/*
********************************************************************************
*   Copyright (C) 1997-1999, International Business Machines
*   Corporation and others.  All Rights Reserved.
********************************************************************************
*
* File CALENDAR.H
*
* Modification History:
*
*   Date        Name        Description
*   04/22/97    aliu        Expanded and corrected comments and other header
*                           contents.
*   05/01/97    aliu        Made equals(), before(), after() arguments const.
*   05/20/97    aliu        Replaced fAreFieldsSet with fAreFieldsInSync and
*                           fAreAllFieldsSet.
*   07/27/98    stephen     Sync up with JDK 1.2
*   11/15/99    weiv        added YEAR_WOY and DOW_LOCAL
*                           to EDateFields
********************************************************************************
*/

#ifndef CALENDAR_H
#define CALENDAR_H

#include "unicode/locid.h"
#include "unicode/timezone.h"

U_NAMESPACE_BEGIN

/**
 * <code>Calendar</code> is an abstract base class for converting between
 * a <code>UDate</code> object and a set of integer fields such as
 * <code>YEAR</code>, <code>MONTH</code>, <code>DAY</code>, <code>HOUR</code>,
 * and so on. (A <code>UDate</code> object represents a specific instant in
 * time with millisecond precision. See
 * {@link UDate}
 * for information about the <code>UDate</code> class.)
 *
 * <p>
 * Subclasses of <code>Calendar</code> interpret a <code>UDate</code>
 * according to the rules of a specific calendar system. The JDK
 * provides one concrete subclass of <code>Calendar</code>:
 * <code>GregorianCalendar</code>. Future subclasses could represent
 * the various types of lunar calendars in use in many parts of the world.
 *
 * <p>
 * Like other locale-sensitive classes, <code>Calendar</code> provides a
 * class method, <code>getInstance</code>, for getting a generally useful
 * object of this type. <code>Calendar</code>'s <code>getInstance</code> method
 * returns a <code>GregorianCalendar</code> object whose
 * time fields have been initialized with the current date and time:
 * <blockquote>
 * <pre>
 * Calendar rightNow = Calendar.getInstance();
 * </pre>
 * </blockquote>
 *
 * <p>
 * A <code>Calendar</code> object can produce all the time field values
 * needed to implement the date-time formatting for a particular language
 * and calendar style (for example, Japanese-Gregorian, Japanese-Traditional).
 *
 * <p>
 * When computing a <code>UDate</code> from time fields, two special circumstances
 * may arise: there may be insufficient information to compute the
 * <code>UDate</code> (such as only year and month but no day in the month),
 * or there may be inconsistent information (such as "Tuesday, July 15, 1996"
 * -- July 15, 1996 is actually a Monday).
 *
 * <p>
 * <strong>Insufficient information.</strong> The calendar will use default
 * information to specify the missing fields. This may vary by calendar; for
 * the Gregorian calendar, the default for a field is the same as that of the
 * start of the epoch: i.e., YEAR = 1970, MONTH = JANUARY, DATE = 1, etc.
 *
 * <p>
 * <strong>Inconsistent information.</strong> If fields conflict, the calendar
 * will give preference to fields set more recently. For example, when
 * determining the day, the calendar will look for one of the following
 * combinations of fields.  The most recent combination, as determined by the
 * most recently set single field, will be used.
 *
 * <blockquote>
 * <pre>
 * MONTH + DAY_OF_MONTH
 * MONTH + WEEK_OF_MONTH + DAY_OF_WEEK
 * MONTH + DAY_OF_WEEK_IN_MONTH + DAY_OF_WEEK
 * DAY_OF_YEAR
 * DAY_OF_WEEK + WEEK_OF_YEAR
 * </pre>
 * </blockquote>
 *
 * For the time of day:
 *
 * <blockquote>
 * <pre>
 * HOUR_OF_DAY
 * AM_PM + HOUR
 * </pre>
 * </blockquote>
 *
 * <p>
 * <strong>Note:</strong> for some non-Gregorian calendars, different
 * fields may be necessary for complete disambiguation. For example, a full
 * specification of the historial Arabic astronomical calendar requires year,
 * month, day-of-month <em>and</em> day-of-week in some cases.
 *
 * <p>
 * <strong>Note:</strong> There are certain possible ambiguities in
 * interpretation of certain singular times, which are resolved in the
 * following ways:
 * <ol>
 *     <li> 24:00:00 "belongs" to the following day. That is,
 *          23:59 on Dec 31, 1969 &lt; 24:00 on Jan 1, 1970 &lt; 24:01:00 on Jan 1, 1970
 *
 *     <li> Although historically not precise, midnight also belongs to "am",
 *          and noon belongs to "pm", so on the same day,
 *          12:00 am (midnight) &lt; 12:01 am, and 12:00 pm (noon) &lt; 12:01 pm
 * </ol>
 *
 * <p>
 * The date or time format strings are not part of the definition of a
 * calendar, as those must be modifiable or overridable by the user at
 * runtime. Use {@link DateFormat}
 * to format dates.
 *
 * <p>
 * <code>Calendar</code> provides an API for field "rolling", where fields
 * can be incremented or decremented, but wrap around. For example, rolling the
 * month up in the date <code>December 12, <b>1996</b></code> results in
 * <code>January 12, <b>1996</b></code>.
 *
 * <p>
 * <code>Calendar</code> also provides a date arithmetic function for
 * adding the specified (signed) amount of time to a particular time field.
 * For example, subtracting 5 days from the date <code>September 12, 1996</code>
 * results in <code>September 7, 1996</code>.
 *
 * @stable
 */
class U_I18N_API Calendar {
public:

