/*
 * Copyright (c) 2007-2013, Stephen Colebourne & Michael Nascimento Santos
 *
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 *  * Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 *
 *  * Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 *
 *  * Neither the name of JSR-310 nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
package org.threeten.bp.format;

import static org.threeten.bp.temporal.ChronoField.DAY_OF_MONTH;
import static org.threeten.bp.temporal.ChronoField.DAY_OF_WEEK;
import static org.threeten.bp.temporal.ChronoField.DAY_OF_YEAR;
import static org.threeten.bp.temporal.ChronoField.HOUR_OF_DAY;
import static org.threeten.bp.temporal.ChronoField.MINUTE_OF_HOUR;
import static org.threeten.bp.temporal.ChronoField.MONTH_OF_YEAR;
import static org.threeten.bp.temporal.ChronoField.NANO_OF_SECOND;
import static org.threeten.bp.temporal.ChronoField.SECOND_OF_MINUTE;
import static org.threeten.bp.temporal.ChronoField.YEAR;

import java.util.HashMap;
import java.util.Locale;
import java.util.Map;
import java.util.Objects;

import org.threeten.bp.ZoneId;
import org.threeten.bp.ZoneOffset;
import org.threeten.bp.temporal.ChronoField;
import org.threeten.bp.temporal.ISOFields;
import org.threeten.bp.temporal.TemporalField;

/**
 * Provides common implementations of {@code DateTimeFormatter}.
 * <p>
 * This utility class provides three different ways to obtain a formatter.
 * <p><ul>
 * <li>Using pattern letters, such as {@code yyyy-MMM-dd}
 * <li>Using localized styles, such as {@code long} or {@code medium}
 * <li>Using predefined constants, such as {@code isoLocalDate()}
 * </ul><p>
 *
 * <h3>Specification for implementors</h3>
 * This is a thread-safe utility class.
 * All returned formatters are immutable and thread-safe.
 */
public final class DateTimeFormatters {

    /**
     * Private constructor since this is a utility class.
     */
    private DateTimeFormatters() {
    }

