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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) 2009-2012, 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.

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package java.time.zone;

import java.io.DataInput;

import java.io.DataOutput;

import java.io.IOException;

import java.io.Serializable;

import java.time.Duration;

import java.time.Instant;

import java.time.LocalDateTime;

import java.time.ZoneOffset;

import java.util.Arrays;

import java.util.Collections;

import java.util.List;

import java.util.Objects;

/**

 * A transition between two offsets caused by a discontinuity in the local time-line.

 * <p>

 * A transition between two offsets is normally the result of a daylight savings cutover.

 * The discontinuity is normally a gap in spring and an overlap in autumn.

 * {@code ZoneOffsetTransition} models the transition between the two offsets.

 * <p>

 * Gaps occur where there are local date-times that simply do not not exist.

 * An example would be when the offset changes from {@code +03:00} to {@code +04:00}.

 * This might be described as 'the clocks will move forward one hour tonight at 1am'.

 * <p>

 * Overlaps occur where there are local date-times that exist twice.

 * An example would be when the offset changes from {@code +04:00} to {@code +03:00}.

 * This might be described as 'the clocks will move back one hour tonight at 2am'.

 *

 * This class is immutable and thread-safe.

 *

 * @since 1.8

 */

public final class ZoneOffsetTransition

        implements Comparable<ZoneOffsetTransition>, Serializable {

    /**

     * Serialization version.

     */

    private static final long serialVersionUID = -6946044323557704546L;

    /**

     * The local transition date-time at the transition.

     */

    private final LocalDateTime transition;

    /**

     * The offset before transition.

     */

    private final ZoneOffset offsetBefore;

    /**

     * The offset after transition.

     */

    private final ZoneOffset offsetAfter;

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

    /**

     * Obtains an instance defining a transition between two offsets.

     * <p>

     * Applications should normally obtain an instance from {@link ZoneRules}.

     * This factory is only intended for use when creating {@link ZoneRules}.

     *

     * @param transition  the transition date-time at the transition, which never

     *  actually occurs, expressed local to the before offset, not null

     * @param offsetBefore  the offset before the transition, not null

     * @param offsetAfter  the offset at and after the transition, not null

     * @return the transition, not null

     * @throws IllegalArgumentException if {@code offsetBefore} and {@code offsetAfter}

     *         are equal, or {@code transition.getNano()} returns non-zero value

     */

    public static ZoneOffsetTransition of(LocalDateTime transition, ZoneOffset offsetBefore, ZoneOffset offsetAfter) {

        Objects.requireNonNull(transition, "transition");

        Objects.requireNonNull(offsetBefore, "offsetBefore");

        Objects.requireNonNull(offsetAfter, "offsetAfter");

        if (offsetBefore.equals(offsetAfter)) {

            throw new IllegalArgumentException("Offsets must not be equal");

        }

        if (transition.getNano() != 0) {

            throw new IllegalArgumentException("Nano-of-second must be zero");

        }

        return new ZoneOffsetTransition(transition, offsetBefore, offsetAfter);

    }

    /**

     * Creates an instance defining a transition between two offsets.

     *

     * @param transition  the transition date-time with the offset before the transition, not null

     * @param offsetBefore  the offset before the transition, not null

     * @param offsetAfter  the offset at and after the transition, not null

     */

    ZoneOffsetTransition(LocalDateTime transition, ZoneOffset offsetBefore, ZoneOffset offsetAfter) {

        this.transition = transition;

        this.offsetBefore = offsetBefore;

        this.offsetAfter = offsetAfter;

    }

    /**

     * Creates an instance from epoch-second and offsets.

     *

     * @param epochSecond  the transition epoch-second

     * @param offsetBefore  the offset before the transition, not null

     * @param offsetAfter  the offset at and after the transition, not null

     */

    ZoneOffsetTransition(long epochSecond, ZoneOffset offsetBefore, ZoneOffset offsetAfter) {

        this.transition = LocalDateTime.ofEpochSecond(epochSecond, 0, offsetBefore);

        this.offsetBefore = offsetBefore;

        this.offsetAfter = offsetAfter;

    }

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

    /**

     * Uses a serialization delegate.