    /**
     * Field IDs for date and time. Used to specify date/time fields. ERA is calendar
     * specific. Example ranges given are for illustration only; see specific Calendar
     * subclasses for actual ranges.
     * @stable
     */
    enum EDateFields {
        ERA,                  // Example: 0..1
        YEAR,                 // Example: 1..big number
        MONTH,                // Example: 0..11
        WEEK_OF_YEAR,         // Example: 1..53
        WEEK_OF_MONTH,        // Example: 1..4
        DATE,                 // Example: 1..31
        DAY_OF_YEAR,          // Example: 1..365
        DAY_OF_WEEK,          // Example: 1..7
        DAY_OF_WEEK_IN_MONTH, // Example: 1..4, may be specified as -1
        AM_PM,                // Example: 0..1
        HOUR,                 // Example: 0..11
        HOUR_OF_DAY,          // Example: 0..23
        MINUTE,               // Example: 0..59
        SECOND,               // Example: 0..59
        MILLISECOND,          // Example: 0..999
        ZONE_OFFSET,          // Example: -12*U_MILLIS_PER_HOUR..12*U_MILLIS_PER_HOUR
        DST_OFFSET,           // Example: 0 or U_MILLIS_PER_HOUR
// here will go names for 'Y' and 'e'
        YEAR_WOY,  // 'Y' Example: 1..big number
        DOW_LOCAL, // 'e' Example: 1..7
        FIELD_COUNT,

        DAY_OF_MONTH = DATE   // Synonyms
    };

    /**
     * Useful constant for days of week. Note: Calendar day-of-week is 1-based. Clients
     * who create locale resources for the field of first-day-of-week should be aware of
     * this. For instance, in US locale, first-day-of-week is set to 1, i.e., SUNDAY.
     * @stable
     */
    enum EDaysOfWeek {
        SUNDAY = 1,
        MONDAY,
        TUESDAY,
        WEDNESDAY,
        THURSDAY,
        FRIDAY,
        SATURDAY
    };

    /**
     * Useful constants for month. Note: Calendar month is 0-based.
     * @stable
     */
    enum EMonths {
        JANUARY,
        FEBRUARY,
        MARCH,
        APRIL,
        MAY,
        JUNE,
        JULY,
        AUGUST,
        SEPTEMBER,
        OCTOBER,
        NOVEMBER,
        DECEMBER,
        UNDECIMBER
    };

    /**
     * Useful constants for hour in 12-hour clock. Used in GregorianCalendar.
     * @stable
     */
    enum EAmpm {
        AM,
        PM
    };

    /**
     * destructor
     * @stable
     */
    virtual ~Calendar();

    /**
     * Create and return a polymorphic copy of this calendar.
     * @stable
     */
    virtual Calendar* clone(void) const = 0;

    /**
     * Creates a Calendar using the default timezone and locale. Clients are responsible
     * for deleting the object returned.
     *
     * @param success  Indicates the success/failure of Calendar creation. Filled in
     *                 with U_ZERO_ERROR if created successfully, set to a failure result
     *                 otherwise.
     * @return         A Calendar if created successfully. NULL otherwise.
     * @stable
     */
    static Calendar* createInstance(UErrorCode& success);

    /**
     * Creates a Calendar using the given timezone and the default locale.
     * The Calendar takes ownership of zoneToAdopt; the
     * client must not delete it.
     *
     * @param zoneToAdopt  The given timezone to be adopted.
     * @param success      Indicates the success/failure of Calendar creation. Filled in
     *                     with U_ZERO_ERROR if created successfully, set to a failure result
     *                     otherwise.
     * @return             A Calendar if created successfully. NULL otherwise.
     * @stable
     */
    static Calendar* createInstance(TimeZone* zoneToAdopt, UErrorCode& success);

    /**
     * Creates a Calendar using the given timezone and the default locale.  The TimeZone
     * is _not_ adopted; the client is still responsible for deleting it.
     *
     * @param zone  The timezone.
     * @param success      Indicates the success/failure of Calendar creation. Filled in
     *                     with U_ZERO_ERROR if created successfully, set to a failure result
     *                     otherwise.
     * @return             A Calendar if created successfully. NULL otherwise.
     * @stable
     */
    static Calendar* createInstance(const TimeZone& zone, UErrorCode& success);