    //-----------------------------------------------------------------------
    /**
     * Creates a formatter using the specified pattern.
     * <p>
     * This method will create a formatter based on a simple pattern of letters and symbols.
     * For example, {@code d MMM yyyy} will format 2011-12-03 as '3 Dec 2011'.
     * <p>
     * The returned formatter will use the default locale, but this can be changed
     * using {@link DateTimeFormatter#withLocale(Locale)}.
     * <p>
     * All letters 'A' to 'Z' and 'a' to 'z' are reserved as pattern letters.
     * The following pattern letters are defined:
     * <pre>
     *  Symbol  Meaning                     Presentation      Examples
     *  ------  -------                     ------------      -------
     *   G       era                         number/text       1; 01; AD; Anno Domini
     *   y       year                        year              2004; 04
     *   D       day-of-year                 number            189
     *   M       month-of-year               number/text       7; 07; Jul; July; J
     *   d       day-of-month                number            10
     *
     *   Q       quarter-of-year             number/text       3; 03; Q3
     *   Y       week-based-year             year              1996; 96
     *   w       week-of-year                number            27
     *   W       week-of-month               number            27
     *   e       localized day-of-week       number            2; Tue; Tuesday; T
     *   E       day-of-week                 number/text       2; Tue; Tuesday; T
     *   F       week-of-month               number            3
     *
     *   a       am-pm-of-day                text              PM
     *   h       clock-hour-of-am-pm (1-12)  number            12
     *   K       hour-of-am-pm (0-11)        number            0
     *   k       clock-hour-of-am-pm (1-24)  number            0
     *
     *   H       hour-of-day (0-23)          number            0
     *   m       minute-of-hour              number            30
     *   s       second-of-minute            number            55
     *   S       fraction-of-second          fraction          978
     *   A       milli-of-day                number            1234
     *   n       nano-of-second              number            987654321
     *   N       nano-of-day                 number            1234000000
     *
     *   I       time-zone ID                zoneId            America/Los_Angeles
     *   z       time-zone name              text              Pacific Standard Time; PST
     *   Z       zone-offset                 offset-Z          +0000; -0800; -08:00;
     *   X       zone-offset 'Z' for zero    offset-X          Z; -08; -0830; -08:30; -083015; -08:30:15;
     *
     *   p       pad next                    pad modifier      1
     *
     *   '       escape for text             delimiter
     *   ''      single quote                literal           '
     *   [       optional section start
     *   ]       optional section end
     *   {}      reserved for future use
     * </pre>
     * <p>
     * The count of pattern letters determine the format.
     * <p>
     * <b>Text</b>: The text style is determined based on the number of pattern letters used.
     * Less than 4 pattern letters will use the {@link TextStyle#SHORT short form}.
     * Exactly 4 pattern letters will use the {@link TextStyle#FULL full form}.
     * Exactly 5 pattern letters will use the {@link TextStyle#NARROW narrow form}.
     * <p>
     * <b>Number</b>: If the count of letters is one, then the value is printed using the minimum number
     * of digits and without padding as per {@link DateTimeFormatterBuilder#appendValue(TemporalField)}.
     * Otherwise, the count of digits is used as the width of the output field as per
     * {@link DateTimeFormatterBuilder#appendValue(TemporalField, int)}.
     * <p>
     * <b>Number/Text</b>: If the count of pattern letters is 3 or greater, use the Text rules above.
     * Otherwise use the Number rules above.
     * <p>
     * <b>Fraction</b>: Outputs the nano-of-second field as a fraction-of-second.
     * The nano-of-second value has nine digits, thus the count of pattern letters is from 1 to 9.
     * If it is less than 9, then the nano-of-second value is truncated, with only the most
     * significant digits being output.
     * When parsing in strict mode, the number of parsed digits must match the count of pattern letters.
     * When parsing in lenient mode, the number of parsed digits must be at least the count of pattern
     * letters, up to 9 digits.
     * <p>
     * <b>Year</b>: The count of letters determines the minimum field width below which padding is used.
     * If the count of letters is two, then a {@link DateTimeFormatterBuilder#appendValueReduced reduced}
     * two digit form is used.
     * For printing, this outputs the rightmost two digits. For parsing, this will parse using the
     * base value of 2000, resulting in a year within the range 2000 to 2099 inclusive.
     * If the count of letters is less than four (but not two), then the sign is only output for negative
     * years as per {@link SignStyle#NORMAL}.
     * Otherwise, the sign is output if the pad width is exceeded, as per {@link SignStyle#EXCEEDS_PAD}
     * <p>
     * <b>ZoneId</b>: 'I' outputs the zone ID, such as 'Europe/Paris'.
     * <p>
     * <b>Offset X</b>: This formats the offset using 'Z' when the offset is zero.
     * One letter outputs just the hour', such as '+01'
     * Two letters outputs the hour and minute, without a colon, such as '+0130'.
     * Three letters outputs the hour and minute, with a colon, such as '+01:30'.
     * Four letters outputs the hour and minute and optional second, without a colon, such as '+013015'.
     * Five letters outputs the hour and minute and optional second, with a colon, such as '+01:30:15'.
     * <p>
     * <b>Offset Z</b>: This formats the offset using '+0000' or '+00:00' when the offset is zero.
     * One or two letters outputs the hour and minute, without a colon, such as '+0130'.
     * Three letters outputs the hour and minute, with a colon, such as '+01:30'.
     * <p>
     * <b>Zone names</b>: Time zone names ('z') cannot be parsed.
     * <p>
     * <b>Optional section</b>: The optional section markers work exactly like calling
     * {@link DateTimeFormatterBuilder#optionalStart()} and {@link DateTimeFormatterBuilder#optionalEnd()}.
     * <p>
     * <b>Pad modifier</b>: Modifies the pattern that immediately follows to be padded with spaces.
     * The pad width is determined by the number of pattern letters.
     * This is the same as calling {@link DateTimeFormatterBuilder#padNext(int)}.
     * <p>
     * For example, 'ppH' outputs the hour-of-day padded on the left with spaces to a width of 2.
     * <p>
     * Any unrecognized letter is an error.
     * Any non-letter character, other than '[', ']', '{', '}' and the single quote will be output directly.
     * Despite this, it is recommended to use single quotes around all characters that you want to
     * output directly to ensure that future changes do not break your application.
     * <p>
     * The pattern string is similar, but not identical, to {@link java.text.SimpleDateFormat SimpleDateFormat}.
     * Pattern letters 'E' and 'u' are merged, which changes the meaning of "E" and "EE" to be numeric.
     * Pattern letters 'Z' and 'X' are extended.
     * Pattern letter 'y' and 'Y' parse years of two digits and more than 4 digits differently.
     * Pattern letters 'n', 'A', 'N', 'I' and 'p' are added.
     * Number types will reject large numbers.
     * The pattern string is also similar, but not identical, to that defined by the
     * Unicode Common Locale Data Repository (CLDR).
     *
     * @param pattern  the pattern to use, not null
     * @return the formatter based on the pattern, not null
     * @throws IllegalArgumentException if the pattern is invalid
     * @see DateTimeFormatterBuilder#appendPattern(String)
     */
    public static DateTimeFormatter pattern(String pattern) {
        return new DateTimeFormatterBuilder().appendPattern(pattern).toFormatter();
    }

