evolution/calendar/cal-util/timeutil.c

/* Miscellaneous time-related utilities
 *
 * Copyright (C) 2000, 2001 Ximian, Inc.
 *
 * Authors: Federico Mena <federico@ximian.com>
 *          Miguel de Icaza <miguel@ximian.com>
 *          Damon Chaplin <damon@ximian.com>
 */

#include <string.h>
#include <ctype.h>
#include <glib.h>
#include <ical.h>
#include "timeutil.h"



#define REFORMATION_DAY 639787	/* First day of the reformation, counted from 1 Jan 1 */
#define MISSING_DAYS 11		/* They corrected out 11 days */
#define THURSDAY 4		/* First day of reformation */
#define SATURDAY 6		/* Offset value; 1 Jan 1 was a Saturday */


/* Number of days in a month, using 0 (Jan) to 11 (Dec). For leap years,
   add 1 to February (month 1). */
static const int days_in_month[12] = {
	31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31
};



/**************************************************************************
 * time_t manipulation functions.
 *
 * NOTE: these use the Unix timezone functions like mktime() and localtime()
 * and so should not be used in Evolution. New Evolution code should use
 * icaltimetype values rather than time_t values wherever possible.
 **************************************************************************/

/* Adds a day onto the time, using local time.
   Note that if clocks go forward due to daylight savings time, there are
   some non-existent local times, so the hour may be changed to make it a
   valid time. This also means that it may not be wise to keep calling
   time_add_day() to step through a certain period - if the hour gets changed
   to make it valid time, any further calls to time_add_day() will also return
   this hour, which may not be what you want. */
time_t
time_add_day (time_t time, int days)
{
	struct tm *tm;

	tm = localtime (&time);
	tm->tm_mday += days;
	tm->tm_isdst = -1;

	return mktime (tm);
}

time_t
time_add_week (time_t time, int weeks)
{
	return time_add_day (time, weeks * 7);
}

/* Returns the start of the day, according to the local time. */
time_t
time_day_begin (time_t t)
{
	struct tm tm;

	tm = *localtime (&t);
	tm.tm_hour = tm.tm_min = tm.tm_sec = 0;
	tm.tm_isdst = -1;

	return mktime (&tm);
}

/* Returns the end of the day, according to the local time. */
time_t
time_day_end (time_t t)
{
	struct tm tm;

	tm = *localtime (&t);
	tm.tm_hour = tm.tm_min = tm.tm_sec = 0;
	tm.tm_mday++;
	tm.tm_isdst = -1;

	return mktime (&tm);
}


/**************************************************************************
 * time_t manipulation functions, using timezones in libical.
 *
 * NOTE: these are only here to make the transition to the timezone
 * functions easier. New code should use icaltimetype values rather than
 * time_t values wherever possible.
 **************************************************************************/


/* Adds or subtracts a number of days to/from the given time_t value, using
   the given timezone.
   NOTE: this function is only here to make the transition to the timezone
   functions easier. New code should use icaltimetype values and
   icaltime_adjust() to add or subtract days, hours, minutes & seconds. */
time_t
time_add_day_with_zone (time_t time, int days, icaltimezone *zone)
{
	struct icaltimetype tt;

	/* Convert to an icaltimetype. */
	tt = icaltime_from_timet_with_zone (time, FALSE, zone);

	/* Add/subtract the number of days. */
	icaltime_adjust (&tt, days, 0, 0, 0);

	/* Convert back to a time_t. */
	return icaltime_as_timet_with_zone (tt, zone);
}


/* Adds or subtracts a number of weeks to/from the given time_t value, using
   the given timezone.
   NOTE: this function is only here to make the transition to the timezone
   functions easier. New code should use icaltimetype values and
   icaltime_adjust() to add or subtract days, hours, minutes & seconds. */
time_t
time_add_week_with_zone (time_t time, int weeks, icaltimezone *zone)
{
	return time_add_day_with_zone (time, weeks * 7, zone);
}


/* Adds or subtracts a number of months to/from the given time_t value, using
   the given timezone.

   If the day would be off the end of the month (e.g. adding 1 month to
   30th January, would lead to an invalid day, 30th February), it moves it
   down to the last day in the month, e.g. 28th Feb (or 29th in a leap year.)

