path: root/src/libical/icaltime.c

/*======================================================================
 FILE: icaltime.c
 CREATOR: eric 02 June 2000

 SPDX-FileCopyrightText: 2000, Eric Busboom <eric@civicknowledge.com>

 The timegm code is Copyright (c) 2001-2006, NLnet Labs. All rights reserved.

 SPDX-License-Identifier: LGPL-2.1-only OR MPL-2.0

 The Original Code is eric. The Initial Developer of the Original
 Code is Eric Busboom

 The timegm code in this file is copyrighted by NLNET LABS 2001-2006,
 according to the following conditions:

 * Redistributions of source code must retain the above copyright notice,
   this list of conditions and the following disclaimer.

 * 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.

 * Neither the name of the NLNET LABS nor the names of its contributors may
   be used to endorse or promote products derived from this software without
   specific prior written permission.

 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
   TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
   PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS 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.
======================================================================*/

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#include "icaltime.h"
#include "astime.h"
#include "icalerror.h"
#include "icalmemory.h"
#include "icaltimezone.h"

#include <ctype.h>
#include <stdlib.h>

/* The first array is for non-leap years, the second for leap years*/
static const int days_in_year_passed_month[2][13] = {
    /* jan feb mar  apr  may  jun  jul  aug  sep  oct  nov  dec */
    {0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365},
    {0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335, 366}
};

static int icaltime_leap_days(int y1, int y2)
{
    --y1;
    --y2;
    return (y2 / 4 - y1 / 4) - (y2 / 100 - y1 / 100) + (y2 / 400 - y1 / 400);
}

/*
 * Code adapted from Python 2.4.1 sources (Lib/calendar.py).
 */
static icaltime_t icaltime_timegm(const struct tm *tm)
{
    int year;
    icaltime_t days;
    icaltime_t hours;
    icaltime_t minutes;
    icaltime_t seconds;

    year = 1900 + tm->tm_year;
    days = (icaltime_t)(365 * (year - 1970) + icaltime_leap_days(1970, year));
    days += days_in_year_passed_month[0][tm->tm_mon];

    if (tm->tm_mon > 1 && icaltime_is_leap_year(year))
        ++days;

    days += tm->tm_mday - 1;
    hours = days * 24 + tm->tm_hour;
    minutes = hours * 60 + tm->tm_min;
    seconds = minutes * 60 + tm->tm_sec;

    return seconds;
}

/*
 *  Function to convert a struct tm time specification
 *  to an ANSI-compatible icaltime_t using the specified time zone.
 *  This is different from the standard mktime() function
 *  in that we don't want the automatic adjustments for
 *  local daylight savings time applied to the result.
 *  This function expects well-formed input.
 */
static icaltime_t make_time(struct tm *tm, int tzm)
{
    icaltime_t tim;
    int febs;

    static int days[] = { -1, 30, 58, 89, 119, 150, 180, 211, 242, 272, 303, 333, 364 };

    /* check that month specification within range */

    if (tm->tm_mon < 0 || tm->tm_mon > 11)
        return ((icaltime_t) - 1);

#if (SIZEOF_ICALTIME_T == 4)
    /* check that year specification within range */

    if (tm->tm_year < 70 || tm->tm_year > 138)
        return ((icaltime_t) - 1);

    /* check for upper bound of Jan 17, 2038 (to avoid possibility of
       32-bit arithmetic overflow) */

    if (tm->tm_year == 138) {
        if (tm->tm_mon > 0) {
            return ((icaltime_t) - 1);
        } else if (tm->tm_mday > 17) {
            return ((icaltime_t) - 1);
        }
    }
#endif /* SIZEOF_ICALTIME_T */

    /*
     *  calculate elapsed days since start of the epoch (midnight Jan
     *  1st, 1970 UTC) 17 = number of leap years between 1900 and 1970
     *  (number of leap days to subtract)
     */

    tim = (icaltime_t) ((tm->tm_year - 70) * 365 + ((tm->tm_year - 1) / 4) - 17);

    /* adjust: no leap days every 100 years, except every 400 years. */

    febs = (tm->tm_year - 100) - ((tm->tm_mon <= 1) ? 1 : 0);
    tim -= febs / 100;
    tim += febs / 400;

