path: root/kalarm/karecurrence.cpp

/*
 *  karecurrence.cpp  -  recurrence with special yearly February 29th handling
 *  Program:  kalarm
 *  Copyright © 2005,2006,2008 by David Jarvie <[email protected]>
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License along
 *  with this program; if not, write to the Free Software Foundation, Inc.,
 *  51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 */

#include "kalarm.h"

#include <tqbitarray.h>
#include <kdebug.h>

#include <libkcal/icalformat.h>

#include "datetime.h"
#include "functions.h"
#include "karecurrence.h"

using namespace KCal;

/*=============================================================================
= Class KARecurrence
= The purpose of this class is to represent the restricted range of recurrence
= types which are handled by KAlarm, and to translate between these and the
= libkcal Recurrence class. In particular, it handles yearly recurrences on
= 29th February specially:
=
= KARecurrence allows annual 29th February recurrences to fall on 28th
= February or 1st March, or not at all, in non-leap years. It allows such
= 29th February recurrences to be combined with the 29th of other months in
= a simple way, represented simply as the 29th of multiple months including
= February. For storage in the libkcal calendar, the 29th day of the month
= recurrence for other months is combined with a last-day-of-February or a
= 60th-day-of-the-year recurrence rule, thereby conforming to RFC2445.
=============================================================================*/


KARecurrence::Feb29Type KARecurrence::mDefaultFeb29 = KARecurrence::FEB29_FEB29;


/******************************************************************************
*  Set up a KARecurrence from recurrence parameters, using the start date to
*  determine the recurrence day/month as appropriate.
*  Only a restricted subset of recurrence types is allowed.
*  Reply = true if successful.
*/
bool KARecurrence::set(Type recurType, int freq, int count, int f29, const DateTime& start, const TQDateTime& end)
{
	mCachedType = -1;
	RecurrenceRule::PeriodType rrtype;
	switch (recurType)
	{
		case MINUTELY:    rrtype = RecurrenceRule::rMinutely;  break;
		case DAILY:       rrtype = RecurrenceRule::rDaily;  break;
		case WEEKLY:      rrtype = RecurrenceRule::rWeekly;  break;
		case MONTHLY_DAY: rrtype = RecurrenceRule::rMonthly;  break;
		case ANNUAL_DATE: rrtype = RecurrenceRule::rYearly;  break;
		case NO_RECUR:    rrtype = RecurrenceRule::rNone;  break;
		default:
			return false;
	}
	if (!init(rrtype, freq, count, f29, start, end))
		return false;
	switch (recurType)
	{
		case WEEKLY:
		{
			TQBitArray days(7);
			days.setBit(start.date().dayOfWeek() - 1);
			addWeeklyDays(days);
			break;
		}
		case MONTHLY_DAY:
			addMonthlyDate(start.date().day());
			break;
		case ANNUAL_DATE:
			addYearlyDate(start.date().day());
			addYearlyMonth(start.date().month());
			break;
		default:
			break;
	}
	return true;
}

