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/*
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 * Copyright (c) 2007-2012, 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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 * * 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.
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 * may be used to endorse or promote products derived from this software
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package java.time;

import static java.time.LocalTime.MINUTES_PER_HOUR;
import static java.time.LocalTime.SECONDS_PER_HOUR;
import static java.time.LocalTime.SECONDS_PER_MINUTE;
import static java.time.temporal.ChronoField.OFFSET_SECONDS;

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.temporal.ChronoField;
import java.time.temporal.Temporal;
import java.time.temporal.TemporalAccessor;
import java.time.temporal.TemporalAdjuster;
import java.time.temporal.TemporalField;
import java.time.temporal.TemporalQueries;
import java.time.temporal.TemporalQuery;
import java.time.temporal.UnsupportedTemporalTypeException;
import java.time.temporal.ValueRange;
import java.time.zone.ZoneRules;
import java.util.Objects;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;

/**
 * A time-zone offset from Greenwich/UTC, such as {@code +02:00}.
 * <p>
 * A time-zone offset is the amount of time that a time-zone differs from Greenwich/UTC.
 * This is usually a fixed number of hours and minutes.
 * <p>
 * Different parts of the world have different time-zone offsets.
 * The rules for how offsets vary by place and time of year are captured in the
 * {@link ZoneId} class.
 * <p>
 * For example, Paris is one hour ahead of Greenwich/UTC in winter and two hours
 * ahead in summer. The {@code ZoneId} instance for Paris will reference two
 * {@code ZoneOffset} instances - a {@code +01:00} instance for winter,
 * and a {@code +02:00} instance for summer.
 * <p>
 * In 2008, time-zone offsets around the world extended from -12:00 to +14:00.
 * To prevent any problems with that range being extended, yet still provide
 * validation, the range of offsets is restricted to -18:00 to 18:00 inclusive.
 * <p>
 * This class is designed for use with the ISO calendar system.
 * The fields of hours, minutes and seconds make assumptions that are valid for the
 * standard ISO definitions of those fields. This class may be used with other
 * calendar systems providing the definition of the time fields matches those
 * of the ISO calendar system.
 * <p>
 * Instances of {@code ZoneOffset} must be compared using {@link #equals}.
 * Implementations may choose to cache certain common offsets, however
 * applications must not rely on such caching.
 *
 * <p>
 * This is a <a href="{@docRoot}/java/lang/doc-files/ValueBased.html">value-based</a>
 * class; use of identity-sensitive operations (including reference equality
 * ({@code ==}), identity hash code, or synchronization) on instances of
 * {@code ZoneOffset} may have unpredictable results and should be avoided.
 * The {@code equals} method should be used for comparisons.
 *
 * @implSpec
 * This class is immutable and thread-safe.
 *
 * @since 1.8
 */
public final class ZoneOffset
 extends ZoneId
 implements TemporalAccessor, TemporalAdjuster, Comparable<ZoneOffset>, Serializable {

 /** Cache of time-zone offset by offset in seconds. */
 private static final ConcurrentMap<Integer, ZoneOffset> SECONDS_CACHE = new ConcurrentHashMap<>(16, 0.75f, 4);
 /** Cache of time-zone offset by ID. */
 private static final ConcurrentMap<String, ZoneOffset> ID_CACHE = new ConcurrentHashMap<>(16, 0.75f, 4);

 /**
 * The abs maximum seconds.
 */
 private static final int MAX_SECONDS = 18 * SECONDS_PER_HOUR;
 /**
 * Serialization version.
 */
 private static final long serialVersionUID = 2357656521762053153L;

 /**
 * The time-zone offset for UTC, with an ID of 'Z'.
 */
 public static final ZoneOffset UTC = ZoneOffset.ofTotalSeconds(0);
 /**
 * Constant for the maximum supported offset.
 */
 public static final ZoneOffset MIN = ZoneOffset.ofTotalSeconds(-MAX_SECONDS);
 /**
 * Constant for the maximum supported offset.
 */
 public static final ZoneOffset MAX = ZoneOffset.ofTotalSeconds(MAX_SECONDS);