    /* add number of days elapsed in the current year */

    tim += days[tm->tm_mon];

    /* check and adjust for leap years */

    if ((tm->tm_year & 3) == 0 && tm->tm_mon > 1)
        tim += 1;

    /* elapsed days to current date */

    tim += tm->tm_mday;

    /* calculate elapsed hours since start of the epoch */

    tim = tim * 24 + tm->tm_hour;

    /* calculate elapsed minutes since start of the epoch */

    tim = tim * 60 + tm->tm_min;

    /* adjust per time zone specification */

    tim -= tzm;

    /* calculate elapsed seconds since start of the epoch */

    tim = tim * 60 + tm->tm_sec;

    /* return number of seconds since start of the epoch */

    return (tim);
}

struct icaltimetype icaltime_from_timet_with_zone(const icaltime_t tm, const int is_date,
                                                  const icaltimezone *zone)
{
    struct icaltimetype tt;
    struct tm t;
    icaltimezone *utc_zone;

    utc_zone = icaltimezone_get_utc_timezone();

    /* Convert the icaltime_t to a struct tm in UTC time. We can trust gmtime for this. */
    if (!icalgmtime_r(&tm, &t))
        return is_date ? icaltime_null_date () : icaltime_null_time ();

    tt.year = t.tm_year + 1900;
    tt.month = t.tm_mon + 1;
    tt.day = t.tm_mday;
    tt.hour = t.tm_hour;
    tt.minute = t.tm_min;
    tt.second = t.tm_sec;
    tt.is_date = 0;
    tt.is_daylight = 0;
    tt.zone = (zone == NULL) ? NULL : utc_zone;

    /* Use our timezone functions to convert to the required timezone. */
    icaltimezone_convert_time(&tt, utc_zone, (icaltimezone *) zone);

    tt.is_date = is_date;

    /* If it is a DATE value, make sure hour, minute & second are 0. */
    if (is_date) {
        tt.hour = 0;
        tt.minute = 0;
        tt.second = 0;
    }

    return tt;
}

struct icaltimetype icaltime_current_time_with_zone(const icaltimezone *zone)
{
    return icaltime_from_timet_with_zone(icaltime(NULL), 0, zone);
}

struct icaltimetype icaltime_today(void)
{
    return icaltime_from_timet_with_zone(icaltime(NULL), 1, NULL);
}

icaltime_t icaltime_as_timet(const struct icaltimetype tt)
{
    struct tm stm;
    icaltime_t t;

    /* If the time is the special null time, return 0. */
    if (icaltime_is_null_time(tt)) {
        return 0;
    }

    /* Copy the icaltimetype to a struct tm. */
    memset(&stm, 0, sizeof(struct tm));

    if (icaltime_is_date(tt)) {
        stm.tm_sec = stm.tm_min = stm.tm_hour = 0;
    } else {
        stm.tm_sec = tt.second;
        stm.tm_min = tt.minute;
        stm.tm_hour = tt.hour;
    }

    stm.tm_mday = tt.day;
    stm.tm_mon = tt.month - 1;
    stm.tm_year = tt.year - 1900;
    stm.tm_isdst = -1;

    t = make_time(&stm, 0);

    return t;
}

icaltime_t icaltime_as_timet_with_zone(const struct icaltimetype tt, const icaltimezone *zone)
{
    icaltimezone *utc_zone;
    struct tm stm;
    icaltime_t t;
    struct icaltimetype local_tt;

    utc_zone = icaltimezone_get_utc_timezone();

    /* If the time is the special null time, return 0. */
    if (icaltime_is_null_time(tt)) {
        return 0;
    }

    local_tt = tt;

    /* Clear the is_date flag, so we can convert the time. */
    local_tt.is_date = 0;

    /* Use our timezone functions to convert to UTC. */
    icaltimezone_convert_time(&local_tt, (icaltimezone *) zone, utc_zone);