    /**
     * Creates a Calendar using the default timezone and the given locale.
     *
     * @param aLocale  The given locale.
     * @param success  Indicates the success/failure of Calendar creation. Filled in
     *                 with U_ZERO_ERROR if created successfully, set to a failure result
     *                 otherwise.
     * @return         A Calendar if created successfully. NULL otherwise.
     * @stable
     */
    static Calendar* createInstance(const Locale& aLocale, UErrorCode& success);

    /**
     * Creates a Calendar using the given timezone and given locale.
     * The Calendar takes ownership of zoneToAdopt; the
     * client must not delete it.
     *
     * @param zoneToAdopt  The given timezone to be adopted.
     * @param aLocale      The given locale.
     * @param success      Indicates the success/failure of Calendar creation. Filled in
     *                     with U_ZERO_ERROR if created successfully, set to a failure result
     *                     otherwise.
     * @return             A Calendar if created successfully. NULL otherwise.
     * @stable
     */
    static Calendar* createInstance(TimeZone* zoneToAdopt, const Locale& aLocale, UErrorCode& success);

    /**
     * Gets a Calendar using the given timezone and given locale.  The TimeZone
     * is _not_ adopted; the client is still responsible for deleting it.
     *
     * @param zone  The timezone.
     * @param aLocale      The given locale.
     * @param success      Indicates the success/failure of Calendar creation. Filled in
     *                     with U_ZERO_ERROR if created successfully, set to a failure result
     *                     otherwise.
     * @return             A Calendar if created successfully. NULL otherwise.
     * @stable
     */
    static Calendar* createInstance(const TimeZone& zoneToAdopt, const Locale& aLocale, UErrorCode& success);

    /**
     * Returns a list of the locales for which Calendars are installed.
     *
     * @param count  Number of locales returned.
     * @return       An array of Locale objects representing the set of locales for which
     *               Calendars are installed.  The system retains ownership of this list;
     *               the caller must NOT delete it.
     * @stable
     */
    static const Locale* getAvailableLocales(int32_t& count);

    /**
     * Returns the current UTC (GMT) time measured in milliseconds since 0:00:00 on 1/1/70 
     * (derived from the system time).
     *
     * @return   The current UTC time in milliseconds.
     * @stable
     */
    static UDate getNow(void);

    /**
     * Gets this Calendar's time as milliseconds. May involve recalculation of time due
     * to previous calls to set time field values. The time specified is non-local UTC
     * (GMT) time. Although this method is const, this object may actually be changed
     * (semantically const).
     *
     * @param status  Output param set to success/failure code on exit. If any value
     *                previously set in the time field is invalid or restricted by
     *                leniency, this will be set to an error status.
     * @return        The current time in UTC (GMT) time, or zero if the operation
     *                failed.
     * @stable
     */
    inline UDate getTime(UErrorCode& status) const { return getTimeInMillis(status); }

    /**
     * Sets this Calendar's current time with the given UDate. The time specified should
     * be in non-local UTC (GMT) time.
     *
     * @param date  The given UDate in UTC (GMT) time.
     * @stable
     */
    inline void setTime(UDate date, UErrorCode& status) { setTimeInMillis(date, status); }

    /**
     * Compares the equality of two Calendar objects. Objects of different subclasses
     * are considered unequal. This comparison is very exacting; two Calendar objects
     * must be in exactly the same state to be considered equal. To compare based on the
     * represented time, use equals() instead.
     *
     * @param that  The Calendar object to be compared with.
     * @return      True if the given Calendar is the same as this Calendar; false
     *              otherwise.
     * @stable
     */
    virtual UBool operator==(const Calendar& that) const;

    /**
     * Compares the inequality of two Calendar objects.
     *
     * @param that  The Calendar object to be compared with.
     * @return      True if the given Calendar is not the same as this Calendar; false
     *              otherwise.
     * @stable
     */
    UBool operator!=(const Calendar& that) const {return !operator==(that);}

    /**
     * Compares the Calendar time, whereas Calendar::operator== compares the equality of
     * Calendar objects.
     *
     * @param when    The Calendar to be compared with this Calendar. Although this is a
     *                const parameter, the object may be modified physically
     *                (semantically const).
     * @param status  Output param set to success/failure code on exit. If any value
     *                previously set in the time field is invalid or restricted by
     *                leniency, this will be set to an error status.
     * @return        True if the current time of this Calendar is equal to the time of
     *                Calendar when; false otherwise.
     * @stable
     */
    UBool equals(const Calendar& when, UErrorCode& status) const;

