poi/src/main/java/org/apache/poi/ss/formula/functions/CalendarFieldFunction.java

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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
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package org.apache.poi.ss.formula.functions;

import java.util.Calendar;

import org.apache.poi.ss.formula.eval.ErrorEval;
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;

/**
 * Implementation of Excel functions Date parsing functions:
 *  Date - DAY, MONTH and YEAR
 *  Time - HOUR, MINUTE and SECOND
 */
public final class CalendarFieldFunction extends Fixed1ArgFunction {
	public static final Function YEAR = new CalendarFieldFunction(Calendar.YEAR);
	public static final Function MONTH = new CalendarFieldFunction(Calendar.MONTH);
	public static final Function DAY = new CalendarFieldFunction(Calendar.DAY_OF_MONTH);
	public static final Function HOUR = new CalendarFieldFunction(Calendar.HOUR_OF_DAY);
    public static final Function MINUTE = new CalendarFieldFunction(Calendar.MINUTE);
    public static final Function SECOND = new CalendarFieldFunction(Calendar.SECOND);

	private final int _dateFieldId;

	private CalendarFieldFunction(int dateFieldId) {
		_dateFieldId = dateFieldId;
	}

	public final ValueEval evaluate(int srcRowIndex, int srcColumnIndex, ValueEval arg0) {
		double val;
		try {
			ValueEval ve = OperandResolver.getSingleValue(arg0, srcRowIndex, srcColumnIndex);
			val = OperandResolver.coerceValueToDouble(ve);
		} catch (EvaluationException e) {
			return e.getErrorEval();
		}
		if (val < 0) {
			return ErrorEval.NUM_ERROR;
		}
		return new NumberEval(getCalField(val));
	}

	private int getCalField(double serialDate) {
	   // For some reason, a date of 0 in Excel gets shown
	   //  as the non existant 1900-01-00
		if (((int)serialDate) == 0) {
			switch (_dateFieldId) {
				case Calendar.YEAR: return 1900;
				case Calendar.MONTH: return 1;
				case Calendar.DAY_OF_MONTH: return 0;
			}
			// They want time, that's normal
		}

		// TODO Figure out if we're in 1900 or 1904
		// EXCEL functions round up nearly a half second (probably to prevent floating point
		// rounding issues); use UTC here to prevent daylight saving issues for HOUR
		Calendar c = DateUtil.getJavaCalendarUTC(serialDate + 0.4995 / DateUtil.SECONDS_PER_DAY, false);
		int result = c.get(_dateFieldId);

		// Month is a special case due to C semantics
		if (_dateFieldId == Calendar.MONTH) {
			result++;
		}

		return result;
	}
}