timezonerule.h

/*
    SPDX-FileCopyrightText: 2002 Jason Harris <kstars@30doradus.org>
 
    SPDX-License-Identifier: GPL-2.0-or-later
*/
 
#pragma once
 
#include "kstarsdatetime.h"
 
#include <QTime>
 
class QString;
 
/** @class TimeZoneRule
    *This class provides the information needed to determine whether Daylight
    *Savings Time (DST; a.k.a. "Summer Time") is currently active at a given
    *location.  There are (at least) 25 different "rules" which govern DST
    *around the world; a string identifying the appropriate rule is attached
    *to each city in citydb.sqlite.
    *
    *The rules themselves are stored in the TZrulebook.dat file, which is read
    *on startup; each line in the file creates a TimeZoneRule object.
    *
    *TimeZoneRule consists of QStrings identifying the months and days on which
    *DST starts and ends, QTime objects identifying the time at which the
    *changes occur, and a double indicating the size of the offset in hours
    *(probably always 1.00).
    *
    *Month names should be the English three-letter abbreviation, uncapitalized.
    *Day names are either an integer indicating the calendar date (i.e., "15" is
    *the fifteenth of the month), or a number paired with a three-letter
    *abbreviation for a weekday.  This indicates the Nth weekday of the month
    *(i.e., "2sun" is the second Sunday of the Month).  Finally, the weekday
    *string on its own indicates the last weekday of the month (i.e.,
    *"mon" is the last Monday of the month).
    *
    *The isDSTActive(KStarsDateTime) function returns true if DST is active for the
    *DateTime given as an argument.
    *
    *The nextDSTChange(KStarsDateTime) function returns the KStarsDateTime of the moment
    *at which the next DST change will occur for the current location.
    *@author Jason Harris
    *@version 1.0
    */
 
class TimeZoneRule
{
  public:
    /** Default Constructor. Makes the "empty" time zone rule (i.e., no DST correction)*/
    TimeZoneRule();
 
    /** Constructor. Create a TZ rule according to the arguments.
            *@param smonth the three-letter code for the month in which DST starts
            *@param sday a string encoding the day on which DST starts (see the class description)
            *@param stime the time at which DST starts
            *@param rmonth the three-letter code for the month in which DST reverts
            *@param rday a string encoding the day on which DST reverts (see the class description)
            *@param rtime the time at which DST reverts
            *@param offset the offset between normal time and DS time (always 1.00?)
            */
    TimeZoneRule(const QString &smonth, const QString &sday, const QTime &stime, const QString &rmonth,
                 const QString &rday, const QTime &rtime, const double &offset = 1.00);
 
    /** Determine whether DST is in effect for the given DateTime, according to this rule
            *@param date the date/time to test for DST
            */
    bool isDSTActive(const KStarsDateTime &date);
 
    /** @return true if the rule is the "empty" TZ rule. */
    bool isEmptyRule() const { return (HourOffset == 0.0); }
 
    /** Toggle DST on/off.  The @p activate argument should probably be isDSTActive()
            *@param activate if true, then set DST active; otherwise, deactivate DST
            */
    void setDST(bool activate = true);
 
    /** @return the current Timezone offset, compared to the timezone's Standard Time.
            *This is typically 0.0 if DST is inactive, and 1.0 if DST is active. */
    double deltaTZ() const { return dTZ; }
 
    /** Recalculate next dst change and if DST is active by a given local time with
            *timezone offset and time direction.
            *@param ltime the time to be tested
            *@param time_runs_forward time direction
            *@param TZoffset offset of timezone in some fictional unit
            *@param automaticDSTchange is automatic DST change?
            *
            * @todo Check dox for TZoffset
            */
    void reset_with_ltime(KStarsDateTime &ltime, const double TZoffset, const bool time_runs_forward,
                          const bool automaticDSTchange = false);
 
    /** @return computed value for next DST change in universal time. */
    KStarsDateTime nextDSTChange() const { return next_change_utc; }
 
    /** @return computed value for next DST change in local time. */
    KStarsDateTime nextDSTChange_LTime() const { return next_change_ltime; }
 
    /** @return true if this rule is the same as the argument.
         * @param r the rule to check for equivalence
         */
    bool equals(TimeZoneRule *r);
 
  private:
    /** @return the KStarsDateTime of the moment when the next DST change will occur in local time
            *This is useful because DST change times are saved in local times*/
    void nextDSTChange_LTime(const KStarsDateTime &date);
 
    /** @return the KStarsDateTime of the moment when the last DST change occurred in local time
            *This is useful because DST change times are saved in local times
            *We need this in case time is running backwards. */
    void previousDSTChange_LTime(const KStarsDateTime &date);
 
    /** calculate the next DST change in universal time for current location */
    void nextDSTChange(const KStarsDateTime &local_date, const double TZoffset);
 
    /** calculate the previous DST change in universal time for current location */
    void previousDSTChange(const KStarsDateTime &local_date, const double TZoffset);
 
    /** Interpret the string as a month of the year;
            *@return the month integer (1=jan ... 12=dec)
            */
    int initMonth(const QString &m);
 
    /** Set up empty time zone rule */
    void setEmpty();
 
    /** Interpret the day string as a week ID and a day-of-week ID.  The day-of-week
            *is an integer between 1 (sunday) and 7 (saturday); the week integer can
            *be 1-3 (1st/2nd/third weekday of the month), or 5 (last weekday of the month)
            *@param day the day integer is returned by reference through this value
            *@param week the week integer is returned by reference through this value
            *@return true if the day string was successfully parsed
            */
    bool initDay(const QString &d, int &day, int &week);
 
    /** Find the calendar date on which DST starts for the calendar year
            *of the given KStarsDateTime.
            *@param d the date containing the year to be tested
            *@return the calendar date, an integer between 1 and 31. */
    int findStartDay(const KStarsDateTime &d);
 
    /** Find the calendar date on which DST ends for the calendar year
            *of the given KStarsDateTime.
            *@param d the date containing the year to be tested
            *@return the calendar date, an integer between 1 and 31. */
    int findRevertDay(const KStarsDateTime &d);
 
    int StartDay { 0 };
    int RevertDay { 0 };
    int StartMonth { 0 };
    int RevertMonth { 0 };
    int StartWeek { 0 };
    int RevertWeek { 0 };
    QTime StartTime, RevertTime;
    KStarsDateTime next_change_utc;
    KStarsDateTime next_change_ltime;
    double dTZ { 0 };
    double HourOffset { 0 };
};