    /**
     * Creates a formatter using the specified pattern.
     * <p>
     * This method will create a formatter based on a simple pattern of letters and symbols.
     * For example, {@code d MMM yyyy} will format 2011-12-03 as '3 Dec 2011'.
     * <p>
     * See {@link #pattern(String)} for details of the pattern.
     * <p>
     * The returned formatter will use the specified locale, but this can be changed
     * using {@link DateTimeFormatter#withLocale(Locale)}.
     *
     * @param pattern  the pattern to use, not null
     * @param locale  the locale to use, not null
     * @return the formatter based on the pattern, not null
     * @throws IllegalArgumentException if the pattern is invalid
     * @see DateTimeFormatterBuilder#appendPattern(String)
     */
    public static DateTimeFormatter pattern(String pattern, Locale locale) {
        return new DateTimeFormatterBuilder().appendPattern(pattern).toFormatter(locale);
    }

    //-----------------------------------------------------------------------
    /**
     * Returns a locale specific date format.
     * <p>
     * This returns a formatter that will print/parse a date.
     * The exact format pattern used varies by locale.
     * <p>
     * The locale is determined from the formatter. The formatter returned directly by
     * this method will use the {@link Locale#getDefault() default locale}.
     * The locale can be controlled using {@link DateTimeFormatter#withLocale(Locale) withLocale(Locale)}
     * on the result of this method.
     * <p>
     * Note that the localized pattern is looked up lazily.
     * This {@code DateTimeFormatter} holds the style required and the locale,
     * looking up the pattern required on demand.
     *
     * @param dateStyle  the formatter style to obtain, not null
     * @return the date formatter, not null
     */
    public static DateTimeFormatter localizedDate(FormatStyle dateStyle) {
        Objects.requireNonNull(dateStyle, "dateStyle");
        return new DateTimeFormatterBuilder().appendLocalized(dateStyle, null).toFormatter();
    }

    /**
     * Returns a locale specific time format.
     * <p>
     * This returns a formatter that will print/parse a time.
     * The exact format pattern used varies by locale.
     * <p>
     * The locale is determined from the formatter. The formatter returned directly by
     * this method will use the {@link Locale#getDefault() default locale}.
     * The locale can be controlled using {@link DateTimeFormatter#withLocale(Locale) withLocale(Locale)}
     * on the result of this method.
     * <p>
     * Note that the localized pattern is looked up lazily.
     * This {@code DateTimeFormatter} holds the style required and the locale,
     * looking up the pattern required on demand.
     *
     * @param timeStyle  the formatter style to obtain, not null
     * @return the time formatter, not null
     */
    public static DateTimeFormatter localizedTime(FormatStyle timeStyle) {
        Objects.requireNonNull(timeStyle, "timeStyle");
        return new DateTimeFormatterBuilder().appendLocalized(null, timeStyle).toFormatter();
    }

    /**
     * Returns a locale specific date-time format, which is typically of short length.
     * <p>
     * This returns a formatter that will print/parse a date-time.
     * The exact format pattern used varies by locale.
     * <p>
     * The locale is determined from the formatter. The formatter returned directly by
     * this method will use the {@link Locale#getDefault() default locale}.
     * The locale can be controlled using {@link DateTimeFormatter#withLocale(Locale) withLocale(Locale)}
     * on the result of this method.
     * <p>
     * Note that the localized pattern is looked up lazily.
     * This {@code DateTimeFormatter} holds the style required and the locale,
     * looking up the pattern required on demand.
     *
     * @param dateTimeStyle  the formatter style to obtain, not null
     * @return the date-time formatter, not null
     */
    public static DateTimeFormatter localizedDateTime(FormatStyle dateTimeStyle) {
        Objects.requireNonNull(dateTimeStyle, "dateTimeStyle");
        return new DateTimeFormatterBuilder().appendLocalized(dateTimeStyle, dateTimeStyle).toFormatter();
    }

    /**
     * Returns a locale specific date and time format.
     * <p>
     * This returns a formatter that will print/parse a date-time.
     * The exact format pattern used varies by locale.
     * <p>
     * The locale is determined from the formatter. The formatter returned directly by
     * this method will use the {@link Locale#getDefault() default locale}.
     * The locale can be controlled using {@link DateTimeFormatter#withLocale(Locale) withLocale(Locale)}
     * on the result of this method.
     * <p>
     * Note that the localized pattern is looked up lazily.
     * This {@code DateTimeFormatter} holds the style required and the locale,
     * looking up the pattern required on demand.
     *
     * @param dateStyle  the date formatter style to obtain, not null
     * @param timeStyle  the time formatter style to obtain, not null
     * @return the date, time or date-time formatter, not null
     */
    public static DateTimeFormatter localizedDateTime(FormatStyle dateStyle, FormatStyle timeStyle) {
        Objects.requireNonNull(dateStyle, "dateStyle");
        Objects.requireNonNull(timeStyle, "timeStyle");
        return new DateTimeFormatterBuilder().appendLocalized(dateStyle, timeStyle).toFormatter();
    }

