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   * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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   * This code is free software; you can redistribute it and/or modify it
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   * This code is distributed in the hope that it will be useful, but WITHOUT
   * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
   * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
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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.
   *
   *  * 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 java.time.temporal;
  
  import java.time.Duration;
  
  /**
   * 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.
       */
      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.
       */
      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.
       */
      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.
       */
      SECONDS("Seconds", Duration.ofSeconds(1)),
      /**
       * 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.
       */
      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.
       */
      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 {@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.
       * <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 {@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 {@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.
       * <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.
       * <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.
       * <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 {@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 {@link TemporalField} to represent unbounded fields
       * such as the year or era.
       * The estimated duration of the era is artificially defined as the largest duration
       * supported by {@code 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.
       * <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.
       * <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.
       * <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.
       * <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;
      }
  
  }
  