/*
 * 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.Calendar;
import java.util.Date;
import java.util.Locale;
import java.util.TimeZone;

/**
 * <p>
 * Date and time formatting utilities and constants.
 * </p>
 *
 * <p>
 * Formatting is performed using the thread-safe
 * {@link org.apache.commons.lang3.time.FastDateFormat} class.
 * </p>
 *
 * <p>
 * Note that the JDK has a bug wherein calling Calendar.get(int) will override
 * any previously called Calendar.clear() calls. See LANG-755.
 * </p>
 *
 * @since 2.0
 */
public class DateFormatUtils {

	/**
	 * The UTC time zone (often referred to as GMT). This is private as it is
	 * mutable.
	 */
	private static final TimeZone UTC_TIME_ZONE = FastTimeZone.getGmtTimeZone();

	/**
	 * ISO 8601 formatter for date-time without time zone.
	 *
	 * <p>
	 * The format used is {@code yyyy-MM-dd'T'HH:mm:ss}. This format uses the
	 * default TimeZone in effect at the time of loading DateFormatUtils class.
	 * </p>
	 *
	 * @since 3.5
	 */
	public static final FastDateFormat ISO_8601_EXTENDED_DATETIME_FORMAT = FastDateFormat
			.getInstance("yyyy-MM-dd'T'HH:mm:ss");

	/**
	 * @deprecated - as of 4.0, ISO_DATETIME_FORMAT will be replaced by
	 *             ISO_8601_EXTENDED_DATETIME_FORMAT.
	 */
	@Deprecated
	public static final FastDateFormat ISO_DATETIME_FORMAT = ISO_8601_EXTENDED_DATETIME_FORMAT;

	/**
	 * ISO 8601 formatter for date-time with time zone.
	 *
	 * <p>
	 * The format used is {@code yyyy-MM-dd'T'HH:mm:ssZZ}. This format uses the
	 * default TimeZone in effect at the time of loading DateFormatUtils class.
	 * </p>
	 *
	 * @since 3.5
	 */
	public static final FastDateFormat ISO_8601_EXTENDED_DATETIME_TIME_ZONE_FORMAT = FastDateFormat
			.getInstance("yyyy-MM-dd'T'HH:mm:ssZZ");

	/**
	 * @deprecated - as of 4.0, ISO_DATETIME_TIME_ZONE_FORMAT will be replaced by
	 *             ISO_8601_EXTENDED_DATETIME_TIME_ZONE_FORMAT.
	 */
	@Deprecated
	public static final FastDateFormat ISO_DATETIME_TIME_ZONE_FORMAT = ISO_8601_EXTENDED_DATETIME_TIME_ZONE_FORMAT;

	/**
	 * ISO 8601 formatter for date without time zone.
	 *
	 * <p>
	 * The format used is {@code yyyy-MM-dd}. This format uses the default TimeZone
	 * in effect at the time of loading DateFormatUtils class.
	 * </p>
	 *
	 * @since 3.5
	 */
	public static final FastDateFormat ISO_8601_EXTENDED_DATE_FORMAT = FastDateFormat.getInstance("yyyy-MM-dd");

	/**
	 * @deprecated - as of 4.0, ISO_DATE_FORMAT will be replaced by
	 *             ISO_8601_EXTENDED_DATE_FORMAT.
	 */
	@Deprecated
	public static final FastDateFormat ISO_DATE_FORMAT = ISO_8601_EXTENDED_DATE_FORMAT;

	/**
	 * ISO 8601-like formatter for date with time zone.
	 *
	 * <p>
	 * The format used is {@code yyyy-MM-ddZZ}. This pattern does not comply with
	 * the formal ISO 8601 specification as the standard does not allow a time zone
	 * without a time. This format uses the default TimeZone in effect at the time
	 * of loading DateFormatUtils class.
	 * </p>
	 *
	 * @deprecated - as of 4.0, ISO_DATE_TIME_ZONE_FORMAT will be removed.
	 */
	@Deprecated
	public static final FastDateFormat ISO_DATE_TIME_ZONE_FORMAT = FastDateFormat.getInstance("yyyy-MM-ddZZ");

	/**
	 * Non-compliant formatter for time without time zone (ISO 8601 does not prefix
	 * 'T' for standalone time value).
	 *
	 * <p>
	 * The format used is {@code 'T'HH:mm:ss}. This format uses the default TimeZone
	 * in effect at the time of loading DateFormatUtils class.
	 * </p>
	 *
	 * @deprecated - as of 4.0, ISO_TIME_FORMAT will be removed.
	 */
	@Deprecated
	public static final FastDateFormat ISO_TIME_FORMAT = FastDateFormat.getInstance("'T'HH:mm:ss");

	/**
	 * Non-compliant formatter for time with time zone (ISO 8601 does not prefix 'T'
	 * for standalone time value).
	 *
	 * <p>
	 * The format used is {@code 'T'HH:mm:ssZZ}. This format uses the default
	 * TimeZone in effect at the time of loading DateFormatUtils class.
	 * </p>
	 *
	 * @deprecated - as of 4.0, ISO_TIME_TIME_ZONE_FORMAT will be removed.
	 */
	@Deprecated
	public static final FastDateFormat ISO_TIME_TIME_ZONE_FORMAT = FastDateFormat.getInstance("'T'HH:mm:ssZZ");