     *

     * @return the replacing object, not null

     */

    private Object writeReplace() {

        return new Ser(Ser.ZOT, this);

    }

    /**

     * Writes the state to the stream.

     *

     * @param out  the output stream, not null

     * @throws IOException if an error occurs

     */

    void writeExternal(DataOutput out) throws IOException {

        Ser.writeEpochSec(toEpochSecond(), out);

        Ser.writeOffset(offsetBefore, out);

        Ser.writeOffset(offsetAfter, out);

    }

    /**

     * Reads the state from the stream.

     *

     * @param in  the input stream, not null

     * @return the created object, not null

     * @throws IOException if an error occurs

     */

    static ZoneOffsetTransition readExternal(DataInput in) throws IOException {

        long epochSecond = Ser.readEpochSec(in);

        ZoneOffset before = Ser.readOffset(in);

        ZoneOffset after = Ser.readOffset(in);

        if (before.equals(after)) {

            throw new IllegalArgumentException("Offsets must not be equal");

        }

        return new ZoneOffsetTransition(epochSecond, before, after);

    }

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

    /**

     * Gets the transition instant.

     * <p>

     * This is the instant of the discontinuity, which is defined as the first

     * instant that the 'after' offset applies.

     * <p>

     * The methods {@link #getInstant()}, {@link #getDateTimeBefore()} and {@link #getDateTimeAfter()}

     * all represent the same instant.

     *

     * @return the transition instant, not null

     */

    public Instant getInstant() {

        return transition.toInstant(offsetBefore);

    }

    /**

     * Gets the transition instant as an epoch second.

     *

     * @return the transition epoch second

     */

    public long toEpochSecond() {

        return transition.toEpochSecond(offsetBefore);

    }

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

    /**

     * Gets the local transition date-time, as would be expressed with the 'before' offset.

     * <p>

     * This is the date-time where the discontinuity begins expressed with the 'before' offset.

     * At this instant, the 'after' offset is actually used, therefore the combination of this

     * date-time and the 'before' offset will never occur.

     * <p>

     * The combination of the 'before' date-time and offset represents the same instant

     * as the 'after' date-time and offset.

     *

     * @return the transition date-time expressed with the before offset, not null

     */

    public LocalDateTime getDateTimeBefore() {

        return transition;

    }

    /**

     * Gets the local transition date-time, as would be expressed with the 'after' offset.

     * <p>

     * This is the first date-time after the discontinuity, when the new offset applies.

     * <p>

     * The combination of the 'before' date-time and offset represents the same instant

     * as the 'after' date-time and offset.

     *

     * @return the transition date-time expressed with the after offset, not null

     */

    public LocalDateTime getDateTimeAfter() {

        return transition.plusSeconds(getDurationSeconds());

    }

    /**

     * Gets the offset before the transition.

     * <p>

     * This is the offset in use before the instant of the transition.

     *

     * @return the offset before the transition, not null

     */

    public ZoneOffset getOffsetBefore() {

        return offsetBefore;

    }

    /**

     * Gets the offset after the transition.

     * <p>

     * This is the offset in use on and after the instant of the transition.

     *

     * @return the offset after the transition, not null

     */

    public ZoneOffset getOffsetAfter() {

        return offsetAfter;

    }

    /**

     * Gets the duration of the transition.

     * <p>

     * In most cases, the transition duration is one hour, however this is not always the case.

     * The duration will be positive for a gap and negative for an overlap.

     * Time-zones are second-based, so the nanosecond part of the duration will be zero.

     *

     * @return the duration of the transition, positive for gaps, negative for overlaps

     */

    public Duration getDuration() {

        return Duration.ofSeconds(getDurationSeconds());

    }

    /**

     * Gets the duration of the transition in seconds.