/******************************************************************************
*  Initialise a KARecurrence from recurrence parameters.
*  Reply = true if successful.
*/
bool KARecurrence::init(RecurrenceRule::PeriodType recurType, int freq, int count, int f29, const DateTime& start,
                        const TQDateTime& end)
{
	mCachedType = -1;
	Feb29Type feb29Type = (f29 == -1) ? mDefaultFeb29 : static_cast<Feb29Type>(f29);
	mFeb29Type = FEB29_FEB29;
	clear();
	if (count < -1)
		return false;
	bool dateOnly = start.isDateOnly();
	if (!count  &&  (!dateOnly && !end.isValid()
	              || dateOnly && !end.date().isValid()))
		return false;
	switch (recurType)
	{
		case RecurrenceRule::rMinutely:
		case RecurrenceRule::rDaily:
		case RecurrenceRule::rWeekly:
		case RecurrenceRule::rMonthly:
		case RecurrenceRule::rYearly:
			break;
		case rNone:
			return true;
		default:
			return false;
	}
	setNewRecurrenceType(recurType, freq);
	if (count)
		setDuration(count);
	else if (dateOnly)
		setEndDate(end.date());
	else
		setEndDateTime(end);
	TQDateTime startdt = start.dateTime();
	if (recurType == RecurrenceRule::rYearly
	&&  feb29Type == FEB29_FEB28  ||  feb29Type == FEB29_MAR1)
	{
		int year = startdt.date().year();
		if (!TQDate::leapYear(year)
		&&  startdt.date().dayOfYear() == (feb29Type == FEB29_MAR1 ? 60 : 59))
		{
			/* The event start date is February 28th or March 1st, but it
			 * is a recurrence on February 29th (recurring on February 28th
			 * or March 1st in non-leap years). Adjust the start date to
			 * be on February 29th in the last previous leap year.
			 * This is necessary because KARecurrence represents all types
			 * of 29th February recurrences by a simple 29th February.
			 */
			while (!TQDate::leapYear(--year)) ;
			startdt.setDate(TQDate(year, 2, 29));
		}
		mFeb29Type = feb29Type;
	}
	if (dateOnly)
		setStartDate(startdt.date());
	else
		setStartDateTime(startdt);
	return true;
}

/******************************************************************************
 * Initialise the recurrence from an iCalendar RRULE string.
 */
bool KARecurrence::set(const TQString& icalRRULE)
{
	static TQString RRULE = TQString::tqfromLatin1("RRULE:");
	mCachedType = -1;
	clear();
	if (icalRRULE.isEmpty())
		return true;
	ICalFormat format;
	if (!format.fromString(defaultRRule(true),
	                       (icalRRULE.startsWith(RRULE) ? icalRRULE.mid(RRULE.length()) : icalRRULE)))
		return false;
	fix();
	return true;
}

/******************************************************************************
* Must be called after presetting with a KCal::Recurrence, to convert the
* recurrence to KARecurrence types:
* - Convert hourly recurrences to minutely.
* - Remove all but the first day in yearly date recurrences.
* - Check for yearly recurrences falling on February 29th and adjust them as
*   necessary. A 29th of the month rule can be combined with either a 60th day
*   of the year rule or a last day of February rule.
*/
void KARecurrence::fix()
{
	mCachedType = -1;
	mFeb29Type = FEB29_FEB29;
	int convert = 0;
	int days[2] = { 0, 0 };
	RecurrenceRule* rrules[2];
	RecurrenceRule::List rrulelist = rRules();
	RecurrenceRule::List::ConstIterator rr = rrulelist.begin();
	for (int i = 0;  i < 2  &&  rr != rrulelist.end();  ++i, ++rr)
	{
		RecurrenceRule* rrule = *rr;
		rrules[i] = rrule;
		bool stop = true;
		int rtype = recurrenceType(rrule);
		switch (rtype)
		{
			case rHourly:
				// Convert an hourly recurrence to a minutely one
				rrule->setRecurrenceType(RecurrenceRule::rMinutely);
				rrule->setFrequency(rrule->frequency() * 60);
				// fall through to rMinutely
			case rMinutely:
			case rDaily:
			case rWeekly:
			case rMonthlyDay:
			case rMonthlyPos:
			case rYearlyPos:
				if (!convert)
					++rr;    // remove all rules except the first
				break;
			case rOther:
				if (dailyType(rrule))
				{                        // it's a daily rule with BYDAYS
					if (!convert)
						++rr;    // remove all rules except the first
				}
				break;
			case rYearlyDay:
			{
				// Ensure that the yearly day number is 60 (i.e. Feb 29th/Mar 1st)
				if (convert)
				{
					// This is the second rule.
					// Ensure that it can be combined with the first one.
					if (days[0] != 29
					||  rrule->frequency() != rrules[0]->frequency()
					||  rrule->startDt()   != rrules[0]->startDt())
						break;
				}
				TQValueList<int> ds = rrule->byYearDays();
				if (!ds.isEmpty()  &&  ds.first() == 60)
				{
					++convert;    // this rule needs to be converted
					days[i] = 60;
					stop = false;
					break;
				}
				break;     // not day 60, so remove this rule
			}
			case rYearlyMonth:
			{
				TQValueList<int> ds = rrule->byMonthDays();
				if (!ds.isEmpty())
				{
					int day = ds.first();
					if (convert)
					{
						// This is the second rule.
						// Ensure that it can be combined with the first one.
						if (day == days[0]  ||  day == -1 && days[0] == 60
						||  rrule->frequency() != rrules[0]->frequency()
						||  rrule->startDt()   != rrules[0]->startDt())
							break;
					}
					if (ds.count() > 1)
					{
						ds.clear();   // remove all but the first day
						ds.append(day);
						rrule->setByMonthDays(ds);
					}
					if (day == -1)
					{
						// Last day of the month - only combine if it's February
						TQValueList<int> months = rrule->byMonths();
						if (months.count() != 1  ||  months.first() != 2)
							day = 0;
					}
					if (day == 29  ||  day == -1)
					{
						++convert;    // this rule may need to be converted
						days[i] = day;
						stop = false;
						break;
					}
				}
				if (!convert)
					++rr;
				break;
			}
			default:
				break;
		}
		if (stop)
			break;
	}

