recurrencerule.cpp

/*
  This file is part of the kcalcore library.

  SPDX-FileCopyrightText: 2005 Reinhold Kainhofer <[email protected]>
  SPDX-FileCopyrightText: 2006-2008 David Jarvie <[email protected]>

  SPDX-License-Identifier: LGPL-2.0-or-later
*/
#include "recurrencerule.h"
#include "kcalendarcore_debug.h"
#include "recurrencehelper_p.h"
#include "utils_p.h"

#include <QDataStream>
#include <QStringList>
#include <QTime>
#include <QVector>

using namespace KCalendarCore;

// Maximum number of intervals to process
const int LOOP_LIMIT = 10000;

#ifndef NDEBUG
static QString dumpTime(const QDateTime &dt, bool allDay); // for debugging
#endif

/*=========================================================================
=                                                                         =
= IMPORTANT CODING NOTE:                                                  =
=                                                                         =
= Recurrence handling code is time critical, especially for sub-daily     =
= recurrences. For example, if getNextDate() is called repeatedly to      =
= check all consecutive occurrences over a few years, on a slow machine   =
= this could take many seconds to complete in the worst case. Simple      =
= sub-daily recurrences are optimised by use of mTimedRepetition.         =
=                                                                         =
==========================================================================*/

/**************************************************************************
 *                               DateHelper                               *
 **************************************************************************/
//@cond PRIVATE
class DateHelper
{
public:
#ifndef NDEBUG
    static QString dayName(short day);
#endif
    static QDate getNthWeek(int year, int weeknumber, short weekstart = 1);
    static int weekNumbersInYear(int year, short weekstart = 1);
    static int getWeekNumber(const QDate &date, short weekstart, int *year = nullptr);
    static int getWeekNumberNeg(const QDate &date, short weekstart, int *year = nullptr);
    // Convert to QDate, allowing for day < 0.
    // month and day must be non-zero.
    static QDate getDate(int year, int month, int day)
    {
        if (day >= 0) {
            return QDate(year, month, day);
        } else {
            if (++month > 12) {
                month = 1;
                ++year;
            }
            return QDate(year, month, 1).addDays(day);
        }
    }
};

#ifndef NDEBUG
// TODO: Move to a general library / class, as we need the same in the iCal
//       generator and in the xcal format
QString DateHelper::dayName(short day)
{
    switch (day) {
    case 1:
        return QStringLiteral("MO");
    case 2:
        return QStringLiteral("TU");
    case 3:
        return QStringLiteral("WE");
    case 4:
        return QStringLiteral("TH");
    case 5:
        return QStringLiteral("FR");
    case 6:
        return QStringLiteral("SA");
    case 7:
        return QStringLiteral("SU");
    default:
        return QStringLiteral("??");
    }
}
#endif

QDate DateHelper::getNthWeek(int year, int weeknumber, short weekstart)
{
    if (weeknumber == 0) {
        return QDate();
    }

    // Adjust this to the first day of week #1 of the year and add 7*weekno days.
    QDate dt(year, 1, 4); // Week #1 is the week that contains Jan 4
    int adjust = -(7 + dt.dayOfWeek() - weekstart) % 7;
    if (weeknumber > 0) {
        dt = dt.addDays(7 * (weeknumber - 1) + adjust);
    } else if (weeknumber < 0) {
        dt = dt.addYears(1);
        dt = dt.addDays(7 * weeknumber + adjust);
    }
    return dt;
}

int DateHelper::getWeekNumber(const QDate &date, short weekstart, int *year)
{
    int y = date.year();
    QDate dt(y, 1, 4); // <= definitely in week #1
    dt = dt.addDays(-(7 + dt.dayOfWeek() - weekstart) % 7); // begin of week #1

    qint64 daysto = dt.daysTo(date);
    if (daysto < 0) {
        // in first week of year
        --y;
        dt = QDate(y, 1, 4);
        dt = dt.addDays(-(7 + dt.dayOfWeek() - weekstart) % 7); // begin of week #1
        daysto = dt.daysTo(date);
    } else if (daysto > 355) {
        // near the end of the year - check if it's next year
        QDate dtn(y + 1, 1, 4); // <= definitely first week of next year
        dtn = dtn.addDays(-(7 + dtn.dayOfWeek() - weekstart) % 7);
        qint64 dayston = dtn.daysTo(date);
        if (dayston >= 0) {
            // in first week of next year;
            ++y;
            daysto = dayston;
        }
    }
    if (year) {
        *year = y;
    }
    return daysto / 7 + 1;
}

int DateHelper::weekNumbersInYear(int year, short weekstart)
{
    QDate dt(year, 1, weekstart);
    QDate dt1(year + 1, 1, weekstart);
    return dt.daysTo(dt1) / 7;
}

// Week number from the end of the year
int DateHelper::getWeekNumberNeg(const QDate &date, short weekstart, int *year)
{
    int weekpos = getWeekNumber(date, weekstart, year);
    return weekNumbersInYear(*year, weekstart) - weekpos - 1;
}
//@endcond

/**************************************************************************
 *                               WDayPos                                  *
 **************************************************************************/

bool RecurrenceRule::WDayPos::operator==(const RecurrenceRule::WDayPos &pos2) const
{
    return mDay == pos2.mDay && mPos == pos2.mPos;
}

bool RecurrenceRule::WDayPos::operator!=(const RecurrenceRule::WDayPos &pos2) const
{
    return !operator==(pos2);
}

/**************************************************************************
 *                               Constraint                               *
 **************************************************************************/
//@cond PRIVATE
class Constraint
{
public:
    typedef QVector<Constraint> List;

    Constraint()
    {
    }
    explicit Constraint(const QTimeZone &, int wkst = 1);
    Constraint(const QDateTime &dt, RecurrenceRule::PeriodType type, int wkst);
    void clear();
    void setYear(int n)
    {
        year = n;
        useCachedDt = false;
    }
    void setMonth(int n)
    {
        month = n;
        useCachedDt = false;
    }
    void setDay(int n)
    {
        day = n;
        useCachedDt = false;
    }
    void setHour(int n)
    {
        hour = n;
        useCachedDt = false;
    }
    void setMinute(int n)
    {
        minute = n;
        useCachedDt = false;
    }
    void setSecond(int n)
    {
        second = n;
        useCachedDt = false;
    }
    void setWeekday(int n)
    {
        weekday = n;
        useCachedDt = false;
    }
    void setWeekdaynr(int n)
    {
        weekdaynr = n;
        useCachedDt = false;
    }
    void setWeeknumber(int n)
    {
        weeknumber = n;
        useCachedDt = false;
    }
    void setYearday(int n)
    {
        yearday = n;
        useCachedDt = false;
    }
    void setWeekstart(int n)
    {
        weekstart = n;
        useCachedDt = false;
    }

    int year; // 0 means unspecified
    int month; // 0 means unspecified
    int day; // 0 means unspecified
    int hour; // -1 means unspecified
    int minute; // -1 means unspecified
    int second; // -1 means unspecified
    int weekday; //  0 means unspecified
    int weekdaynr; // index of weekday in month/year (0=unspecified)
    int weeknumber; //  0 means unspecified
    int yearday; //  0 means unspecified
    int weekstart; //  first day of week (1=monday, 7=sunday, 0=unspec.)
    QTimeZone timeZone; // time zone etc. to use

    bool readDateTime(const QDateTime &dt, RecurrenceRule::PeriodType type);
    bool matches(const QDate &dt, RecurrenceRule::PeriodType type) const;
    bool matches(const QDateTime &dt, RecurrenceRule::PeriodType type) const;
    bool merge(const Constraint &interval);
    bool isConsistent(RecurrenceRule::PeriodType period) const;
    bool increase(RecurrenceRule::PeriodType type, int freq);
    QDateTime intervalDateTime(RecurrenceRule::PeriodType type) const;
    QList<QDateTime> dateTimes(RecurrenceRule::PeriodType type) const;
    void appendDateTime(const QDate &date, const QTime &time, QList<QDateTime> &list) const;
    void dump() const;

private:
    mutable bool useCachedDt;
    mutable QDateTime cachedDt;
};

Constraint::Constraint(const QTimeZone &timeZone, int wkst)
    : weekstart(wkst)
    , timeZone(timeZone)
{
    clear();
}