    //-----------------------------------------------------------------------
    /**
     * Returns the ISO date formatter that prints/parses a date without an offset,
     * such as '2011-12-03'.
     * <p>
     * This returns an immutable formatter capable of printing and parsing
     * the ISO-8601 extended local date format.
     * The format consists of:
     * <p><ul>
     * <li>Four digits or more for the {@link ChronoField#YEAR year}.
     * Years in the range 0000 to 9999 will be pre-padded by zero to ensure four digits.
     * Years outside that range will have a prefixed positive or negative symbol.
     * <li>A dash
     * <li>Two digits for the {@link ChronoField#MONTH_OF_YEAR month-of-year}.
     *  This is pre-padded by zero to ensure two digits.
     * <li>A dash
     * <li>Two digits for the {@link ChronoField#DAY_OF_MONTH day-of-month}.
     *  This is pre-padded by zero to ensure two digits.
     * </ul><p>
     *
     * @return the ISO local date formatter, not null
     */
    public static DateTimeFormatter isoLocalDate() {
        return ISO_LOCAL_DATE;
    }

    /** Singleton date formatter. */
    private static final DateTimeFormatter ISO_LOCAL_DATE;
    static {
        ISO_LOCAL_DATE = new DateTimeFormatterBuilder()
            .appendValue(YEAR, 4, 10, SignStyle.EXCEEDS_PAD)
            .appendLiteral('-')
            .appendValue(MONTH_OF_YEAR, 2)
            .appendLiteral('-')
            .appendValue(DAY_OF_MONTH, 2)
            .toFormatter();
    }

    //-----------------------------------------------------------------------
    /**
     * Returns the ISO date formatter that prints/parses a date with an offset,
     * such as '2011-12-03+01:00'.
     * <p>
     * This returns an immutable formatter capable of printing and parsing
     * the ISO-8601 extended offset date format.
     * The format consists of:
     * <p><ul>
     * <li>The {@link #isoLocalDate()}
     * <li>The {@link ZoneOffset#getId() offset ID}. If the offset has seconds then
     *  they will be handled even though this is not part of the ISO-8601 standard.
     *  Parsing is case insensitive.
     * </ul><p>
     *
     * @return the ISO offset date formatter, not null
     */
    public static DateTimeFormatter isoOffsetDate() {
        return ISO_OFFSET_DATE;
    }

    /** Singleton date formatter. */
    private static final DateTimeFormatter ISO_OFFSET_DATE;
    static {
        ISO_OFFSET_DATE = new DateTimeFormatterBuilder()
            .parseCaseInsensitive()
            .append(ISO_LOCAL_DATE)
            .appendOffsetId()
            .toFormatter();
    }

    //-----------------------------------------------------------------------
    /**
     * Returns the ISO date formatter that prints/parses a date with the
     * offset if available, such as '2011-12-03' or '2011-12-03+01:00'.
     * <p>
     * This returns an immutable formatter capable of printing and parsing
     * the ISO-8601 extended date format.
     * The format consists of:
     * <p><ul>
     * <li>The {@link #isoLocalDate()}
     * <li>If the offset is not available to print/parse then the format is complete.
     * <li>The {@link ZoneOffset#getId() offset ID}. If the offset has seconds then
     *  they will be handled even though this is not part of the ISO-8601 standard.
     *  Parsing is case insensitive.
     * </ul><p>
     * As this formatter has an optional element, it may be necessary to parse using
     * {@link DateTimeFormatter#parseBest}.
     *
     * @return the ISO date formatter, not null
     */
    public static DateTimeFormatter isoDate() {
        return ISO_DATE;
    }

    /** Singleton date formatter. */
    private static final DateTimeFormatter ISO_DATE;
    static {
        ISO_DATE = new DateTimeFormatterBuilder()
            .parseCaseInsensitive()
            .append(ISO_LOCAL_DATE)
            .optionalStart()
            .appendOffsetId()
            .toFormatter();
    }

    //-----------------------------------------------------------------------
    /**
     * Returns the ISO time formatter that prints/parses a time without an offset,
     * such as '10:15' or '10:15:30'.
     * <p>
     * This returns an immutable formatter capable of printing and parsing
     * the ISO-8601 extended local time format.
     * The format consists of:
     * <p><ul>
     * <li>Two digits for the {@link ChronoField#HOUR_OF_DAY hour-of-day}.
     *  This is pre-padded by zero to ensure two digits.
     * <li>A colon
     * <li>Two digits for the {@link ChronoField#MINUTE_OF_HOUR minute-of-hour}.
     *  This is pre-padded by zero to ensure two digits.
     * <li>If the second-of-minute is not available to print/parse then the format is complete.
     * <li>A colon
     * <li>Two digits for the {@link ChronoField#SECOND_OF_MINUTE second-of-minute}.
     *  This is pre-padded by zero to ensure two digits.
     * <li>If the nano-of-second is zero or not available to print/parse then the format is complete.
     * <li>A decimal point
     * <li>One to nine digits for the {@link ChronoField#NANO_OF_SECOND nano-of-second}.
     *  As many digits will be printed as required.
     * </ul><p>
     *
     * @return the ISO local time formatter, not null
     */
    public static DateTimeFormatter isoLocalTime() {
        return ISO_LOCAL_TIME;
    }

