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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

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 * "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.Period;

/**

 * 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.

 *

 * 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 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, not null

     */

    String getName();

    /**

     * 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 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) {

        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 period cannot be added

     * @throws UnsupportedTemporalTypeException if the unit is not supported by the temporal

     */

    <R extends Temporal> R addTo(R temporal, long amount);

    //-----------------------------------------------------------------------

    /**

     * <p>

     * The result will be negative if the end is before the start.

     * calculated using {@code HOURS.between(startTime, endTime)}.

     * <p>

     * The calculation returns a whole number, representing the number of

     * complete units between the two temporals.

     * 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#periodUntil(Temporal, TemporalUnit)}:

     * <pre>

     *   // these two lines are equivalent

     *   between = thisUnit.between(start, end);

     *   between = start.periodUntil(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.periodUntil(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.

     *

     * @param temporal1  the base temporal object, not null

     * @param temporal2  the other temporal object, not null

     *  positive if temporal2 is later than temporal1, negative if earlier

     * @throws UnsupportedTemporalTypeException if the unit is not supported by the temporal

     * @throws ArithmeticException if numeric overflow occurs

     */

    long between(Temporal temporal1, Temporal temporal2);

    //-----------------------------------------------------------------------

    /**

     * Outputs this unit as a {@code String} using the name.

     *

     * @return the name of this unit, not null

     */

    @Override

    String toString();

}