Constraint::Constraint(const QDateTime &dt, RecurrenceRule::PeriodType type, int wkst)
    : weekstart(wkst)
    , timeZone(dt.timeZone())
{
    clear();
    readDateTime(dt, type);
}

void Constraint::clear()
{
    year = 0;
    month = 0;
    day = 0;
    hour = -1;
    minute = -1;
    second = -1;
    weekday = 0;
    weekdaynr = 0;
    weeknumber = 0;
    yearday = 0;
    useCachedDt = false;
}

bool Constraint::matches(const QDate &dt, RecurrenceRule::PeriodType type) const
{
    // If the event recurs in week 53 or 1, the day might not belong to the same
    // year as the week it is in. E.g. Jan 1, 2005 is in week 53 of year 2004.
    // So we can't simply check the year in that case!
    if (weeknumber == 0) {
        if (year > 0 && year != dt.year()) {
            return false;
        }
    } else {
        int y = 0;
        if (weeknumber > 0 && weeknumber != DateHelper::getWeekNumber(dt, weekstart, &y)) {
            return false;
        }
        if (weeknumber < 0 && weeknumber != DateHelper::getWeekNumberNeg(dt, weekstart, &y)) {
            return false;
        }
        if (year > 0 && year != y) {
            return false;
        }
    }

    if (month > 0 && month != dt.month()) {
        return false;
    }
    if (day > 0 && day != dt.day()) {
        return false;
    }
    if (day < 0 && dt.day() != (dt.daysInMonth() + day + 1)) {
        return false;
    }
    if (weekday > 0) {
        if (weekday != dt.dayOfWeek()) {
            return false;
        }
        if (weekdaynr != 0) {
            // If it's a yearly recurrence and a month is given, the position is
            // still in the month, not in the year.
            if ((type == RecurrenceRule::rMonthly) || (type == RecurrenceRule::rYearly && month > 0)) {
                // Monthly
                if (weekdaynr > 0 && weekdaynr != (dt.day() - 1) / 7 + 1) {
                    return false;
                }
                if (weekdaynr < 0 && weekdaynr != -((dt.daysInMonth() - dt.day()) / 7 + 1)) {
                    return false;
                }
            } else {
                // Yearly
                if (weekdaynr > 0 && weekdaynr != (dt.dayOfYear() - 1) / 7 + 1) {
                    return false;
                }
                if (weekdaynr < 0 && weekdaynr != -((dt.daysInYear() - dt.dayOfYear()) / 7 + 1)) {
                    return false;
                }
            }
        }
    }
    if (yearday > 0 && yearday != dt.dayOfYear()) {
        return false;
    }
    if (yearday < 0 && yearday != dt.daysInYear() - dt.dayOfYear() + 1) {
        return false;
    }
    return true;
}

/* Check for a match with the specified date/time.
 * The date/time's time specification must correspond with that of the start date/time.
 */
bool Constraint::matches(const QDateTime &dt, RecurrenceRule::PeriodType type) const
{
    if ((hour >= 0 && hour != dt.time().hour()) || (minute >= 0 && minute != dt.time().minute()) || (second >= 0 && second != dt.time().second())
        || !matches(dt.date(), type)) {
        return false;
    }
    return true;
}

bool Constraint::isConsistent(RecurrenceRule::PeriodType /*period*/) const
{
    // TODO: Check for consistency, e.g. byyearday=3 and bymonth=10
    return true;
}

// Return a date/time set to the constraint values, but with those parts less
// significant than the given period type set to 1 (for dates) or 0 (for times).
QDateTime Constraint::intervalDateTime(RecurrenceRule::PeriodType type) const
{
    if (useCachedDt) {
        return cachedDt;
    }
    QDate d;
    QTime t(0, 0, 0);
    bool subdaily = true;
    switch (type) {
    case RecurrenceRule::rSecondly:
        t.setHMS(hour, minute, second);
        break;
    case RecurrenceRule::rMinutely:
        t.setHMS(hour, minute, 0);
        break;
    case RecurrenceRule::rHourly:
        t.setHMS(hour, 0, 0);
        break;
    case RecurrenceRule::rDaily:
        break;
    case RecurrenceRule::rWeekly:
        d = DateHelper::getNthWeek(year, weeknumber, weekstart);
        subdaily = false;
        break;
    case RecurrenceRule::rMonthly:
        d.setDate(year, month, 1);
        subdaily = false;
        break;
    case RecurrenceRule::rYearly:
        d.setDate(year, 1, 1);
        subdaily = false;
        break;
    default:
        break;
    }
    if (subdaily) {
        d = DateHelper::getDate(year, (month > 0) ? month : 1, day ? day : 1);
    }
    cachedDt = QDateTime(d, t, timeZone);
    useCachedDt = true;
    return cachedDt;
}

bool Constraint::merge(const Constraint &interval)
{
// clang-format off
#define mergeConstraint( name, cmparison ) \
    if ( interval.name cmparison ) { \
        if ( !( name cmparison ) ) { \
            name = interval.name; \
        } else if ( name != interval.name ) { \
            return false;\
        } \
    }
    // clang-format on

    useCachedDt = false;

    mergeConstraint(year, > 0);
    mergeConstraint(month, > 0);
    mergeConstraint(day, != 0);
    mergeConstraint(hour, >= 0);
    mergeConstraint(minute, >= 0);
    mergeConstraint(second, >= 0);

    mergeConstraint(weekday, != 0);
    mergeConstraint(weekdaynr, != 0);
    mergeConstraint(weeknumber, != 0);
    mergeConstraint(yearday, != 0);

#undef mergeConstraint
    return true;
}

//           Y  M  D | H  Mn S | WD #WD | WN | YD
// required:
//           x       | x  x  x |        |    |
// 0) Trivial: Exact date given, maybe other restrictions
//           x  x  x | x  x  x |        |    |
// 1) Easy case: no weekly restrictions -> at most a loop through possible dates
//           x  +  + | x  x  x |  -  -  |  - |  -
// 2) Year day is given -> date known
//           x       | x  x  x |        |    |  +
// 3) week number is given -> loop through all days of that week. Further
//    restrictions will be applied in the end, when we check all dates for
//    consistency with the constraints
//           x       | x  x  x |        |  + | (-)
// 4) week day is specified ->
//           x       | x  x  x |  x  ?  | (-)| (-)
// 5) All possiblecases have already been treated, so this must be an error!

QList<QDateTime> Constraint::dateTimes(RecurrenceRule::PeriodType type) const
{
    QList<QDateTime> result;
    if (!isConsistent(type)) {
        return result;
    }

    // TODO_Recurrence: Handle all-day
    QTime tm(hour, minute, second);

    bool done = false;
    if (day && month > 0) {
        appendDateTime(DateHelper::getDate(year, month, day), tm, result);
        done = true;
    }

    if (!done && weekday == 0 && weeknumber == 0 && yearday == 0) {
        // Easy case: date is given, not restrictions by week or yearday
        uint mstart = (month > 0) ? month : 1;
        uint mend = (month <= 0) ? 12 : month;
        for (uint m = mstart; m <= mend; ++m) {
            uint dstart;
            uint dend;
            if (day > 0) {
                dstart = dend = day;
            } else if (day < 0) {
                QDate date(year, month, 1);
                dstart = dend = date.daysInMonth() + day + 1;
            } else {
                QDate date(year, month, 1);
                dstart = 1;
                dend = date.daysInMonth();
            }
            uint d = dstart;
            for (QDate dt(year, m, dstart);; dt = dt.addDays(1)) {
                appendDateTime(dt, tm, result);
                if (++d > dend) {
                    break;
                }
            }
        }
        done = true;
    }

    // Else: At least one of the week / yearday restrictions was given...
    // If we have a yearday (and of course a year), we know the exact date
    if (!done && yearday != 0) {
        // yearday < 0 means from end of year, so we'll need Jan 1 of the next year
        QDate d(year + ((yearday > 0) ? 0 : 1), 1, 1);
        d = d.addDays(yearday - ((yearday > 0) ? 1 : 0));
        appendDateTime(d, tm, result);
        done = true;
    }

    // Else: If we have a weeknumber, we have at most 7 possible dates, loop through them
    if (!done && weeknumber != 0) {
        QDate wst(DateHelper::getNthWeek(year, weeknumber, weekstart));
        if (weekday != 0) {
            wst = wst.addDays((7 + weekday - weekstart) % 7);
            appendDateTime(wst, tm, result);
        } else {
            for (int i = 0; i < 7; ++i) {
                appendDateTime(wst, tm, result);
                wst = wst.addDays(1);
            }
        }
        done = true;
    }

    // weekday is given
    if (!done && weekday != 0) {
        QDate dt(year, 1, 1);
        // If type == yearly and month is given, pos is still in month not year!
        // TODO_Recurrence: Correct handling of n-th  BYDAY...
        int maxloop = 53;
        bool inMonth = (type == RecurrenceRule::rMonthly) || (type == RecurrenceRule::rYearly && month > 0);
        if (inMonth && month > 0) {
            dt = QDate(year, month, 1);
            maxloop = 5;
        }
        if (weekdaynr < 0) {
            // From end of period (month, year) => relative to begin of next period
            if (inMonth) {
                dt = dt.addMonths(1);
            } else {
                dt = dt.addYears(1);
            }
        }
        int adj = (7 + weekday - dt.dayOfWeek()) % 7;
        dt = dt.addDays(adj); // correct first weekday of the period

        if (weekdaynr > 0) {
            dt = dt.addDays((weekdaynr - 1) * 7);
            appendDateTime(dt, tm, result);
        } else if (weekdaynr < 0) {
            dt = dt.addDays(weekdaynr * 7);
            appendDateTime(dt, tm, result);
        } else {
            // loop through all possible weeks, non-matching will be filtered later
            for (int i = 0; i < maxloop; ++i) {
                appendDateTime(dt, tm, result);
                dt = dt.addDays(7);
            }
        }
    } // weekday != 0

    // Only use those times that really match all other constraints, too
    QList<QDateTime> valid;
    for (int i = 0, iend = result.count(); i < iend; ++i) {
        if (matches(result[i], type)) {
            valid.append(result[i]);
        }
    }
    // Don't sort it here, would be unnecessary work. The results from all
    // constraints will be merged to one big list of the interval. Sort that one!
    return valid;
}

void Constraint::appendDateTime(const QDate &date, const QTime &time, QList<QDateTime> &list) const
{
    QDateTime dt(date, time, timeZone);
    if (dt.isValid()) {
        list.append(dt);
    }
}

bool Constraint::increase(RecurrenceRule::PeriodType type, int freq)
{
    // convert the first day of the interval to QDateTime
    intervalDateTime(type);

