/*
 * Zmanim Java API
 * Copyright (C) 2017 - 2025 Eliyahu Hershfeld
 *
 * This library is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General
 * Public License as published by the Free Software Foundation; either version 2.1 of the License, or (at your option)
 * any later version.
 *
 * This library 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 Lesser General Public License for more
 * details.
 * You should have received a copy of the GNU Lesser General Public License along with this library; if not, write to
 * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA,
 * or connect to: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html
 */
package com.kosherjava.zmanim.hebrewcalendar;

import java.util.Calendar;
import java.util.GregorianCalendar;


/**
 * This class calculates the <a href="https://en.wikipedia.org/wiki/Jerusalem_Talmud">Talmud Yerusalmi</a> <a href=
 * "https://en.wikipedia.org/wiki/Daf_Yomi">Daf Yomi</a> page ({@link Daf}) for the a given date.
 * 
 * @author &copy; elihaidv
 * @author &copy; Eliyahu Hershfeld 2017 - 2025
 */
public class YerushalmiYomiCalculator {
        
        /**
         * The start date of the first Daf Yomi Yerushalmi cycle of February 2, 1980 / 15 Shevat, 5740.
         */
        private final static Calendar DAF_YOMI_START_DAY = new GregorianCalendar(1980, Calendar.FEBRUARY, 2);
        /** The number of milliseconds in a day. */
        private final static int DAY_MILIS = 1000 * 60 * 60 * 24;
        /** The number of pages in the Talmud Yerushalmi.*/
        private final static int WHOLE_SHAS_DAFS = 1554;
        /** The number of pages per <em>masechta</em> (tractate).*/
        private final static int[] BLATT_PER_MASECHTA = { 
                        68, 37, 34, 44, 31, 59, 26, 33, 28, 20, 13, 92, 65, 71, 22, 22, 42, 26, 26, 33, 34, 22,
                        19, 85, 72, 47, 40, 47, 54, 48, 44, 37, 34, 44, 9, 57, 37, 19, 13};

        /**
         * Default constructor.
         */
        public YerushalmiYomiCalculator() {
                // nothing here
        }
        
        /**
         * Returns the <a href="https://en.wikipedia.org/wiki/Daf_Yomi">Daf Yomi</a>
         * <a href="https://en.wikipedia.org/wiki/Jerusalem_Talmud">Yerusalmi</a> page ({@link Daf}) for a given date.
         * The first Daf Yomi cycle started on 15 Shevat (Tu Bishvat), 5740 (February, 2, 1980) and calculations
         * prior to this date will result in an IllegalArgumentException thrown. A null will be returned on Tisha B'Av or
         * Yom Kippur.
         *
         * @param calendar
         *            the calendar date for calculation
         * @return the {@link Daf} or null if the date is on Tisha B'Av or Yom Kippur.
         *
         * @throws IllegalArgumentException
         *             if the date is prior to the February 2, 1980, the start of the first Daf Yomi Yerushalmi cycle
         */
        public static Daf getDafYomiYerushalmi(JewishCalendar calendar) {
                
                Calendar nextCycle = new GregorianCalendar();
                Calendar prevCycle = new GregorianCalendar();
                Calendar requested = calendar.getGregorianCalendar();
                int masechta = 0;
                Daf dafYomi = null;

                // There isn't Daf Yomi on Yom Kippur or Tisha B'Av.
                if ( calendar.getYomTovIndex() == JewishCalendar.YOM_KIPPUR ||
                                calendar.getYomTovIndex() == JewishCalendar.TISHA_BEAV ) {
                        return null;
                }
                
                
                if (requested.before(DAF_YOMI_START_DAY)) {
                        throw new IllegalArgumentException(requested + " is prior to organized Daf Yomi Yerushalmi cycles that started on "
                                        + DAF_YOMI_START_DAY);
                }
                
                // Start to calculate current cycle. init the start day
                nextCycle.setTime(DAF_YOMI_START_DAY.getTime());
                
                // Go cycle by cycle, until we get the next cycle
                while (requested.after(nextCycle)) {
                        prevCycle.setTime(nextCycle.getTime());
                        
                        // Adds the number of whole shas dafs. and the number of days that not have daf.
                        nextCycle.add(Calendar.DAY_OF_MONTH, WHOLE_SHAS_DAFS);
                        nextCycle.add(Calendar.DAY_OF_MONTH, getNumOfSpecialDays(prevCycle, nextCycle));                
                }
                
                // Get the number of days from cycle start until request.
                int dafNo = (int)(getDiffBetweenDays(prevCycle, requested));
                
                // Get the number of special day to subtract
                int specialDays = getNumOfSpecialDays(prevCycle, requested);
                int total = dafNo - specialDays;
                                
                // Finally find the daf.
                for (int i : BLATT_PER_MASECHTA) {
                        if (total < i) {
                                dafYomi = new Daf(masechta, total + 1);
                                break;
                        }
                        total -= i;
                        masechta++;
                }

                return dafYomi;
        }
        
        /**
         * Return the number of special days (Yom Kippur and Tisha Beav, where there are no dafim), between the start date
         * (as a <code>Calendar</code>) and end date (also as a <code>Calendar</code>).
         * 
         * @param start date to start calculating from
         * @param end date to finish calculating at
         * @return the number of special days between the start and end dates
         */
        private static int getNumOfSpecialDays(Calendar start, Calendar end) {
                
                // Find the start and end Jewish years
                int startYear = new JewishCalendar(start).getJewishYear();
                int endYear = new JewishCalendar(end).getJewishYear();
                
                // Value to return
                int specialDays = 0;
                
                //Instant of special Dates
                JewishCalendar yom_kippur = new JewishCalendar(5770, 7, 10);
                JewishCalendar tisha_beav = new JewishCalendar(5770, 5, 9);

                // Go over the years and find special dates
                for (int i = startYear; i <= endYear; i++) {
                        yom_kippur.setJewishYear(i);
                        tisha_beav.setJewishYear(i);
                        
                        if (isBetween(start, yom_kippur.getGregorianCalendar(), end)) {
                                specialDays++;
                        }
                        if (isBetween(start, tisha_beav.getGregorianCalendar(), end)) {
                                specialDays++;
                        }
                }
                
                return specialDays;
        }

        /**
         * Return if the date is between two dates
         * 
         * @param start the start date
         * @param date the date being compared
         * @param end the end date
         * @return if the date is between the start and end dates
         */
        private static boolean isBetween(Calendar start, Calendar date, Calendar end ) {
                return start.before(date) && end.after(date);
        }
        
        /**
         * Return the number of days between the dates passed in
         * @param start the start date
         * @param end the end date
         * @return the number of days between the start and end dates
         */
        private static long getDiffBetweenDays(Calendar start, Calendar end) {
                return  (end.getTimeInMillis() - start.getTimeInMillis()) / DAY_MILIS;
        }
}