    /* Copy the icaltimetype to a struct tm. */
    memset(&stm, 0, sizeof(struct tm));

    stm.tm_sec = local_tt.second;
    stm.tm_min = local_tt.minute;
    stm.tm_hour = local_tt.hour;
    stm.tm_mday = local_tt.day;
    stm.tm_mon = local_tt.month - 1;
    stm.tm_year = local_tt.year - 1900;
    stm.tm_isdst = -1;

    t = icaltime_timegm(&stm);

    return t;
}

const char *icaltime_as_ical_string(const struct icaltimetype tt)
{
    char *buf;

    buf = icaltime_as_ical_string_r(tt);
    icalmemory_add_tmp_buffer(buf);
    return buf;
}

char *icaltime_as_ical_string_r(const struct icaltimetype tt)
{
    size_t size = 17;
    char *buf = icalmemory_new_buffer(size);

    if (tt.is_date) {
        snprintf(buf, size, "%04d%02d%02d", tt.year, tt.month, tt.day);
    } else {
        const char *fmt;

        if (icaltime_is_utc(tt)) {
            fmt = "%04d%02d%02dT%02d%02d%02dZ";
        } else {
            fmt = "%04d%02d%02dT%02d%02d%02d";
        }
        snprintf(buf, size, fmt, tt.year, tt.month, tt.day, tt.hour, tt.minute, tt.second);
    }

    return buf;
}

/* Implementation note: we call icaltime_adjust() with no adjustment. */
struct icaltimetype icaltime_normalize(const struct icaltimetype tt)
{
    struct icaltimetype ret = tt;

    icaltime_adjust(&ret, 0, 0, 0, 0);
    return ret;
}

struct icaltimetype icaltime_from_string(const char *str)
{
    struct icaltimetype tt = icaltime_null_time();
    size_t size;

    icalerror_check_arg_re(str != 0, "str", icaltime_null_time());

    size = strlen(str);

    if ((size == 15) || (size == 19)) { /* floating time with/without separators */
        tt.is_date = 0;
    } else if ((size == 16) || (size == 20)) {  /* UTC time, ends in 'Z' */
        if ((str[size-1] != 'Z'))
            goto FAIL;

        tt.zone = icaltimezone_get_utc_timezone();
        tt.is_date = 0;
    } else if ((size == 8) || (size == 10)) {   /* A DATE */
        tt.is_date = 1;
    } else {    /* error */
        goto FAIL;
    }

    if (tt.is_date == 1) {
        if (size == 10) {
            char dsep1, dsep2;

            if (sscanf(str, "%04d%c%02d%c%02d",
                       &tt.year, &dsep1, &tt.month, &dsep2, &tt.day) < 5) {
                goto FAIL;
            }

            if ((dsep1 != '-') || (dsep2 != '-')) {
                goto FAIL;
            }
        } else if (sscanf(str, "%04d%02d%02d", &tt.year, &tt.month, &tt.day) < 3) {
            goto FAIL;
        }
    } else {
        if (size > 16) {
            char dsep1, dsep2, tsep, tsep1, tsep2;

            if (sscanf(str, "%04d%c%02d%c%02d%c%02d%c%02d%c%02d",
                       &tt.year, &dsep1, &tt.month, &dsep2, &tt.day, &tsep,
                       &tt.hour, &tsep1, &tt.minute, &tsep2, &tt.second) < 11) {
                goto FAIL;
            }

            if ((tsep != 'T') ||
                (dsep1 != '-') || (dsep2 != '-') ||
                (tsep1 != ':') || (tsep2 != ':')) {
                goto FAIL;
            }

        } else {
            char tsep;

            if (sscanf(str, "%04d%02d%02d%c%02d%02d%02d",
                       &tt.year, &tt.month, &tt.day, &tsep,
                       &tt.hour, &tt.minute, &tt.second) < 7) {
                goto FAIL;
            }

            if (tsep != 'T') {
                goto FAIL;
            }
        }
    }

    return tt;

  FAIL:
    icalerror_set_errno(ICAL_MALFORMEDDATA_ERROR);
    return icaltime_null_time();
}

int icaltime_is_leap_year(const int year)
{
    if (year <= 1752) {
        return (year % 4 == 0);
    } else {
        return ((year % 4 == 0) && (year % 100 != 0)) || (year % 400 == 0);
    }
}

int icaltime_days_in_year(const int year)
{
    if (icaltime_is_leap_year(year)) {
        return 366;
    } else {
        return 365;
    }
}

static const int _days_in_month[] = { 0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };

int icaltime_days_in_month(const int month, const int year)
{
    int days;