    // Now add the intervals
    switch (type) {
    case RecurrenceRule::rSecondly:
        cachedDt = cachedDt.addSecs(freq);
        break;
    case RecurrenceRule::rMinutely:
        cachedDt = cachedDt.addSecs(60 * freq);
        break;
    case RecurrenceRule::rHourly:
        cachedDt = cachedDt.addSecs(3600 * freq);
        break;
    case RecurrenceRule::rDaily:
        cachedDt = cachedDt.addDays(freq);
        break;
    case RecurrenceRule::rWeekly:
        cachedDt = cachedDt.addDays(7 * freq);
        break;
    case RecurrenceRule::rMonthly:
        cachedDt = cachedDt.addMonths(freq);
        break;
    case RecurrenceRule::rYearly:
        cachedDt = cachedDt.addYears(freq);
        break;
    default:
        break;
    }
    // Convert back from QDateTime to the Constraint class
    readDateTime(cachedDt, type);
    useCachedDt = true; // readDateTime() resets this

    return true;
}

// Set the constraint's value appropriate to 'type', to the value contained in a date/time.
bool Constraint::readDateTime(const QDateTime &dt, RecurrenceRule::PeriodType type)
{
    switch (type) {
    // Really fall through! Only weekly needs to be treated differently!
    case RecurrenceRule::rSecondly:
        second = dt.time().second();
        Q_FALLTHROUGH();
    case RecurrenceRule::rMinutely:
        minute = dt.time().minute();
        Q_FALLTHROUGH();
    case RecurrenceRule::rHourly:
        hour = dt.time().hour();
        Q_FALLTHROUGH();
    case RecurrenceRule::rDaily:
        day = dt.date().day();
        Q_FALLTHROUGH();
    case RecurrenceRule::rMonthly:
        month = dt.date().month();
        Q_FALLTHROUGH();
    case RecurrenceRule::rYearly:
        year = dt.date().year();
        break;
    case RecurrenceRule::rWeekly:
        // Determine start day of the current week, calculate the week number from that
        weeknumber = DateHelper::getWeekNumber(dt.date(), weekstart, &year);
        break;
    default:
        break;
    }
    useCachedDt = false;
    return true;
}
//@endcond

/**************************************************************************
 *                        RecurrenceRule::Private                         *
 **************************************************************************/

//@cond PRIVATE
class Q_DECL_HIDDEN KCalendarCore::RecurrenceRule::Private
{
public:
    Private(RecurrenceRule *parent)
        : mParent(parent)
        , mPeriod(rNone)
        , mFrequency(0)
        , mDuration(-1)
        , mWeekStart(1)
        , mIsReadOnly(false)
        , mAllDay(false)
    {
        setDirty();
    }

    Private(RecurrenceRule *parent, const Private &p);

    Private &operator=(const Private &other);
    bool operator==(const Private &other) const;
    void clear();
    void setDirty();
    void buildConstraints();
    bool buildCache() const;
    Constraint getNextValidDateInterval(const QDateTime &preDate, PeriodType type) const;
    Constraint getPreviousValidDateInterval(const QDateTime &afterDate, PeriodType type) const;
    QList<QDateTime> datesForInterval(const Constraint &interval, PeriodType type) const;

    RecurrenceRule *mParent;
    QString mRRule; // RRULE string
    PeriodType mPeriod;
    QDateTime mDateStart; // start of recurrence (but mDateStart is not an occurrence
    // unless it matches the rule)
    uint mFrequency;
    /** how often it recurs:
           < 0 means no end date,
           0 means an explicit end date,
           positive values give the number of occurrences */
    int mDuration;
    QDateTime mDateEnd;

    QList<int> mBySeconds; // values: second 0-59
    QList<int> mByMinutes; // values: minute 0-59
    QList<int> mByHours; // values: hour 0-23

    QList<WDayPos> mByDays; // n-th weekday of the month or year
    QList<int> mByMonthDays; // values: day -31 to -1 and 1-31
    QList<int> mByYearDays; // values: day -366 to -1 and 1-366
    QList<int> mByWeekNumbers; // values: week -53 to -1 and 1-53
    QList<int> mByMonths; // values: month 1-12
    QList<int> mBySetPos; // values: position -366 to -1 and 1-366
    short mWeekStart; // first day of the week (1=Monday, 7=Sunday)

    Constraint::List mConstraints;
    QList<RuleObserver *> mObservers;

    // Cache for duration
    mutable QList<QDateTime> mCachedDates;
    mutable QDateTime mCachedDateEnd;
    mutable QDateTime mCachedLastDate; // when mCachedDateEnd invalid, last date checked
    mutable bool mCached;

    bool mIsReadOnly;
    bool mAllDay;
    bool mNoByRules; // no BySeconds, ByMinutes, ... rules exist
    uint mTimedRepetition; // repeats at a regular number of seconds interval, or 0
};

RecurrenceRule::Private::Private(RecurrenceRule *parent, const Private &p)
    : mParent(parent)
    , mRRule(p.mRRule)
    , mPeriod(p.mPeriod)
    , mDateStart(p.mDateStart)
    , mFrequency(p.mFrequency)
    , mDuration(p.mDuration)
    , mDateEnd(p.mDateEnd)
    ,

    mBySeconds(p.mBySeconds)
    , mByMinutes(p.mByMinutes)
    , mByHours(p.mByHours)
    , mByDays(p.mByDays)
    , mByMonthDays(p.mByMonthDays)
    , mByYearDays(p.mByYearDays)
    , mByWeekNumbers(p.mByWeekNumbers)
    , mByMonths(p.mByMonths)
    , mBySetPos(p.mBySetPos)
    , mWeekStart(p.mWeekStart)
    ,

    mIsReadOnly(p.mIsReadOnly)
    , mAllDay(p.mAllDay)
    , mNoByRules(p.mNoByRules)
{
    setDirty();
}

RecurrenceRule::Private &RecurrenceRule::Private::operator=(const Private &p)
{
    // check for self assignment
    if (&p == this) {
        return *this;
    }

    mRRule = p.mRRule;
    mPeriod = p.mPeriod;
    mDateStart = p.mDateStart;
    mFrequency = p.mFrequency;
    mDuration = p.mDuration;
    mDateEnd = p.mDateEnd;

    mBySeconds = p.mBySeconds;
    mByMinutes = p.mByMinutes;
    mByHours = p.mByHours;
    mByDays = p.mByDays;
    mByMonthDays = p.mByMonthDays;
    mByYearDays = p.mByYearDays;
    mByWeekNumbers = p.mByWeekNumbers;
    mByMonths = p.mByMonths;
    mBySetPos = p.mBySetPos;
    mWeekStart = p.mWeekStart;

    mIsReadOnly = p.mIsReadOnly;
    mAllDay = p.mAllDay;
    mNoByRules = p.mNoByRules;

    setDirty();

    return *this;
}

bool RecurrenceRule::Private::operator==(const Private &r) const
{
    return mPeriod == r.mPeriod && ((mDateStart == r.mDateStart) || (!mDateStart.isValid() && !r.mDateStart.isValid())) && mDuration == r.mDuration
        && ((mDateEnd == r.mDateEnd) || (!mDateEnd.isValid() && !r.mDateEnd.isValid())) && mFrequency == r.mFrequency && mIsReadOnly == r.mIsReadOnly
        && mAllDay == r.mAllDay && mBySeconds == r.mBySeconds && mByMinutes == r.mByMinutes && mByHours == r.mByHours && mByDays == r.mByDays
        && mByMonthDays == r.mByMonthDays && mByYearDays == r.mByYearDays && mByWeekNumbers == r.mByWeekNumbers && mByMonths == r.mByMonths
        && mBySetPos == r.mBySetPos && mWeekStart == r.mWeekStart && mNoByRules == r.mNoByRules;
}

void RecurrenceRule::Private::clear()
{
    if (mIsReadOnly) {
        return;
    }
    mPeriod = rNone;
    mBySeconds.clear();
    mByMinutes.clear();
    mByHours.clear();
    mByDays.clear();
    mByMonthDays.clear();
    mByYearDays.clear();
    mByWeekNumbers.clear();
    mByMonths.clear();
    mBySetPos.clear();
    mWeekStart = 1;
    mNoByRules = false;

    setDirty();
}

void RecurrenceRule::Private::setDirty()
{
    buildConstraints();
    mCached = false;
    mCachedDates.clear();
    for (int i = 0, iend = mObservers.count(); i < iend; ++i) {
        if (mObservers[i]) {
            mObservers[i]->recurrenceChanged(mParent);
        }
    }
}
//@endcond

/**************************************************************************
 *                              RecurrenceRule                            *
 **************************************************************************/

RecurrenceRule::RecurrenceRule()
    : d(new Private(this))
{
}

RecurrenceRule::RecurrenceRule(const RecurrenceRule &r)
    : d(new Private(this, *r.d))
{
}

RecurrenceRule::~RecurrenceRule()
{
    delete d;
}

bool RecurrenceRule::operator==(const RecurrenceRule &r) const
{
    return *d == *r.d;
}

RecurrenceRule &RecurrenceRule::operator=(const RecurrenceRule &r)
{
    // check for self assignment
    if (&r == this) {
        return *this;
    }