	/**
	 * ISO 8601 formatter for time without time zone.
	 *
	 * <p>
	 * The format used is {@code HH:mm:ss}. This format uses the default TimeZone in
	 * effect at the time of loading DateFormatUtils class.
	 * </p>
	 *
	 * @since 3.5
	 */
	public static final FastDateFormat ISO_8601_EXTENDED_TIME_FORMAT = FastDateFormat.getInstance("HH:mm:ss");

	/**
	 * @deprecated - as of 4.0, ISO_TIME_NO_T_FORMAT will be replaced by
	 *             ISO_8601_EXTENDED_TIME_FORMAT.
	 */
	@Deprecated
	public static final FastDateFormat ISO_TIME_NO_T_FORMAT = ISO_8601_EXTENDED_TIME_FORMAT;

	/**
	 * ISO 8601 formatter for time with time zone.
	 *
	 * <p>
	 * The format used is {@code HH:mm:ssZZ}. This format uses the default TimeZone
	 * in effect at the time of loading DateFormatUtils class.
	 * </p>
	 *
	 * @since 3.5
	 */
	public static final FastDateFormat ISO_8601_EXTENDED_TIME_TIME_ZONE_FORMAT = FastDateFormat
			.getInstance("HH:mm:ssZZ");

	/**
	 * @deprecated - as of 4.0, ISO_TIME_NO_T_TIME_ZONE_FORMAT will be replaced by
	 *             ISO_8601_EXTENDED_TIME_TIME_ZONE_FORMAT.
	 */
	@Deprecated
	public static final FastDateFormat ISO_TIME_NO_T_TIME_ZONE_FORMAT = ISO_8601_EXTENDED_TIME_TIME_ZONE_FORMAT;

	/**
	 * SMTP (and probably other) date headers.
	 *
	 * <p>
	 * The format used is {@code EEE, dd MMM yyyy HH:mm:ss Z} in US locale. This
	 * format uses the default TimeZone in effect at the time of loading
	 * DateFormatUtils class.
	 * </p>
	 */
	public static final FastDateFormat SMTP_DATETIME_FORMAT = FastDateFormat.getInstance("EEE, dd MMM yyyy HH:mm:ss Z",
			Locale.US);

	// -----------------------------------------------------------------------
	/**
	 * <p>
	 * DateFormatUtils instances should NOT be constructed in standard programming.
	 * </p>
	 *
	 * <p>
	 * This constructor is public to permit tools that require a JavaBean instance
	 * to operate.
	 * </p>
	 */
	public DateFormatUtils() {
	}

	/**
	 * <p>
	 * Formats a date/time into a specific pattern using the UTC time zone.
	 * </p>
	 *
	 * @param millis  the date to format expressed in milliseconds
	 * @param pattern the pattern to use to format the date, not null
	 * @return the formatted date
	 */
	public static String formatUTC(final long millis, final String pattern) {
		return format(new Date(millis), pattern, UTC_TIME_ZONE, null);
	}

	/**
	 * <p>
	 * Formats a date/time into a specific pattern using the UTC time zone.
	 * </p>
	 *
	 * @param date    the date to format, not null
	 * @param pattern the pattern to use to format the date, not null
	 * @return the formatted date
	 */
	public static String formatUTC(final Date date, final String pattern) {
		return format(date, pattern, UTC_TIME_ZONE, null);
	}

	/**
	 * <p>
	 * Formats a date/time into a specific pattern using the UTC time zone.
	 * </p>
	 *
	 * @param millis  the date to format expressed in milliseconds
	 * @param pattern the pattern to use to format the date, not null
	 * @param locale  the locale to use, may be {@code null}
	 * @return the formatted date
	 */
	public static String formatUTC(final long millis, final String pattern, final Locale locale) {
		return format(new Date(millis), pattern, UTC_TIME_ZONE, locale);
	}

	/**
	 * <p>
	 * Formats a date/time into a specific pattern using the UTC time zone.
	 * </p>
	 *
	 * @param date    the date to format, not null
	 * @param pattern the pattern to use to format the date, not null
	 * @param locale  the locale to use, may be {@code null}
	 * @return the formatted date
	 */
	public static String formatUTC(final Date date, final String pattern, final Locale locale) {
		return format(date, pattern, UTC_TIME_ZONE, locale);
	}

	/**
	 * <p>
	 * Formats a date/time into a specific pattern.
	 * </p>
	 *
	 * @param millis  the date to format expressed in milliseconds
	 * @param pattern the pattern to use to format the date, not null
	 * @return the formatted date
	 */
	public static String format(final long millis, final String pattern) {
		return format(new Date(millis), pattern, null, null);
	}

	/**
	 * <p>
	 * Formats a date/time into a specific pattern.
	 * </p>
	 *
	 * @param date    the date to format, not null
	 * @param pattern the pattern to use to format the date, not null
	 * @return the formatted date
	 */
	public static String format(final Date date, final String pattern) {
		return format(date, pattern, null, null);
	}

