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   * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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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.
   *
   *  * 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
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   */
  package java.time.temporal;
  
  import java.time.DateTimeException;
  import java.time.Duration;
  import java.time.LocalTime;
  import java.time.Period;
  import java.time.chrono.ChronoLocalDate;
  import java.time.chrono.ChronoLocalDateTime;
  import java.time.chrono.ChronoZonedDateTime;
  
  /**
   * A unit of date-time, such as Days or Hours.
   * <p>
   * Measurement of time is built on units, such as years, months, days, hours, minutes and seconds.
   * Implementations of this interface represent those units.
   * <p>
   * An instance of this interface represents the unit itself, rather than an amount of the unit.
   * See {@link Period} for a class that represents an amount in terms of the common units.
   * <p>
   * The most commonly used units are defined in {@link ChronoUnit}.
   * Further units are supplied in {@link IsoFields}.
   * Units can also be written by application code by implementing this interface.
   * <p>
   * The unit works using double dispatch. Client code calls methods on a date-time like
   * {@code LocalDateTime} which check if the unit is a {@code ChronoUnit}.
   * If it is, then the date-time must handle it.
   * Otherwise, the method call is re-dispatched to the matching method in this interface.
   *
   * @implSpec
   * This interface must be implemented with care to ensure other classes operate correctly.
   * All implementations that can be instantiated must be final, immutable and thread-safe.
   * It is recommended to use an enum where possible.
   *
   * @since 1.8
   */
  public interface TemporalUnit {
  
      /**
       * Gets the duration of this unit, which may be an estimate.
       * <p>
       * All units return a duration measured in standard nanoseconds from this method.
       * The duration will be positive and non-zero.
       * For example, an hour has a duration of {@code 60 * 60 * 1,000,000,000ns}.
       * <p>
       * Some units may return an accurate duration while others return an estimate.
       * For example, days have an estimated duration due to the possibility of
       * daylight saving time changes.
       * To determine if the duration is an estimate, use {@link #isDurationEstimated()}.
       *
       * @return the duration of this unit, which may be an estimate, not null
       */
      Duration getDuration();
  
      /**
       * Checks if the duration of the unit is an estimate.
       * <p>
       * All units have a duration, however the duration is not always accurate.
       * For example, days have an estimated duration due to the possibility of
       * daylight saving time changes.
       * This method returns true if the duration is an estimate and false if it is
       * accurate. Note that accurate/estimated ignores leap seconds.
       *
       * @return true if the duration is estimated, false if accurate
       */
      boolean isDurationEstimated();
  
      //-----------------------------------------------------------------------
      /**
       * Checks if this unit represents a component of a date.
       * <p>
       * A date is time-based if it can be used to imply meaning from a date.
       * It must have a {@linkplain #getDuration() duration} that is an integral
       * multiple of the length of a standard day.
       * Note that it is valid for both {@code isDateBased()} and {@code isTimeBased()}
       * to return false, such as when representing a unit like 36 hours.
       *
       * @return true if this unit is a component of a date
       */
      boolean isDateBased();
  
      /**
       * Checks if this unit represents a component of a time.
       * <p>
       * A unit is time-based if it can be used to imply meaning from a time.
       * It must have a {@linkplain #getDuration() duration} that divides into
       * the length of a standard day without remainder.
       * Note that it is valid for both {@code isDateBased()} and {@code isTimeBased()}
       * to return false, such as when representing a unit like 36 hours.
       *
       * @return true if this unit is a component of a time
       */
      boolean isTimeBased();
  
      //-----------------------------------------------------------------------
      /**
       * Checks if this unit is supported by the specified temporal object.
       * <p>
       * This checks that the implementing date-time can add/subtract this unit.
       * This can be used to avoid throwing an exception.
       * <p>
       * This default implementation derives the value using
       * {@link Temporal#plus(long, TemporalUnit)}.
       *
       * @param temporal  the temporal object to check, not null
       * @return true if the unit is supported
       */
      default boolean isSupportedBy(Temporal temporal) {
          if (temporal instanceof LocalTime) {
              return isTimeBased();
          }
          if (temporal instanceof ChronoLocalDate) {
              return isDateBased();
          }
          if (temporal instanceof ChronoLocalDateTime || temporal instanceof ChronoZonedDateTime) {
              return true;
          }
          try {
              temporal.plus(1, this);
              return true;
          } catch (UnsupportedTemporalTypeException ex) {
              return false;
          } catch (RuntimeException ex) {
              try {
                  temporal.plus(-1, this);
                  return true;
              } catch (RuntimeException ex2) {
                  return false;
              }
          }
      }
  