    *d = *r.d;

    return *this;
}

void RecurrenceRule::addObserver(RuleObserver *observer)
{
    if (!d->mObservers.contains(observer)) {
        d->mObservers.append(observer);
    }
}

void RecurrenceRule::removeObserver(RuleObserver *observer)
{
    d->mObservers.removeAll(observer);
}

void RecurrenceRule::setRecurrenceType(PeriodType period)
{
    if (isReadOnly()) {
        return;
    }
    d->mPeriod = period;
    d->setDirty();
}

QDateTime RecurrenceRule::endDt(bool *result) const
{
    if (result) {
        *result = false;
    }
    if (d->mPeriod == rNone) {
        return QDateTime();
    }
    if (d->mDuration < 0) {
        return QDateTime();
    }
    if (d->mDuration == 0) {
        if (result) {
            *result = true;
        }
        return d->mDateEnd;
    }

    // N occurrences. Check if we have a full cache. If so, return the cached end date.
    if (!d->mCached) {
        // If not enough occurrences can be found (i.e. inconsistent constraints)
        if (!d->buildCache()) {
            return QDateTime();
        }
    }
    if (result) {
        *result = true;
    }
    return d->mCachedDateEnd;
}

void RecurrenceRule::setEndDt(const QDateTime &dateTime)
{
    if (isReadOnly()) {
        return;
    }
    d->mDateEnd = dateTime;
    if (d->mDateEnd.isValid()) {
        d->mDuration = 0; // set to 0 because there is an end date/time
    }
    d->setDirty();
}

void RecurrenceRule::setDuration(int duration)
{
    if (isReadOnly()) {
        return;
    }
    d->mDuration = duration;
    d->setDirty();
}

void RecurrenceRule::setAllDay(bool allDay)
{
    if (isReadOnly()) {
        return;
    }
    d->mAllDay = allDay;
    d->setDirty();
}

void RecurrenceRule::clear()
{
    d->clear();
}

void RecurrenceRule::setDirty()
{
    d->setDirty();
}

void RecurrenceRule::setStartDt(const QDateTime &start)
{
    if (isReadOnly()) {
        return;
    }
    d->mDateStart = start;
    d->setDirty();
}

void RecurrenceRule::setFrequency(int freq)
{
    if (isReadOnly() || freq <= 0) {
        return;
    }
    d->mFrequency = freq;
    d->setDirty();
}

void RecurrenceRule::setBySeconds(const QList<int> &bySeconds)
{
    if (isReadOnly()) {
        return;
    }
    d->mBySeconds = bySeconds;
    d->setDirty();
}

void RecurrenceRule::setByMinutes(const QList<int> &byMinutes)
{
    if (isReadOnly()) {
        return;
    }
    d->mByMinutes = byMinutes;
    d->setDirty();
}

void RecurrenceRule::setByHours(const QList<int> &byHours)
{
    if (isReadOnly()) {
        return;
    }
    d->mByHours = byHours;
    d->setDirty();
}

void RecurrenceRule::setByDays(const QList<WDayPos> &byDays)
{
    if (isReadOnly()) {
        return;
    }
    d->mByDays = byDays;
    d->setDirty();
}

void RecurrenceRule::setByMonthDays(const QList<int> &byMonthDays)
{
    if (isReadOnly()) {
        return;
    }
    d->mByMonthDays = byMonthDays;
    d->setDirty();
}

void RecurrenceRule::setByYearDays(const QList<int> &byYearDays)
{
    if (isReadOnly()) {
        return;
    }
    d->mByYearDays = byYearDays;
    d->setDirty();
}

void RecurrenceRule::setByWeekNumbers(const QList<int> &byWeekNumbers)
{
    if (isReadOnly()) {
        return;
    }
    d->mByWeekNumbers = byWeekNumbers;
    d->setDirty();
}

void RecurrenceRule::setByMonths(const QList<int> &byMonths)
{
    if (isReadOnly()) {
        return;
    }
    d->mByMonths = byMonths;
    d->setDirty();
}

void RecurrenceRule::setBySetPos(const QList<int> &bySetPos)
{
    if (isReadOnly()) {
        return;
    }
    d->mBySetPos = bySetPos;
    d->setDirty();
}

void RecurrenceRule::setWeekStart(short weekStart)
{
    if (isReadOnly()) {
        return;
    }
    d->mWeekStart = weekStart;
    d->setDirty();
}

void RecurrenceRule::shiftTimes(const QTimeZone &oldTz, const QTimeZone &newTz)
{
    d->mDateStart = d->mDateStart.toTimeZone(oldTz);
    d->mDateStart.setTimeZone(newTz);
    if (d->mDuration == 0) {
        d->mDateEnd = d->mDateEnd.toTimeZone(oldTz);
        d->mDateEnd.setTimeZone(newTz);
    }
    d->setDirty();
}

// Taken from recurrence.cpp
// int RecurrenceRule::maxIterations() const
// {
//   /* Find the maximum number of iterations which may be needed to reach the
//    * next actual occurrence of a monthly or yearly recurrence.
//    * More than one iteration may be needed if, for example, it's the 29th February,
//    * the 31st day of the month or the 5th Monday, and the month being checked is
//    * February or a 30-day month.
//    * The following recurrences may never occur:
//    * - For rMonthlyDay: if the frequency is a whole number of years.
//    * - For rMonthlyPos: if the frequency is an even whole number of years.
//    * - For rYearlyDay, rYearlyMonth: if the frequency is a multiple of 4 years.
//    * - For rYearlyPos: if the frequency is an even number of years.
//    * The maximum number of iterations needed, assuming that it does actually occur,
//    * was found empirically.
//    */
//   switch (recurs) {
//     case rMonthlyDay:
//       return (rFreq % 12) ? 6 : 8;
//
//     case rMonthlyPos:
//       if (rFreq % 12 == 0) {
//         // Some of these frequencies may never occur
//         return (rFreq % 84 == 0) ? 364         // frequency = multiple of 7 years
//              : (rFreq % 48 == 0) ? 7           // frequency = multiple of 4 years
//              : (rFreq % 24 == 0) ? 14 : 28;    // frequency = multiple of 2 or 1 year
//       }
//       // All other frequencies will occur sometime
//       if (rFreq > 120)
//         return 364;    // frequencies of > 10 years will hit the date limit first
//       switch (rFreq) {
//         case 23:   return 50;
//         case 46:   return 38;
//         case 56:   return 138;
//         case 66:   return 36;
//         case 89:   return 54;
//         case 112:  return 253;
//         default:   return 25;       // most frequencies will need < 25 iterations
//       }
//
//     case rYearlyMonth:
//     case rYearlyDay:
//       return 8;          // only 29th Feb or day 366 will need more than one iteration
//
//     case rYearlyPos:
//       if (rFreq % 7 == 0)
//         return 364;    // frequencies of a multiple of 7 years will hit the date limit first
//       if (rFreq % 2 == 0) {
//         // Some of these frequencies may never occur
//         return (rFreq % 4 == 0) ? 7 : 14;    // frequency = even number of years
//       }
//       return 28;
//   }
//   return 1;
// }

//@cond PRIVATE
void RecurrenceRule::Private::buildConstraints()
{
    mTimedRepetition = 0;
    mNoByRules = mBySetPos.isEmpty();
    mConstraints.clear();
    Constraint con(mDateStart.timeZone());
    if (mWeekStart > 0) {
        con.setWeekstart(mWeekStart);
    }
    mConstraints.append(con);

    int c;
    int cend;
    int i;
    int iend;
    Constraint::List tmp;

// clang-format off
#define intConstraint( list, setElement ) \
    if ( !list.isEmpty() ) { \
        mNoByRules = false; \
        iend = list.count(); \
        if ( iend == 1 ) { \
            for ( c = 0, cend = mConstraints.count();  c < cend;  ++c ) { \
                mConstraints[c].setElement( list[0] ); \
            } \
        } else { \
            tmp.reserve(mConstraints.count() * iend); \
            for ( c = 0, cend = mConstraints.count();  c < cend;  ++c ) { \
                for ( i = 0;  i < iend;  ++i ) { \
                    con = mConstraints[c]; \
                    con.setElement( list[i] ); \
                    tmp.append( con ); \
                } \
            } \
            mConstraints = tmp; \
            tmp.clear(); \
        } \
    }
    // clang-format on

    intConstraint(mBySeconds, setSecond);
    intConstraint(mByMinutes, setMinute);
    intConstraint(mByHours, setHour);
    intConstraint(mByMonthDays, setDay);
    intConstraint(mByMonths, setMonth);
    intConstraint(mByYearDays, setYearday);
    intConstraint(mByWeekNumbers, setWeeknumber);
#undef intConstraint

    if (!mByDays.isEmpty()) {
        mNoByRules = false;
        tmp.reserve(mConstraints.count() * mByDays.count());
        for (c = 0, cend = mConstraints.count(); c < cend; ++c) {
            for (i = 0, iend = mByDays.count(); i < iend; ++i) {
                con = mConstraints[c];
                con.setWeekday(mByDays[i].day());
                con.setWeekdaynr(mByDays[i].pos());
                tmp.append(con);
            }
        }
        mConstraints = tmp;
        tmp.clear();
    }

// clang-format off
#define fixConstraint( setElement, value ) \
    { \
        for ( c = 0, cend = mConstraints.count();  c < cend;  ++c ) { \
            mConstraints[c].setElement( value );                        \
        } \
    }
    // clang-format on
    // Now determine missing values from DTSTART. This can speed up things,
    // because we have more restrictions and save some loops.