	/**
	 * <p>
	 * Formats a calendar into a specific pattern.
	 * </p>
	 *
	 * @param calendar the calendar to format, not null
	 * @param pattern  the pattern to use to format the calendar, not null
	 * @return the formatted calendar
	 * @see FastDateFormat#format(Calendar)
	 * @since 2.4
	 */
	public static String format(final Calendar calendar, final String pattern) {
		return format(calendar, pattern, null, null);
	}

	/**
	 * <p>
	 * Formats a date/time into a specific pattern in a time zone.
	 * </p>
	 *
	 * @param millis   the time expressed in milliseconds
	 * @param pattern  the pattern to use to format the date, not null
	 * @param timeZone the time zone to use, may be {@code null}
	 * @return the formatted date
	 */
	public static String format(final long millis, final String pattern, final TimeZone timeZone) {
		return format(new Date(millis), pattern, timeZone, null);
	}

	/**
	 * <p>
	 * Formats a date/time into a specific pattern in a time zone.
	 * </p>
	 *
	 * @param date     the date to format, not null
	 * @param pattern  the pattern to use to format the date, not null
	 * @param timeZone the time zone to use, may be {@code null}
	 * @return the formatted date
	 */
	public static String format(final Date date, final String pattern, final TimeZone timeZone) {
		return format(date, pattern, timeZone, null);
	}

	/**
	 * <p>
	 * Formats a calendar into a specific pattern in a time zone.
	 * </p>
	 *
	 * @param calendar the calendar to format, not null
	 * @param pattern  the pattern to use to format the calendar, not null
	 * @param timeZone the time zone to use, may be {@code null}
	 * @return the formatted calendar
	 * @see FastDateFormat#format(Calendar)
	 * @since 2.4
	 */
	public static String format(final Calendar calendar, final String pattern, final TimeZone timeZone) {
		return format(calendar, pattern, timeZone, null);
	}

	/**
	 * <p>
	 * Formats a date/time into a specific pattern in a locale.
	 * </p>
	 *
	 * @param millis  the date to format expressed in milliseconds
	 * @param pattern the pattern to use to format the date, not null
	 * @param locale  the locale to use, may be {@code null}
	 * @return the formatted date
	 */
	public static String format(final long millis, final String pattern, final Locale locale) {
		return format(new Date(millis), pattern, null, locale);
	}

	/**
	 * <p>
	 * Formats a date/time into a specific pattern in a locale.
	 * </p>
	 *
	 * @param date    the date to format, not null
	 * @param pattern the pattern to use to format the date, not null
	 * @param locale  the locale to use, may be {@code null}
	 * @return the formatted date
	 */
	public static String format(final Date date, final String pattern, final Locale locale) {
		return format(date, pattern, null, locale);
	}

	/**
	 * <p>
	 * Formats a calendar into a specific pattern in a locale.
	 * </p>
	 *
	 * @param calendar the calendar to format, not null
	 * @param pattern  the pattern to use to format the calendar, not null
	 * @param locale   the locale to use, may be {@code null}
	 * @return the formatted calendar
	 * @see FastDateFormat#format(Calendar)
	 * @since 2.4
	 */
	public static String format(final Calendar calendar, final String pattern, final Locale locale) {
		return format(calendar, pattern, null, locale);
	}

	/**
	 * <p>
	 * Formats a date/time into a specific pattern in a time zone and locale.
	 * </p>
	 *
	 * @param millis   the date to format expressed in milliseconds
	 * @param pattern  the pattern to use to format the date, not null
	 * @param timeZone the time zone to use, may be {@code null}
	 * @param locale   the locale to use, may be {@code null}
	 * @return the formatted date
	 */
	public static String format(final long millis, final String pattern, final TimeZone timeZone, final Locale locale) {
		return format(new Date(millis), pattern, timeZone, locale);
	}

	/**
	 * <p>
	 * Formats a date/time into a specific pattern in a time zone and locale.
	 * </p>
	 *
	 * @param date     the date to format, not null
	 * @param pattern  the pattern to use to format the date, not null, not null
	 * @param timeZone the time zone to use, may be {@code null}
	 * @param locale   the locale to use, may be {@code null}
	 * @return the formatted date
	 */
	public static String format(final Date date, final String pattern, final TimeZone timeZone, final Locale locale) {
		final FastDateFormat df = FastDateFormat.getInstance(pattern, timeZone, locale);
		return df.format(date);
	}

	/**
	 * <p>
	 * Formats a calendar into a specific pattern in a time zone and locale.
	 * </p>
	 *
	 * @param calendar the calendar to format, not null
	 * @param pattern  the pattern to use to format the calendar, not null
	 * @param timeZone the time zone to use, may be {@code null}
	 * @param locale   the locale to use, may be {@code null}
	 * @return the formatted calendar
	 * @see FastDateFormat#format(Calendar)
	 * @since 2.4
	 */
	public static String format(final Calendar calendar, final String pattern, final TimeZone timeZone,
			final Locale locale) {
		final FastDateFormat df = FastDateFormat.getInstance(pattern, timeZone, locale);
		return df.format(calendar);
	}

}