	// Remove surplus rules
	for ( ;  rr != rrulelist.end();  ++rr)
	{
		removeRRule(*rr);
		delete *rr;
	}

	TQDate end;
	int count;
	TQValueList<int> months;
	if (convert == 2)
	{
		// There are two yearly recurrence rules to combine into a February 29th recurrence.
		// Combine the two recurrence rules into a single rYearlyMonth rule falling on Feb 29th.
		// Find the duration of the two RRULEs combined, using the shorter of the two if they differ.
		if (days[0] != 29)
		{
			// Swap the two rules so that the 29th rule is the first
			RecurrenceRule* rr = rrules[0];
			rrules[0] = rrules[1];    // the 29th rule
			rrules[1] = rr;
			int d = days[0];
			days[0] = days[1];
			days[1] = d;        // the non-29th day
		}
		// If February is included in the 29th rule, remove it to avoid duplication
		months = rrules[0]->byMonths();
		if (months.remove(2))
			rrules[0]->setByMonths(months);

		count = combineDurations(rrules[0], rrules[1], end);
		mFeb29Type = (days[1] == 60) ? FEB29_MAR1 : FEB29_FEB28;
	}
	else if (convert == 1  &&  days[0] == 60)
	{
		// There is a single 60th day of the year rule.
		// Convert it to a February 29th recurrence.
		count = duration();
		if (!count)
			end = endDate();
		mFeb29Type = FEB29_MAR1;
	}
	else
		return;

	// Create the new February 29th recurrence
	setNewRecurrenceType(RecurrenceRule::rYearly, frequency());
	RecurrenceRule* rrule = defaultRRule();
	months.append(2);
	rrule->setByMonths(months);
	TQValueList<int> ds;
	ds.append(29);
	rrule->setByMonthDays(ds);
	if (count)
		setDuration(count);
	else
		setEndDate(end);
}

/******************************************************************************
* Get the next time the recurrence occurs, strictly after a specified time.
*/
TQDateTime KARecurrence::getNextDateTime(const TQDateTime& preDateTime) const
{
	switch (type())
	{
		case ANNUAL_DATE:
		case ANNUAL_POS:
		{
			Recurrence recur;
			writeRecurrence(recur);
			return recur.getNextDateTime(preDateTime);
		}
		default:
			return Recurrence::getNextDateTime(preDateTime);
	}
}

/******************************************************************************
* Get the previous time the recurrence occurred, strictly before a specified time.
*/
TQDateTime KARecurrence::getPreviousDateTime(const TQDateTime& afterDateTime) const
{
	switch (type())
	{
		case ANNUAL_DATE:
		case ANNUAL_POS:
		{
			Recurrence recur;
			writeRecurrence(recur);
			return recur.getPreviousDateTime(afterDateTime);
		}
		default:
			return Recurrence::getPreviousDateTime(afterDateTime);
	}
}