   NOTE: this function is only here to make the transition to the timezone
   functions easier. New code should use icaltimetype values and
   icaltime_adjust() to add or subtract days, hours, minutes & seconds. */
time_t
time_add_month_with_zone (time_t time, int months, icaltimezone *zone)
{
	struct icaltimetype tt;
	int day, days_in_month;

	/* Convert to an icaltimetype. */
	tt = icaltime_from_timet_with_zone (time, FALSE, zone);

	/* Add on the number of months. */
	tt.month += months;

	/* Save the day, and set it to 1, so we don't overflow into the next
	   month. */
	day = tt.day;
	tt.day = 1;

	/* Normalize it, fixing any month overflow. */
	tt = icaltime_normalize (tt);

	/* If we go past the end of a month, set it to the last day. */
	days_in_month = time_days_in_month (tt.year, tt.month - 1);
	if (day > days_in_month)
		day = days_in_month;

	tt.day = day;

	/* Convert back to a time_t. */
	return icaltime_as_timet_with_zone (tt, zone);
}


/* Returns the start of the year containing the given time_t, using the given
   timezone.
   NOTE: this function is only here to make the transition to the timezone
   functions easier. New code should use icaltimetype values and
   icaltime_adjust() to add or subtract days, hours, minutes & seconds. */
time_t
time_year_begin_with_zone (time_t time, icaltimezone *zone)
{
	struct icaltimetype tt;

	/* Convert to an icaltimetype. */
	tt = icaltime_from_timet_with_zone (time, FALSE, zone);

	/* Set it to the start of the year. */
	tt.month  = 1;
	tt.day    = 1;
	tt.hour   = 0;
	tt.minute = 0;
	tt.second = 0;

	/* Convert back to a time_t. */
	return icaltime_as_timet_with_zone (tt, zone);
}


/* Returns the start of the month containing the given time_t, using the given
   timezone.
   NOTE: this function is only here to make the transition to the timezone
   functions easier. New code should use icaltimetype values and
   icaltime_adjust() to add or subtract days, hours, minutes & seconds. */
time_t
time_month_begin_with_zone (time_t time, icaltimezone *zone)
{
	struct icaltimetype tt;

	/* Convert to an icaltimetype. */
	tt = icaltime_from_timet_with_zone (time, FALSE, zone);

	/* Set it to the start of the month. */
	tt.day    = 1;
	tt.hour   = 0;
	tt.minute = 0;
	tt.second = 0;

	/* Convert back to a time_t. */
	return icaltime_as_timet_with_zone (tt, zone);
}


/* Returns the start of the week containing the given time_t, using the given
   timezone. week_start_day should use the same values as mktime(),
   i.e. 0 (Sun) to 6 (Sat).
   NOTE: this function is only here to make the transition to the timezone
   functions easier. New code should use icaltimetype values and
   icaltime_adjust() to add or subtract days, hours, minutes & seconds. */
time_t
time_week_begin_with_zone (time_t time, int week_start_day, icaltimezone *zone)
{
	struct icaltimetype tt;
	int weekday, offset;

	/* Convert to an icaltimetype. */
	tt = icaltime_from_timet_with_zone (time, FALSE, zone);

	/* Get the weekday. */
	weekday = time_day_of_week (tt.day, tt.month - 1, tt.year);

	/* Calculate the current offset from the week start day. */
	offset = (weekday + 7 - week_start_day) % 7;

	/* Set it to the start of the month. */
	tt.day -= offset;
	tt.hour   = 0;
	tt.minute = 0;
	tt.second = 0;

	/* Normalize it, to fix any overflow. */
	tt = icaltime_normalize (tt);

	/* Convert back to a time_t. */
	return icaltime_as_timet_with_zone (tt, zone);
}


/* Returns the start of the day containing the given time_t, using the given
   timezone.
   NOTE: this function is only here to make the transition to the timezone
   functions easier. New code should use icaltimetype values and
   icaltime_adjust() to add or subtract days, hours, minutes & seconds. */
time_t
time_day_begin_with_zone (time_t time, icaltimezone *zone)
{
	struct icaltimetype tt;

	/* Convert to an icaltimetype. */
	tt = icaltime_from_timet_with_zone (time, FALSE, zone);

