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/*

 * This file is available under and governed by the GNU General Public

 * License version 2 only, as published by the Free Software Foundation.

 * However, the following notice accompanied the original version of this

 * file:

 *

 * Copyright (c) 2012, 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.

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package java.time.chrono;

import java.io.Serializable;

import java.time.Clock;

import java.time.DateTimeException;

import java.time.Instant;

import java.time.LocalDate;

import java.time.LocalDateTime;

import java.time.ZoneId;

import java.time.ZonedDateTime;

import java.time.temporal.ChronoField;

import java.time.temporal.TemporalAccessor;

import java.time.temporal.ValueRange;

import java.util.Arrays;

import java.util.List;

import java.util.Locale;

import java.util.Objects;

/**

 * The ISO calendar system.

 * <p>

 * This chronology defines the rules of the ISO calendar system.

 * This calendar system is based on the ISO-8601 standard, which is the

 * <i>de facto</i> world calendar.

 * <p>

 * The fields are defined as follows:

 * <p><ul>

 * <li>era - There are two eras, 'Current Era' (CE) and 'Before Current Era' (BCE).

 * <li>year-of-era - The year-of-era is the same as the proleptic-year for the current CE era.

 *  For the BCE era before the ISO epoch the year increases from 1 upwards as time goes backwards.

 * <li>proleptic-year - The proleptic year is the same as the year-of-era for the

 *  current era. For the previous era, years have zero, then negative values.

 * <li>month-of-year - There are 12 months in an ISO year, numbered from 1 to 12.

 * <li>day-of-month - There are between 28 and 31 days in each of the ISO month, numbered from 1 to 31.

 *  Months 4, 6, 9 and 11 have 30 days, Months 1, 3, 5, 7, 8, 10 and 12 have 31 days.

 *  Month 2 has 28 days, or 29 in a leap year.

 * <li>day-of-year - There are 365 days in a standard ISO year and 366 in a leap year.

 *  The days are numbered from 1 to 365 or 1 to 366.

 * <li>leap-year - Leap years occur every 4 years, except where the year is divisble by 100 and not divisble by 400.

 * </ul><p>

 *

 * <h3>Specification for implementors</h3>

 * This class is immutable and thread-safe.

 *

 * @since 1.8

 */

public final class IsoChronology extends Chronology implements Serializable {

    /**

     * Singleton instance of the ISO chronology.

     */

    public static final IsoChronology INSTANCE = new IsoChronology();

    /**

     * The singleton instance for the era BCE - 'Before Current Era'.

     * The 'ISO' part of the name emphasizes that this differs from the BCE

     * era in the Gregorian calendar system.

     * This has the numeric value of {@code 0}.

     */

    public static final Era ERA_BCE = IsoEra.BCE;

    /**

     * The singleton instance for the era CE - 'Current Era'.

     * The 'ISO' part of the name emphasizes that this differs from the CE

     * era in the Gregorian calendar system.

     * This has the numeric value of {@code 1}.

     */

    public static final Era ERA_CE = IsoEra.CE;

    /**

     * Serialization version.

     */

    private static final long serialVersionUID = -1440403870442975015L;

    /**

     * Restricted constructor.

     */

    private IsoChronology() {

    }

    /**

     * Resolve singleton.

     *

     * @return the singleton instance, not null

     */

    private Object readResolve() {

        return INSTANCE;

    }

    //-----------------------------------------------------------------------

    /**

     * Gets the ID of the chronology - 'ISO'.

     * <p>

     * The ID uniquely identifies the {@code Chronology}.

     * It can be used to lookup the {@code Chronology} using {@link #of(String)}.

     *

     * @return the chronology ID - 'ISO'

     * @see #getCalendarType()

     */

    @Override

    public String getId() {

        return "ISO";

    }

    /**

     * Gets the calendar type of the underlying calendar system - 'iso8601'.

     * <p>

     * The calendar type is an identifier defined by the

     * <em>Unicode Locale Data Markup Language (LDML)</em> specification.

     * It can be used to lookup the {@code Chronology} using {@link #of(String)}.