/* The old code aborting if it was passed a parameter like BYMONTH=0
 * Unfortunately it's not practical right now to pass an error all
 * the way up the stack, so instead of aborting we're going to apply
 * the GIGO principle and simply return '30 days' if we get an
 * invalid month.  Modern applications cannot tolerate crashing.
 *  assert(month > 0);
 *  assert(month <= 12);
 */
    if ((month < 1) || (month > 12)) {
        return 30;
    }

    days = _days_in_month[month];

    if (month == 2) {
        days += icaltime_is_leap_year(year);
    }

    return days;
}

/* 1-> Sunday, 7->Saturday */
int icaltime_day_of_week(const struct icaltimetype t)
{
    UTinstantInt jt;

    memset(&jt, 0, sizeof(UTinstantInt));

    jt.year = t.year;
    jt.month = t.month;
    jt.day = t.day;

    juldat_int(&jt);

    return jt.weekday + 1;
}

int icaltime_start_doy_week(const struct icaltimetype t, int fdow)
{
    UTinstantInt jt;
    int delta;

    memset(&jt, 0, sizeof(UTinstantInt));

    jt.year = t.year;
    jt.month = t.month;
    jt.day = t.day;

    juldat_int(&jt);
    caldat_int(&jt);

    delta = jt.weekday - (fdow - 1);
    if (delta < 0) {
        delta += 7;
    }
    return jt.day_of_year - delta;
}

int icaltime_week_number(const struct icaltimetype ictt)
{
    UTinstantInt jt;

    memset(&jt, 0, sizeof(UTinstantInt));

    jt.year = ictt.year;
    jt.month = ictt.month;
    jt.day = ictt.day;

    juldat_int(&jt);
    caldat_int(&jt);

    return (jt.day_of_year - jt.weekday) / 7;
}

int icaltime_day_of_year(const struct icaltimetype t)
{
    int is_leap = icaltime_is_leap_year(t.year);

    return days_in_year_passed_month[is_leap][t.month - 1] + t.day;
}

struct icaltimetype icaltime_from_day_of_year(const int _doy, const int _year)
{
    struct icaltimetype tt = icaltime_null_date();
    int is_leap;
    int month;
    int doy = _doy;
    int year = _year;

    is_leap = icaltime_is_leap_year(year);

    /* Zero and neg numbers represent days  of the previous year */
    if (doy < 1) {
        year--;
        is_leap = icaltime_is_leap_year(year);
        doy += days_in_year_passed_month[is_leap][12];
    } else if (doy > days_in_year_passed_month[is_leap][12]) {
        /* Move on to the next year */
        is_leap = icaltime_is_leap_year(year);
        doy -= days_in_year_passed_month[is_leap][12];
        year++;
    }

    tt.year = year;

    for (month = 11; month >= 0; month--) {
        if (doy > days_in_year_passed_month[is_leap][month]) {
            tt.month = month + 1;
            tt.day = doy - days_in_year_passed_month[is_leap][month];
            break;
        }
    }

    return tt;
}

struct icaltimetype icaltime_null_time(void)
{
    struct icaltimetype t;

    memset(&t, 0, sizeof(struct icaltimetype));

    return t;
}

struct icaltimetype icaltime_null_date(void)
{
    struct icaltimetype t;

    memset(&t, 0, sizeof(struct icaltimetype));

    t.is_date = 1;

    /*
     * Init to -1 to match what icalyacc.y used to do.
     * Does anything depend on this?
     */
    t.hour = -1;
    t.minute = -1;
    t.second = -1;

    return t;
}

int icaltime_is_valid_time(const struct icaltimetype t)
{
    if (t.year < 0 || t.year > 3000 || t.is_date > 1 || t.is_date < 0) {
        return 0;
    } else {
        return 1;
    }
}

int icaltime_is_date(const struct icaltimetype t)
{
    return t.is_date;
}

int icaltime_is_utc(const struct icaltimetype t)
{
    return t.zone == icaltimezone_get_utc_timezone();
}

int icaltime_is_null_time(const struct icaltimetype t)
{
    if (t.second + t.minute + t.hour + t.day + t.month + t.year == 0) {
        return 1;
    }

    return 0;
}

int icaltime_compare(const struct icaltimetype a_in, const struct icaltimetype b_in)
{
    struct icaltimetype a, b;

