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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, 2013 Stephen Colebourne & Michael Nascimento Santos

 *

 * All rights reserved.

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 * modification, are permitted provided that the following conditions are met:

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package java.time.temporal;

import java.time.DateTimeException;

import java.time.Duration;

import java.time.Period;

import java.util.List;

/**

 * Framework-level interface defining an amount of time, such as

 * "6 hours", "8 days" or "2 years and 3 months".

 * <p>

 * This is the base interface type for amounts of time.

 * An amount is distinct from a date or time-of-day in that it is not tied

 * to any specific point on the time-line.

 * <p>

 * The amount can be thought of as a {@code Map} of {@link TemporalUnit} to

 * {@code long}, exposed via {@link #getUnits()} and {@link #get(TemporalUnit)}.

 * A simple case might have a single unit-value pair, such as "6 hours".

 * A more complex case may have multiple unit-value pairs, such as

 * "7 years, 3 months and 5 days".

 * <p>

 * There are two common implementations.

 * {@link Period} is a date-based implementation, storing years, months and days.

 * {@link Duration} is a time-based implementation, storing seconds and nanoseconds,

 * but providing some access using other duration based units such as minutes,

 * hours and fixed 24-hour days.

 * <p>

 * This interface is a framework-level interface that should not be widely

 * used in application code. Instead, applications should create and pass

 * around instances of concrete types, such as {@code Period} and {@code Duration}.

 *

 * This interface places no restrictions on the mutability of implementations,

 * however immutability is strongly recommended.

 *

 * @since 1.8

 */

public interface TemporalAmount {

    /**

     * Returns the value of the requested unit.

     * The units returned from {@link #getUnits()} uniquely define the

     * value of the {@code TemporalAmount}.  A value must be returned

     * for each unit listed in {@code getUnits}.

     *

     * Implementations may declare support for units not listed by {@link #getUnits()}.

     * Typically, the implementation would define additional units

     * as conversions for the convenience of developers.

     *

     * @param unit the {@code TemporalUnit} for which to return the value

     * @return the long value of the unit

     * @throws DateTimeException if a value for the unit cannot be obtained

     * @throws UnsupportedTemporalTypeException if the {@code unit} is not supported

     */

    long get(TemporalUnit unit);

    /**

     * Returns the list of units uniquely defining the value of this TemporalAmount.

     * The list of {@code TemporalUnits} is defined by the implementation class.

     * The list is a snapshot of the units at the time {@code getUnits}

     * is called and is not mutable.

     * The units are ordered from longest duration to the shortest duration

     * of the unit.

     *

     * The list of units completely and uniquely represents the

     * state of the object without omissions, overlaps or duplication.

     * The units are in order from longest duration to shortest.

     *

     * @return the List of {@code TemporalUnits}; not null

     */

    List<TemporalUnit> getUnits();

    /**

     * Adds to the specified temporal object.

     * <p>

     * Adds the amount to the specified temporal object using the logic

     * encapsulated in the implementing class.

     * <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(TemporalAmount)}:

     * <pre>

     *   // These two lines are equivalent, but the second approach is recommended

     *   dateTime = amount.addTo(dateTime);

     *   dateTime = dateTime.plus(adder);

     * </pre>

     * It is recommended to use the second approach, {@code plus(TemporalAmount)},

     * as it is a lot clearer to read in code.

     *

     * The implementation must take the input object and add to it.

     * The implementation defines the logic of the addition and is responsible for

     * documenting that logic. It may use any method on {@code Temporal} to

     * query the temporal object and perform the addition.

     * The returned object must have the same observable type as the input object

     * <p>

     * The input object must not be altered.

     * Instead, an adjusted copy of the original must be returned.

     * This provides equivalent, safe behavior for immutable and mutable temporal objects.

     * <p>

     * The input temporal object may be in a calendar system other than ISO.

     * Implementations may choose to document compatibility with other calendar systems,

     * or reject non-ISO temporal objects by {@link TemporalQuery#chronology() querying the chronology}.

     * <p>

     * This method may be called from multiple threads in parallel.

     * It must be thread-safe when invoked.

     *

     * @param temporal  the temporal object to add the amount to, not null

     * @return an object of the same observable type with the addition made, not null

     * @throws DateTimeException if unable to add

     * @throws ArithmeticException if numeric overflow occurs

     */

    Temporal addTo(Temporal temporal);

    /**

     * Subtracts this object from the specified temporal object.

     * <p>

     * Subtracts the amount from the specified temporal object using the logic

     * encapsulated in the implementing class.

     * <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#minus(TemporalAmount)}:

     * <pre>

     *   // these two lines are equivalent, but the second approach is recommended

     *   dateTime = amount.subtractFrom(dateTime);

     *   dateTime = dateTime.minus(amount);

     * </pre>

     * It is recommended to use the second approach, {@code minus(TemporalAmount)},

     * as it is a lot clearer to read in code.

     *

     * The implementation must take the input object and subtract from it.

     * The implementation defines the logic of the subtraction and is responsible for

     * documenting that logic. It may use any method on {@code Temporal} to

     * query the temporal object and perform the subtraction.

     * The returned object must have the same observable type as the input object

     * <p>

     * The input object must not be altered.

     * Instead, an adjusted copy of the original must be returned.

     * This provides equivalent, safe behavior for immutable and mutable temporal objects.

     * <p>

     * The input temporal object may be in a calendar system other than ISO.

     * Implementations may choose to document compatibility with other calendar systems,

     * or reject non-ISO temporal objects by {@link TemporalQuery#chronology() querying the chronology}.

     * <p>

     * This method may be called from multiple threads in parallel.

     * It must be thread-safe when invoked.

     *

     * @param temporal  the temporal object to subtract the amount from, not null

     * @return an object of the same observable type with the subtraction made, not null

     * @throws DateTimeException if unable to subtract

     * @throws ArithmeticException if numeric overflow occurs

     */

    Temporal subtractFrom(Temporal temporal);

}