/******************************************************************************
* Initialise a KCal::Recurrence to be the same as this instance.
* Additional recurrence rules are created as necessary if it recurs on Feb 29th.
*/
void KARecurrence::writeRecurrence(KCal::Recurrence& recur) const
{
	recur.clear();
	recur.setStartDateTime(startDateTime());
	recur.setExDates(exDates());
	recur.setExDateTimes(exDateTimes());
	const RecurrenceRule* rrule = defaultRRuleConst();
	if (!rrule)
		return;
	int freq  = frequency();
	int count = duration();
	static_cast<KARecurrence*>(&recur)->setNewRecurrenceType(rrule->recurrenceType(), freq);
	if (count)
		recur.setDuration(count);
	else
		recur.setEndDateTime(endDateTime());
	switch (type())
	{
		case DAILY:
			if (rrule->byDays().isEmpty())
				break;
			// fall through to rWeekly
		case WEEKLY:
		case MONTHLY_POS:
			recur.defaultRRule(true)->setByDays(rrule->byDays());
			break;
		case MONTHLY_DAY:
			recur.defaultRRule(true)->setByMonthDays(rrule->byMonthDays());
			break;
		case ANNUAL_POS:
			recur.defaultRRule(true)->setByMonths(rrule->byMonths());
			recur.defaultRRule()->setByDays(rrule->byDays());
			break;
		case ANNUAL_DATE:
		{
			TQValueList<int> months = rrule->byMonths();
			TQValueList<int> days   = monthDays();
			bool special = (mFeb29Type != FEB29_FEB29  &&  !days.isEmpty()
			                &&  days.first() == 29  &&  months.remove(2));
			RecurrenceRule* rrule1 = recur.defaultRRule();
			rrule1->setByMonths(months);
			rrule1->setByMonthDays(days);
			if (!special)
				break;

			// It recurs on the 29th February.
			// Create an additional 60th day of the year, or last day of February, rule.
			RecurrenceRule* rrule2 = new RecurrenceRule();
			rrule2->setRecurrenceType(RecurrenceRule::rYearly);
			rrule2->setFrequency(freq);
			rrule2->setStartDt(startDateTime());
			rrule2->setFloats(doesFloat());
			if (!count)
				rrule2->setEndDt(endDateTime());
			if (mFeb29Type == FEB29_MAR1)
			{
				TQValueList<int> ds;
				ds.append(60);
				rrule2->setByYearDays(ds);
			}
			else
			{
				TQValueList<int> ds;
				ds.append(-1);
				rrule2->setByMonthDays(ds);
				TQValueList<int> ms;
				ms.append(2);
				rrule2->setByMonths(ms);
			}

			if (months.isEmpty())
			{
				// Only February recurs.
				// Replace the RRULE and keep the recurrence count the same.
				if (count)
					rrule2->setDuration(count);
				recur.unsetRecurs();
			}
			else
			{
				// Months other than February also recur on the 29th.
				// Remove February from the list and add a separate RRULE for February.
				if (count)
				{
					rrule1->setDuration(-1);
					rrule2->setDuration(-1);
					if (count > 0)
					{
						/* Adjust counts in the two rules to keep the correct occurrence total.
						 * Note that durationTo() always includes the start date. Since for an
						 * individual RRULE the start date may not actually be included, we need
						 * to decrement the count if the start date doesn't actually recur in
						 * this RRULE.
						 * Note that if the count is small, one of the rules may not recur at
						 * all. In that case, retain it so that the February 29th characteristic
						 * is not lost should the user later change the recurrence count.
						 */
						TQDateTime end = endDateTime();
kdDebug()<<"29th recurrence: count="<<count<<", end date="<<end.toString()<<endl;
						int count1 = rrule1->durationTo(end)
						             - (rrule1->recursOn(startDate()) ? 0 : 1);
						if (count1 > 0)
							rrule1->setDuration(count1);
						else
							rrule1->setEndDt(startDateTime());
						int count2 = rrule2->durationTo(end)
						             - (rrule2->recursOn(startDate()) ? 0 : 1);
						if (count2 > 0)
							rrule2->setDuration(count2);
						else
							rrule2->setEndDt(startDateTime());
					}
				}
			}
			recur.addRRule(rrule2);
			break;
		}
		default:
			break;
	}
}