	/* Set it to the start of the day. */
	tt.hour   = 0;
	tt.minute = 0;
	tt.second = 0;

	/* Convert back to a time_t. */
	return icaltime_as_timet_with_zone (tt, zone);
}


/* Returns the end of the day containing the given time_t, using the given
   timezone. (The end of the day is the start of the next day.)
   NOTE: this function is only here to make the transition to the timezone
   functions easier. New code should use icaltimetype values and
   icaltime_adjust() to add or subtract days, hours, minutes & seconds. */
time_t
time_day_end_with_zone (time_t time, icaltimezone *zone)
{
	struct icaltimetype tt;

	/* Convert to an icaltimetype. */
	tt = icaltime_from_timet_with_zone (time, FALSE, zone);

	/* Set it to the start of the next day. */
	tt.day++;
	tt.hour   = 0;
	tt.minute = 0;
	tt.second = 0;

	/* Normalize it, to fix any overflow. */
	tt = icaltime_normalize (tt);

	/* Convert back to a time_t. */
	return icaltime_as_timet_with_zone (tt, zone);
}

/**
 * time_to_gdate_with_zone:
 * @date: Destination #GDate value.
 * @time: A time value.
 * @zone: Desired timezone for destination @date, or NULL if the UTC timezone
 * is desired.
 * 
 * Converts a time_t value to a #GDate structure using the specified timezone.
 * This is analogous to g_date_set_time() but takes the timezone into account.
 **/
void
time_to_gdate_with_zone (GDate *date, time_t time, icaltimezone *zone)
{
	struct icaltimetype tt;

	g_return_if_fail (date != NULL);
	g_return_if_fail (time != -1);

	tt = icaltime_from_timet_with_zone (time, FALSE,
					    zone ? zone : icaltimezone_get_utc_timezone ());

	g_date_set_dmy (date, tt.day, tt.month, tt.year);
}


/**************************************************************************
 * General time functions.
 **************************************************************************/


/* Returns the number of days in the month. Year is the normal year, e.g. 2001.
   Month is 0 (Jan) to 11 (Dec). */
int
time_days_in_month (int year, int month)
{
	int days;

	g_return_val_if_fail (year >= 1900, 0);
	g_return_val_if_fail ((month >= 0) && (month < 12), 0);

	days = days_in_month[month];
	if (month == 1 && time_is_leap_year (year))
		days++;

	return days;
}


/* Returns the 1-based day number within the year of the specified date.
   Year is the normal year, e.g. 2001. Month is 0 to 11. */
int
time_day_of_year (int day, int month, int year)
{
	int i;

	for (i = 0; i < month; i++) {
		day += days_in_month[i];

		if (i == 1 && time_is_leap_year (year))
			day++;
	}

	return day;
}


/* Returns the day of the week for the specified date, 0 (Sun) to 6 (Sat).
   For the days that were removed on the Gregorian reformation, it returns
   Thursday. Year is the normal year, e.g. 2001. Month is 0 to 11. */
int
time_day_of_week (int day, int month, int year)
{
	int n;

	n = (year - 1) * 365 + time_leap_years_up_to (year - 1)
	  + time_day_of_year (day, month, year);

	if (n < REFORMATION_DAY)
		return (n - 1 + SATURDAY) % 7;

	if (n >= (REFORMATION_DAY + MISSING_DAYS))
		return (n - 1 + SATURDAY - MISSING_DAYS) % 7;

	return THURSDAY;
}


/* Returns whether the specified year is a leap year. Year is the normal year,
   e.g. 2001. */
gboolean
time_is_leap_year (int year)
{
	if (year <= 1752)
		return !(year % 4);
	else
		return (!(year % 4) && (year % 100)) || !(year % 400);
}


/* Returns the number of leap years since year 1 up to (but not including) the
   specified year. Year is the normal year, e.g. 2001. */
int
time_leap_years_up_to (int year)
{
  /* There is normally a leap year every 4 years, except at the turn of
     centuries since 1700. But there is a leap year on centuries since 1700
     which are divisible by 400. */
  return (year / 4
	  - ((year > 1700) ? (year / 100 - 17) : 0)
	  + ((year > 1600) ? ((year - 1600) / 400) : 0));
}