    /** Singleton date formatter. */
    private static final DateTimeFormatter ISO_LOCAL_TIME;
    static {
        ISO_LOCAL_TIME = new DateTimeFormatterBuilder()
            .appendValue(HOUR_OF_DAY, 2)
            .appendLiteral(':')
            .appendValue(MINUTE_OF_HOUR, 2)
            .optionalStart()
            .appendLiteral(':')
            .appendValue(SECOND_OF_MINUTE, 2)
            .optionalStart()
            .appendFraction(NANO_OF_SECOND, 0, 9, true)
            .toFormatter();
    }

    //-----------------------------------------------------------------------
    /**
     * Returns the ISO time formatter that prints/parses a time with an offset,
     * such as '10:15+01:00' or '10:15:30+01:00'.
     * <p>
     * This returns an immutable formatter capable of printing and parsing
     * the ISO-8601 extended offset time format.
     * The format consists of:
     * <p><ul>
     * <li>The {@link #isoLocalTime()}
     * <li>The {@link ZoneOffset#getId() offset ID}. If the offset has seconds then
     *  they will be handled even though this is not part of the ISO-8601 standard.
     *  Parsing is case insensitive.
     * </ul><p>
     *
     * @return the ISO offset time formatter, not null
     */
    public static DateTimeFormatter isoOffsetTime() {
        return ISO_OFFSET_TIME;
    }

    /** Singleton date formatter. */
    private static final DateTimeFormatter ISO_OFFSET_TIME;
    static {
        ISO_OFFSET_TIME = new DateTimeFormatterBuilder()
            .parseCaseInsensitive()
            .append(ISO_LOCAL_TIME)
            .appendOffsetId()
            .toFormatter();
    }

    //-----------------------------------------------------------------------
    /**
     * Returns the ISO time formatter that prints/parses a time, with the
     * offset if available, such as '10:15', '10:15:30' or '10:15:30+01:00'.
     * <p>
     * This returns an immutable formatter capable of printing and parsing
     * the ISO-8601 extended offset time format.
     * The format consists of:
     * <p><ul>
     * <li>The {@link #isoLocalTime()}
     * <li>If the offset is not available to print/parse then the format is complete.
     * <li>The {@link ZoneOffset#getId() offset ID}. If the offset has seconds then
     *  they will be handled even though this is not part of the ISO-8601 standard.
     *  Parsing is case insensitive.
     * </ul><p>
     * As this formatter has an optional element, it may be necessary to parse using
     * {@link DateTimeFormatter#parseBest}.
     *
     * @return the ISO time formatter, not null
     */
    public static DateTimeFormatter isoTime() {
        return ISO_TIME;
    }

    /** Singleton date formatter. */
    private static final DateTimeFormatter ISO_TIME;
    static {
        ISO_TIME = new DateTimeFormatterBuilder()
            .parseCaseInsensitive()
            .append(ISO_LOCAL_TIME)
            .optionalStart()
            .appendOffsetId()
            .toFormatter();
    }

    //-----------------------------------------------------------------------
    /**
     * Returns the ISO date formatter that prints/parses a date-time
     * without an offset, such as '2011-12-03T10:15:30'.
     * <p>
     * This returns an immutable formatter capable of printing and parsing
     * the ISO-8601 extended offset date-time format.
     * The format consists of:
     * <p><ul>
     * <li>The {@link #isoLocalDate()}
     * <li>The letter 'T'. Parsing is case insensitive.
     * <li>The {@link #isoLocalTime()}
     * </ul><p>
     *
     * @return the ISO local date-time formatter, not null
     */
    public static DateTimeFormatter isoLocalDateTime() {
        return ISO_LOCAL_DATE_TIME;
    }

    /** Singleton date formatter. */
    private static final DateTimeFormatter ISO_LOCAL_DATE_TIME;
    static {
        ISO_LOCAL_DATE_TIME = new DateTimeFormatterBuilder()
            .parseCaseInsensitive()
            .append(ISO_LOCAL_DATE)
            .appendLiteral('T')
            .append(ISO_LOCAL_TIME)
            .toFormatter();
    }

    //-----------------------------------------------------------------------
    /**
     * Returns the ISO date formatter that prints/parses a date-time
     * with an offset, such as '2011-12-03T10:15:30+01:00'.
     * <p>
     * This returns an immutable formatter capable of printing and parsing
     * the ISO-8601 extended offset date-time format.
     * The format consists of:
     * <p><ul>
     * <li>The {@link #isoLocalDateTime()}
     * <li>The {@link ZoneOffset#getId() offset ID}. If the offset has seconds then
     *  they will be handled even though this is not part of the ISO-8601 standard.
     *  Parsing is case insensitive.
     * </ul><p>
     *
     * @return the ISO offset date-time formatter, not null
     */
    public static DateTimeFormatter isoOffsetDateTime() {
        return ISO_OFFSET_DATE_TIME;
    }

