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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.

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 * Redistribution and use in source and binary forms, with or without

 * 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;

/**

 * Strategy for subtracting from a temporal object.

 * <p>

 * Subtractors are a key tool for modifying temporal objects.

 * They exist to externalize the process of subtraction, permitting different

 * approaches, as per the strategy design pattern.

 * <p>

 * There are two equivalent ways of using a {@code TemporalSubtractor}.

 * The first is to invoke the method on this interface directly.

 * The second is to use {@link Temporal#minus(TemporalSubtractor)}:

 * <pre>

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

 *   dateTime = subtractor.subtractFrom(dateTime);

 *   dateTime = dateTime.minus(subtractor);

 * </pre>

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

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

 * <p>

 * The {@link Period} and {@link Duration} classes implement this interface.

 * Subtractors may also be defined by applications.

 *

 * <h3>Specification for implementors</h3>

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

 * however immutability is strongly recommended.

 *

 * @since 1.8

 */

public interface TemporalSubtractor {

    /**

     * Subtracts this object from the specified temporal object.

     * <p>

     * This adds 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#minus(TemporalSubtractor)}:

     * <pre>

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

     *   dateTime = subtractor.subtractFrom(dateTime);

     *   dateTime = dateTime.minus(subtractor);

     * </pre>

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

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

     *

     * <h3>Specification for implementors</h3>

     * 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 Queries#chrono() 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 adjust, 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);

}