yday >= start_of_month[isleap][i])
            i++;
          if (i > 12)
            {
              i = 1;
              wct->tm.tm_yday -= start_of_month[isleap][12];
              wct->tm.tm_year++;
            }
          wct->tm.tm_mon = i - 1;
          state |= S_MON;
        }

      if (!HAVE_MDAY(state))
        {
          /* calculate day of month */
          isleap = isleap_sum(wct->tm.tm_year, TM_YEAR_BASE);
          wct->tm.tm_mday = wct->tm.tm_yday -
                            start_of_month[isleap][wct->tm.tm_mon] + 1;
          state |= S_MDAY;
        }

      if (!HAVE_WDAY(state))
        {
          /* calculate day of week */
          i = 0;
          week_offset = first_wday_of(wct->tm.tm_year);
          while (i++ <= wct->tm.tm_yday)
            {
              if (week_offset++ >= 6)
                week_offset = 0;
            }
          wct->tm.tm_wday = week_offset;
          state |= S_WDAY;
        }
    }

  if (!HAVE_USEC(state))
    {
      wct->wct_usec = 0;
    }

  return __UNCONST(bp);
}

/* Determine (guess) the year for the month.
 *
 * It can be used for BSD logs, where year is missing.
 */
static gint
determine_year_for_month(gint month, const struct tm *now)
{
  if (month == 11 && now->tm_mon == 0)
    return now->tm_year - 1;
  else if (month == 0 && now->tm_mon == 11)
    return now->tm_year + 1;
  else
    return now->tm_year;
}

void
wall_clock_time_guess_missing_year(WallClockTime *self)
{
  if (self->wct_year == -1)
    {
      time_t now = get_cached_realtime_sec();
      struct tm tm;

      cached_localtime(&now, &tm);
      self->wct_year = determine_year_for_month(self->wct_mon, &tm);
    }
}

void
wall_clock_time_guess_missing_fields(WallClockTime *self)
{
  /*
   * The missing cases for date can be divided into three types:
   * 1) missing all fileds -> use current date
   * 2) only miss year -> guess year based on current year and month (current
   * year, last year or next year)
   * 3) the rest of the cases don't make much sense, so zero initialization of
   * the missing field makes sense. And the year is initializeed to the current
   *  one.
   */
  time_t now = get_cached_realtime_sec();
  struct tm tm;

  cached_localtime(&now, &tm);

  if (self->wct_year == -1 && self->wct_mon == -1 && self->wct_mday == -1)
    {
      self->wct_year = tm.tm_year;
      self->wct_mon = tm.tm_mon;
      self->wct_mday = tm.tm_mday;
    }
  else if (self->wct_year == -1 && self->wct_mon != -1 && self->wct_mday != -1)
    {
      self->wct_year = determine_year_for_month(self->wct_mon, &tm);
    }
  else
    {
      if (self->wct_year == -1)
        self->wct_year = tm.tm_year;
      if (self->wct_mon == -1)
        self->wct_mon = 0;
      if (self->wct_mday == -1)
        self->wct_mday = 1;  // day of the month - [1, 31]
    }

  if (self->wct_hour == -1)
    self->wct_hour = 0;
  if (self->wct_min == -1)
    self->wct_min = 0;
  if (self->wct_sec == -1)
    self->wct_sec = 0;
}


/*
 * Calculate the week day of the first day of a year. Valid for
 * the Gregorian calendar, which began Sept 14, 1752 in the UK
 * and its colonies. Ref:
 * http://en.wikipedia.org/wiki/Determination_of_the_day_of_the_week
 */

static int
first_wday_of(int yr)
{
  return ((2 * (3 - (yr / 100) % 4)) + (yr % 100) + ((yr % 100) /  4) +
          (isleap(yr) ? 6 : 0) + 1) % 7;
}


static const unsigned char *
conv_num(const unsigned char *input, int *dest, unsigned int llim, unsigned int ulim)
{
  unsigned int result = 0;
  unsigned char ch;

  /* The limit also determines the number of valid digits. */
  unsigned int rulim = ulim;

  ch = *input;
  if (ch < '0' || ch > '9')
    return NULL;

  do
    {
      result *= 10;
      result += ch - '0';
      rulim /= 10;
      ch = *++input;
    }
  while ((result * 10 <= ulim) && rulim && ch >= '0' && ch <= '9');

  if (result < llim || result > ulim)
    return NULL;

  *dest = result;
  return input;
}

static const unsigned char *
find_string(const unsigned char *bp, int *tgt, const char *const *n1,
            const char *const *n2, int c)
{
  int i;
  size_t len;

  /* check full name - then abbreviated ones */
  for (; n1 != NULL; n1 = n2, n2 = NULL)
    {
      for (i = 0; i < c; i++, n1++)
        {
          len = strlen(*n1);
          if (strncasecmp(*n1, (const char *)bp, len) == 0)
            {
              *tgt = i;
              return bp + len;
            }
        }
    }

  /* Nothing matched */
  return NULL;
}