 /**
 * The total offset in seconds.
 */
 private final int totalSeconds;
 /**
 * The string form of the time-zone offset.
 */
 private final transient String id;

 //-----------------------------------------------------------------------
 /**
 * Obtains an instance of {@code ZoneOffset} using the ID.
 * <p>
 * This method parses the string ID of a {@code ZoneOffset} to
 * return an instance. The parsing accepts all the formats generated by
 * {@link #getId()}, plus some additional formats:
 * <ul>
 * <li>{@code Z} - for UTC
 * <li>{@code +h}
 * <li>{@code +hh}
 * <li>{@code +hh:mm}
 * <li>{@code -hh:mm}
 * <li>{@code +hhmm}
 * <li>{@code -hhmm}
 * <li>{@code +hh:mm:ss}
 * <li>{@code -hh:mm:ss}
 * <li>{@code +hhmmss}
 * <li>{@code -hhmmss}
 * </ul>
 * Note that &plusmn; means either the plus or minus symbol.
 * <p>
 * The ID of the returned offset will be normalized to one of the formats
 * described by {@link #getId()}.
 * <p>
 * The maximum supported range is from +18:00 to -18:00 inclusive.
 *
 * @param offsetId the offset ID, not null
 * @return the zone-offset, not null
 * @throws DateTimeException if the offset ID is invalid
 */
 @SuppressWarnings("fallthrough")
 public static ZoneOffset of(String offsetId) {
 Objects.requireNonNull(offsetId, "offsetId");
 // "Z" is always in the cache
 ZoneOffset offset = ID_CACHE.get(offsetId);
 if (offset != null) {
 return offset;
 }

 // parse - +h, +hh, +hhmm, +hh:mm, +hhmmss, +hh:mm:ss
 final int hours, minutes, seconds;
 switch (offsetId.length()) {
 case 2:
 offsetId = offsetId.charAt(0) + "0" + offsetId.charAt(1); // fallthru
 case 3:
 hours = parseNumber(offsetId, 1, false);
 minutes = 0;
 seconds = 0;
 break;
 case 5:
 hours = parseNumber(offsetId, 1, false);
 minutes = parseNumber(offsetId, 3, false);
 seconds = 0;
 break;
 case 6:
 hours = parseNumber(offsetId, 1, false);
 minutes = parseNumber(offsetId, 4, true);
 seconds = 0;
 break;
 case 7:
 hours = parseNumber(offsetId, 1, false);
 minutes = parseNumber(offsetId, 3, false);
 seconds = parseNumber(offsetId, 5, false);
 break;
 case 9:
 hours = parseNumber(offsetId, 1, false);
 minutes = parseNumber(offsetId, 4, true);
 seconds = parseNumber(offsetId, 7, true);
 break;
 default:
 throw new DateTimeException("Invalid ID for ZoneOffset, invalid format: " + offsetId);
 }
 char first = offsetId.charAt(0);
 if (first != '+' && first != '-') {
 throw new DateTimeException("Invalid ID for ZoneOffset, plus/minus not found when expected: " + offsetId);
 }
 if (first == '-') {
 return ofHoursMinutesSeconds(-hours, -minutes, -seconds);
 } else {
 return ofHoursMinutesSeconds(hours, minutes, seconds);
 }
 }

 /**
 * Parse a two digit zero-prefixed number.
 *
 * @param offsetId the offset ID, not null
 * @param pos the position to parse, valid
 * @param precededByColon should this number be prefixed by a precededByColon
 * @return the parsed number, from 0 to 99
 */
 private static int parseNumber(CharSequence offsetId, int pos, boolean precededByColon) {
 if (precededByColon && offsetId.charAt(pos - 1) != ':') {
 throw new DateTimeException("Invalid ID for ZoneOffset, colon not found when expected: " + offsetId);
 }
 char ch1 = offsetId.charAt(pos);
 char ch2 = offsetId.charAt(pos + 1);
 if (ch1 < '0' || ch1 > '9' || ch2 < '0' || ch2 > '9') {
 throw new DateTimeException("Invalid ID for ZoneOffset, non numeric characters found: " + offsetId);
 }
 return (ch1 - 48) * 10 + (ch2 - 48);
 }

