IslamicCalendar is a subclass of Calendar
+ * that implements the Islamic civil and religious calendars. It
+ * is used as the civil calendar in most of the Arab world and the
+ * liturgical calendar of the Islamic faith worldwide. This calendar
+ * is also known as the "Hijri" calendar, since it starts at the time
+ * of Mohammed's emigration (or "hijra") to Medinah on Thursday,
+ * July 15, 622 AD (Julian).
+ * + * The Islamic calendar is strictly lunar, and thus an Islamic year of twelve + * lunar months does not correspond to the solar year used by most other + * calendar systems, including the Gregorian. An Islamic year is, on average, + * about 354 days long, so each successive Islamic year starts about 11 days + * earlier in the corresponding Gregorian year. + *
+ * Each month of the calendar starts when the new moon's crescent is visible + * at sunset. However, in order to keep the time fields in this class + * synchronized with those of the other calendars and with local clock time, + * we treat days and months as beginning at midnight, + * roughly 6 hours after the corresponding sunset. + *
+ * There are two main variants of the Islamic calendar in existence. The first
+ * is the civil calendar, which uses a fixed cycle of alternating 29-
+ * and 30-day months, with a leap day added to the last month of 11 out of
+ * every 30 years. This calendar is easily calculated and thus predictable in
+ * advance, so it is used as the civil calendar in a number of Arab countries.
+ * This is the default behavior of a newly-created IslamicCalendar
+ * object.
+ *
+ * The Islamic religious calendar, however, is based on the observation + * of the crescent moon. It is thus affected by the position at which the + * observations are made, seasonal variations in the time of sunset, the + * eccentricities of the moon's orbit, and even the weather at the observation + * site. This makes it impossible to calculate in advance, and it causes the + * start of a month in the religious calendar to differ from the civil calendar + * by up to three days. + *
+ * Using astronomical calculations for the position of the sun and moon, the + * moon's illumination, and other factors, it is possible to determine the start + * of a lunar month with a fairly high degree of certainty. However, these + * calculations are extremely complicated and thus slow, so most algorithms, + * including the one used here, are only approximations of the true astronical + * calculations. At present, the approximations used in this class are fairly + * simplistic; they will be improved in later versions of the code. + *
+ * The {@link #setCivil setCivil} method determines
+ * which approach is used to determine the start of a month. By default, the
+ * fixed-cycle civil calendar is used. However, if setCivil(false)
+ * is called, an approximation of the true lunar calendar will be used.
+ *
+ * @see GregorianCalendar
+ *
+ * @author Laura Werner
+ * @author Alan Liu
+ * @author Steven R. Loomis
+ * @internal
+ */
+class U_I18N_API IslamicCalendar : public Calendar {
+ public:
+ //-------------------------------------------------------------------------
+ // Constants...
+ //-------------------------------------------------------------------------
+
+ /**
+ * Calendar type - civil or religious or um alqura
+ * @internal
+ */
+ enum ECalculationType {
+ ASTRONOMICAL,
+ CIVIL,
+ UMALQURA,
+ TBLA
+ };
+
+ /**
+ * Constants for the months
+ * @internal
+ */
+ enum EMonths {
+ /**
+ * Constant for Muharram, the 1st month of the Islamic year.
+ * @internal
+ */
+ MUHARRAM = 0,
+
+ /**
+ * Constant for Safar, the 2nd month of the Islamic year.
+ * @internal
+ */
+ SAFAR = 1,
+
+ /**
+ * Constant for Rabi' al-awwal (or Rabi' I), the 3rd month of the Islamic year.
+ * @internal
+ */
+ RABI_1 = 2,
+
+ /**
+ * Constant for Rabi' al-thani or (Rabi' II), the 4th month of the Islamic year.
+ * @internal
+ */
+ RABI_2 = 3,
+
+ /**
+ * Constant for Jumada al-awwal or (Jumada I), the 5th month of the Islamic year.
+ * @internal
+ */
+ JUMADA_1 = 4,
+
+ /**
+ * Constant for Jumada al-thani or (Jumada II), the 6th month of the Islamic year.
+ * @internal
+ */
+ JUMADA_2 = 5,
+
+ /**
+ * Constant for Rajab, the 7th month of the Islamic year.
+ * @internal
+ */
+ RAJAB = 6,
+
+ /**
+ * Constant for Sha'ban, the 8th month of the Islamic year.
+ * @internal
+ */
+ SHABAN = 7,
+
+ /**
+ * Constant for Ramadan, the 9th month of the Islamic year.
+ * @internal
+ */
+ RAMADAN = 8,
+
+ /**
+ * Constant for Shawwal, the 10th month of the Islamic year.
+ * @internal
+ */
+ SHAWWAL = 9,
+
+ /**
+ * Constant for Dhu al-Qi'dah, the 11th month of the Islamic year.
