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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();
    }

}