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

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

import org.apache.poi.ss.util.DateParser;
import org.apache.poi.ss.formula.eval.BlankEval;
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 for the DATEVALUE() Excel function.<p>
 *
 * <b>Syntax:</b><br>
 * <b>DATEVALUE</b>(<b>date_text</b>)<p>
 * <p>
 * The <b>DATEVALUE</b> function converts a date that is stored as text to a serial number that Excel
 * recognizes as a date. For example, the formula <b>=DATEVALUE("1/1/2008")</b> returns 39448, the
 * serial number of the date 1/1/2008. Remember, though, that your computer's system date setting may
 * cause the results of a <b>DATEVALUE</b> function to vary from this example
 * <p>
 * The <b>DATEVALUE</b> function is helpful in cases where a worksheet contains dates in a text format
 * that you want to filter, sort, or format as dates, or use in date calculations.
 * <p>
 * To view a date serial number as a date, you must apply a date format to the cell. Find links to more
 * information about displaying numbers as dates in the See Also section.
 */
public class DateValue extends Fixed1ArgFunction {

    @Override
    public ValueEval evaluate(int srcRowIndex, int srcColumnIndex, ValueEval dateTextArg) {
        try {
            String dateText = OperandResolver.coerceValueToString(
                    OperandResolver.getSingleValue(dateTextArg, srcRowIndex, srcColumnIndex));

            if (dateText == null || dateText.isEmpty()) {
                return BlankEval.instance;
            }

            return new NumberEval(DateUtil.getExcelDate(DateParser.parseLocalDate(dateText)));
        } catch (EvaluationException e) {
            return e.getErrorEval();
        }
    }
}