    /* We only need to perform time zone conversion if times aren't in the same time zone
       or neither of them is floating (zone equals NULL) */
    if (a_in.zone != b_in.zone && a_in.zone != NULL && b_in.zone != NULL) {
        a = icaltime_convert_to_zone(a_in, icaltimezone_get_utc_timezone());
        b = icaltime_convert_to_zone(b_in, icaltimezone_get_utc_timezone());
    } else {
        a = a_in;
        b = b_in;
    }

    if (a.year > b.year) {
        return 1;
    } else if (a.year < b.year) {
        return -1;
    } else if (a.month > b.month) {
        return 1;
    } else if (a.month < b.month) {
        return -1;
    } else if (a.day > b.day) {
        return 1;
    } else if (a.day < b.day) {
        return -1;
    }

    /* if both are dates, we are done */
    if (a.is_date && b.is_date) {
        return 0;

    /* else, if only one is a date (and we already know the date part is equal),
       then the other is greater */
    } else if (b.is_date) {
        return 1;
    } else if (a.is_date) {
        return -1;
    } else if (a.hour > b.hour) {
        return 1;
    } else if (a.hour < b.hour) {
        return -1;
    } else if (a.minute > b.minute) {
        return 1;
    } else if (a.minute < b.minute) {
        return -1;
    } else if (a.second > b.second) {
        return 1;
    } else if (a.second < b.second) {
        return -1;
    }

    return 0;
}

int icaltime_compare_date_only(const struct icaltimetype a_in,
                               const struct icaltimetype b_in)
{
    struct icaltimetype a, b;
    icaltimezone *tz = icaltimezone_get_utc_timezone();

    a = icaltime_convert_to_zone(a_in, tz);
    b = icaltime_convert_to_zone(b_in, tz);

    if (a.year > b.year) {
        return 1;
    } else if (a.year < b.year) {
        return -1;
    }

    if (a.month > b.month) {
        return 1;
    } else if (a.month < b.month) {
        return -1;
    }

    if (a.day > b.day) {
        return 1;
    } else if (a.day < b.day) {
        return -1;
    }

    return 0;
}

int icaltime_compare_date_only_tz(const struct icaltimetype a_in,
                                  const struct icaltimetype b_in,
                                  icaltimezone *tz)
{
    struct icaltimetype a, b;

    a = icaltime_convert_to_zone(a_in, tz);
    b = icaltime_convert_to_zone(b_in, tz);

    if (a.year > b.year) {
        return 1;
    } else if (a.year < b.year) {
        return -1;
    }

    if (a.month > b.month) {
        return 1;
    } else if (a.month < b.month) {
        return -1;
    }

    if (a.day > b.day) {
        return 1;
    } else if (a.day < b.day) {
        return -1;
    }

    return 0;
}

/* These are defined in icalduration.c:
struct icaltimetype  icaltime_add(struct icaltimetype t,
                                  struct icaldurationtype  d)
struct icaldurationtype  icaltime_subtract(struct icaltimetype t1,
                                           struct icaltimetype t2)
*/

void icaltime_adjust(struct icaltimetype *tt,
                     const int days, const int hours,
                     const int minutes, const int seconds)
{
    int second, minute, hour, day;
    int minutes_overflow, hours_overflow, days_overflow = 0, years_overflow;
    int days_in_month;

    /* If we are passed a date make sure to ignore hour minute and second */
    if (tt->is_date)
        goto IS_DATE;

    /* Add on the seconds. */
    second = tt->second + seconds;
    tt->second = second % 60;
    minutes_overflow = second / 60;
    if (tt->second < 0) {
        tt->second += 60;
        minutes_overflow--;
    }

    /* Add on the minutes. */
    minute = tt->minute + minutes + minutes_overflow;
    tt->minute = minute % 60;
    hours_overflow = minute / 60;
    if (tt->minute < 0) {
        tt->minute += 60;
        hours_overflow--;
    }

    /* Add on the hours. */
    hour = tt->hour + hours + hours_overflow;
    tt->hour = hour % 24;
    days_overflow = hour / 24;
    if (tt->hour < 0) {
        tt->hour += 24;
        days_overflow--;
    }