    /** Singleton date formatter. */
    private static final DateTimeFormatter ISO_OFFSET_DATE_TIME;
    static {
        ISO_OFFSET_DATE_TIME = new DateTimeFormatterBuilder()
            .parseCaseInsensitive()
            .append(ISO_LOCAL_DATE_TIME)
            .appendOffsetId()
            .toFormatter();
    }

    //-----------------------------------------------------------------------
    /**
     * Returns the ISO date formatter that prints/parses a date-time with
     * offset and zone, such as '2011-12-03T10:15:30+01:00[Europe/Paris]'.
     * <p>
     * This returns an immutable formatter capable of printing and parsing
     * a format that extends the ISO-8601 extended offset date-time format
     * to add the time-zone.
     * The format consists of:
     * <p><ul>
     * <li>The {@link #isoOffsetDateTime()}
     * <li>If the zone ID is not available or is a {@code ZoneOffset} then the format is complete.
     * <li>An open square bracket '['.
     * <li>The {@link ZoneId#getId() zone ID}. This is not part of the ISO-8601 standard.
     *  Parsing is case sensitive.
     * <li>A close square bracket ']'.
     * </ul><p>
     *
     * @return the ISO zoned date-time formatter, not null
     */
    public static DateTimeFormatter isoZonedDateTime() {
        return ISO_ZONED_DATE_TIME;
    }

    /** Singleton date formatter. */
    private static final DateTimeFormatter ISO_ZONED_DATE_TIME;
    static {
        ISO_ZONED_DATE_TIME = new DateTimeFormatterBuilder()
            .append(ISO_OFFSET_DATE_TIME)
            .optionalStart()
            .appendLiteral('[')
            .parseCaseSensitive()
            .appendZoneRegionId()
            .appendLiteral(']')
            .toFormatter();
    }

    //-----------------------------------------------------------------------
    /**
     * Returns the ISO date formatter that prints/parses a date-time
     * with the offset and zone if available, such as '2011-12-03T10:15:30',
     * '2011-12-03T10:15:30+01:00' or '2011-12-03T10:15:30+01:00[Europe/Paris]'.
     * <p>
     * This returns an immutable formatter capable of printing and parsing
     * the ISO-8601 extended offset date-time format.
     * The format consists of:
     * <p><ul>
     * <li>The {@link #isoLocalDateTime()}
     * <li>If the offset is not available to print/parse then the format is complete.
     * <li>The {@link ZoneOffset#getId() offset ID}. If the offset has seconds then
     *  they will be handled even though this is not part of the ISO-8601 standard.
     * <li>If the zone ID is not available or is a {@code ZoneOffset} then the format is complete.
     * <li>An open square bracket '['.
     * <li>The {@link ZoneId#getId() zone ID}. This is not part of the ISO-8601 standard.
     *  Parsing is case sensitive.
     * <li>A close square bracket ']'.
     * </ul><p>
     * As this formatter has an optional element, it may be necessary to parse using
     * {@link DateTimeFormatter#parseBest}.
     *
     * @return the ISO date-time formatter, not null
     */
    public static DateTimeFormatter isoDateTime() {
        return ISO_DATE_TIME;
    }

    /** Singleton date formatter. */
    private static final DateTimeFormatter ISO_DATE_TIME;
    static {
        ISO_DATE_TIME = new DateTimeFormatterBuilder()
            .append(ISO_LOCAL_DATE_TIME)
            .optionalStart()
            .appendOffsetId()
            .optionalStart()
            .appendLiteral('[')
            .parseCaseSensitive()
            .appendZoneRegionId()
            .appendLiteral(']')
            .toFormatter();
    }

    //-----------------------------------------------------------------------
    /**
     * Returns the ISO date formatter that prints/parses the ordinal date
     * without an offset, such as '2012-337'.
     * <p>
     * This returns an immutable formatter capable of printing and parsing
     * the ISO-8601 extended ordinal date format.
     * The format consists of:
     * <p><ul>
     * <li>Four digits or more for the {@link ChronoField#YEAR year}.
     * Years in the range 0000 to 9999 will be pre-padded by zero to ensure four digits.
     * Years outside that range will have a prefixed positive or negative symbol.
     * <li>A dash
     * <li>Three digits for the {@link ChronoField#DAY_OF_YEAR day-of-year}.
     *  This is pre-padded by zero to ensure three digits.
     * <li>If the offset is not available to print/parse then the format is complete.
     * <li>The {@link ZoneOffset#getId() offset ID}. If the offset has seconds then
     *  they will be handled even though this is not part of the ISO-8601 standard.
     *  Parsing is case insensitive.
     * </ul><p>
     * As this formatter has an optional element, it may be necessary to parse using
     * {@link DateTimeFormatter#parseBest}.
     *
     * @return the ISO ordinal date formatter, not null
     */
    public static DateTimeFormatter isoOrdinalDate() {
        return ISO_ORDINAL_DATE;
    }