    /**
     * Returns true if this Calendar's current time is before "when"'s current time.
     *
     * @param when    The Calendar to be compared with this Calendar. Although this is a
     *                const parameter, the object may be modified physically
     *                (semantically const).
     * @param status  Output param set to success/failure code on exit. If any value
     *                previously set in the time field is invalid or restricted by
     *                leniency, this will be set to an error status.
     * @return        True if the current time of this Calendar is before the time of
     *                Calendar when; false otherwise.
     * @stable
     */
    UBool before(const Calendar& when, UErrorCode& status) const;

    /**
     * Returns true if this Calendar's current time is after "when"'s current time.
     *
     * @param when    The Calendar to be compared with this Calendar. Although this is a
     *                const parameter, the object may be modified physically
     *                (semantically const).
     * @param status  Output param set to success/failure code on exit. If any value
     *                previously set in the time field is invalid or restricted by
     *                leniency, this will be set to an error status.
     * @return        True if the current time of this Calendar is after the time of
     *                Calendar when; false otherwise.
     * @stable
     */
    UBool after(const Calendar& when, UErrorCode& status) const;

    /**
     * Return true if another Calendar object is equivalent to this one.  An equivalent
     * Calendar will behave exactly as this one does, but may be set to a different time.
     * @deprecated not in Java API!
     */
    virtual UBool equivalentTo(const Calendar& other) const;

    /**
     * UDate Arithmetic function. Adds the specified (signed) amount of time to the given
     * time field, based on the calendar's rules. For example, to subtract 5 days from
     * the current time of the calendar, call add(Calendar::DATE, -5). When adding on
     * the month or Calendar::MONTH field, other fields like date might conflict and
     * need to be changed. For instance, adding 1 month on the date 01/31/96 will result
     * in 02/29/96.
     *
     * @param field   Specifies which date field to modify.
     * @param amount  The amount of time to be added to the field, in the natural unit
     *                for that field (e.g., days for the day fields, hours for the hour
     *                field.)
     * @param status  Output param set to success/failure code on exit. If any value
     *                previously set in the time field is invalid or restricted by
     *                leniency, this will be set to an error status.
     * @stable
     */
    virtual void add(EDateFields field, int32_t amount, UErrorCode& status) = 0;

    /**
     * Time Field Rolling function. Rolls (up/down) a single unit of time on the given
     * time field. For example, to roll the current date up by one day, call
     * roll(Calendar::DATE, true). When rolling on the year or Calendar::YEAR field, it
     * will roll the year value in the range between getMinimum(Calendar::YEAR) and the
     * value returned by getMaximum(Calendar::YEAR). When rolling on the month or
     * Calendar::MONTH field, other fields like date might conflict and, need to be
     * changed. For instance, rolling the month up on the date 01/31/96 will result in
     * 02/29/96. Rolling up always means rolling forward in time; e.g., rolling the year
     * up on "100 BC" will result in "99 BC", for Gregorian calendar. When rolling on the
     * hour-in-day or Calendar::HOUR_OF_DAY field, it will roll the hour value in the range
     * between 0 and 23, which is zero-based.
     * <P>
     * NOTE: Do not use this method -- use roll(EDateFields, int, UErrorCode&) instead.
     *
     * @param field   The time field.
     * @param up      Indicates if the value of the specified time field is to be rolled
     *                up or rolled down. Use true if rolling up, false otherwise.
     * @param status  Output param set to success/failure code on exit. If any value
     *                previously set in the time field is invalid or restricted by
     *                leniency, this will be set to an error status.
     * @stable
     */
    void roll(EDateFields field, UBool up, UErrorCode& status);

    /**
     * Time Field Rolling function. Rolls by the given amount on the given
     * time field. For example, to roll the current date up by one day, call
     * roll(Calendar::DATE, +1, status). When rolling on the month or
     * Calendar::MONTH field, other fields like date might conflict and, need to be
     * changed. For instance, rolling the month up on the date 01/31/96 will result in
     * 02/29/96.  Rolling by a positive value always means rolling forward in time;
     * e.g., rolling the year by +1 on "100 BC" will result in "99 BC", for Gregorian
     * calendar. When rolling on the hour-in-day or Calendar::HOUR_OF_DAY field, it will
     * roll the hour value in the range between 0 and 23, which is zero-based.
     * <P>
     * The only difference between roll() and add() is that roll() does not change
     * the value of more significant fields when it reaches the minimum or maximum
     * of its range, whereas add() does.
     *
     * @param field   The time field.
     * @param amount  Indicates amount to roll.
     * @param status  Output param set to success/failure code on exit. If any value
     *                previously set in the time field is invalid, this will be set to
     *                an error status.
     * @stable
     */
    virtual void roll(EDateFields field, int32_t amount, UErrorCode& status) = 0;

