package eu.dnetlib.dhp.utils.saxon;

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.GregorianCalendar;

import net.sf.saxon.expr.XPathContext;
import net.sf.saxon.om.Item;
import net.sf.saxon.om.Sequence;
import net.sf.saxon.trans.XPathException;
import net.sf.saxon.value.SequenceType;
import net.sf.saxon.value.StringValue;

public class ExtractYear extends AbstractExtensionFunction {

	private static final String[] dateFormats = {
		"yyyy-MM-dd", "yyyy/MM/dd"
	};

	@Override
	public String getName() {
		return "extractYear";
	}

	@Override
	public Sequence doCall(XPathContext context, Sequence[] arguments) throws XPathException {
		if (arguments == null || arguments.length == 0) {
			return new StringValue("");
		}
		final Item item = arguments[0].head();
		if (item == null) {
			return new StringValue("");
		}
		return new StringValue(_year(item.getStringValue()));
	}

	@Override
	public int getMinimumNumberOfArguments() {
		return 0;
	}

	@Override
	public int getMaximumNumberOfArguments() {
		return 1;
	}

	@Override
	public SequenceType[] getArgumentTypes() {
		return new SequenceType[] {
			SequenceType.OPTIONAL_ITEM
		};
	}

	@Override
	public SequenceType getResultType(SequenceType[] suppliedArgumentTypes) {
		return SequenceType.SINGLE_STRING;
	}

	private String _year(String s) {
		Calendar c = new GregorianCalendar();
		for (String format : dateFormats) {
			try {
				c.setTime(new SimpleDateFormat(format).parse(s));
				return String.valueOf(c.get(Calendar.YEAR));
			} catch (ParseException e) {
			}
		}
		return "";
	}
}