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/*
 * 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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 *    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
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 */
package java.time.temporal;

import java.time.Duration;

A standard set of date periods units.
 This set of units provide unit-based access to manipulate a date, time or date-time. The standard set of units can be extended by implementing TemporalUnit. 

These units are intended to be applicable in multiple calendar systems.
For example, most non-ISO calendar systems define units of years, months and days,
just with slightly different rules.
The documentation of each unit explains how it operates.
Implementation Requirements:

This is a final, immutable and thread-safe enum.
Since:
1.8/**
 * A standard set of date periods units.
 * <p>
 * This set of units provide unit-based access to manipulate a date, time or date-time.
 * The standard set of units can be extended by implementing {@link TemporalUnit}.
 * <p>
 * These units are intended to be applicable in multiple calendar systems.
 * For example, most non-ISO calendar systems define units of years, months and days,
 * just with slightly different rules.
 * The documentation of each unit explains how it operates.
 *
 * @implSpec
 * This is a final, immutable and thread-safe enum.
 *
 * @since 1.8
 */
public enum ChronoUnit implements TemporalUnit {

    
Unit that represents the concept of a nanosecond, the smallest supported unit of time.
For the ISO calendar system, it is equal to the 1,000,000,000th part of the second unit.
/**
     * Unit that represents the concept of a nanosecond, the smallest supported unit of time.
     * For the ISO calendar system, it is equal to the 1,000,000,000th part of the second unit.
     */
    NANOS("Nanos", Duration.ofNanos(1)),
    
Unit that represents the concept of a microsecond.
For the ISO calendar system, it is equal to the 1,000,000th part of the second unit.
/**
     * Unit that represents the concept of a microsecond.
     * For the ISO calendar system, it is equal to the 1,000,000th part of the second unit.
     */
    MICROS("Micros", Duration.ofNanos(1000)),
    
Unit that represents the concept of a millisecond.
For the ISO calendar system, it is equal to the 1000th part of the second unit.
/**
     * Unit that represents the concept of a millisecond.
     * For the ISO calendar system, it is equal to the 1000th part of the second unit.
     */
    MILLIS("Millis", Duration.ofNanos(1000_000)),
    
Unit that represents the concept of a second.
For the ISO calendar system, it is equal to the second in the SI system
of units, except around a leap-second.
/**
     * Unit that represents the concept of a second.
     * For the ISO calendar system, it is equal to the second in the SI system
     * of units, except around a leap-second.
     */
    SECONDS("Seconds", Duration.ofSeconds(1)),
    
Unit that represents the concept of a minute.
For the ISO calendar system, it is equal to 60 seconds.
/**
     * Unit that represents the concept of a minute.
     * For the ISO calendar system, it is equal to 60 seconds.
     */
    MINUTES("Minutes", Duration.ofSeconds(60)),
    
Unit that represents the concept of an hour.
For the ISO calendar system, it is equal to 60 minutes.
/**
     * Unit that represents the concept of an hour.
     * For the ISO calendar system, it is equal to 60 minutes.
     */
    HOURS("Hours", Duration.ofSeconds(3600)),
    
Unit that represents the concept of half a day, as used in AM/PM.
For the ISO calendar system, it is equal to 12 hours.
/**
     * Unit that represents the concept of half a day, as used in AM/PM.
     * For the ISO calendar system, it is equal to 12 hours.
     */
    HALF_DAYS("HalfDays", Duration.ofSeconds(43200)),
    
Unit that represents the concept of a day. For the ISO calendar system, it is the standard day from midnight to midnight. The estimated duration of a day is 24 Hours. 

