// License: GPL. For details, see LICENSE file.
package org.openstreetmap.josm.tools;

import java.text.ParsePosition;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
import java.util.GregorianCalendar;
import java.util.TimeZone;

import javax.xml.datatype.DatatypeConfigurationException;
import javax.xml.datatype.DatatypeFactory;
import javax.xml.datatype.XMLGregorianCalendar;

/**
 * A static utility class dealing with parsing XML date quickly and formatting
 * a date to the XML UTC format regardless of current locale.
 *
 * @author nenik
 */
public final class DateUtils {
    private DateUtils() {}
    /**
     * A shared instance used for conversion between individual date fields
     * and long millis time. It is guarded against conflict by the class lock.
     * The shared instance is used because the construction, together
     * with the timezone lookup, is very expensive.
     */
    private static GregorianCalendar calendar = new GregorianCalendar(TimeZone.getTimeZone("UTC"));
    private static final DatatypeFactory XML_DATE;

    static {
        calendar.setTimeInMillis(0);

        DatatypeFactory fact = null;
        try {
            fact = DatatypeFactory.newInstance();
        } catch(DatatypeConfigurationException ce) {
            ce.printStackTrace();
        }
        XML_DATE = fact;
    }

    public static synchronized Date fromString(String str) {
        // "2007-07-25T09:26:24{Z|{+|-}01:00}"
        if (checkLayout(str, "xxxx-xx-xxTxx:xx:xxZ") ||
                checkLayout(str, "xxxx-xx-xxTxx:xx:xx") ||
                checkLayout(str, "xxxx-xx-xxTxx:xx:xx+xx:00") ||
                checkLayout(str, "xxxx-xx-xxTxx:xx:xx-xx:00")) {
            calendar.set(
                parsePart(str, 0, 4),
                parsePart(str, 5, 2)-1,
                parsePart(str, 8, 2),
                parsePart(str, 11, 2),
                parsePart(str, 14,2),
                parsePart(str, 17, 2));

            if (str.length() == 25) {
                int plusHr = parsePart(str, 20, 2);
                int mul = str.charAt(19) == '+' ? -3600000 : 3600000;
                calendar.setTimeInMillis(calendar.getTimeInMillis()+plusHr*mul);
            }

            return calendar.getTime();
        }
        else if(checkLayout(str, "xxxx-xx-xxTxx:xx:xx.xxxZ") ||
                checkLayout(str, "xxxx-xx-xxTxx:xx:xx.xxx") ||
                checkLayout(str, "xxxx-xx-xxTxx:xx:xx.xxx+xx:00") ||
                checkLayout(str, "xxxx-xx-xxTxx:xx:xx.xxx-xx:00")) {
            calendar.set(
                parsePart(str, 0, 4),
                parsePart(str, 5, 2)-1,
                parsePart(str, 8, 2),
                parsePart(str, 11, 2),
                parsePart(str, 14,2),
                parsePart(str, 17, 2));
            long millis = parsePart(str, 20, 3);
            if (str.length() == 29)
                millis += parsePart(str, 24, 2) * (str.charAt(23) == '+' ? -3600000 : 3600000);
            calendar.setTimeInMillis(calendar.getTimeInMillis()+millis);

            return calendar.getTime();
        }
        else
        {
            // example date format "18-AUG-08 13:33:03"
            SimpleDateFormat f = new SimpleDateFormat("dd-MMM-yy HH:mm:ss");
            Date d = f.parse(str, new ParsePosition(0));
            if(d != null)
                return d;
        }

        try {
            return XML_DATE.newXMLGregorianCalendar(str).toGregorianCalendar().getTime();
        } catch (Exception ex) {
            return new Date();
        }
    }

    public static synchronized String fromDate(Date date) {
        calendar.setTime(date);
        XMLGregorianCalendar xgc = XML_DATE.newXMLGregorianCalendar(calendar);
        if (calendar.get(Calendar.MILLISECOND) == 0) xgc.setFractionalSecond(null);
        return xgc.toXMLFormat();
    }

    private static boolean checkLayout(String text, String pattern) {
        if (text.length() != pattern.length()) return false;
        for (int i=0; i<pattern.length(); i++) {
            char pc = pattern.charAt(i);
            char tc = text.charAt(i);
            if(pc == 'x' && tc >= '0' && tc <= '9') continue;
            else if(pc == 'x' || pc != tc) return false;
        }
        return true;
    }

    private static int parsePart(String str, int off, int len) {
        return Integer.valueOf(str.substring(off, off+len));
    }

}