 //-----------------------------------------------------------------------
 /**
 * Obtains an instance of {@code ZoneOffset} using an offset in hours.
 *
 * @param hours the time-zone offset in hours, from -18 to +18
 * @return the zone-offset, not null
 * @throws DateTimeException if the offset is not in the required range
 */
 public static ZoneOffset ofHours(int hours) {
 return ofHoursMinutesSeconds(hours, 0, 0);
 }

 /**
 * Obtains an instance of {@code ZoneOffset} using an offset in
 * hours and minutes.
 * <p>
 * The sign of the hours and minutes components must match.
 * Thus, if the hours is negative, the minutes must be negative or zero.
 * If the hours is zero, the minutes may be positive, negative or zero.
 *
 * @param hours the time-zone offset in hours, from -18 to +18
 * @param minutes the time-zone offset in minutes, from 0 to &plusmn;59, sign matches hours
 * @return the zone-offset, not null
 * @throws DateTimeException if the offset is not in the required range
 */
 public static ZoneOffset ofHoursMinutes(int hours, int minutes) {
 return ofHoursMinutesSeconds(hours, minutes, 0);
 }

 /**
 * Obtains an instance of {@code ZoneOffset} using an offset in
 * hours, minutes and seconds.
 * <p>
 * The sign of the hours, minutes and seconds components must match.
 * Thus, if the hours is negative, the minutes and seconds must be negative or zero.
 *
 * @param hours the time-zone offset in hours, from -18 to +18
 * @param minutes the time-zone offset in minutes, from 0 to &plusmn;59, sign matches hours and seconds
 * @param seconds the time-zone offset in seconds, from 0 to &plusmn;59, sign matches hours and minutes
 * @return the zone-offset, not null
 * @throws DateTimeException if the offset is not in the required range
 */
 public static ZoneOffset ofHoursMinutesSeconds(int hours, int minutes, int seconds) {
 validate(hours, minutes, seconds);
 int totalSeconds = totalSeconds(hours, minutes, seconds);
 return ofTotalSeconds(totalSeconds);
 }

 //-----------------------------------------------------------------------
 /**
 * Obtains an instance of {@code ZoneOffset} from a temporal object.
 * <p>
 * This obtains an offset based on the specified temporal.
 * A {@code TemporalAccessor} represents an arbitrary set of date and time information,
 * which this factory converts to an instance of {@code ZoneOffset}.
 * <p>
 * A {@code TemporalAccessor} represents some form of date and time information.
 * This factory converts the arbitrary temporal object to an instance of {@code ZoneOffset}.
 * <p>
 * The conversion uses the {@link TemporalQueries#offset()} query, which relies
 * on extracting the {@link ChronoField#OFFSET_SECONDS OFFSET_SECONDS} field.
 * <p>
 * This method matches the signature of the functional interface {@link TemporalQuery}
 * allowing it to be used as a query via method reference, {@code ZoneOffset::from}.
 *
 * @param temporal the temporal object to convert, not null
 * @return the zone-offset, not null
 * @throws DateTimeException if unable to convert to an {@code ZoneOffset}
 */
 public static ZoneOffset from(TemporalAccessor temporal) {
 Objects.requireNonNull(temporal, "temporal");
 ZoneOffset offset = temporal.query(TemporalQueries.offset());
 if (offset == null) {
 throw new DateTimeException("Unable to obtain ZoneOffset from TemporalAccessor: " +
 temporal + " of type " + temporal.getClass().getName());
 }
 return offset;
 }

