/*
 * 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
 *
 *      https://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.
     *
     * <p>
     * Note: the underlying regex is lenient — every capture group (sign, hours, minutes, and the {@code GMT} prefix) is optional. Inputs that lack any digit
     * group, such as the empty string, {@code "+"}, {@code "-"}, or {@code "GMT"} alone, still match and the method returns the GMT TimeZone with a raw offset
     * of zero (mirroring {@link TimeZone#getTimeZone(String)} JDK-parity for unrecognized ids). Inputs that fail the regex outright, or that match but specify
     * an out-of-range offset (24 hours or 60 minutes and above), return {@code null}.
     * </p>
     *
     * @param pattern The GMT offset.
     * @return A TimeZone matching the (possibly partial or empty) GMT offset pattern, defaulting to GMT for an unrecognized but parseable input, or
     *         {@code null} if the pattern fails the regex or specifies an out-of-range offset.
     */
    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;
            }
            if (hours >= 24 || minutes >= 60) {
                // A matching but out-of-range offset is not a valid GMT id; report it the documented
                // way instead of letting the GmtTimeZone constructor throw IllegalArgumentException.
                return null;
            }
            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);
        return tz != null ? tz : TimeZones.getTimeZone(id);
    }

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

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

    // do not instantiate
    private FastTimeZone() {
    }

}