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   this work for additional information regarding copyright ownership.
   The ASF licenses this file to You under the Apache License, Version 2.0
   (the "License"); you may not use this file except in compliance with
   the License.  You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

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   distributed under the License is distributed on an "AS IS" BASIS,
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   See the License for the specific language governing permissions and
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package org.apache.poi.ss.formula.functions;

import java.util.Calendar;

import org.apache.poi.ss.formula.eval.EvaluationException;
import org.apache.poi.ss.formula.eval.NumberEval;
import org.apache.poi.ss.formula.eval.OperandResolver;
import org.apache.poi.ss.formula.eval.ValueEval;
import org.apache.poi.ss.usermodel.DateUtil;
import org.apache.poi.util.LocaleUtil;

/**
 * <p>Calculates the number of days between two dates based on a 360-day year
 * (twelve 30-day months), which is used in some accounting calculations. Use
 * this function to help compute payments if your accounting system is based on
 * twelve 30-day months.<p>
 * 
 * {@code DAYS360(start_date,end_date,[method])}
 * 
 * <ul>
 * <li>Start_date, end_date (required):<br/>
 * The two dates between which you want to know the number of days.<br/>
 * If start_date occurs after end_date, the DAYS360 function returns a negative number.</li>
 * 
 * <li>Method (optional):<br/>
 * A logical value that specifies whether to use the U.S. or European method in the calculation</li>
 * 
 * <li>Method set to false or omitted:<br/>
 * the DAYS360 function uses the U.S. (NASD) method. If the starting date is the 31st of a month,
 * it becomes equal to the 30th of the same month. If the ending date is the 31st of a month and
 * the starting date is earlier than the 30th of a month, the ending date becomes equal to the
 * 1st of the next month, otherwise the ending date becomes equal to the 30th of the same month.
 * The month February and leap years are handled in the following way:<br/>
 * On a non-leap year the function {@code =DAYS360("2/28/93", "3/1/93", FALSE)} returns 1 day
 * because the DAYS360 function ignores the extra days added to February.<br/>
 * On a leap year the function {@code =DAYS360("2/29/96","3/1/96", FALSE)} returns 1 day for
 * the same reason.</li>
 * 
 * <li>Method Set to true:<br/>
 * When you set the method parameter to TRUE, the DAYS360 function uses the European method.
 * Starting dates or ending dates that occur on the 31st of a month become equal to the 30th of
 * the same month. The month February and leap years are handled in the following way:<br/>
 * On a non-leap year the function {@code =DAYS360("2/28/93", "3/1/93", TRUE)} returns
 * 3 days because the DAYS360 function is counting the extra days added to February to give
 * February 30 days.<br/>
 * On a leap year the function {@code =DAYS360("2/29/96", "3/1/96", TRUE)} returns
 * 2 days for the same reason.</li>
 * </ul>
 * 
 * @see <a href="https://support.microsoft.com/en-us/kb/235575">DAYS360 Function Produces Different Values Depending on the Version of Excel</a>
 */
public class Days360 extends Var2or3ArgFunction {
    public ValueEval evaluate(int srcRowIndex, int srcColumnIndex, ValueEval arg0, ValueEval arg1) {
        try {
            double d0 = NumericFunction.singleOperandEvaluate(arg0, srcRowIndex, srcColumnIndex);
            double d1 = NumericFunction.singleOperandEvaluate(arg1, srcRowIndex, srcColumnIndex);
            return new NumberEval(evaluate(d0, d1, false));
        } catch (EvaluationException e) {
            return e.getErrorEval();
        }
    }

    public ValueEval evaluate(int srcRowIndex, int srcColumnIndex, ValueEval arg0, ValueEval arg1,
            ValueEval arg2) {
        try {
            double d0 = NumericFunction.singleOperandEvaluate(arg0, srcRowIndex, srcColumnIndex);
            double d1 = NumericFunction.singleOperandEvaluate(arg1, srcRowIndex, srcColumnIndex);
            ValueEval ve = OperandResolver.getSingleValue(arg2, srcRowIndex, srcColumnIndex);
            Boolean method = OperandResolver.coerceValueToBoolean(ve, false);
            return new NumberEval(evaluate(d0, d1, method != null && method.booleanValue()));
        } catch (EvaluationException e) {
            return e.getErrorEval();
        }
    }

    private static double evaluate(double d0, double d1, boolean method) {
        Calendar realStart = getDate(d0);
        Calendar realEnd = getDate(d1);
        int startingDate[] = getStartingDate(realStart, method);
        int endingDate[] = getEndingDate(realEnd, startingDate, method);
        return
            (endingDate[0]*360+endingDate[1]*30+endingDate[2])-
            (startingDate[0]*360+startingDate[1]*30+startingDate[2]);
    }

    private static Calendar getDate(double date) {
        Calendar processedDate = LocaleUtil.getLocaleCalendar();
        processedDate.setTime(DateUtil.getJavaDate(date, false));
        return processedDate;
    }

    private static int[] getStartingDate(Calendar realStart, boolean method) {
        int yyyy = realStart.get(Calendar.YEAR);
        int mm = realStart.get(Calendar.MONTH);
        int dd = Math.min(30, realStart.get(Calendar.DAY_OF_MONTH));
        
        if (!method && isLastDayOfMonth(realStart)) dd = 30;
        
        return new int[]{yyyy,mm,dd};
    }

    private static int[] getEndingDate(Calendar realEnd, int startingDate[], boolean method) {
        int yyyy = realEnd.get(Calendar.YEAR);
        int mm = realEnd.get(Calendar.MONTH);
        int dd = Math.min(30, realEnd.get(Calendar.DAY_OF_MONTH));

        if (!method && realEnd.get(Calendar.DAY_OF_MONTH) == 31) {
            if (startingDate[2] < 30) {
                realEnd.set(Calendar.DAY_OF_MONTH, 1);
                realEnd.add(Calendar.MONTH, 1);
                yyyy = realEnd.get(Calendar.YEAR);
                mm = realEnd.get(Calendar.MONTH);
                dd = 1;
            } else {
                dd = 30;
            }
        }

        return new int[]{yyyy,mm,dd};
    }
    
    private static boolean isLastDayOfMonth(Calendar date) {
        int dayOfMonth = date.get(Calendar.DAY_OF_MONTH);
        int lastDayOfMonth = date.getActualMaximum(Calendar.DAY_OF_MONTH);
        return (dayOfMonth == lastDayOfMonth);
    }
}