PersianCalendarUtils.java

/**
 * Persian Calendar see: http://code.google.com/p/persian-calendar/
   Copyright (C) 2012  Mortezaadi@gmail.com
   PersianCalendarUtils.java
   
   Persian Calendar is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation, either version 3 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
package com.mohamadamin.persianmaterialdatetimepicker.utils;

/**
 * algorithms for converting Julian days to the Persian calendar, and vice versa
 * are adopted from <a
 * href="casema.nl/couprie/calmath/persian/index.html">couprie.nl</a> written in
 * VB. The algorithms is not exactly the same as its original. I've done some
 * minor changes in the sake of performances and corrected some bugs.
 * 
 * @author Morteza contact: <a
 *         href="mailto:Mortezaadi@gmail.com">Mortezaadi@gmail.com</a>
 * @version 1.0
 * 
 */
public class PersianCalendarUtils {

	/**
	 * Converts a provided Persian (Shamsi) date to the Julian Day Number (i.e.
	 * the number of days since January 1 in the year 4713 BC). Since the
	 * Persian calendar is a highly regular calendar, converting to and from a
	 * Julian Day Number is not as difficult as it looks. Basically it's a
	 * mather of dividing, rounding and multiplying. This routine uses Julian
	 * Day Number 1948321 as focal point, since that Julian Day Number
	 * corresponds with 1 Farvardin (1) 1.
	 * 
	 * @param year
	 *            int persian year
	 * @param month
	 *            int persian month
	 * @param day
	 *            int persian day
	 * @return long
	 */
	public static long persianToJulian(long year, int month, int day) {
		return 365L * ((ceil(year - 474L, 2820D) + 474L) - 1L) + ((long) Math.floor((682L * (ceil(year - 474L, 2820D) + 474L) - 110L) / 2816D)) + (PersianCalendarConstants.PERSIAN_EPOCH - 1L) + 1029983L
				* ((long) Math.floor((year - 474L) / 2820D)) + (month < 7 ? 31 * month : 30 * month + 6) + day;
	}

	/**
	 * Calculate whether current year is Leap year in persian or not
	 * 
	 * @return boolean
	 */
	public static boolean isPersianLeapYear(int persianYear) {
		return PersianCalendarUtils.ceil((38D + (PersianCalendarUtils.ceil(persianYear - 474L, 2820L) + 474L)) * 682D, 2816D) < 682L;
	}

	/**
	 * Converts a provided Julian Day Number (i.e. the number of days since
	 * January 1 in the year 4713 BC) to the Persian (Shamsi) date. Since the
	 * Persian calendar is a highly regular calendar, converting to and from a
	 * Julian Day Number is not as difficult as it looks. Basically it's a
	 * mather of dividing, rounding and multiplying.
	 * 
	 * @param julianDate
	 * @return long
	 */
	public static long julianToPersian(long julianDate) {
		long persianEpochInJulian = julianDate - persianToJulian(475L, 0, 1);
		long cyear = ceil(persianEpochInJulian, 1029983D);
		long ycycle = cyear != 1029982L ? ((long) Math.floor((2816D * (double) cyear + 1031337D) / 1028522D)) : 2820L;
		long year = 474L + 2820L * ((long) Math.floor(persianEpochInJulian / 1029983D)) + ycycle;
		long aux = (1L + julianDate) - persianToJulian(year, 0, 1);
		int month = (int) (aux > 186L ? Math.ceil((double) (aux - 6L) / 30D) - 1 : Math.ceil((double) aux / 31D) - 1);
		int day = (int) (julianDate - (persianToJulian(year, month, 1) - 1L));
		return (year << 16) | (month << 8) | day;
	}

	/**
	 * Ceil function in original algorithm
	 * 
	 * @param double1
	 * @param double2
	 * @return long
	 */
	public static long ceil(double double1, double double2) {
		return (long) (double1 - double2 * Math.floor(double1 / double2));
	}

}