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	/*
	* Copyright (c) 2012, 2013, Oracle and/or its affiliates. All rights reserved.
	* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
	*
	* This code is free software; you can redistribute it and/or modify it
	* under the terms of the GNU General Public License version 2 only, as
	* published by the Free Software Foundation. Oracle designates this
	* particular file as subject to the "Classpath" exception as provided
	* by Oracle in the LICENSE file that accompanied this code.
	*
	* 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
	* version 2 for more details (a copy is included in the LICENSE file that
	* accompanied this code).
	*
	* You should have received a copy of the GNU General Public License version
	* 2 along with this work; if not, write to the Free Software Foundation,
	* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
	*
	* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
	* or visit www.oracle.com if you need additional information or have any
	* questions.
	*/

	/*
	* 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
	* 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.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();

	}

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