/******************************************************************************
* Return the date/time of the last recurrence.
*/
TQDateTime KARecurrence::endDateTime() const
{
	if (mFeb29Type == FEB29_FEB29  ||  duration() <= 1)
	{
		/* Either it doesn't have any special February 29th treatment,
		 * it's infinite (count = -1), the end date is specified
		 * (count = 0), or it ends on the start date (count = 1).
		 * So just use the normal KCal end date calculation.
		 */
		return Recurrence::endDateTime();
	}

	/* Create a temporary recurrence rule to find the end date.
	 * In a standard KCal recurrence, the 29th February only occurs once every
	 * 4 years. So shift the temporary recurrence date to the 28th to ensure
	 * that it occurs every year, thus giving the correct occurrence count.
	 */
	RecurrenceRule* rrule = new RecurrenceRule();
	rrule->setRecurrenceType(RecurrenceRule::rYearly);
	TQDateTime dt = startDateTime();
	TQDate d = dt.date();
	switch (d.day())
	{
		case 29:
			// The start date is definitely a recurrence date, so shift
			// start date to the temporary recurrence date of the 28th
			d.setYMD(d.year(), d.month(), 28);
			break;
		case 28:
			if (d.month() != 2  ||  mFeb29Type != FEB29_FEB28  ||  TQDate::leapYear(d.year()))
			{
				// Start date is not a recurrence date, so shift it to 27th
				d.setYMD(d.year(), d.month(), 27);
			}
			break;
		case 1:
			if (d.month() == 3  &&  mFeb29Type == FEB29_MAR1  &&  !TQDate::leapYear(d.year()))
			{
				// Start date is a March 1st recurrence date, so shift
				// start date to the temporary recurrence date of the 28th
				d.setYMD(d.year(), 2, 28);
			}
			break;
		default:
			break;
	}
	dt.setDate(d);
	rrule->setStartDt(dt);
	rrule->setFloats(doesFloat());
	rrule->setFrequency(frequency());
	rrule->setDuration(duration());
	TQValueList<int> ds;
	ds.append(28);
	rrule->setByMonthDays(ds);
	rrule->setByMonths(defaultRRuleConst()->byMonths());
	dt = rrule->endDt();
	delete rrule;

	// We've found the end date for a recurrence on the 28th. Unless that date
	// is a real February 28th recurrence, adjust to the actual recurrence date.
	if (mFeb29Type == FEB29_FEB28  &&  dt.date().month() == 2  &&  !TQDate::leapYear(dt.date().year()))
		return dt;
	return dt.addDays(1);
}

/******************************************************************************
* Return the date/time of the last recurrence.
*/
TQDate KARecurrence::endDate() const
{
	TQDateTime end = endDateTime();
	return end.isValid() ? end.date() : TQDate();
}

/******************************************************************************
* Return whether the event will recur on the specified date.
* The start date only returns true if it matches the recurrence rules.
*/
bool KARecurrence::recursOn(const TQDate& dt) const
{
	if (!Recurrence::recursOn(dt))
		return false;
	if (dt != startDate())
		return true;
	// We know now that it isn't in EXDATES or EXRULES,
	// so we just need to check if it's in RDATES or RRULES
	if (rDates().contains(dt))
		return true;
	RecurrenceRule::List rulelist = rRules();
	for (RecurrenceRule::List::ConstIterator rr = rulelist.begin();  rr != rulelist.end();  ++rr)
		if ((*rr)->recursOn(dt))
			return true;
	DateTimeList dtlist = rDateTimes();
	for (DateTimeList::ConstIterator rdt = dtlist.begin();  rdt != dtlist.end();  ++rdt)
		if ((*rdt).date() == dt)
			return true;
	return false;
}