+ * @internal
+ */
+ DHU_AL_QIDAH = 10,
+
+ /**
+ * Constant for Dhu al-Hijjah, the 12th month of the Islamic year.
+ * @internal
+ */
+ DHU_AL_HIJJAH = 11,
+
+ ISLAMIC_MONTH_MAX
+ };
+
+
+ //-------------------------------------------------------------------------
+ // Constructors...
+ //-------------------------------------------------------------------------
+
+ /**
+ * Constructs an IslamicCalendar based on the current time in the default time zone
+ * with the given locale.
+ *
+ * @param aLocale The given locale.
+ * @param success Indicates the status of IslamicCalendar object construction.
+ * Returns U_ZERO_ERROR if constructed successfully.
+ * @param type The Islamic calendar calculation type. The default value is CIVIL.
+ * @internal
+ */
+ IslamicCalendar(const Locale& aLocale, UErrorCode &success, ECalculationType type = CIVIL);
+
+ /**
+ * Copy Constructor
+ * @internal
+ */
+ IslamicCalendar(const IslamicCalendar& other);
+
+ /**
+ * Destructor.
+ * @internal
+ */
+ virtual ~IslamicCalendar();
+
+ /**
+ * Sets Islamic calendar calculation type used by this instance.
+ *
+ * @param type The calendar calculation type, CIVIL to use the civil
+ * calendar, ASTRONOMICAL to use the astronomical calendar.
+ * @internal
+ */
+ void setCalculationType(ECalculationType type, UErrorCode &status);
+
+ /**
+ * Returns true if this object is using the fixed-cycle civil
+ * calendar, or false if using the religious, astronomical
+ * calendar.
+ * @internal
+ */
+ UBool isCivil();
+
+
+ // TODO: copy c'tor, etc
+
+ // clone
+ virtual Calendar* clone() const;
+
+ private:
+ /**
+ * Determine whether a year is a leap year in the Islamic civil calendar
+ */
+ static UBool civilLeapYear(int32_t year);
+
+ /**
+ * Return the day # on which the given year starts. Days are counted
+ * from the Hijri epoch, origin 0.
+ */
+ int32_t yearStart(int32_t year) const;
+
+ /**
+ * Return the day # on which the given month starts. Days are counted
+ * from the Hijri epoch, origin 0.
+ *
+ * @param year The hijri year
+ * @param year The hijri month, 0-based
+ */
+ int32_t monthStart(int32_t year, int32_t month) const;
+
+ /**
+ * Find the day number on which a particular month of the true/lunar
+ * Islamic calendar starts.
+ *
+ * @param month The month in question, origin 0 from the Hijri epoch
+ *
+ * @return The day number on which the given month starts.
+ */
+ int32_t trueMonthStart(int32_t month) const;
+
+ /**
+ * Return the "age" of the moon at the given time; this is the difference
+ * in ecliptic latitude between the moon and the sun. This method simply
+ * calls CalendarAstronomer.moonAge, converts to degrees,
+ * and adjusts the resultto be in the range [-180, 180].
+ *
+ * @param time The time at which the moon's age is desired,
+ * in millis since 1/1/1970.
+ */
+ static double moonAge(UDate time, UErrorCode &status);
+
+ //-------------------------------------------------------------------------
+ // Internal data....
+ //
+
+ /**
+ * CIVIL if this object uses the fixed-cycle Islamic civil calendar,
+ * and ASTRONOMICAL if it approximates the true religious calendar using
+ * astronomical calculations for the time of the new moon.
+ */
+ ECalculationType cType;
+
+ //----------------------------------------------------------------------
+ // Calendar framework
+ //----------------------------------------------------------------------
+ protected:
+ /**
+ * @internal
+ */
+ virtual int32_t handleGetLimit(UCalendarDateFields field, ELimitType limitType) const;
+
+ /**
+ * Return the length (in days) of the given month.
+ *
+ * @param year The hijri year
+ * @param year The hijri month, 0-based
+ * @internal
+ */
+ virtual int32_t handleGetMonthLength(int32_t extendedYear, int32_t month) const;
+
+ /**
+ * Return the number of days in the given Islamic year
+ * @internal
+ */
+ virtual int32_t handleGetYearLength(int32_t extendedYear) const;
+
+ //-------------------------------------------------------------------------
+ // Functions for converting from field values to milliseconds....
+ //-------------------------------------------------------------------------
+
+ // Return JD of start of given month/year
+ /**
+ * @internal
+ */
+ virtual int32_t handleComputeMonthStart(int32_t eyear, int32_t month, UBool useMonth) const;
+
+ //-------------------------------------------------------------------------
+ // Functions for converting from milliseconds to field values
+ //-------------------------------------------------------------------------
+
+ /**
+ * @internal
+ */
+ virtual int32_t handleGetExtendedYear();
+
+ /**
+ * Override Calendar to compute several fields specific to the Islamic
+ * calendar system. These are:
+ *
+ *