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	/*
	* Copyright (c) 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) 2013, 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.chrono;

	import java.time.DateTimeException;
	import java.time.temporal.ChronoUnit;
	import java.time.temporal.Temporal;
	import java.time.temporal.TemporalAmount;
	import java.time.temporal.TemporalUnit;
	import java.time.temporal.UnsupportedTemporalTypeException;
	import java.util.List;
	import java.util.Objects;

	/**
	* A date-based amount of time, such as '3 years, 4 months and 5 days' in an
	* arbitrary chronology, intended for advanced globalization use cases.
	* <p>
	* This interface models a date-based amount of time in a calendar system.
	* While most calendar systems use years, months and days, some do not.
	* Therefore, this interface operates solely in terms of a set of supported
	* units that are defined by the {@code Chronology}.
	* The set of supported units is fixed for a given chronology.
	* The amount of a supported unit may be set to zero.
	* <p>
	* The period is modeled as a directed amount of time, meaning that individual
	* parts of the period may be negative.
	*
	* @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.
	* Subclasses should be Serializable wherever possible.
	*
	* @since 1.8
	*/
	public interface ChronoPeriod
	extends TemporalAmount {

	/**
	* Obtains a {@code ChronoPeriod} consisting of amount of time between two dates.
	* <p>
	* The start date is included, but the end date is not.
	* The period is calculated using {@link ChronoLocalDate#until(ChronoLocalDate)}.
	* As such, the calculation is chronology specific.
	* <p>
	* The chronology of the first date is used.
	* The chronology of the second date is ignored, with the date being converted
	* to the target chronology system before the calculation starts.
	* <p>
	* The result of this method can be a negative period if the end is before the start.
	* In most cases, the positive/negative sign will be the same in each of the supported fields.
	*
	* @param startDateInclusive the start date, inclusive, specifying the chronology of the calculation, not null
	* @param endDateExclusive the end date, exclusive, in any chronology, not null
	* @return the period between this date and the end date, not null
	* @see ChronoLocalDate#until(ChronoLocalDate)
	*/
	public static ChronoPeriod between(ChronoLocalDate startDateInclusive, ChronoLocalDate endDateExclusive) {
	Objects.requireNonNull(startDateInclusive, "startDateInclusive");
	Objects.requireNonNull(endDateExclusive, "endDateExclusive");
	return startDateInclusive.until(endDateExclusive);
	}

	//-----------------------------------------------------------------------
	/**
	* Gets the value of the requested unit.
	* <p>
	* The supported units are chronology specific.
	* They will typically be {@link ChronoUnit#YEARS YEARS},
	* {@link ChronoUnit#MONTHS MONTHS} and {@link ChronoUnit#DAYS DAYS}.
	* Requesting an unsupported unit will throw an exception.
	*
	* @param unit the {@code TemporalUnit} for which to return the value
	* @return the long value of the unit
	* @throws DateTimeException if the unit is not supported
	* @throws UnsupportedTemporalTypeException if the unit is not supported
	*/
	@Override
	long get(TemporalUnit unit);

	/**
	* Gets the set of units supported by this period.
	* <p>
	* The supported units are chronology specific.
	* They will typically be {@link ChronoUnit#YEARS YEARS},
	* {@link ChronoUnit#MONTHS MONTHS} and {@link ChronoUnit#DAYS DAYS}.
	* They are returned in order from largest to smallest.
	* <p>
	* This set can be used in conjunction with {@link #get(TemporalUnit)}
	* to access the entire state of the period.
	*
	* @return a list containing the supported units, not null
	*/
	@Override
	List<TemporalUnit> getUnits();

	/**
	* Gets the chronology that defines the meaning of the supported units.
	* <p>
	* The period is defined by the chronology.
	* It controls the supported units and restricts addition/subtraction
	* to {@code ChronoLocalDate} instances of the same chronology.
	*
	* @return the chronology defining the period, not null
	*/
	Chronology getChronology();

	//-----------------------------------------------------------------------
	/**
	* Checks if all the supported units of this period are zero.
	*
	* @return true if this period is zero-length
	*/
	default boolean isZero() {
	for (TemporalUnit unit : getUnits()) {
	if (get(unit) != 0) {
	return false;
	}
	}
	return true;
	}

	/**
	* Checks if any of the supported units of this period are negative.
	*
	* @return true if any unit of this period is negative
	*/
	default boolean isNegative() {
	for (TemporalUnit unit : getUnits()) {
	if (get(unit) < 0) {
	return true;
	}
	}
	return false;
	}

	//-----------------------------------------------------------------------
	/**
	* Returns a copy of this period with the specified period added.
	* <p>
	* If the specified amount is a {@code ChronoPeriod} then it must have
	* the same chronology as this period. Implementations may choose to
	* accept or reject other {@code TemporalAmount} implementations.
	* <p>
	* This instance is immutable and unaffected by this method call.
	*
	* @param amountToAdd the period to add, not null
	* @return a {@code ChronoPeriod} based on this period with the requested period added, not null
	* @throws ArithmeticException if numeric overflow occurs
	*/
	ChronoPeriod plus(TemporalAmount amountToAdd);