    /** Singleton date formatter. */
    private static final DateTimeFormatter ISO_ORDINAL_DATE;
    static {
        ISO_ORDINAL_DATE = new DateTimeFormatterBuilder()
            .parseCaseInsensitive()
            .appendValue(YEAR, 4, 10, SignStyle.EXCEEDS_PAD)
            .appendLiteral('-')
            .appendValue(DAY_OF_YEAR, 3)
            .optionalStart()
            .appendOffsetId()
            .toFormatter();
    }

    //-----------------------------------------------------------------------
    /**
     * Returns the ISO date formatter that prints/parses the week-based date
     * without an offset, such as '2012-W48-6'.
     * <p>
     * This returns an immutable formatter capable of printing and parsing
     * the ISO-8601 extended week-based date format.
     * The format consists of:
     * <p><ul>
     * <li>Four digits or more for the {@link ISOFields#WEEK_BASED_YEAR week-based-year}.
     * Years in the range 0000 to 9999 will be pre-padded by zero to ensure four digits.
     * Years outside that range will have a prefixed positive or negative symbol.
     * <li>A dash
     * <li>The letter 'W'. Parsing is case insensitive.
     * <li>Two digits for the {@link ISOFields#WEEK_OF_WEEK_BASED_YEAR week-of-week-based-year}.
     *  This is pre-padded by zero to ensure three digits.
     * <li>A dash
     * <li>One digit for the {@link ChronoField#DAY_OF_WEEK day-of-week}.
     *  The value run from Monday (1) to Sunday (7).
     * <li>If the offset is not available to print/parse then the format is complete.
     * <li>The {@link ZoneOffset#getId() offset ID}. If the offset has seconds then
     *  they will be handled even though this is not part of the ISO-8601 standard.
     *  Parsing is case insensitive.
     * </ul><p>
     * As this formatter has an optional element, it may be necessary to parse using
     * {@link DateTimeFormatter#parseBest}.
     *
     * @return the ISO week-based date formatter, not null
     */
    public static DateTimeFormatter isoWeekDate() {
        return ISO_WEEK_DATE;
    }

    /** Singleton date formatter. */
    private static final DateTimeFormatter ISO_WEEK_DATE;
    static {
        ISO_WEEK_DATE = new DateTimeFormatterBuilder()
            .parseCaseInsensitive()
            .appendValue(ISOFields.WEEK_BASED_YEAR, 4, 10, SignStyle.EXCEEDS_PAD)
            .appendLiteral("-W")
            .appendValue(ISOFields.WEEK_OF_WEEK_BASED_YEAR, 2)
            .appendLiteral('-')
            .appendValue(DAY_OF_WEEK, 1)
            .optionalStart()
            .appendOffsetId()
            .toFormatter();
    }

    //-----------------------------------------------------------------------
    /**
     * Returns the ISO instant formatter that prints/parses an instant in UTC.
     * <p>
     * This returns an immutable formatter capable of printing and parsing
     * the ISO-8601 instant format.
     * The format consists of:
     * <p><ul>
     * <li>The {@link #isoOffsetDateTime()} where the instant is converted from
     *  {@link ChronoField#INSTANT_SECONDS} and {@link ChronoField#NANO_OF_SECOND}
     *  using the {@code UTC} offset. Parsing is case insensitive.
     * </ul><p>
     *
     * @return the ISO instant formatter, not null
     */
    public static DateTimeFormatter isoInstant() {
        return ISO_INSTANT;
    }

    /** Singleton formatter. */
    private static final DateTimeFormatter ISO_INSTANT;
    static {
        ISO_INSTANT = new DateTimeFormatterBuilder()
            .parseCaseInsensitive()
            .appendInstant()
            .toFormatter();
    }

    //-----------------------------------------------------------------------
    /**
     * Returns the ISO date formatter that prints/parses a date without an offset,
     * such as '20111203'.
     * <p>
     * This returns an immutable formatter capable of printing and parsing
     * the ISO-8601 basic local date format.
     * The format consists of:
     * <p><ul>
     * <li>Four digits for the {@link ChronoField#YEAR year}.
     *  Only years in the range 0000 to 9999 are supported.
     * <li>Two digits for the {@link ChronoField#MONTH_OF_YEAR month-of-year}.
     *  This is pre-padded by zero to ensure two digits.
     * <li>Two digits for the {@link ChronoField#DAY_OF_MONTH day-of-month}.
     *  This is pre-padded by zero to ensure two digits.
     * <li>If the offset is not available to print/parse then the format is complete.
     * <li>The {@link ZoneOffset#getId() offset ID} without colons. If the offset has
     *  seconds then they will be handled even though this is not part of the ISO-8601 standard.
     *  Parsing is case insensitive.
     * </ul><p>
     * As this formatter has an optional element, it may be necessary to parse using
     * {@link DateTimeFormatter#parseBest}.
     *
     * @return the ISO basic local date formatter, not null
     */
    public static DateTimeFormatter basicIsoDate() {
        return BASIC_ISO_DATE;
    }