    // TODO: Does RFC 2445 intend to restrict the weekday in all cases of weekly?
    if (mPeriod == rWeekly && mByDays.isEmpty()) {
        fixConstraint(setWeekday, mDateStart.date().dayOfWeek());
    }

    // Really fall through in the cases, because all smaller time intervals are
    // constrained from dtstart
    switch (mPeriod) {
    case rYearly:
        if (mByDays.isEmpty() && mByWeekNumbers.isEmpty() && mByYearDays.isEmpty() && mByMonths.isEmpty()) {
            fixConstraint(setMonth, mDateStart.date().month());
        }
        Q_FALLTHROUGH();
    case rMonthly:
        if (mByDays.isEmpty() && mByWeekNumbers.isEmpty() && mByYearDays.isEmpty() && mByMonthDays.isEmpty()) {
            fixConstraint(setDay, mDateStart.date().day());
        }
        Q_FALLTHROUGH();
    case rWeekly:
    case rDaily:
        if (mByHours.isEmpty()) {
            fixConstraint(setHour, mDateStart.time().hour());
        }
        Q_FALLTHROUGH();
    case rHourly:
        if (mByMinutes.isEmpty()) {
            fixConstraint(setMinute, mDateStart.time().minute());
        }
        Q_FALLTHROUGH();
    case rMinutely:
        if (mBySeconds.isEmpty()) {
            fixConstraint(setSecond, mDateStart.time().second());
        }
        Q_FALLTHROUGH();
    case rSecondly:
    default:
        break;
    }
#undef fixConstraint

    if (mNoByRules) {
        switch (mPeriod) {
        case rHourly:
            mTimedRepetition = mFrequency * 3600;
            break;
        case rMinutely:
            mTimedRepetition = mFrequency * 60;
            break;
        case rSecondly:
            mTimedRepetition = mFrequency;
            break;
        default:
            break;
        }
    } else {
        for (c = 0, cend = mConstraints.count(); c < cend;) {
            if (mConstraints[c].isConsistent(mPeriod)) {
                ++c;
            } else {
                mConstraints.removeAt(c);
                --cend;
            }
        }
    }
}

// Build and cache a list of all occurrences.
// Only call buildCache() if mDuration > 0.
bool RecurrenceRule::Private::buildCache() const
{
    Q_ASSERT(mDuration > 0);
    // Build the list of all occurrences of this event (we need that to determine
    // the end date!)
    Constraint interval(getNextValidDateInterval(mDateStart, mPeriod));

    auto dts = datesForInterval(interval, mPeriod);
    // Only use dates after the event has started (start date is only included
    // if it matches)
    const auto it = strictLowerBound(dts.begin(), dts.end(), mDateStart);
    if (it != dts.end()) {
        dts.erase(dts.begin(), it + 1);
    }

    // some validity checks to avoid infinite loops (i.e. if we have
    // done this loop already 10000 times, bail out )
    for (int loopnr = 0; loopnr < LOOP_LIMIT && dts.count() < mDuration; ++loopnr) {
        interval.increase(mPeriod, mFrequency);
        // The returned date list is already sorted!
        dts += datesForInterval(interval, mPeriod);
    }
    if (dts.count() > mDuration) {
        // we have picked up more occurrences than necessary, remove them
        dts.erase(dts.begin() + mDuration, dts.end());
    }
    mCached = true;
    mCachedDates = dts;

    // it = dts.begin();
    // while ( it != dts.end() ) {
    //   qCDebug(KCALCORE_LOG) << "            -=>" << dumpTime(*it);
    //   ++it;
    // }
    if (int(dts.count()) == mDuration) {
        mCachedDateEnd = dts.last();
        return true;
    } else {
        // The cached date list is incomplete
        mCachedDateEnd = QDateTime();
        mCachedLastDate = interval.intervalDateTime(mPeriod);
        return false;
    }
}
//@endcond

bool RecurrenceRule::dateMatchesRules(const QDateTime &kdt) const
{
    QDateTime dt = kdt.toTimeZone(d->mDateStart.timeZone());
    for (int i = 0, iend = d->mConstraints.count(); i < iend; ++i) {
        if (d->mConstraints[i].matches(dt, recurrenceType())) {
            return true;
        }
    }
    return false;
}

bool RecurrenceRule::recursOn(const QDate &qd, const QTimeZone &timeZone) const
{
    int i;
    int iend;

    if (!qd.isValid() || !d->mDateStart.isValid()) {
        // There can't be recurrences on invalid dates
        return false;
    }

    if (allDay()) {
        // It's a date-only rule, so it has no time specification.
        // Therefore ignore 'timeSpec'.
        if (qd < d->mDateStart.date()) {
            return false;
        }
        // Start date is only included if it really matches
        QDate endDate;
        if (d->mDuration >= 0) {
            endDate = endDt().date();
            if (qd > endDate) {
                return false;
            }
        }

        // The date must be in an appropriate interval (getNextValidDateInterval),
        // Plus it must match at least one of the constraints
        bool match = false;
        for (i = 0, iend = d->mConstraints.count(); i < iend && !match; ++i) {
            match = d->mConstraints[i].matches(qd, recurrenceType());
        }
        if (!match) {
            return false;
        }

        QDateTime start(qd, QTime(0, 0, 0), timeZone); // d->mDateStart.timeZone());
        Constraint interval(d->getNextValidDateInterval(start, recurrenceType()));
        // Constraint::matches is quite efficient, so first check if it can occur at
        // all before we calculate all actual dates.
        if (!interval.matches(qd, recurrenceType())) {
            return false;
        }
        // We really need to obtain the list of dates in this interval, since
        // otherwise BYSETPOS will not work (i.e. the date will match the interval,
        // but BYSETPOS selects only one of these matching dates!
        QDateTime end = start.addDays(1);
        do {
            auto dts = d->datesForInterval(interval, recurrenceType());
            for (i = 0, iend = dts.count(); i < iend; ++i) {
                if (dts[i].date() >= qd) {
                    return dts[i].date() == qd;
                }
            }
            interval.increase(recurrenceType(), frequency());
        } while (interval.intervalDateTime(recurrenceType()) < end);
        return false;
    }

    // It's a date-time rule, so we need to take the time specification into account.
    QDateTime start(qd, QTime(0, 0, 0), timeZone);
    QDateTime end = start.addDays(1).toTimeZone(d->mDateStart.timeZone());
    start = start.toTimeZone(d->mDateStart.timeZone());
    if (end < d->mDateStart) {
        return false;
    }
    if (start < d->mDateStart) {
        start = d->mDateStart;
    }

    // Start date is only included if it really matches
    if (d->mDuration >= 0) {
        QDateTime endRecur = endDt();
        if (endRecur.isValid()) {
            if (start > endRecur) {
                return false;
            }
            if (end > endRecur) {
                end = endRecur; // limit end-of-day time to end of recurrence rule
            }
        }
    }

    if (d->mTimedRepetition) {
        // It's a simple sub-daily recurrence with no constraints
        int n = static_cast<int>((d->mDateStart.secsTo(start) - 1) % d->mTimedRepetition);
        return start.addSecs(d->mTimedRepetition - n) < end;
    }

    // Find the start and end dates in the time spec for the rule
    QDate startDay = start.date();
    QDate endDay = end.addSecs(-1).date();
    int dayCount = startDay.daysTo(endDay) + 1;

    // The date must be in an appropriate interval (getNextValidDateInterval),
    // Plus it must match at least one of the constraints
    bool match = false;
    for (i = 0, iend = d->mConstraints.count(); i < iend && !match; ++i) {
        match = d->mConstraints[i].matches(startDay, recurrenceType());
        for (int day = 1; day < dayCount && !match; ++day) {
            match = d->mConstraints[i].matches(startDay.addDays(day), recurrenceType());
        }
    }
    if (!match) {
        return false;
    }

    Constraint interval(d->getNextValidDateInterval(start, recurrenceType()));
    // Constraint::matches is quite efficient, so first check if it can occur at
    // all before we calculate all actual dates.
    Constraint intervalm = interval;
    do {
        match = intervalm.matches(startDay, recurrenceType());
        for (int day = 1; day < dayCount && !match; ++day) {
            match = intervalm.matches(startDay.addDays(day), recurrenceType());
        }
        if (match) {
            break;
        }
        intervalm.increase(recurrenceType(), frequency());
    } while (intervalm.intervalDateTime(recurrenceType()).isValid() && intervalm.intervalDateTime(recurrenceType()) < end);
    if (!match) {
        return false;
    }

    // We really need to obtain the list of dates in this interval, since
    // otherwise BYSETPOS will not work (i.e. the date will match the interval,
    // but BYSETPOS selects only one of these matching dates!
    do {
        auto dts = d->datesForInterval(interval, recurrenceType());
        const auto it = std::lower_bound(dts.constBegin(), dts.constEnd(), start);
        if (it != dts.constEnd()) {
            return *it <= end;
        }
        interval.increase(recurrenceType(), frequency());
    } while (interval.intervalDateTime(recurrenceType()).isValid() && interval.intervalDateTime(recurrenceType()) < end);

    return false;
}

bool RecurrenceRule::recursAt(const QDateTime &kdt) const
{
    // Convert to the time spec used by this recurrence rule
    QDateTime dt(kdt.toTimeZone(d->mDateStart.timeZone()));

    if (allDay()) {
        return recursOn(dt.date(), dt.timeZone());
    }
    if (dt < d->mDateStart) {
        return false;
    }
    // Start date is only included if it really matches
    if (d->mDuration >= 0 && dt > endDt()) {
        return false;
    }

    if (d->mTimedRepetition) {
        // It's a simple sub-daily recurrence with no constraints
        return !(d->mDateStart.secsTo(dt) % d->mTimedRepetition);
    }