      /**
       * Returns a copy of the specified temporal object with the specified period added.
       * <p>
       * The period added is a multiple of this unit. For example, this method
       * could be used to add "3 days" to a date by calling this method on the
       * instance representing "days", passing the date and the period "3".
       * The period to be added may be negative, which is equivalent to subtraction.
       * <p>
       * There are two equivalent ways of using this method.
       * The first is to invoke this method directly.
       * The second is to use {@link Temporal#plus(long, TemporalUnit)}:
       * <pre>
       *   // these two lines are equivalent, but the second approach is recommended
       *   temporal = thisUnit.addTo(temporal);
       *   temporal = temporal.plus(thisUnit);
       * </pre>
       * It is recommended to use the second approach, {@code plus(TemporalUnit)},
       * as it is a lot clearer to read in code.
       * <p>
       * Implementations should perform any queries or calculations using the units
       * available in {@link ChronoUnit} or the fields available in {@link ChronoField}.
       * If the unit is not supported an {@code UnsupportedTemporalTypeException} must be thrown.
       * <p>
       * Implementations must not alter the specified temporal object.
       * Instead, an adjusted copy of the original must be returned.
       * This provides equivalent, safe behavior for immutable and mutable implementations.
       *
       * @param <R>  the type of the Temporal object
       * @param temporal  the temporal object to adjust, not null
       * @param amount  the amount of this unit to add, positive or negative
       * @return the adjusted temporal object, not null
       * @throws DateTimeException if the amount cannot be added
       * @throws UnsupportedTemporalTypeException if the unit is not supported by the temporal
       */
      <R extends Temporal> R addTo(R temporal, long amount);
  
      //-----------------------------------------------------------------------
      /**
       * Calculates the amount of time between two temporal objects.
       * <p>
       * This calculates the amount in terms of this unit. The start and end
       * points are supplied as temporal objects and must be of compatible types.
       * The implementation will convert the second type to be an instance of the
       * first type before the calculating the amount.
       * The result will be negative if the end is before the start.
       * For example, the amount in hours between two temporal objects can be
       * calculated using {@code HOURS.between(startTime, endTime)}.
       * <p>
       * The calculation returns a whole number, representing the number of
       * complete units between the two temporals.
       * For example, the amount in hours between the times 11:30 and 13:29
       * will only be one hour as it is one minute short of two hours.
       * <p>
       * There are two equivalent ways of using this method.
       * The first is to invoke this method directly.
       * The second is to use {@link Temporal#until(Temporal, TemporalUnit)}:
       * <pre>
       *   // these two lines are equivalent
       *   between = thisUnit.between(start, end);
       *   between = start.until(end, thisUnit);
       * </pre>
       * The choice should be made based on which makes the code more readable.
       * <p>
       * For example, this method allows the number of days between two dates to
       * be calculated:
       * <pre>
       *  long daysBetween = DAYS.between(start, end);
       *  // or alternatively
       *  long daysBetween = start.until(end, DAYS);
       * </pre>
       * <p>
       * Implementations should perform any queries or calculations using the units
       * available in {@link ChronoUnit} or the fields available in {@link ChronoField}.
       * If the unit is not supported an {@code UnsupportedTemporalTypeException} must be thrown.
       * Implementations must not alter the specified temporal objects.
       *
       * @implSpec
       * Implementations must begin by checking to if the two temporals have the
       * same type using {@code getClass()}. If they do not, then the result must be
       * obtained by calling {@code temporal1Inclusive.until(temporal2Exclusive, this)}.
       *
       * @param temporal1Inclusive  the base temporal object, not null
       * @param temporal2Exclusive  the other temporal object, exclusive, not null
       * @return the amount of time between temporal1Inclusive and temporal2Exclusive
       *  in terms of this unit; positive if temporal2Exclusive is later than
       *  temporal1Inclusive, negative if earlier
       * @throws DateTimeException if the amount cannot be calculated, or the end
       *  temporal cannot be converted to the same type as the start temporal
       * @throws UnsupportedTemporalTypeException if the unit is not supported by the temporal
       * @throws ArithmeticException if numeric overflow occurs
       */
      long between(Temporal temporal1Inclusive, Temporal temporal2Exclusive);
  
      //-----------------------------------------------------------------------
      /**
       * Gets a descriptive name for the unit.
       * <p>
       * This should be in the plural and upper-first camel case, such as 'Days' or 'Minutes'.
       *
       * @return the name of this unit, not null
       */
      @Override
      String toString();
  
  }
  