    /**
     * Return the difference between the given time and the time this
     * calendar object is set to.  If this calendar is set
     * <em>before</em> the given time, the returned value will be
     * positive.  If this calendar is set <em>after</em> the given
     * time, the returned value will be negative.  The
     * <code>field</code> parameter specifies the units of the return
     * value.  For example, if <code>fieldDifference(when,
     * Calendar.MONTH)</code> returns 3, then this calendar is set to
     * 3 months before <code>when</code>, and possibly some addition
     * time less than one month.
     *
     * <p>As a side effect of this call, this calendar is advanced
     * toward <code>when</code> by the given amount.  That is, calling
     * this method has the side effect of calling <code>add(field,
     * n)</code>, where <code>n</code> is the return value.
     *
     * <p>Usage: To use this method, call it first with the largest
     * field of interest, then with progressively smaller fields.  For
     * example:
     *
     * <pre>
     * int y = cal.fieldDifference(when, Calendar.YEAR);
     * int m = cal.fieldDifference(when, Calendar.MONTH);
     * int d = cal.fieldDifference(when, Calendar.DATE);</pre>
     *
     * computes the difference between <code>cal</code> and
     * <code>when</code> in years, months, and days.
     *
     * <p>Note: <code>fieldDifference()</code> is
     * <em>asymmetrical</em>.  That is, in the following code:
     *
     * <pre>
     * cal.setTime(date1);
     * int m1 = cal.fieldDifference(date2, Calendar.MONTH);
     * int d1 = cal.fieldDifference(date2, Calendar.DATE);
     * cal.setTime(date2);
     * int m2 = cal.fieldDifference(date1, Calendar.MONTH);
     * int d2 = cal.fieldDifference(date1, Calendar.DATE);</pre>
     *
     * one might expect that <code>m1 == -m2 && d1 == -d2</code>.
     * However, this is not generally the case, because of
     * irregularities in the underlying calendar system (e.g., the
     * Gregorian calendar has a varying number of days per month).
     *
     * @param when the date to compare this calendar's time to
     * @param field the field in which to compute the result
     * @return the difference, either positive or negative, between
     * this calendar's time and <code>when</code>, in terms of
     * <code>field</code>.
     * @stable
     */
    virtual int32_t fieldDifference(UDate when, EDateFields field, UErrorCode& status);

    /**
     * Sets the calendar's time zone to be the one passed in. The Calendar takes ownership
     * of the TimeZone; the caller is no longer responsible for deleting it.  If the
     * given time zone is NULL, this function has no effect.
     *
     * @param value  The given time zone.
     * @stable
     */
    void adoptTimeZone(TimeZone* value);

    /**
     * Sets the calendar's time zone to be the same as the one passed in. The TimeZone
     * passed in is _not_ adopted; the client is still responsible for deleting it.
     *
     * @param value  The given time zone.
     * @stable
     */
    void setTimeZone(const TimeZone& zone);

    /**
     * Returns a reference to the time zone owned by this calendar. The returned reference
     * is only valid until clients make another call to adoptTimeZone or setTimeZone,
     * or this Calendar is destroyed.
     *
     * @return   The time zone object associated with this calendar.
     * @stable
     */
    const TimeZone& getTimeZone(void) const;

    /**
     * Returns the time zone owned by this calendar. The caller owns the returned object
     * and must delete it when done.  After this call, the new time zone associated
     * with this Calendar is the default TimeZone as returned by TimeZone::createDefault().
     *
     * @return   The time zone object which was associated with this calendar.
     * @stable
     */
    TimeZone* orphanTimeZone(void);

    /**
     * Queries if the current date for this Calendar is in Daylight Savings Time.
     *
     * @param status Fill-in parameter which receives the status of this operation.
     * @return   True if the current date for this Calendar is in Daylight Savings Time,
     *           false, otherwise.
     * @stable
     */
    virtual UBool inDaylightTime(UErrorCode& status) const = 0;

    /**
     * Specifies whether or not date/time interpretation is to be lenient. With lenient
     * interpretation, a date such as "February 942, 1996" will be treated as being
     * equivalent to the 941st day after February 1, 1996. With strict interpretation,
     * such dates will cause an error when computing time from the time field values
     * representing the dates.
     *
     * @param lenient  True specifies date/time interpretation to be lenient.
     *
     * @see            DateFormat#setLenient
     * @stable
     */
    void setLenient(UBool lenient);

    /**
     * Tells whether date/time interpretation is to be lenient.
     *
     * @return   True tells that date/time interpretation is to be lenient.
     * @stable
     */
    UBool isLenient(void) const;

    /**
     * Sets what the first day of the week is; e.g., Sunday in US, Monday in France.
     *
     * @param value  The given first day of the week.
     * @stable
     */
    void setFirstDayOfWeek(EDaysOfWeek value);

    /**
     * Gets what the first day of the week is; e.g., Sunday in US, Monday in France.
     *
     * @return   The first day of the week.
     * @stable
     */
    EDaysOfWeek getFirstDayOfWeek(void) const;

    /**
     * Sets what the minimal days required in the first week of the year are; For
     * example, if the first week is defined as one that contains the first day of the
     * first month of a year, call the method with value 1. If it must be a full week,
     * use value 7.
     *
     * @param value  The given minimal days required in the first week of the year.
     * @stable
     */
    void setMinimalDaysInFirstWeek(uint8_t value);