     * It can also be used as part of a locale, accessible via

     * {@link Locale#getUnicodeLocaleType(String)} with the key 'ca'.

     *

     * @return the calendar system type - 'iso8601'

     * @see #getId()

     */

    @Override

    public String getCalendarType() {

        return "iso8601";

    }

    //-----------------------------------------------------------------------

    /**

     * Obtains an ISO local date from the era, year-of-era, month-of-year

     * and day-of-month fields.

     *

     * @param era  the ISO era, not null

     * @param yearOfEra  the ISO year-of-era

     * @param month  the ISO month-of-year

     * @param dayOfMonth  the ISO day-of-month

     * @return the ISO local date, not null

     * @throws DateTimeException if unable to create the date

     */

    @Override  // override with covariant return type

    public LocalDate date(Era era, int yearOfEra, int month, int dayOfMonth) {

        return date(prolepticYear(era, yearOfEra), month, dayOfMonth);

    }

    /**

     * Obtains an ISO local date from the proleptic-year, month-of-year

     * and day-of-month fields.

     * <p>

     * This is equivalent to {@link LocalDate#of(int, int, int)}.

     *

     * @param prolepticYear  the ISO proleptic-year

     * @param month  the ISO month-of-year

     * @param dayOfMonth  the ISO day-of-month

     * @return the ISO local date, not null

     * @throws DateTimeException if unable to create the date

     */

    @Override  // override with covariant return type

    public LocalDate date(int prolepticYear, int month, int dayOfMonth) {

        return LocalDate.of(prolepticYear, month, dayOfMonth);

    }

    /**

     * Obtains an ISO local date from the era, year-of-era and day-of-year fields.

     *

     * @param era  the ISO era, not null

     * @param yearOfEra  the ISO year-of-era

     * @param dayOfYear  the ISO day-of-year

     * @return the ISO local date, not null

     * @throws DateTimeException if unable to create the date

     */

    @Override  // override with covariant return type

    public LocalDate dateYearDay(Era era, int yearOfEra, int dayOfYear) {

        return dateYearDay(prolepticYear(era, yearOfEra), dayOfYear);

    }

    /**

     * Obtains an ISO local date from the proleptic-year and day-of-year fields.

     * <p>

     * This is equivalent to {@link LocalDate#ofYearDay(int, int)}.

     *

     * @param prolepticYear  the ISO proleptic-year

     * @param dayOfYear  the ISO day-of-year

     * @return the ISO local date, not null

     * @throws DateTimeException if unable to create the date

     */

    @Override  // override with covariant return type

    public LocalDate dateYearDay(int prolepticYear, int dayOfYear) {

        return LocalDate.ofYearDay(prolepticYear, dayOfYear);

    }

    //-----------------------------------------------------------------------

    /**

     * Obtains an ISO local date from another date-time object.

     * <p>

     * This is equivalent to {@link LocalDate#from(TemporalAccessor)}.

     *

     * @param temporal  the date-time object to convert, not null

     * @return the ISO local date, not null

     * @throws DateTimeException if unable to create the date

     */

    @Override  // override with covariant return type

    public LocalDate date(TemporalAccessor temporal) {

        return LocalDate.from(temporal);

    }

    /**

     * Obtains an ISO local date-time from another date-time object.

     * <p>

     * This is equivalent to {@link LocalDateTime#from(TemporalAccessor)}.

     *

     * @param temporal  the date-time object to convert, not null

     * @return the ISO local date-time, not null

     * @throws DateTimeException if unable to create the date-time

     */

    @Override  // override with covariant return type

    public LocalDateTime localDateTime(TemporalAccessor temporal) {

        return LocalDateTime.from(temporal);

    }

    /**

     * Obtains an ISO zoned date-time from another date-time object.

     * <p>

     * This is equivalent to {@link ZonedDateTime#from(TemporalAccessor)}.

     *

     * @param temporal  the date-time object to convert, not null

     * @return the ISO zoned date-time, not null

     * @throws DateTimeException if unable to create the date-time

     */

    @Override  // override with covariant return type

    public ZonedDateTime zonedDateTime(TemporalAccessor temporal) {

        return ZonedDateTime.from(temporal);

    }

    /**

     * Obtains an ISO zoned date-time in this chronology from an {@code Instant}.