/******************************************************************************
* Find the duration of two RRULEs combined.
* Use the shorter of the two if they differ.
*/
int KARecurrence::combineDurations(const RecurrenceRule* rrule1, const RecurrenceRule* rrule2, TQDate& end) const
{
	int count1 = rrule1->duration();
	int count2 = rrule2->duration();
	if (count1 == -1  &&  count2 == -1)
		return -1;

	// One of the RRULEs may not recur at all if the recurrence count is small.
	// In this case, its end date will have been set to the start date.
	if (count1  &&  !count2  &&  rrule2->endDt().date() == startDateTime().date())
		return count1;
	if (count2  &&  !count1  &&  rrule1->endDt().date() == startDateTime().date())
		return count2;

	/* The duration counts will be different even for RRULEs of the same length,
	 * because the first RRULE only actually occurs every 4 years. So we need to
	 * compare the end dates.
	 */
	if (!count1  ||  !count2)
		count1 = count2 = 0;
	// Get the two rules sorted by end date.
	TQDateTime end1 = rrule1->endDt();
	TQDateTime end2 = rrule2->endDt();
	if (end1.date() == end2.date())
	{
		end = end1.date();
		return count1 + count2;
	}
	const RecurrenceRule* rr1;    // earlier end date
	const RecurrenceRule* rr2;    // later end date
	if (end2.isValid()
	&&  (!end1.isValid()  ||  end1.date() > end2.date()))
	{
		// Swap the two rules to make rr1 have the earlier end date
		rr1 = rrule2;
		rr2 = rrule1;
		TQDateTime e = end1;
		end1 = end2;
		end2 = e;
	}
	else
	{
		rr1 = rrule1;
		rr2 = rrule2;
	}

	// Get the date of the next occurrence after the end of the earlier ending rule
	RecurrenceRule rr(*rr1);
	rr.setDuration(-1);
	TQDateTime next1(rr.getNextDate(end1).date());
	if (!next1.isValid())
		end = end1.date();
	else
	{
		if (end2.isValid()  &&  next1 > end2)
		{
			// The next occurrence after the end of the earlier ending rule
			// is later than the end of the later ending rule. So simply use
			// the end date of the later rule.
			end = end2.date();
			return count1 + count2;
		}
		TQDate prev2 = rr2->getPreviousDate(next1).date();
		end = (prev2 > end1.date()) ? prev2 : end1.date();
	}
	if (count2)
		count2 = rr2->durationTo(end);
	return count1 + count2;
}

/******************************************************************************
 * Return the longest interval (in minutes) between recurrences.
 * Reply = 0 if it never recurs.
 */
int KARecurrence::longestInterval() const
{
	int freq = frequency();
	switch (type())
	{
		case MINUTELY:
			return freq;

		case DAILY:
		{
			TQValueList<RecurrenceRule::WDayPos> days = defaultRRuleConst()->byDays();
			if (days.isEmpty())
				return freq * 1440;

			// It recurs only on certain days of the week, so the maximum interval
			// may be greater than the frequency.
			bool ds[7] = { false, false, false, false, false, false, false };
			for (TQValueList<RecurrenceRule::WDayPos>::ConstIterator it = days.begin();  it != days.end();  ++it)
				if ((*it).pos() == 0)
					ds[(*it).day() - 1] = true;
			if (freq % 7)
			{
				// It will recur on every day of the week in some week or other
				// (except for those days which are excluded).
				int first = -1;
				int last  = -1;
				int maxgap = 1;
				for (int i = 0;  i < freq*7;  i += freq)
				{
					if (ds[i % 7])
					{
						if (first < 0)
							first = i;
						else if (i - last > maxgap)
							maxgap = i - last;
						last = i;
					}
				}
				int wrap = freq*7 - last + first;
				if (wrap > maxgap)
					maxgap = wrap;
				return maxgap * 1440;
			}
			else
			{
				// It will recur on the same day of the week every time.
				// Ensure that the day is a day which is not excluded.
				return ds[startDate().dayOfWeek() - 1] ? freq * 1440 : 0;
			}
		}
		case WEEKLY:
		{
			// Find which days of the week it recurs on, and if on more than
			// one, reduce the maximum interval accordingly.
			TQBitArray ds = days();
			int first = -1;
			int last  = -1;
			int maxgap = 1;
			for (int i = 0;  i < 7;  ++i)
			{
				if (ds.testBit(KAlarm::localeDayInWeek_to_weekDay(i) - 1))
				{
					if (first < 0)
						first = i;
					else if (i - last > maxgap)
						maxgap = i - last;
					last = i;
				}
			}
			if (first < 0)
				break;    // no days recur
			int span = last - first;
			if (freq > 1)
				return (freq*7 - span) * 1440;
			if (7 - span > maxgap)
				return (7 - span) * 1440;
			return maxgap * 1440;
		}
		case MONTHLY_DAY:
		case MONTHLY_POS:
			return freq * 1440 * 31;