    // The date must be in an appropriate interval (getNextValidDateInterval),
    // Plus it must match at least one of the constraints
    if (!dateMatchesRules(dt)) {
        return false;
    }
    // if it recurs every interval, speed things up...
    //   if ( d->mFrequency == 1 && d->mBySetPos.isEmpty() && d->mByDays.isEmpty() ) return true;
    Constraint interval(d->getNextValidDateInterval(dt, recurrenceType()));
    // TODO_Recurrence: Does this work with BySetPos???
    if (interval.matches(dt, recurrenceType())) {
        return true;
    }
    return false;
}

TimeList RecurrenceRule::recurTimesOn(const QDate &date, const QTimeZone &timeZone) const
{
    TimeList lst;
    if (allDay()) {
        return lst;
    }
    QDateTime start(date, QTime(0, 0, 0), timeZone);
    QDateTime end = start.addDays(1).addSecs(-1);
    auto dts = timesInInterval(start, end); // returns between start and end inclusive
    for (int i = 0, iend = dts.count(); i < iend; ++i) {
        lst += dts[i].toTimeZone(timeZone).time();
    }
    return lst;
}

/** Returns the number of recurrences up to and including the date/time specified. */
int RecurrenceRule::durationTo(const QDateTime &dt) const
{
    // Convert to the time spec used by this recurrence rule
    QDateTime toDate(dt.toTimeZone(d->mDateStart.timeZone()));
    // Easy cases:
    // either before start, or after all recurrences and we know their number
    if (toDate < d->mDateStart) {
        return 0;
    }
    // Start date is only included if it really matches
    if (d->mDuration > 0 && toDate >= endDt()) {
        return d->mDuration;
    }

    if (d->mTimedRepetition) {
        // It's a simple sub-daily recurrence with no constraints
        return static_cast<int>(d->mDateStart.secsTo(toDate) / d->mTimedRepetition);
    }

    return timesInInterval(d->mDateStart, toDate).count();
}

int RecurrenceRule::durationTo(const QDate &date) const
{
    return durationTo(QDateTime(date, QTime(23, 59, 59), d->mDateStart.timeZone()));
}

QDateTime RecurrenceRule::getPreviousDate(const QDateTime &afterDate) const
{
    // Convert to the time spec used by this recurrence rule
    QDateTime toDate(afterDate.toTimeZone(d->mDateStart.timeZone()));

    // Invalid starting point, or beyond end of recurrence
    if (!toDate.isValid() || toDate < d->mDateStart) {
        return QDateTime();
    }

    if (d->mTimedRepetition) {
        // It's a simple sub-daily recurrence with no constraints
        QDateTime prev = toDate;
        if (d->mDuration >= 0 && endDt().isValid() && toDate > endDt()) {
            prev = endDt().addSecs(1).toTimeZone(d->mDateStart.timeZone());
        }
        int n = static_cast<int>((d->mDateStart.secsTo(prev) - 1) % d->mTimedRepetition);
        if (n < 0) {
            return QDateTime(); // before recurrence start
        }
        prev = prev.addSecs(-n - 1);
        return prev >= d->mDateStart ? prev : QDateTime();
    }

    // If we have a cache (duration given), use that
    if (d->mDuration > 0) {
        if (!d->mCached) {
            d->buildCache();
        }
        const auto it = strictLowerBound(d->mCachedDates.constBegin(), d->mCachedDates.constEnd(), toDate);
        if (it != d->mCachedDates.constEnd()) {
            return *it;
        }
        return QDateTime();
    }

    QDateTime prev = toDate;
    if (d->mDuration >= 0 && endDt().isValid() && toDate > endDt()) {
        prev = endDt().addSecs(1).toTimeZone(d->mDateStart.timeZone());
    }

    Constraint interval(d->getPreviousValidDateInterval(prev, recurrenceType()));
    const auto dts = d->datesForInterval(interval, recurrenceType());
    const auto it = strictLowerBound(dts.begin(), dts.end(), prev);
    if (it != dts.end()) {
        return ((*it) >= d->mDateStart) ? (*it) : QDateTime();
    }

    // Previous interval. As soon as we find an occurrence, we're done.
    while (interval.intervalDateTime(recurrenceType()) > d->mDateStart) {
        interval.increase(recurrenceType(), -int(frequency()));
        // The returned date list is sorted
        auto dts = d->datesForInterval(interval, recurrenceType());
        // The list is sorted, so take the last one.
        if (!dts.isEmpty()) {
            prev = dts.last();
            if (prev.isValid() && prev >= d->mDateStart) {
                return prev;
            } else {
                return QDateTime();
            }
        }
    }
    return QDateTime();
}

QDateTime RecurrenceRule::getNextDate(const QDateTime &preDate) const
{
    // Convert to the time spec used by this recurrence rule
    QDateTime fromDate(preDate.toTimeZone(d->mDateStart.timeZone()));
    // Beyond end of recurrence
    if (d->mDuration >= 0 && endDt().isValid() && fromDate >= endDt()) {
        return QDateTime();
    }

    // Start date is only included if it really matches
    if (fromDate < d->mDateStart) {
        fromDate = d->mDateStart.addSecs(-1);
    }

    if (d->mTimedRepetition) {
        // It's a simple sub-daily recurrence with no constraints
        int n = static_cast<int>((d->mDateStart.secsTo(fromDate) + 1) % d->mTimedRepetition);
        QDateTime next = fromDate.addSecs(d->mTimedRepetition - n + 1);
        return d->mDuration < 0 || !endDt().isValid() || next <= endDt() ? next : QDateTime();
    }

    if (d->mDuration > 0) {
        if (!d->mCached) {
            d->buildCache();
        }
        const auto it = std::upper_bound(d->mCachedDates.constBegin(), d->mCachedDates.constEnd(), fromDate);
        if (it != d->mCachedDates.constEnd()) {
            return *it;
        }
    }

    QDateTime end = endDt();
    Constraint interval(d->getNextValidDateInterval(fromDate, recurrenceType()));
    const auto dts = d->datesForInterval(interval, recurrenceType());
    const auto it = std::upper_bound(dts.begin(), dts.end(), fromDate);
    if (it != dts.end()) {
        return (d->mDuration < 0 || *it <= end) ? *it : QDateTime();
    }
    interval.increase(recurrenceType(), frequency());
    if (d->mDuration >= 0 && interval.intervalDateTime(recurrenceType()) > end) {
        return QDateTime();
    }

    // Increase the interval. The first occurrence that we find is the result (if
    // if's before the end date).
    // TODO: some validity checks to avoid infinite loops for contradictory constraints
    int loop = 0;
    do {
        auto dts = d->datesForInterval(interval, recurrenceType());
        if (!dts.isEmpty()) {
            QDateTime ret(dts[0]);
            if (d->mDuration >= 0 && ret > end) {
                return QDateTime();
            } else {
                return ret;
            }
        }
        interval.increase(recurrenceType(), frequency());
    } while (++loop < LOOP_LIMIT && (d->mDuration < 0 || interval.intervalDateTime(recurrenceType()) < end));
    return QDateTime();
}

QList<QDateTime> RecurrenceRule::timesInInterval(const QDateTime &dtStart, const QDateTime &dtEnd) const
{
    const QDateTime start = dtStart.toTimeZone(d->mDateStart.timeZone());
    const QDateTime end = dtEnd.toTimeZone(d->mDateStart.timeZone());
    QList<QDateTime> result;
    if (end < d->mDateStart) {
        return result; // before start of recurrence
    }
    QDateTime enddt = end;
    if (d->mDuration >= 0) {
        const QDateTime endRecur = endDt();
        if (endRecur.isValid()) {
            if (start > endRecur) {
                return result; // beyond end of recurrence
            }
            if (end >= endRecur) {
                enddt = endRecur; // limit end time to end of recurrence rule
            }
        }
    }

    if (d->mTimedRepetition) {
        // It's a simple sub-daily recurrence with no constraints

        // Seconds to add to interval start, to get first occurrence which is within interval
        qint64 offsetFromNextOccurrence;
        if (d->mDateStart < start) {
            offsetFromNextOccurrence = d->mTimedRepetition - (d->mDateStart.secsTo(start) % d->mTimedRepetition);
        } else {
            offsetFromNextOccurrence = -(d->mDateStart.secsTo(start) % d->mTimedRepetition);
        }
        QDateTime dt = start.addSecs(offsetFromNextOccurrence);
        if (dt <= enddt) {
            int numberOfOccurrencesWithinInterval = static_cast<int>(dt.secsTo(enddt) / d->mTimedRepetition) + 1;
            // limit n by a sane value else we can "explode".
            numberOfOccurrencesWithinInterval = qMin(numberOfOccurrencesWithinInterval, LOOP_LIMIT);
            for (int i = 0; i < numberOfOccurrencesWithinInterval; dt = dt.addSecs(d->mTimedRepetition), ++i) {
                result += dt;
            }
        }
        return result;
    }