     * <p>

     * This is equivalent to {@link ZonedDateTime#ofInstant(Instant, ZoneId)}.

     *

     * @param instant  the instant to create the date-time from, not null

     * @param zone  the time-zone, not null

     * @return the zoned date-time, not null

     * @throws DateTimeException if the result exceeds the supported range

     */

    @Override

    public ZonedDateTime zonedDateTime(Instant instant, ZoneId zone) {

        return ZonedDateTime.ofInstant(instant, zone);

    }

    //-----------------------------------------------------------------------

    /**

     * Obtains the current ISO local date from the system clock in the default time-zone.

     * <p>

     * This will query the {@link Clock#systemDefaultZone() system clock} in the default

     * time-zone to obtain the current date.

     * <p>

     * Using this method will prevent the ability to use an alternate clock for testing

     * because the clock is hard-coded.

     *

     * @return the current ISO local date using the system clock and default time-zone, not null

     * @throws DateTimeException if unable to create the date

     */

    @Override  // override with covariant return type

    public LocalDate dateNow() {

        return dateNow(Clock.systemDefaultZone());

    }

    /**

     * Obtains the current ISO local date from the system clock in the specified time-zone.

     * <p>

     * This will query the {@link Clock#system(ZoneId) system clock} to obtain the current date.

     * Specifying the time-zone avoids dependence on the default time-zone.

     * <p>

     * Using this method will prevent the ability to use an alternate clock for testing

     * because the clock is hard-coded.

     *

     * @return the current ISO local date using the system clock, not null

     * @throws DateTimeException if unable to create the date

     */

    @Override  // override with covariant return type

    public LocalDate dateNow(ZoneId zone) {

        return dateNow(Clock.system(zone));

    }

    /**

     * Obtains the current ISO local date from the specified clock.

     * <p>

     * This will query the specified clock to obtain the current date - today.

     * Using this method allows the use of an alternate clock for testing.

     * The alternate clock may be introduced using {@link Clock dependency injection}.

     *

     * @param clock  the clock to use, not null

     * @return the current ISO local date, not null

     * @throws DateTimeException if unable to create the date

     */

    @Override  // override with covariant return type

    public LocalDate dateNow(Clock clock) {

        Objects.requireNonNull(clock, "clock");

        return date(LocalDate.now(clock));

    }

    //-----------------------------------------------------------------------

    /**

     * Checks if the year is a leap year, according to the ISO proleptic

     * calendar system rules.

     * <p>

     * This method applies the current rules for leap years across the whole time-line.

     * In general, a year is a leap year if it is divisible by four without

     * remainder. However, years divisible by 100, are not leap years, with

     * the exception of years divisible by 400 which are.

     * <p>

     * For example, 1904 is a leap year it is divisible by 4.

     * 1900 was not a leap year as it is divisible by 100, however 2000 was a

     * leap year as it is divisible by 400.

     * <p>

     * The calculation is proleptic - applying the same rules into the far future and far past.

     * This is historically inaccurate, but is correct for the ISO-8601 standard.

     *

     * @param prolepticYear  the ISO proleptic year to check

     * @return true if the year is leap, false otherwise

     */

    @Override

    public boolean isLeapYear(long prolepticYear) {

        return ((prolepticYear & 3) == 0) && ((prolepticYear % 100) != 0 || (prolepticYear % 400) == 0);

    }

    @Override

    public int prolepticYear(Era era, int yearOfEra) {

        if (era instanceof IsoEra == false) {

            throw new DateTimeException("Era must be IsoEra");

        }

        return (era == IsoEra.CE ? yearOfEra : 1 - yearOfEra);

    }

    @Override

    public Era eraOf(int eraValue) {

        return IsoEra.of(eraValue);

    }

    @Override

    public List<Era> eras() {

        return Arrays.<Era>asList(IsoEra.values());

    }

    //-----------------------------------------------------------------------

    @Override

    public ValueRange range(ChronoField field) {

        return field.range();

    }

}