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/*
 * -----------------------------------------------------------------------
 * Copyright © 2013-2014 Meno Hochschild, 
 * -----------------------------------------------------------------------
 * This file (UnitRule.java) is part of project Time4J.
 *
 * Time4J is free software: You can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License as published
 * by the Free Software Foundation, either version 2.1 of the License, or
 * (at your option) any later version.
 *
 * Time4J 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 Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with Time4J. If not, see .
 * -----------------------------------------------------------------------
 */

package net.time4j.engine;


/**
 * Represents a rule for the addition or subtraction associated with
 * a time unit. 
 *
 * A unit rule will usually be registered together with an unit for a
 * {@code TimeAxis}, during loading of the concrete {@code TimePoint}-class.
 * For every time axis and every time unit there is exactly one rule
 * instance. Implementations must be always immutable. 
 *
 * @param    generic type of time context compatible to {@code TimePoint}
 * @author  Meno Hochschild
 */
/*[deutsch]
 * Repräsentiert die Additions- und Subtraktionsregel einer
 * Zeiteinheit. 
 *
 * Eine Zeiteinheitsregel wird in der {@code TimeAxis} zusammen mit
 * der assoziierten Zeiteinheit registriert, was gewöhnlich beim Laden
 * der jeweiligen {@code TimePoint}-Klasse geschieht. Pro Chronologie und
 * pro Zeiteinheit gibt es genau eine Regelinstanz. Implementierungen
 * müssen immer immutable sein. 
 *
 * @param    generic type of time context compatible to {@code TimePoint}
 * @author  Meno Hochschild
 */
public interface UnitRule {

    //~ Methoden ----------------------------------------------------------

    /**
     * Adds given amount to a time point in the context of an
     * associated time unit. 
     *
     * This method is called by the {@code plus()}- and
     * {@code minus()}-methods in the class {@code TimePoint}. If not
     * specified otherwise then a possible range overflow will be
     * resolved such that the last valid time point is choosen. For
     * example the addition of one month to date of 31th of may will
     * yield June, 30th. 
     *
     * @param   timepoint   time point
     * @param   amount      count of units to be added to
     * @return  result of addition as changed copy, given time point
     *          remains unaffected
     * @throws  ArithmeticException in case of numerical overflow
     * @see     TimePoint#plus(long, Object) TimePoint.plus(long, U)
     * @see     TimePoint#minus(long, Object) TimePoint.minus(long, U)
     */
    /*[deutsch]
     * Addiert den angegebenen Betrag zu einem Zeitpunkt im Kontext der
     * assoziierten Zeiteinheit. 
     *
     * Wird von den {@code plus()}- und {@code minus()}-Methoden
     * in der Klasse {@code TimePoint} aufgerufen. Wenn nicht besonders
     * spezifiziert, wird ein eventueller Überlauf so aufgelöst,
     * daß der zuletzt gültige Zeitpunkt gesucht wird. Zum
     * Beispiel wird die Addition eines Monats zum 31. Mai gewöhnlich
     * den 30. Juni ergeben (weil der 31. Juni nicht existiert). 
     *
     * @param   timepoint   time point
     * @param   amount      count of units to be added to
     * @return  result of addition as changed copy, given time point
     *          remains unaffected
     * @throws  ArithmeticException in case of numerical overflow
     * @see     TimePoint#plus(long, Object) TimePoint.plus(long, U)
     * @see     TimePoint#minus(long, Object) TimePoint.minus(long, U)
     */
    T addTo(T timepoint, long amount);

    /**
     * Queries how many units are between given time points. 
     *
     * This method is called by {@code TimePoint.until(T, U)}. The
     * expression {@code start.until(end, unit)} corresponds to
     * {@code ruleForUnit.between(start, end)}. Only full units will
     * be counted. A possible remainder of subtraction will always
     * be truncated. 
     *
     * @param   start   start time point
     * @param   end     end time point
     * @return  difference in units (negative if {@code end} is before
     *          {@code start})
     * @throws  ArithmeticException in case of numerical overflow
     * @see     TimePoint#until(TimePoint, Object) TimePoint.until(T, U)
     */
    /*[deutsch]
     * Ermittelt die Differenz zwischen den angegebenen Zeitwertpunkten
     * als Anzahl der assoziierten Zeiteinheit. 
     *
     * Wird von der {@code TimePoint.until(T, U)}-Methode aufgerufen,
     * d.h., der Ausdruck {@code start.until(end, unit)} entspricht
     * gerade {@code ruleForUnit.between(start, end)}. Es werden nur
     * volle Zeiteinheiten gezählt. Ein Subtraktionsrest wird immer
     * unterschlagen. 
     *
     * @param   start   start time point
     * @param   end     end time point
     * @return  difference in units (negative if {@code end} is before
     *          {@code start})
     * @throws  ArithmeticException in case of numerical overflow
     * @see     TimePoint#until(TimePoint, Object) TimePoint.until(T, U)
     */
    long between(T start, T end);

}