    QDateTime st = start < d->mDateStart ? d->mDateStart : start;
    bool done = false;
    if (d->mDuration > 0) {
        if (!d->mCached) {
            d->buildCache();
        }
        if (d->mCachedDateEnd.isValid() && start > d->mCachedDateEnd) {
            return result; // beyond end of recurrence
        }
        const auto it = std::lower_bound(d->mCachedDates.constBegin(), d->mCachedDates.constEnd(), start);
        if (it != d->mCachedDates.constEnd()) {
            const auto itEnd = std::upper_bound(it, d->mCachedDates.constEnd(), enddt);
            if (itEnd != d->mCachedDates.constEnd()) {
                done = true;
            }
            std::copy(it, itEnd, std::back_inserter(result));
        }
        if (d->mCachedDateEnd.isValid()) {
            done = true;
        } else if (!result.isEmpty()) {
            result += QDateTime(); // indicate that the returned list is incomplete
            done = true;
        }
        if (done) {
            return result;
        }
        // We don't have any result yet, but we reached the end of the incomplete cache
        st = d->mCachedLastDate.addSecs(1);
    }

    Constraint interval(d->getNextValidDateInterval(st, recurrenceType()));
    int loop = 0;
    do {
        auto dts = d->datesForInterval(interval, recurrenceType());
        auto it = dts.begin();
        auto itEnd = dts.end();
        if (loop == 0) {
            it = std::lower_bound(dts.begin(), dts.end(), st);
        }
        itEnd = std::upper_bound(it, dts.end(), enddt);
        if (itEnd != dts.end()) {
            loop = LOOP_LIMIT;
        }
        std::copy(it, itEnd, std::back_inserter(result));
        // Increase the interval.
        interval.increase(recurrenceType(), frequency());
    } while (++loop < LOOP_LIMIT && interval.intervalDateTime(recurrenceType()) < end);
    return result;
}

//@cond PRIVATE
// Find the date/time of the occurrence at or before a date/time,
// for a given period type.
// Return a constraint whose value appropriate to 'type', is set to
// the value contained in the date/time.
Constraint RecurrenceRule::Private::getPreviousValidDateInterval(const QDateTime &dt, PeriodType type) const
{
    long periods = 0;
    QDateTime start = mDateStart;
    QDateTime nextValid(start);
    int modifier = 1;
    QDateTime toDate(dt.toTimeZone(start.timeZone()));
    // for super-daily recurrences, don't care about the time part

    // Find the #intervals since the dtstart and round to the next multiple of
    // the frequency
    switch (type) {
    // Really fall through for sub-daily, since the calculations only differ
    // by the factor 60 and 60*60! Same for weekly and daily (factor 7)
    case rHourly:
        modifier *= 60;
        Q_FALLTHROUGH();
    case rMinutely:
        modifier *= 60;
        Q_FALLTHROUGH();
    case rSecondly:
        periods = static_cast<int>(start.secsTo(toDate) / modifier);
        // round it down to the next lower multiple of frequency:
        if (mFrequency > 0) {
            periods = (periods / mFrequency) * mFrequency;
        }
        nextValid = start.addSecs(modifier * periods);
        break;
    case rWeekly:
        toDate = toDate.addDays(-(7 + toDate.date().dayOfWeek() - mWeekStart) % 7);
        start = start.addDays(-(7 + start.date().dayOfWeek() - mWeekStart) % 7);
        modifier *= 7;
        Q_FALLTHROUGH();
    case rDaily:
        periods = start.daysTo(toDate) / modifier;
        // round it down to the next lower multiple of frequency:
        if (mFrequency > 0) {
            periods = (periods / mFrequency) * mFrequency;
        }
        nextValid = start.addDays(modifier * periods);
        break;
    case rMonthly: {
        periods = 12 * (toDate.date().year() - start.date().year()) + (toDate.date().month() - start.date().month());
        // round it down to the next lower multiple of frequency:
        if (mFrequency > 0) {
            periods = (periods / mFrequency) * mFrequency;
        }
        // set the day to the first day of the month, so we don't have problems
        // with non-existent days like Feb 30 or April 31
        start.setDate(QDate(start.date().year(), start.date().month(), 1));
        nextValid.setDate(start.date().addMonths(periods));
        break;
    }
    case rYearly:
        periods = (toDate.date().year() - start.date().year());
        // round it down to the next lower multiple of frequency:
        if (mFrequency > 0) {
            periods = (periods / mFrequency) * mFrequency;
        }
        nextValid.setDate(start.date().addYears(periods));
        break;
    default:
        break;
    }

    return Constraint(nextValid, type, mWeekStart);
}

// Find the date/time of the next occurrence at or after a date/time,
// for a given period type.
// Return a constraint whose value appropriate to 'type', is set to the
// value contained in the date/time.
Constraint RecurrenceRule::Private::getNextValidDateInterval(const QDateTime &dt, PeriodType type) const
{
    // TODO: Simplify this!
    long periods = 0;
    QDateTime start = mDateStart;
    QDateTime nextValid(start);
    int modifier = 1;
    QDateTime toDate(dt.toTimeZone(start.timeZone()));
    // for super-daily recurrences, don't care about the time part

    // Find the #intervals since the dtstart and round to the next multiple of
    // the frequency
    switch (type) {
    // Really fall through for sub-daily, since the calculations only differ
    // by the factor 60 and 60*60! Same for weekly and daily (factor 7)
    case rHourly:
        modifier *= 60;
        Q_FALLTHROUGH();
    case rMinutely:
        modifier *= 60;
        Q_FALLTHROUGH();
    case rSecondly:
        periods = static_cast<int>(start.secsTo(toDate) / modifier);
        periods = qMax(0L, periods);
        if (periods > 0 && mFrequency > 0) {
            periods += (mFrequency - 1 - ((periods - 1) % mFrequency));
        }
        nextValid = start.addSecs(modifier * periods);
        break;
    case rWeekly:
        // correct both start date and current date to start of week
        toDate = toDate.addDays(-(7 + toDate.date().dayOfWeek() - mWeekStart) % 7);
        start = start.addDays(-(7 + start.date().dayOfWeek() - mWeekStart) % 7);
        modifier *= 7;
        Q_FALLTHROUGH();
    case rDaily:
        periods = start.daysTo(toDate) / modifier;
        periods = qMax(0L, periods);
        if (periods > 0 && mFrequency > 0) {
            periods += (mFrequency - 1 - ((periods - 1) % mFrequency));
        }
        nextValid = start.addDays(modifier * periods);
        break;
    case rMonthly: {
        periods = 12 * (toDate.date().year() - start.date().year()) + (toDate.date().month() - start.date().month());
        periods = qMax(0L, periods);
        if (periods > 0 && mFrequency > 0) {
            periods += (mFrequency - 1 - ((periods - 1) % mFrequency));
        }
        // set the day to the first day of the month, so we don't have problems
        // with non-existent days like Feb 30 or April 31
        start.setDate(QDate(start.date().year(), start.date().month(), 1));
        nextValid.setDate(start.date().addMonths(periods));
        break;
    }
    case rYearly:
        periods = (toDate.date().year() - start.date().year());
        periods = qMax(0L, periods);
        if (periods > 0 && mFrequency > 0) {
            periods += (mFrequency - 1 - ((periods - 1) % mFrequency));
        }
        nextValid.setDate(start.date().addYears(periods));
        break;
    default:
        break;
    }

    return Constraint(nextValid, type, mWeekStart);
}

QList<QDateTime> RecurrenceRule::Private::datesForInterval(const Constraint &interval, PeriodType type) const
{
    /* -) Loop through constraints,
       -) merge interval with each constraint
       -) if merged constraint is not consistent => ignore that constraint
       -) if complete => add that one date to the date list
       -) Loop through all missing fields => For each add the resulting
    */
    QList<QDateTime> lst;
    for (int i = 0, iend = mConstraints.count(); i < iend; ++i) {
        Constraint merged(interval);
        if (merged.merge(mConstraints[i])) {
            // If the information is incomplete, we can't use this constraint
            if (merged.year > 0 && merged.hour >= 0 && merged.minute >= 0 && merged.second >= 0) {
                // We have a valid constraint, so get all datetimes that match it and
                // append it to all date/times of this interval
                QList<QDateTime> lstnew = merged.dateTimes(type);
                lst += lstnew;
            }
        }
    }
    // Sort it so we can apply the BySetPos. Also some logic relies on this being sorted
    sortAndRemoveDuplicates(lst);