/**
 * isodate_from_time_t:
 * @t: A time value.
 * 
 * Creates an ISO 8601 UTC representation from a time value.
 * 
 * Return value: String with the ISO 8601 representation of the UTC time.
 **/
char *
isodate_from_time_t (time_t t)
{
	gchar *ret;

	ret = g_malloc (17); /* 4+2+2+1+2+2+2+1 + 1 */
	strftime (ret, 17, "%Y%m%dT%H%M%SZ", gmtime (&t));

	return ret;
}

/**
 * time_from_isodate:
 * @str: Date/time value in ISO 8601 format.
 * 
 * Converts an ISO 8601 UTC time string into a time_t value.
 * 
 * Return value: Time_t corresponding to the specified ISO string.
 * Note that we only allow UTC times at present.
 **/
time_t
time_from_isodate (const char *str)
{
	struct icaltimetype tt = icaltime_null_time ();
	icaltimezone *utc_zone;
	int len, i;

	g_return_val_if_fail (str != NULL, -1);

	/* yyyymmdd[Thhmmss[Z]] */

	len = strlen (str);

	if (!(len == 8 || len == 15 || len == 16))
		return -1;

	for (i = 0; i < len; i++)
		if (!((i != 8 && i != 15 && isdigit (str[i]))
		      || (i == 8 && str[i] == 'T')
		      || (i == 15 && str[i] == 'Z')))
			return -1;

#define digit_at(x,y) (x[y] - '0')

	tt.year = digit_at (str, 0) * 1000
		+ digit_at (str, 1) * 100
		+ digit_at (str, 2) * 10
		+ digit_at (str, 3);

	tt.month = digit_at (str, 4) * 10
		 + digit_at (str, 5);

	tt.day = digit_at (str, 6) * 10
	       + digit_at (str, 7);

	if (len > 8) {
		tt.hour = digit_at (str, 9) * 10
			+ digit_at (str, 10);
		tt.minute  = digit_at (str, 11) * 10
			   + digit_at (str, 12);
		tt.second  = digit_at (str, 13) * 10
			   + digit_at (str, 14);
	}

	utc_zone = icaltimezone_get_utc_timezone ();

	return icaltime_as_timet_with_zone (tt, utc_zone);
}

struct tm
icaltimetype_to_tm (struct icaltimetype *itt)
{
	struct tm tm;
	
	memset (&tm, 0, sizeof (struct tm));

	if (!itt->is_date) {
		tm.tm_sec = itt->second;
		tm.tm_min = itt->minute;
		tm.tm_hour = itt->hour;
	}

	tm.tm_mday = itt->day;
	tm.tm_mon = itt->month - 1;
	tm.tm_year = itt->year - 1900;
	tm.tm_wday = time_day_of_week (itt->day, itt->month - 1, itt->year);
	tm.tm_isdst = -1;
	
	return tm;
}

/**
 * icaltimetype_to_tm_with_zone:
 * @itt: A time value.
 * @from_zone: Source timezone.
 * @to_zone: Destination timezone.
 * 
 * Converts a time value from one timezone to another, and returns a struct tm
 * representation of the time.
 * 
 * Return value: The converted time as a struct tm.  All fields will be
 * set properly except for tm.tm_yday.
 **/
struct tm
icaltimetype_to_tm_with_zone (struct icaltimetype *itt,
			      icaltimezone *from_zone,
			      icaltimezone *to_zone)
{
	struct tm tm;
	struct icaltimetype itt_copy;

	memset (&tm, 0, sizeof (tm));
	tm.tm_isdst = -1;

	g_return_val_if_fail (itt != NULL, tm);

	itt_copy = *itt;

	icaltimezone_convert_time (&itt_copy, from_zone, to_zone);
	tm = icaltimetype_to_tm (&itt_copy);

	return tm;
}

struct icaltimetype
tm_to_icaltimetype (struct tm *tm, gboolean is_date)
{
	struct icaltimetype itt;

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

	if (!is_date) {
		itt.second = tm->tm_sec;
		itt.minute = tm->tm_min;
		itt.hour = tm->tm_hour;
	}

	itt.day = tm->tm_mday;
	itt.month = tm->tm_mon + 1;
	itt.year = tm->tm_year+ 1900;
    
	itt.is_utc = 0;
	itt.is_date = is_date; 
	
	return itt;
}