    /**
     * Gets what the minimal days required in the first week of the year are; e.g., if
     * the first week is defined as one that contains the first day of the first month
     * of a year, getMinimalDaysInFirstWeek returns 1. If the minimal days required must
     * be a full week, getMinimalDaysInFirstWeek returns 7.
     *
     * @return   The minimal days required in the first week of the year.
     * @stable
     */
    uint8_t getMinimalDaysInFirstWeek(void) const;

    /**
     * Gets the minimum value for the given time field. e.g., for Gregorian
     * DAY_OF_MONTH, 1.
     *
     * @param field  The given time field.
     * @return       The minimum value for the given time field.
     * @stable
     */
    virtual int32_t getMinimum(EDateFields field) const = 0;

    /**
     * Gets the maximum value for the given time field. e.g. for Gregorian DAY_OF_MONTH,
     * 31.
     *
     * @param field  The given time field.
     * @return       The maximum value for the given time field.
     * @stable
     */
    virtual int32_t getMaximum(EDateFields field) const = 0;

    /**
     * Gets the highest minimum value for the given field if varies. Otherwise same as
     * getMinimum(). For Gregorian, no difference.
     *
     * @param field  The given time field.
     * @return       The highest minimum value for the given time field.
     * @stable
     */
    virtual int32_t getGreatestMinimum(EDateFields field) const = 0;

    /**
     * Gets the lowest maximum value for the given field if varies. Otherwise same as
     * getMaximum(). e.g., for Gregorian DAY_OF_MONTH, 28.
     *
     * @param field  The given time field.
     * @return       The lowest maximum value for the given time field.
     * @stable
     */
    virtual int32_t getLeastMaximum(EDateFields field) const = 0;

    /**
     * Return the minimum value that this field could have, given the current date.
     * For the Gregorian calendar, this is the same as getMinimum() and getGreatestMinimum().
     *
     * The version of this function on Calendar uses an iterative algorithm to determine the
     * actual minimum value for the field.  There is almost always a more efficient way to
     * accomplish this (in most cases, you can simply return getMinimum()).  GregorianCalendar
     * overrides this function with a more efficient implementation.
     *
     * @param field the field to determine the minimum of
     * @return the minimum of the given field for the current date of this Calendar
     * @stable
     */
    int32_t getActualMinimum(EDateFields field, UErrorCode& status) const;

    /**
     * Return the maximum value that this field could have, given the current date.
     * For example, with the date "Feb 3, 1997" and the DAY_OF_MONTH field, the actual
     * maximum would be 28; for "Feb 3, 1996" it s 29.  Similarly for a Hebrew calendar,
     * for some years the actual maximum for MONTH is 12, and for others 13.
     *
     * The version of this function on Calendar uses an iterative algorithm to determine the
     * actual maximum value for the field.  There is almost always a more efficient way to
     * accomplish this (in most cases, you can simply return getMaximum()).  GregorianCalendar
     * overrides this function with a more efficient implementation.
     *
     * @param field the field to determine the maximum of
     * @return the maximum of the given field for the current date of this Calendar
     * @stable
     */
    int32_t getActualMaximum(EDateFields field, UErrorCode& status) const;

    /**
     * Gets the value for a given time field. Recalculate the current time field values
     * if the time value has been changed by a call to setTime(). Return zero for unset
     * fields if any fields have been explicitly set by a call to set(). To force a
     * recomputation of all fields regardless of the previous state, call complete().
     * This method is semantically const, but may alter the object in memory.
     *
     * @param field  The given time field.
     * @param status Fill-in parameter which receives the status of the operation.
     * @return       The value for the given time field, or zero if the field is unset,
     *               and set() has been called for any other field.
     * @stable
     */
    int32_t get(EDateFields field, UErrorCode& status) const;

    /**
     * Determines if the given time field has a value set. This can affect in the
     * resolving of time in Calendar. Unset fields have a value of zero, by definition.
     *
     * @return   True if the given time field has a value set; false otherwise.
     * @stable
     */
    UBool isSet(EDateFields field) const;

    /**
     * Sets the given time field with the given value.
     *
     * @param field  The given time field.
     * @param value  The value to be set for the given time field.
     * @stable
     */
    void set(EDateFields field, int32_t value);

    /**
     * Sets the values for the fields YEAR, MONTH, and DATE. Other field values are
     * retained; call clear() first if this is not desired.
     *
     * @param year   The value used to set the YEAR time field.
     * @param month  The value used to set the MONTH time field. Month value is 0-based.
     *               e.g., 0 for January.
     * @param date   The value used to set the DATE time field.
     * @stable
     */
    void set(int32_t year, int32_t month, int32_t date);