    /*if ( lst.isEmpty() ) {
      qCDebug(KCALCORE_LOG) << "         No Dates in Interval";
    } else {
      qCDebug(KCALCORE_LOG) << "         Dates:";
      for ( int i = 0, iend = lst.count();  i < iend;  ++i ) {
        qCDebug(KCALCORE_LOG)<< "              -)" << dumpTime(lst[i]);
      }
      qCDebug(KCALCORE_LOG) << "       ---------------------";
    }*/
    if (!mBySetPos.isEmpty()) {
        auto tmplst = lst;
        lst.clear();
        for (int i = 0, iend = mBySetPos.count(); i < iend; ++i) {
            int pos = mBySetPos[i];
            if (pos > 0) {
                --pos;
            }
            if (pos < 0) {
                pos += tmplst.count();
            }
            if (pos >= 0 && pos < tmplst.count()) {
                lst.append(tmplst[pos]);
            }
        }
        sortAndRemoveDuplicates(lst);
    }

    return lst;
}
//@endcond

void RecurrenceRule::dump() const
{
#ifndef NDEBUG
    if (!d->mRRule.isEmpty()) {
        qCDebug(KCALCORE_LOG) << "   RRULE=" << d->mRRule;
    }
    qCDebug(KCALCORE_LOG) << "   Read-Only:" << isReadOnly();

    qCDebug(KCALCORE_LOG) << "   Period type:" << int(recurrenceType()) << ", frequency:" << frequency();
    qCDebug(KCALCORE_LOG) << "   #occurrences:" << duration();
    qCDebug(KCALCORE_LOG) << "   start date:" << dumpTime(startDt(), allDay()) << ", end date:" << dumpTime(endDt(), allDay());
// clang-format off
#define dumpByIntList(list,label) \
    if ( !list.isEmpty() ) {\
        QStringList lst;\
        for ( int i = 0, iend = list.count();  i < iend;  ++i ) {\
            lst.append( QString::number( list[i] ) );\
        }\
        qCDebug(KCALCORE_LOG) << "  " << label << lst.join(QLatin1String(", ") );\
    }
    // clang-format on
    dumpByIntList(d->mBySeconds, QStringLiteral("BySeconds:  "));
    dumpByIntList(d->mByMinutes, QStringLiteral("ByMinutes:  "));
    dumpByIntList(d->mByHours, QStringLiteral("ByHours:    "));
    if (!d->mByDays.isEmpty()) {
        QStringList lst;
        for (int i = 0, iend = d->mByDays.count(); i < iend; ++i) {
            lst.append((d->mByDays[i].pos() ? QString::number(d->mByDays[i].pos()) : QLatin1String("")) + DateHelper::dayName(d->mByDays[i].day()));
        }
        qCDebug(KCALCORE_LOG) << "   ByDays:    " << lst.join(QLatin1String(", "));
    }
    dumpByIntList(d->mByMonthDays, QStringLiteral("ByMonthDays:"));
    dumpByIntList(d->mByYearDays, QStringLiteral("ByYearDays: "));
    dumpByIntList(d->mByWeekNumbers, QStringLiteral("ByWeekNr:   "));
    dumpByIntList(d->mByMonths, QStringLiteral("ByMonths:   "));
    dumpByIntList(d->mBySetPos, QStringLiteral("BySetPos:   "));
#undef dumpByIntList

    qCDebug(KCALCORE_LOG) << "   Week start:" << DateHelper::dayName(d->mWeekStart);

    qCDebug(KCALCORE_LOG) << "   Constraints:";
    // dump constraints
    for (int i = 0, iend = d->mConstraints.count(); i < iend; ++i) {
        d->mConstraints[i].dump();
    }
#endif
}

//@cond PRIVATE
void Constraint::dump() const
{
    qCDebug(KCALCORE_LOG) << "     ~> Y=" << year << ", M=" << month << ", D=" << day << ", H=" << hour << ", m=" << minute << ", S=" << second
                          << ", wd=" << weekday << ",#wd=" << weekdaynr << ", #w=" << weeknumber << ", yd=" << yearday;
}
//@endcond

QString dumpTime(const QDateTime &dt, bool isAllDay)
{
#ifndef NDEBUG
    if (!dt.isValid()) {
        return QString();
    }
    QString result;
    if (isAllDay) {
        result = dt.toString(QStringLiteral("ddd yyyy-MM-dd t"));
    } else {
        result = dt.toString(QStringLiteral("ddd yyyy-MM-dd hh:mm:ss t"));
    }
    return result;
#else
    Q_UNUSED(dt);
    Q_UNUSED(isAllDay);
    return QString();
#endif
}

QDateTime RecurrenceRule::startDt() const
{
    return d->mDateStart;
}

RecurrenceRule::PeriodType RecurrenceRule::recurrenceType() const
{
    return d->mPeriod;
}

uint RecurrenceRule::frequency() const
{
    return d->mFrequency;
}

int RecurrenceRule::duration() const
{
    return d->mDuration;
}

QString RecurrenceRule::rrule() const
{
    return d->mRRule;
}

void RecurrenceRule::setRRule(const QString &rrule)
{
    d->mRRule = rrule;
}

bool RecurrenceRule::isReadOnly() const
{
    return d->mIsReadOnly;
}

void RecurrenceRule::setReadOnly(bool readOnly)
{
    d->mIsReadOnly = readOnly;
}

bool RecurrenceRule::recurs() const
{
    return d->mPeriod != rNone;
}

bool RecurrenceRule::allDay() const
{
    return d->mAllDay;
}

const QList<int> &RecurrenceRule::bySeconds() const
{
    return d->mBySeconds;
}

const QList<int> &RecurrenceRule::byMinutes() const
{
    return d->mByMinutes;
}

const QList<int> &RecurrenceRule::byHours() const
{
    return d->mByHours;
}

const QList<RecurrenceRule::WDayPos> &RecurrenceRule::byDays() const
{
    return d->mByDays;
}

const QList<int> &RecurrenceRule::byMonthDays() const
{
    return d->mByMonthDays;
}

const QList<int> &RecurrenceRule::byYearDays() const
{
    return d->mByYearDays;
}

const QList<int> &RecurrenceRule::byWeekNumbers() const
{
    return d->mByWeekNumbers;
}

const QList<int> &RecurrenceRule::byMonths() const
{
    return d->mByMonths;
}

const QList<int> &RecurrenceRule::bySetPos() const
{
    return d->mBySetPos;
}

short RecurrenceRule::weekStart() const
{
    return d->mWeekStart;
}

RecurrenceRule::RuleObserver::~RuleObserver()
{
}

RecurrenceRule::WDayPos::WDayPos(int ps, short dy)
    : mDay(dy)
    , mPos(ps)
{
}

void RecurrenceRule::WDayPos::setDay(short dy)
{
    mDay = dy;
}

short RecurrenceRule::WDayPos::day() const
{
    return mDay;
}

void RecurrenceRule::WDayPos::setPos(int ps)
{
    mPos = ps;
}

int RecurrenceRule::WDayPos::pos() const
{
    return mPos;
}

QDataStream &operator<<(QDataStream &out, const Constraint &c)
{
    out << c.year << c.month << c.day << c.hour << c.minute << c.second << c.weekday << c.weekdaynr << c.weeknumber << c.yearday << c.weekstart;
    serializeQTimeZoneAsSpec(out, c.timeZone);
    out << false; // for backwards compatibility

    return out;
}

QDataStream &operator>>(QDataStream &in, Constraint &c)
{
    bool secondOccurrence; // no longer used
    in >> c.year >> c.month >> c.day >> c.hour >> c.minute >> c.second >> c.weekday >> c.weekdaynr >> c.weeknumber >> c.yearday >> c.weekstart;
    deserializeSpecAsQTimeZone(in, c.timeZone);
    in >> secondOccurrence;
    return in;
}

KCALENDARCORE_EXPORT QDataStream &KCalendarCore::operator<<(QDataStream &out, const KCalendarCore::RecurrenceRule::WDayPos &w)
{
    out << w.mDay << w.mPos;
    return out;
}

KCALENDARCORE_EXPORT QDataStream &KCalendarCore::operator>>(QDataStream &in, KCalendarCore::RecurrenceRule::WDayPos &w)
{
    in >> w.mDay >> w.mPos;
    return in;
}

KCALENDARCORE_EXPORT QDataStream &KCalendarCore::operator<<(QDataStream &out, const KCalendarCore::RecurrenceRule *r)
{
    if (!r) {
        return out;
    }

    RecurrenceRule::Private *d = r->d;
    out << d->mRRule << static_cast<quint32>(d->mPeriod);
    serializeQDateTimeAsKDateTime(out, d->mDateStart);
    out << d->mFrequency << d->mDuration;
    serializeQDateTimeAsKDateTime(out, d->mDateEnd);
    out << d->mBySeconds << d->mByMinutes << d->mByHours << d->mByDays << d->mByMonthDays << d->mByYearDays << d->mByWeekNumbers << d->mByMonths << d->mBySetPos
        << d->mWeekStart << d->mConstraints << d->mAllDay << d->mNoByRules << d->mTimedRepetition << d->mIsReadOnly;

    return out;
}

KCALENDARCORE_EXPORT QDataStream &KCalendarCore::operator>>(QDataStream &in, const KCalendarCore::RecurrenceRule *r)
{
    if (!r) {
        return in;
    }

    RecurrenceRule::Private *d = r->d;
    quint32 period;
    in >> d->mRRule >> period;
    deserializeKDateTimeAsQDateTime(in, d->mDateStart);
    in >> d->mFrequency >> d->mDuration;
    deserializeKDateTimeAsQDateTime(in, d->mDateEnd);
    in >> d->mBySeconds >> d->mByMinutes >> d->mByHours >> d->mByDays >> d->mByMonthDays >> d->mByYearDays >> d->mByWeekNumbers >> d->mByMonths >> d->mBySetPos
        >> d->mWeekStart >> d->mConstraints >> d->mAllDay >> d->mNoByRules >> d->mTimedRepetition >> d->mIsReadOnly;

    d->mPeriod = static_cast<RecurrenceRule::PeriodType>(period);

    return in;
}