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	/*
	* Copyright (c) 2012, 2015, Oracle and/or its affiliates. All rights reserved.
	* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
	*
	* This code is free software; you can redistribute it and/or modify it
	* under the terms of the GNU General Public License version 2 only, as
	* published by the Free Software Foundation. Oracle designates this
	* particular file as subject to the "Classpath" exception as provided
	* by Oracle in the LICENSE file that accompanied this code.
	*
	* This code 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 General Public License
	* version 2 for more details (a copy is included in the LICENSE file that
	* accompanied this code).
	*
	* You should have received a copy of the GNU General Public License version
	* 2 along with this work; if not, write to the Free Software Foundation,
	* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
	*
	* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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	* questions.
	*/

	/*
	* 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.
	*
	* * 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
	* without specific prior written permission.
	*
	* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
	* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
	* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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	* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
	*/
	package java.time.zone;

	import java.io.DataInput;
	import java.io.DataOutput;
	import java.io.IOException;
	import java.io.InvalidObjectException;
	import java.io.ObjectInputStream;
	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 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'.
	*
	* @implSpec
	* 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 transition epoch-second.
	*/
	private final long epochSecond;
	/**
	* 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) {
	assert transition.getNano() == 0;
	this.epochSecond = transition.toEpochSecond(offsetBefore);
	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.epochSecond = epochSecond;
	this.transition = LocalDateTime.ofEpochSecond(epochSecond, 0, offsetBefore);
	this.offsetBefore = offsetBefore;
	this.offsetAfter = offsetAfter;
	}

	//-----------------------------------------------------------------------
	/**
	* Defend against malicious streams.
	*
	* @param s the stream to read
	* @throws InvalidObjectException always
	*/
	private void readObject(ObjectInputStream s) throws InvalidObjectException {
	throw new InvalidObjectException("Deserialization via serialization delegate");
	}

	/**
	* Writes the object using a
	* <a href="../../../serialized-form.html#java.time.zone.Ser">dedicated serialized form</a>.
	* @serialData
	* Refer to the serialized form of
	* <a href="../../../serialized-form.html#java.time.zone.ZoneRules">ZoneRules.writeReplace</a>
	* for the encoding of epoch seconds and offsets.
	* <pre style="font-size:1.0em">{@code
	*
	* out.writeByte(2); // identifies a ZoneOffsetTransition
	* out.writeEpochSec(toEpochSecond);
	* out.writeOffset(offsetBefore);
	* out.writeOffset(offsetAfter);
	* }
	* </pre>
	* @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(epochSecond, 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 Instant.ofEpochSecond(epochSecond);
	}

	/**
	* Gets the transition instant as an epoch second.
	*
	* @return the transition epoch second
	*/
	public long toEpochSecond() {
	return epochSecond;
	}

	//-------------------------------------------------------------------------
	/**
	* 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 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 List.of();
	}
	return List.of(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 Long.compare(epochSecond, transition.epochSecond);
	}

	//-----------------------------------------------------------------------
	/**
	* 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 epochSecond == d.epochSecond &&
	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();
	}

	}

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