    /** Singleton date formatter. */
    private static final DateTimeFormatter BASIC_ISO_DATE;
    static {
        BASIC_ISO_DATE = new DateTimeFormatterBuilder()
            .parseCaseInsensitive()
            .appendValue(YEAR, 4)
            .appendValue(MONTH_OF_YEAR, 2)
            .appendValue(DAY_OF_MONTH, 2)
            .optionalStart()
            .appendOffset("+HHMMss", "Z")
            .toFormatter();
    }

    //-----------------------------------------------------------------------
    /**
     * Returns the RFC-1123 date-time formatter, such as 'Tue, 3 Jun 2008 11:05:30 GMT'.
     * <p>
     * This returns an immutable formatter capable of printing and parsing
     * most of the RFC-1123 format.
     * RFC-1123 updates RFC-822 changing the year from two digits to four.
     * This implementation requires a four digit year.
     * This implementation also does not handle North American or military zone
     * names, only 'GMT' and offset amounts.
     * <p>
     * The format consists of:
     * <p><ul>
     * <li>If the day-of-week is not available to print/parse then jump to day-of-month.
     * <li>Three letter {@link ChronoField#DAY_OF_WEEK day-of-week} in English.
     * <li>A comma
     * <li>A space
     * <li>One or two digits for the {@link ChronoField#DAY_OF_MONTH day-of-month}.
     * <li>A space
     * <li>Three letter {@link ChronoField#MONTH_OF_YEAR month-of-year} in English.
     * <li>A space
     * <li>Four digits for the {@link ChronoField#YEAR year}.
     *  Only years in the range 0000 to 9999 are supported.
     * <li>A space
     * <li>Two digits for the {@link ChronoField#HOUR_OF_DAY hour-of-day}.
     *  This is pre-padded by zero to ensure two digits.
     * <li>A colon
     * <li>Two digits for the {@link ChronoField#MINUTE_OF_HOUR minute-of-hour}.
     *  This is pre-padded by zero to ensure two digits.
     * <li>If the second-of-minute is not available to print/parse then jump to the next space.
     * <li>A colon
     * <li>Two digits for the {@link ChronoField#SECOND_OF_MINUTE second-of-minute}.
     *  This is pre-padded by zero to ensure two digits.
     * <li>A space
     * <li>The {@link ZoneOffset#getId() offset ID} without colons or seconds.
     *  An offset of zero uses "GMT". North American zone names and military zone names are not handled.
     * </ul><p>
     * Parsing is case insensitive.
     *
     * @return the RFC-1123 formatter, not null
     */
    public static DateTimeFormatter rfc1123() {
        return RFC_1123_DATE_TIME;
    }

    /** Singleton date formatter. */
    private static final DateTimeFormatter RFC_1123_DATE_TIME;
    static {
        // manually code maps to ensure correct data always used
        // (locale data can be changed by application code)
        Map<Long, String> dow = new HashMap<>();
        dow.put(1L, "Mon");
        dow.put(2L, "Tue");
        dow.put(3L, "Wed");
        dow.put(4L, "Thu");
        dow.put(5L, "Fri");
        dow.put(6L, "Sat");
        dow.put(7L, "Sun");
        Map<Long, String> moy = new HashMap<>();
        moy.put(1L, "Jan");
        moy.put(2L, "Feb");
        moy.put(3L, "Mar");
        moy.put(4L, "Apr");
        moy.put(5L, "May");
        moy.put(6L, "Jun");
        moy.put(7L, "Jul");
        moy.put(8L, "Aug");
        moy.put(9L, "Sep");
        moy.put(10L, "Oct");
        moy.put(11L, "Nov");
        moy.put(12L, "Dec");
        RFC_1123_DATE_TIME = new DateTimeFormatterBuilder()
            .parseCaseInsensitive()
            .parseLenient()
            .optionalStart()
            .appendText(DAY_OF_WEEK, dow)
            .appendLiteral(", ")
            .optionalEnd()
            .appendValue(DAY_OF_MONTH, 1, 2, SignStyle.NOT_NEGATIVE)
            .appendLiteral(' ')
            .appendText(MONTH_OF_YEAR, moy)
            .appendLiteral(' ')
            .appendValue(YEAR, 4)  // 2 digit year not handled
            .appendLiteral(' ')
            .appendValue(HOUR_OF_DAY, 2)
            .appendLiteral(':')
            .appendValue(MINUTE_OF_HOUR, 2)
            .optionalStart()
            .appendLiteral(':')
            .appendValue(SECOND_OF_MINUTE, 2)
            .optionalEnd()
            .appendLiteral(' ')
            .appendOffset("+HHMM", "GMT")  // should handle UT/Z/EST/EDT/CST/CDT/MST/MDT/PST/MDT
            .toFormatter();
    }

}