		case ANNUAL_DATE:
		case ANNUAL_POS:
		{
			// Find which months of the year it recurs on, and if on more than
			// one, reduce the maximum interval accordingly.
			const TQValueList<int> months = yearMonths();  // month list is sorted
			if (months.isEmpty())
				break;    // no months recur
			if (months.count() == 1)
				return freq * 1440 * 365;
			int first = -1;
			int last  = -1;
			int maxgap = 0;
			for (TQValueListConstIterator<int> it = months.begin();  it != months.end();  ++it)
			{
				if (first < 0)
					first = *it;
				else
				{
					int span = TQDate(2001, last, 1).daysTo(TQDate(2001, *it, 1));
					if (span > maxgap)
						maxgap = span;
				}
				last = *it;
			}
			int span = TQDate(2001, first, 1).daysTo(TQDate(2001, last, 1));
			if (freq > 1)
				return (freq*365 - span) * 1440;
			if (365 - span > maxgap)
				return (365 - span) * 1440;
			return maxgap * 1440;
		}
		default:
			break;
	}
	return 0;
}

/******************************************************************************
 * Return the recurrence's period type.
 */
KARecurrence::Type KARecurrence::type() const
{
	if (mCachedType == -1)
		mCachedType = type(defaultRRuleConst());
	return static_cast<Type>(mCachedType);
}

KARecurrence::Type KARecurrence::type(const RecurrenceRule* rrule)
{
	switch (recurrenceType(rrule))
	{
		case rMinutely:     return MINUTELY;
		case rDaily:        return DAILY;
		case rWeekly:       return WEEKLY;
		case rMonthlyDay:   return MONTHLY_DAY;
		case rMonthlyPos:   return MONTHLY_POS;
		case rYearlyMonth:  return ANNUAL_DATE;
		case rYearlyPos:    return ANNUAL_POS;
		default:
			if (dailyType(rrule))
				return DAILY;
			return NO_RECUR;
	}
}

/******************************************************************************
 * Check if the rule is a daily rule with or without BYDAYS specified.
 */
bool KARecurrence::dailyType(const RecurrenceRule* rrule)
{
	if (rrule->recurrenceType() != RecurrenceRule::rDaily
	||  !rrule->bySeconds().isEmpty()
	||  !rrule->byMinutes().isEmpty()
	||  !rrule->byHours().isEmpty()
	||  !rrule->byWeekNumbers().isEmpty()
	||  !rrule->byMonthDays().isEmpty()
	||  !rrule->byMonths().isEmpty()
	||  !rrule->bySetPos().isEmpty()
	||  !rrule->byYearDays().isEmpty())
		return false;
	TQValueList<RecurrenceRule::WDayPos> days = rrule->byDays();
	if (days.isEmpty())
		return true;
	// Check that all the positions are zero (i.e. every time)
	bool found = false;
	for (TQValueList<RecurrenceRule::WDayPos>::ConstIterator it = days.begin();  it != days.end();  ++it)
	{
		if ((*it).pos() != 0)
			return false;
		found = true;
	}
	return found;

}