When used with other calendar systems it must correspond to the day defined by
the rising and setting of the Sun on Earth. It is not required that days begin
at midnight - when converting between calendar systems, the date should be
equivalent at midday.
/**
     * Unit that represents the concept of a day.
     * For the ISO calendar system, it is the standard day from midnight to midnight.
     * The estimated duration of a day is {@code 24 Hours}.
     * <p>
     * When used with other calendar systems it must correspond to the day defined by
     * the rising and setting of the Sun on Earth. It is not required that days begin
     * at midnight - when converting between calendar systems, the date should be
     * equivalent at midday.
     */
    DAYS("Days", Duration.ofSeconds(86400)),
    
Unit that represents the concept of a week.
For the ISO calendar system, it is equal to 7 days.

When used with other calendar systems it must correspond to an integral number of days.
/**
     * Unit that represents the concept of a week.
     * For the ISO calendar system, it is equal to 7 days.
     * <p>
     * When used with other calendar systems it must correspond to an integral number of days.
     */
    WEEKS("Weeks", Duration.ofSeconds(7 * 86400L)),
    
Unit that represents the concept of a month. For the ISO calendar system, the length of the month varies by month-of-year. The estimated duration of a month is one twelfth of 365.2425 Days. 

When used with other calendar systems it must correspond to an integral number of days.
/**
     * Unit that represents the concept of a month.
     * For the ISO calendar system, the length of the month varies by month-of-year.
     * The estimated duration of a month is one twelfth of {@code 365.2425 Days}.
     * <p>
     * When used with other calendar systems it must correspond to an integral number of days.
     */
    MONTHS("Months", Duration.ofSeconds(31556952L / 12)),
    
Unit that represents the concept of a year. For the ISO calendar system, it is equal to 12 months. The estimated duration of a year is 365.2425 Days. 

When used with other calendar systems it must correspond to an integral number of days
or months roughly equal to a year defined by the passage of the Earth around the Sun.
/**
     * Unit that represents the concept of a year.
     * For the ISO calendar system, it is equal to 12 months.
     * The estimated duration of a year is {@code 365.2425 Days}.
     * <p>
     * When used with other calendar systems it must correspond to an integral number of days
     * or months roughly equal to a year defined by the passage of the Earth around the Sun.
     */
    YEARS("Years", Duration.ofSeconds(31556952L)),
    
Unit that represents the concept of a decade.
For the ISO calendar system, it is equal to 10 years.

When used with other calendar systems it must correspond to an integral number of days
and is normally an integral number of years.
/**
     * Unit that represents the concept of a decade.
     * For the ISO calendar system, it is equal to 10 years.
     * <p>
     * When used with other calendar systems it must correspond to an integral number of days
     * and is normally an integral number of years.
     */
    DECADES("Decades", Duration.ofSeconds(31556952L * 10L)),
    
Unit that represents the concept of a century.
For the ISO calendar system, it is equal to 100 years.

When used with other calendar systems it must correspond to an integral number of days
and is normally an integral number of years.
/**
     * Unit that represents the concept of a century.
     * For the ISO calendar system, it is equal to 100 years.
     * <p>
     * When used with other calendar systems it must correspond to an integral number of days
     * and is normally an integral number of years.
     */
    CENTURIES("Centuries", Duration.ofSeconds(31556952L * 100L)),
    
Unit that represents the concept of a millennium.
For the ISO calendar system, it is equal to 1000 years.

When used with other calendar systems it must correspond to an integral number of days
and is normally an integral number of years.
/**
     * Unit that represents the concept of a millennium.
     * For the ISO calendar system, it is equal to 1000 years.
     * <p>
     * When used with other calendar systems it must correspond to an integral number of days
     * and is normally an integral number of years.
     */
    MILLENNIA("Millennia", Duration.ofSeconds(31556952L * 1000L)),
    
Unit that represents the concept of an era. The ISO calendar system doesn't have eras thus it is impossible to add an era to a date or date-time. The estimated duration of the era is artificially defined as 1,000,000,000 Years. 

