/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * 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
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.commons.lang3.time;

import java.util.TimeZone;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 * Faster methods to produce custom time zones.
 *
 * @since 3.7
 */
public class FastTimeZone {

	private static final Pattern GMT_PATTERN = Pattern.compile("^(?:(?i)GMT)?([+-])?(\\d\\d?)?(:?(\\d\\d?))?$");

	private static final TimeZone GREENWICH = new GmtTimeZone(false, 0, 0);

	/**
	 * Gets the GMT TimeZone.
	 * 
	 * @return A TimeZone with a raw offset of zero.
	 */
	public static TimeZone getGmtTimeZone() {
		return GREENWICH;
	}

	/**
	 * Gets a TimeZone with GMT offsets. A GMT offset must be either 'Z', or 'UTC',
	 * or match <em>(GMT)? hh?(:?mm?)?</em>, where h and m are digits representing
	 * hours and minutes.
	 *
	 * @param pattern The GMT offset
	 * @return A TimeZone with offset from GMT or null, if pattern does not match.
	 */
	public static TimeZone getGmtTimeZone(final String pattern) {
		if ("Z".equals(pattern) || "UTC".equals(pattern)) {
			return GREENWICH;
		}

		final Matcher m = GMT_PATTERN.matcher(pattern);
		if (m.matches()) {
			final int hours = parseInt(m.group(2));
			final int minutes = parseInt(m.group(4));
			if (hours == 0 && minutes == 0) {
				return GREENWICH;
			}
			return new GmtTimeZone(parseSign(m.group(1)), hours, minutes);
		}
		return null;
	}

	/**
	 * Gets a TimeZone, looking first for GMT custom ids, then falling back to Olson
	 * ids. A GMT custom id can be 'Z', or 'UTC', or has an optional prefix of GMT,
	 * followed by sign, hours digit(s), optional colon(':'), and optional minutes
	 * digits. i.e. <em>[GMT] (+|-) Hours [[:] Minutes]</em>
	 *
	 * @param id A GMT custom id (or Olson id
	 * @return A time zone
	 */
	public static TimeZone getTimeZone(final String id) {
		final TimeZone tz = getGmtTimeZone(id);
		if (tz != null) {
			return tz;
		}
		return TimeZone.getTimeZone(id);
	}

	private static int parseInt(final String group) {
		return group != null ? Integer.parseInt(group) : 0;
	}

	private static boolean parseSign(final String group) {
		return group != null && group.charAt(0) == '-';
	}

	// do not instantiate
	private FastTimeZone() {
	}

}