	/**
	* Returns a copy of this period with the specified period subtracted.
	* <p>
	* If the specified amount is a {@code ChronoPeriod} then it must have
	* the same chronology as this period. Implementations may choose to
	* accept or reject other {@code TemporalAmount} implementations.
	* <p>
	* This instance is immutable and unaffected by this method call.
	*
	* @param amountToSubtract the period to subtract, not null
	* @return a {@code ChronoPeriod} based on this period with the requested period subtracted, not null
	* @throws ArithmeticException if numeric overflow occurs
	*/
	ChronoPeriod minus(TemporalAmount amountToSubtract);

	//-----------------------------------------------------------------------
	/**
	* Returns a new instance with each amount in this period in this period
	* multiplied by the specified scalar.
	* <p>
	* This returns a period with each supported unit individually multiplied.
	* For example, a period of "2 years, -3 months and 4 days" multiplied by
	* 3 will return "6 years, -9 months and 12 days".
	* No normalization is performed.
	*
	* @param scalar the scalar to multiply by, not null
	* @return a {@code ChronoPeriod} based on this period with the amounts multiplied
	* by the scalar, not null
	* @throws ArithmeticException if numeric overflow occurs
	*/
	ChronoPeriod multipliedBy(int scalar);

	/**
	* Returns a new instance with each amount in this period negated.
	* <p>
	* This returns a period with each supported unit individually negated.
	* For example, a period of "2 years, -3 months and 4 days" will be
	* negated to "-2 years, 3 months and -4 days".
	* No normalization is performed.
	*
	* @return a {@code ChronoPeriod} based on this period with the amounts negated, not null
	* @throws ArithmeticException if numeric overflow occurs, which only happens if
	* one of the units has the value {@code Long.MIN_VALUE}
	*/
	default ChronoPeriod negated() {
	return multipliedBy(-1);
	}

	//-----------------------------------------------------------------------
	/**
	* Returns a copy of this period with the amounts of each unit normalized.
	* <p>
	* The process of normalization is specific to each calendar system.
	* For example, in the ISO calendar system, the years and months are
	* normalized but the days are not, such that "15 months" would be
	* normalized to "1 year and 3 months".
	* <p>
	* This instance is immutable and unaffected by this method call.
	*
	* @return a {@code ChronoPeriod} based on this period with the amounts of each
	* unit normalized, not null
	* @throws ArithmeticException if numeric overflow occurs
	*/
	ChronoPeriod normalized();

	//-------------------------------------------------------------------------
	/**
	* Adds this period to the specified temporal object.
	* <p>
	* This returns a temporal object of the same observable type as the input
	* with this period added.
	* <p>
	* In most cases, it is clearer to reverse the calling pattern by using
	* {@link Temporal#plus(TemporalAmount)}.
	* <pre>
	* // these two lines are equivalent, but the second approach is recommended
	* dateTime = thisPeriod.addTo(dateTime);
	* dateTime = dateTime.plus(thisPeriod);
	* </pre>
	* <p>
	* The specified temporal must have the same chronology as this period.
	* This returns a temporal with the non-zero supported units added.
	* <p>
	* This instance is immutable and unaffected by this method call.
	*
	* @param temporal the temporal object to adjust, not null
	* @return an object of the same type with the adjustment made, not null
	* @throws DateTimeException if unable to add
	* @throws ArithmeticException if numeric overflow occurs
	*/
	@Override
	Temporal addTo(Temporal temporal);

	/**
	* Subtracts this period from the specified temporal object.
	* <p>
	* This returns a temporal object of the same observable type as the input
	* with this period subtracted.
	* <p>
	* In most cases, it is clearer to reverse the calling pattern by using
	* {@link Temporal#minus(TemporalAmount)}.
	* <pre>
	* // these two lines are equivalent, but the second approach is recommended
	* dateTime = thisPeriod.subtractFrom(dateTime);
	* dateTime = dateTime.minus(thisPeriod);
	* </pre>
	* <p>
	* The specified temporal must have the same chronology as this period.
	* This returns a temporal with the non-zero supported units subtracted.
	* <p>
	* This instance is immutable and unaffected by this method call.
	*
	* @param temporal the temporal object to adjust, not null
	* @return an object of the same type with the adjustment made, not null
	* @throws DateTimeException if unable to subtract
	* @throws ArithmeticException if numeric overflow occurs
	*/
	@Override
	Temporal subtractFrom(Temporal temporal);

	//-----------------------------------------------------------------------
	/**
	* Checks if this period is equal to another period, including the chronology.
	* <p>
	* Compares this period with another ensuring that the type, each amount and
	* the chronology are the same.
	* Note that this means that a period of "15 Months" is not equal to a period
	* of "1 Year and 3 Months".
	*
	* @param obj the object to check, null returns false
	* @return true if this is equal to the other period
	*/
	@Override
	boolean equals(Object obj);

	/**
	* A hash code for this period.
	*
	* @return a suitable hash code
	*/
	@Override
	int hashCode();

	//-----------------------------------------------------------------------
	/**
	* Outputs this period as a {@code String}.
	* <p>
	* The output will include the period amounts and chronology.
	*
	* @return a string representation of this period, not null
	*/
	@Override
	String toString();

	}

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