    /**
     * Sets the values for the fields YEAR, MONTH, DATE, HOUR_OF_DAY, and MINUTE. Other
     * field values are retained; call clear() first if this is not desired.
     *
     * @param year    The value used to set the YEAR time field.
     * @param month   The value used to set the MONTH time field. Month value is
     *                0-based. E.g., 0 for January.
     * @param date    The value used to set the DATE time field.
     * @param hour    The value used to set the HOUR_OF_DAY time field.
     * @param minute  The value used to set the MINUTE time field.
     * @stable
     */
    void set(int32_t year, int32_t month, int32_t date, int32_t hour, int32_t minute);

    /**
     * Sets the values for the fields YEAR, MONTH, DATE, HOUR_OF_DAY, MINUTE, and SECOND.
     * Other field values are retained; call clear() first if this is not desired.
     *
     * @param year    The value used to set the YEAR time field.
     * @param month   The value used to set the MONTH time field. Month value is
     *                0-based. E.g., 0 for January.
     * @param date    The value used to set the DATE time field.
     * @param hour    The value used to set the HOUR_OF_DAY time field.
     * @param minute  The value used to set the MINUTE time field.
     * @param second  The value used to set the SECOND time field.
     * @stable
     */
    void set(int32_t year, int32_t month, int32_t date, int32_t hour, int32_t minute, int32_t second);

    /**
     * Clears the values of all the time fields, making them both unset and assigning
     * them a value of zero. The field values will be determined during the next
     * resolving of time into time fields.
     * @stable
     */
    void clear(void);

    /**
     * Clears the value in the given time field, both making it unset and assigning it a
     * value of zero. This field value will be determined during the next resolving of
     * time into time fields.
     *
     * @param field  The time field to be cleared.
     * @stable
     */
    void clear(EDateFields field);

    /**
     * Returns a unique class ID POLYMORPHICALLY. Pure virtual method. This method is to
     * implement a simple version of RTTI, since not all C++ compilers support genuine
     * RTTI. Polymorphic operator==() and clone() methods call this method.
     * <P>
     * Concrete subclasses of Calendar must implement getDynamicClassID() and also a
     * static method and data member:
     *
     *      static UClassID getStaticClassID() { return (UClassID)&fgClassID; }
     *      static char fgClassID;
     *
     * @return   The class ID for this object. All objects of a given class have the
     *           same class ID. Objects of other classes have different class IDs.
     * @stable
     */
    virtual UClassID getDynamicClassID(void) const = 0;

protected:

     /**
      * Constructs a Calendar with the default time zone as returned by
      * TimeZone::createInstance(), and the default locale.
      *
      * @param success  Indicates the status of Calendar object construction. Returns
      *                 U_ZERO_ERROR if constructed successfully.
     * @stable
      */
    Calendar(UErrorCode& success);

    /**
     * Copy constructor
     * @stable
     */
    Calendar(const Calendar& source);

    /**
     * Default assignment operator
     * @stable
     */
    Calendar& operator=(const Calendar& right);

    /**
     * Constructs a Calendar with the given time zone and locale. Clients are no longer
     * responsible for deleting the given time zone object after it's adopted.
     *
     * @param zoneToAdopt     The given time zone.
     * @param aLocale  The given locale.
     * @param success  Indicates the status of Calendar object construction. Returns
     *                 U_ZERO_ERROR if constructed successfully.
     * @stable
     */
    Calendar(TimeZone* zone, const Locale& aLocale, UErrorCode& success);

    /**
     * Constructs a Calendar with the given time zone and locale.
     *
     * @param zone     The given time zone.
     * @param aLocale  The given locale.
     * @param success  Indicates the status of Calendar object construction. Returns
     *                 U_ZERO_ERROR if constructed successfully.
     * @stable
     */
    Calendar(const TimeZone& zone, const Locale& aLocale, UErrorCode& success);

    /**
     * Converts Calendar's time field values to GMT as milliseconds.
     *
     * @param status  Output param set to success/failure code on exit. If any value
     *                previously set in the time field is invalid or restricted by
     *                leniency, this will be set to an error status.
     * @stable
     */
    virtual void computeTime(UErrorCode& status) = 0;

    /**
     * Converts GMT as milliseconds to time field values. This allows you to sync up the
     * time field values with a new time that is set for the calendar.  This method
     * does NOT recompute the time first; to recompute the time, then the fields, use
     * the method complete().
     * @stable
     */
    virtual void computeFields(UErrorCode& status) = 0;

    /**
     * Gets this Calendar's current time as a long.
     * @return the current time as UTC milliseconds from the epoch.
     * @stable
     */
    double getTimeInMillis(UErrorCode& status) const;

    /**
     * Sets this Calendar's current time from the given long value.
     * @param date the new time in UTC milliseconds from the epoch.
     * @stable
     */
    void setTimeInMillis( double millis, UErrorCode& status );