     *

     * @return the duration in seconds

     */

    private int getDurationSeconds() {

        return getOffsetAfter().getTotalSeconds() - getOffsetBefore().getTotalSeconds();

    }

    /**

     * Does this transition represent a gap in the local time-line.

     * <p>

     * Gaps occur where there are local date-times that simply do not not exist.

     * An example would be when the offset changes from {@code +01:00} to {@code +02:00}.

     * This might be described as 'the clocks will move forward one hour tonight at 1am'.

     *

     * @return true if this transition is a gap, false if it is an overlap

     */

    public boolean isGap() {

        return getOffsetAfter().getTotalSeconds() > getOffsetBefore().getTotalSeconds();

    }

    /**

     * Does this transition represent an overlap in the local time-line.

     * <p>

     * Overlaps occur where there are local date-times that exist twice.

     * An example would be when the offset changes from {@code +02:00} to {@code +01:00}.

     * This might be described as 'the clocks will move back one hour tonight at 2am'.

     *

     * @return true if this transition is an overlap, false if it is a gap

     */

    public boolean isOverlap() {

        return getOffsetAfter().getTotalSeconds() < getOffsetBefore().getTotalSeconds();

    }

    /**

     * Checks if the specified offset is valid during this transition.

     * <p>

     * This checks to see if the given offset will be valid at some point in the transition.

     * A gap will always return false.

     * An overlap will return true if the offset is either the before or after offset.

     *

     * @param offset  the offset to check, null returns false

     * @return true if the offset is valid during the transition

     */

    public boolean isValidOffset(ZoneOffset offset) {

        return isGap() ? false : (getOffsetBefore().equals(offset) || getOffsetAfter().equals(offset));

    }

    /**

     * Gets the valid offsets during this transition.

     * <p>

     * A gap will return an empty list, while an overlap will return both offsets.

     *

     * @return the list of valid offsets

     */

    List<ZoneOffset> getValidOffsets() {

        if (isGap()) {

            return Collections.emptyList();

        }

        return Arrays.asList(getOffsetBefore(), getOffsetAfter());

    }

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

    /**

     * Compares this transition to another based on the transition instant.

     * <p>

     * This compares the instants of each transition.

     * The offsets are ignored, making this order inconsistent with equals.

     *

     * @param transition  the transition to compare to, not null

     * @return the comparator value, negative if less, positive if greater

     */

    @Override

    public int compareTo(ZoneOffsetTransition transition) {

        return this.getInstant().compareTo(transition.getInstant());

    }

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

    /**

     * Checks if this object equals another.

     * <p>

     * The entire state of the object is compared.

     *

     * @param other  the other object to compare to, null returns false

     * @return true if equal

     */

    @Override

    public boolean equals(Object other) {

        if (other == this) {

            return true;

        }

        if (other instanceof ZoneOffsetTransition) {

            ZoneOffsetTransition d = (ZoneOffsetTransition) other;

            return transition.equals(d.transition) &&

                offsetBefore.equals(d.offsetBefore) && offsetAfter.equals(d.offsetAfter);

        }

        return false;

    }

    /**

     * Returns a suitable hash code.

     *

     * @return the hash code

     */

    @Override

    public int hashCode() {

        return transition.hashCode() ^ offsetBefore.hashCode() ^ Integer.rotateLeft(offsetAfter.hashCode(), 16);

    }

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

    /**

     * Returns a string describing this object.

     *

     * @return a string for debugging, not null

     */

    @Override

    public String toString() {

        StringBuilder buf = new StringBuilder();

        buf.append("Transition[")

            .append(isGap() ? "Gap" : "Overlap")

            .append(" at ")

            .append(transition)

            .append(offsetBefore)

            .append(" to ")

            .append(offsetAfter)

            .append(']');

        return buf.toString();

    }

}