  IS_DATE:
    /* Normalize the month. We do this before handling the day since we may
       need to know what month it is to get the number of days in it.
       Note that months are 1 to 12, so we have to be a bit careful. */
    if (tt->month >= 13) {
        years_overflow = (tt->month - 1) / 12;
        tt->year += years_overflow;
        tt->month -= years_overflow * 12;
    } else if (tt->month <= 0) {
        /* 0 to -11 is -1 year out, -12 to -23 is -2 years. */
        years_overflow = (tt->month / 12) - 1;
        tt->year += years_overflow;
        tt->month -= years_overflow * 12;
    }

    /* Add on the days. */
    day = tt->day + days + days_overflow;
    if (day > 0) {
        for (;;) {
            days_in_month = icaltime_days_in_month(tt->month, tt->year);
            if (day <= days_in_month)
                break;

            tt->month++;
            if (tt->month >= 13) {
                tt->year++;
                tt->month = 1;
            }

            day -= days_in_month;
        }
    } else {
        while (day <= 0) {
            if (tt->month == 1) {
                tt->year--;
                tt->month = 12;
            } else {
                tt->month--;
            }

            day += icaltime_days_in_month(tt->month, tt->year);
        }
    }
    tt->day = day;
}

struct icaltimetype icaltime_convert_to_zone(const struct icaltimetype tt, icaltimezone *zone)
{
    struct icaltimetype ret = tt;

    /* If it's a date do nothing */
    if (tt.is_date) {
        return ret;
    }

    if (tt.zone == zone) {
        return ret;
    }

    /* If it's a floating time we don't want to adjust the time */
    if (tt.zone != NULL) {
        icaltimezone *from_zone = (icaltimezone *) tt.zone;

        if (!from_zone) {
            from_zone = icaltimezone_get_utc_timezone();
        }

        icaltimezone_convert_time(&ret, from_zone, zone);
    }

    ret.zone = zone;

    return ret;
}

const icaltimezone *icaltime_get_timezone(const struct icaltimetype t)
{
    return t.zone;
}

const char *icaltime_get_tzid(const struct icaltimetype t)
{
    if (t.zone != NULL) {
        return icaltimezone_get_tzid((icaltimezone *) t.zone);
    } else {
        return NULL;
    }
}

struct icaltimetype icaltime_set_timezone(struct icaltimetype *t, const icaltimezone *zone)
{
    /* If it's a date do nothing */
    if (t->is_date) {
        return *t;
    }

    if (t->zone == zone) {
        return *t;
    }

    t->zone = zone;

    return *t;
}

icaltime_span icaltime_span_new(struct icaltimetype dtstart, struct icaltimetype dtend, int is_busy)
{
    icaltime_span span;

    span.is_busy = is_busy;

    span.start = icaltime_as_timet_with_zone(dtstart,
                                             dtstart.zone ? dtstart.
                                             zone : icaltimezone_get_utc_timezone());

    if (icaltime_is_null_time(dtend)) {
        if (!icaltime_is_date(dtstart)) {
            /* If dtstart is a DATE-TIME and there is no DTEND nor DURATION
               it takes no time */
            span.end = span.start;
            return span;
        } else {
            dtend = dtstart;
        }
    }

    span.end = icaltime_as_timet_with_zone(dtend,
                                           dtend.zone ? dtend.
                                           zone : icaltimezone_get_utc_timezone());

    if (icaltime_is_date(dtstart)) {
        /* no time specified, go until the end of the day.. */
        span.end += 60 * 60 * 24 - 1;
    }
    return span;
}

int icaltime_span_overlaps(icaltime_span *s1, icaltime_span *s2)
{
    /* s1->start in s2 */
    if (s1->start > s2->start && s1->start < s2->end)
        return 1;

    /* s1->end in s2 */
    if (s1->end > s2->start && s1->end < s2->end)
        return 1;

    /* s2->start in s1 */
    if (s2->start > s1->start && s2->start < s1->end)
        return 1;

    /* s2->end in s1 */
    if (s2->end > s1->start && s2->end < s1->end)
        return 1;

    if (s1->start == s2->start && s1->end == s2->end)
        return 1;

    return 0;
}

int icaltime_span_contains(icaltime_span *s, icaltime_span *container)
{
    if ((s->start >= container->start && s->start < container->end) &&
        (s->end <= container->end && s->end > container->start)) {
        return 1;
    }

    return 0;
}