    /**
     * Recomputes the current time from currently set fields, and then fills in any
     * unset fields in the time field list.
     *
     * @param status  Output param set to success/failure code on exit. If any value
     *                previously set in the time field is invalid or restricted by
     *                leniency, this will be set to an error status.
     * @stable
     */
    void complete(UErrorCode& status);

    /**
     * Gets the value for a given time field. Subclasses can use this function to get
     * field values without forcing recomputation of time.
     *
     * @param field  The given time field.
     * @return       The value for the given time field.
     * @stable
     */
    int32_t internalGet(EDateFields field) const {return fFields[field];}

    /**
     * Sets the value for a given time field.  This is a fast internal method for
     * subclasses.  It does not affect the areFieldsInSync, isTimeSet, or areAllFieldsSet
     * flags.
     * @stable
     */
    void internalSet(EDateFields field, int32_t value);

protected:
    /**
     * The flag which indicates if the current time is set in the calendar.
     * @stable
     */
    UBool      fIsTimeSet;

    /**
     * True if the fields are in sync with the currently set time of this Calendar.
     * If false, then the next attempt to get the value of a field will
     * force a recomputation of all fields from the current value of the time
     * field.
     * <P>
     * This should really be named areFieldsInSync, but the old name is retained
     * for backward compatibility.
     * @stable
     */
    UBool      fAreFieldsSet;

    /**
     * True if all of the fields have been set.  This is initially false, and set to
     * true by computeFields().
     * @stable
     */
    UBool      fAreAllFieldsSet;

    /**
     * Get the current time without recomputing.
     * @stable
     */
    UDate        internalGetTime(void) const     { return fTime; }

    /**
     * Set the current time without affecting flags or fields.
     * @stable
     */
    void        internalSetTime(UDate time)     { fTime = time; }

    /**
     * The time fields containing values into which the millis is computed.
     * @stable
     */
    int32_t     fFields[FIELD_COUNT];

    /**
     * The flags which tell if a specified time field for the calendar is set.
     * @stable
     */
    UBool      fIsSet[FIELD_COUNT];

    /** Special values of stamp[]
     * @stable
     */
    enum {
        kUnset                 = 0,
        kInternallySet,
        kMinimumUserStamp
    };

    /**
     * Pseudo-time-stamps which specify when each field was set. There
     * are two special values, UNSET and INTERNALLY_SET. Values from
     * MINIMUM_USER_SET to Integer.MAX_VALUE are legal user set values.
     * @stable
     */
    int32_t        fStamp[FIELD_COUNT];

private:

    // The next available value for stampp[]
    int32_t fNextStamp;// = MINIMUM_USER_STAMP;

    /**
     * The current time set for the calendar.
     */
    UDate        fTime;

    /**
     * @see   #setLenient
     */
    UBool      fLenient;

    /**
     * Time zone affects the time calculation done by Calendar. Calendar subclasses use
     * the time zone data to produce the local time.
     */
    TimeZone*   fZone;

    /**
     * Both firstDayOfWeek and minimalDaysInFirstWeek are locale-dependent. They are
     * used to figure out the week count for a specific date for a given locale. These
     * must be set when a Calendar is constructed. For example, in US locale,
     * firstDayOfWeek is SUNDAY; minimalDaysInFirstWeek is 1. They are used to figure
     * out the week count for a specific date for a given locale. These must be set when
     * a Calendar is constructed.
     */
    EDaysOfWeek fFirstDayOfWeek;
    uint8_t     fMinimalDaysInFirstWeek;

    /**
     * Sets firstDayOfWeek and minimalDaysInFirstWeek. Called at Calendar construction
     * time.
     *
     * @param desiredLocale  The given locale.
     * @param success        Indicates the status of setting the week count data from
     *                       the resource for the given locale. Returns U_ZERO_ERROR if
     *                       constructed successfully.
     */
    void        setWeekCountData(const Locale& desiredLocale, UErrorCode& success);

    /**
     * Recompute the time and update the status fields isTimeSet
     * and areFieldsSet.  Callers should check isTimeSet and only
     * call this method if isTimeSet is false.
     */
    void updateTime(UErrorCode& status);

    /**
     * The resource tag for the resource where the week-count data is stored.
     */
    static const char kDateTimeElements[];
};

// -------------------------------------

inline Calendar*
Calendar::createInstance(TimeZone* zone, UErrorCode& errorCode)
{
    // since the Locale isn't specified, use the default locale
    return createInstance(zone, Locale::getDefault(), errorCode);
}

// -------------------------------------

inline void 
Calendar::roll(EDateFields field, UBool up, UErrorCode& status)
{
    roll(field, (int32_t)(up ? +1 : -1), status);
}

// -------------------------------------

/**
 * Fast method for subclasses.  The caller must maintain fUserSetDSTOffset and
 * fUserSetZoneOffset, as well as the isSet[] array.
 */
inline void
Calendar::internalSet(EDateFields field, int32_t value)
{
    fFields[field] = value;
}

U_NAMESPACE_END

#endif // _CALENDAR