package eu.dnetlib.openaire.common;

import java.text.FieldPosition;
import java.util.*;

import com.fasterxml.jackson.databind.util.StdDateFormat;

public class RFC3339DateFormat extends StdDateFormat {

	private static final TimeZone TIMEZONE_Z = TimeZone.getTimeZone("UTC");

	// Same as ISO8601DateFormat but serializing milliseconds.
	@Override
	public StringBuffer format(Date date, StringBuffer toAppendTo, FieldPosition fieldPosition) {
		String value = format(date, true, TIMEZONE_Z, Locale.US);
		toAppendTo.append(value);
		return toAppendTo;
	}

	/**
	 * Format date into yyyy-MM-ddThh:mm:ss[.sss][Z|[+-]hh:mm]
	 *
	 * @param date   the date to format
	 * @param millis true to include millis precision otherwise false
	 * @param tz     timezone to use for the formatting (UTC will produce 'Z')
	 * @return the date formatted as yyyy-MM-ddThh:mm:ss[.sss][Z|[+-]hh:mm]
	 */
	private static String format(Date date, boolean millis, TimeZone tz, Locale loc) {
		Calendar calendar = new GregorianCalendar(tz, loc);
		calendar.setTime(date);

		// estimate capacity of buffer as close as we can (yeah, that's pedantic ;)
		StringBuilder sb = new StringBuilder(30);
		sb.append(String.format(
				"%04d-%02d-%02dT%02d:%02d:%02d",
				calendar.get(Calendar.YEAR),
				calendar.get(Calendar.MONTH) + 1,
				calendar.get(Calendar.DAY_OF_MONTH),
				calendar.get(Calendar.HOUR_OF_DAY),
				calendar.get(Calendar.MINUTE),
				calendar.get(Calendar.SECOND)
		));
		if (millis) {
			sb.append(String.format(".%03d", calendar.get(Calendar.MILLISECOND)));
		}

		int offset = tz.getOffset(calendar.getTimeInMillis());
		if (offset != 0) {
			int hours = Math.abs((offset / (60 * 1000)) / 60);
			int minutes = Math.abs((offset / (60 * 1000)) % 60);
			sb.append(String.format("%c%02d:%02d",
					(offset < 0 ? '-' : '+'),
					hours, minutes));
		} else {
			sb.append('Z');
		}
		return sb.toString();
	}

}