When used with other calendar systems there are no restrictions on the unit.
/**
     * Unit that represents the concept of an era.
     * The ISO calendar system doesn't have eras thus it is impossible to add
     * an era to a date or date-time.
     * The estimated duration of the era is artificially defined as {@code 1,000,000,000 Years}.
     * <p>
     * When used with other calendar systems there are no restrictions on the unit.
     */
    ERAS("Eras", Duration.ofSeconds(31556952L * 1000_000_000L)),
    
Artificial unit that represents the concept of forever. This is primarily used with TemporalField to represent unbounded fields such as the year or era. The estimated duration of this unit is artificially defined as the largest duration supported by Duration. /**
     * Artificial unit that represents the concept of forever.
     * This is primarily used with {@link TemporalField} to represent unbounded fields
     * such as the year or era.
     * The estimated duration of this unit is artificially defined as the largest duration
     * supported by {@link Duration}.
     */
    FOREVER("Forever", Duration.ofSeconds(Long.MAX_VALUE, 999_999_999));

    private final String name;
    private final Duration duration;

    private ChronoUnit(String name, Duration estimatedDuration) {
        this.name = name;
        this.duration = estimatedDuration;
    }

    //-----------------------------------------------------------------------
    
Gets the estimated duration of this unit in the ISO calendar system.

All of the units in this class have an estimated duration.
Days vary due to daylight saving time, while months have different lengths.
Returns:
the estimated duration of this unit, not null/**
     * Gets the estimated duration of this unit in the ISO calendar system.
     * <p>
     * All of the units in this class have an estimated duration.
     * Days vary due to daylight saving time, while months have different lengths.
     *
     * @return the estimated duration of this unit, not null
     */
    @Override
    public Duration getDuration() {
        return duration;
    }

    
Checks if the duration of the unit is an estimate.

All time units in this class are considered to be accurate, while all date
units in this class are considered to be estimated.

This definition ignores leap seconds, but considers that Days vary due to
daylight saving time and months have different lengths.
Returns:
true if the duration is estimated, false if accurate/**
     * Checks if the duration of the unit is an estimate.
     * <p>
     * All time units in this class are considered to be accurate, while all date
     * units in this class are considered to be estimated.
     * <p>
     * This definition ignores leap seconds, but considers that Days vary due to
     * daylight saving time and months have different lengths.
     *
     * @return true if the duration is estimated, false if accurate
     */
    @Override
    public boolean isDurationEstimated() {
        return this.compareTo(DAYS) >= 0;
    }

    //-----------------------------------------------------------------------
    
Checks if this unit is a date unit.
 All units from days to eras inclusive are date-based. Time-based units and FOREVER return false. 
Returns:
true if a date unit, false if a time unit/**
     * Checks if this unit is a date unit.
     * <p>
     * All units from days to eras inclusive are date-based.
     * Time-based units and {@code FOREVER} return false.
     *
     * @return true if a date unit, false if a time unit
     */
    @Override
    public boolean isDateBased() {
        return this.compareTo(DAYS) >= 0 && this != FOREVER;
    }

    
Checks if this unit is a time unit.
 All units from nanos to half-days inclusive are time-based. Date-based units and FOREVER return false. 
Returns:
true if a time unit, false if a date unit/**
     * Checks if this unit is a time unit.
     * <p>
     * All units from nanos to half-days inclusive are time-based.
     * Date-based units and {@code FOREVER} return false.
     *
     * @return true if a time unit, false if a date unit
     */
    @Override
    public boolean isTimeBased() {
        return this.compareTo(DAYS) < 0;
    }

    //-----------------------------------------------------------------------
    @Override
    public boolean isSupportedBy(Temporal temporal) {
        return temporal.isSupported(this);
    }

    @SuppressWarnings("unchecked")
    @Override
    public <R extends Temporal> R addTo(R temporal, long amount) {
        return (R) temporal.plus(amount, this);
    }

    //-----------------------------------------------------------------------
    @Override
    public long between(Temporal temporal1Inclusive, Temporal temporal2Exclusive) {
        return temporal1Inclusive.until(temporal2Exclusive, this);
    }

    //-----------------------------------------------------------------------
    @Override
    public String toString() {
        return name;
    }

}