 //-----------------------------------------------------------------------
 /**
 * Validates the offset fields.
 *
 * @param hours the time-zone offset in hours, from -18 to +18
 * @param minutes the time-zone offset in minutes, from 0 to &plusmn;59
 * @param seconds the time-zone offset in seconds, from 0 to &plusmn;59
 * @throws DateTimeException if the offset is not in the required range
 */
 private static void validate(int hours, int minutes, int seconds) {
 if (hours < -18 || hours > 18) {
 throw new DateTimeException("Zone offset hours not in valid range: value " + hours +
 " is not in the range -18 to 18");
 }
 if (hours > 0) {
 if (minutes < 0 || seconds < 0) {
 throw new DateTimeException("Zone offset minutes and seconds must be positive because hours is positive");
 }
 } else if (hours < 0) {
 if (minutes > 0 || seconds > 0) {
 throw new DateTimeException("Zone offset minutes and seconds must be negative because hours is negative");
 }
 } else if ((minutes > 0 && seconds < 0) || (minutes < 0 && seconds > 0)) {
 throw new DateTimeException("Zone offset minutes and seconds must have the same sign");
 }
 if (minutes < -59 || minutes > 59) {
 throw new DateTimeException("Zone offset minutes not in valid range: value " +
 minutes + " is not in the range -59 to 59");
 }
 if (seconds < -59 || seconds > 59) {
 throw new DateTimeException("Zone offset seconds not in valid range: value " +
 seconds + " is not in the range -59 to 59");
 }
 if (Math.abs(hours) == 18 && (minutes | seconds) != 0) {
 throw new DateTimeException("Zone offset not in valid range: -18:00 to +18:00");
 }
 }

 /**
 * Calculates the total offset in seconds.
 *
 * @param hours the time-zone offset in hours, from -18 to +18
 * @param minutes the time-zone offset in minutes, from 0 to &plusmn;59, sign matches hours and seconds
 * @param seconds the time-zone offset in seconds, from 0 to &plusmn;59, sign matches hours and minutes
 * @return the total in seconds
 */
 private static int totalSeconds(int hours, int minutes, int seconds) {
 return hours * SECONDS_PER_HOUR + minutes * SECONDS_PER_MINUTE + seconds;
 }

 //-----------------------------------------------------------------------
 /**
 * Obtains an instance of {@code ZoneOffset} specifying the total offset in seconds
 * <p>
 * The offset must be in the range {@code -18:00} to {@code +18:00}, which corresponds to -64800 to +64800.
 *
 * @param totalSeconds the total time-zone offset in seconds, from -64800 to +64800
 * @return the ZoneOffset, not null
 * @throws DateTimeException if the offset is not in the required range
 */
 public static ZoneOffset ofTotalSeconds(int totalSeconds) {
 if (totalSeconds < -MAX_SECONDS || totalSeconds > MAX_SECONDS) {
 throw new DateTimeException("Zone offset not in valid range: -18:00 to +18:00");
 }
 if (totalSeconds % (15 * SECONDS_PER_MINUTE) == 0) {
 Integer totalSecs = totalSeconds;
 ZoneOffset result = SECONDS_CACHE.get(totalSecs);
 if (result == null) {
 result = new ZoneOffset(totalSeconds);
 SECONDS_CACHE.putIfAbsent(totalSecs, result);
 result = SECONDS_CACHE.get(totalSecs);
 ID_CACHE.putIfAbsent(result.getId(), result);
 }
 return result;
 } else {
 return new ZoneOffset(totalSeconds);
 }
 }

 //-----------------------------------------------------------------------
 /**
 * Constructor.
 *
 * @param totalSeconds the total time-zone offset in seconds, from -64800 to +64800
 */
 private ZoneOffset(int totalSeconds) {
 super();
 this.totalSeconds = totalSeconds;
 id = buildId(totalSeconds);
 }

 private static String buildId(int totalSeconds) {
 if (totalSeconds == 0) {
 return "Z";
 } else {
 int absTotalSeconds = Math.abs(totalSeconds);
 StringBuilder buf = new StringBuilder();
 int absHours = absTotalSeconds / SECONDS_PER_HOUR;
 int absMinutes = (absTotalSeconds / SECONDS_PER_MINUTE) % MINUTES_PER_HOUR;
 buf.append(totalSeconds < 0 ? "-" : "+")
 .append(absHours < 10 ? "0" : "").append(absHours)
 .append(absMinutes < 10 ? ":0" : ":").append(absMinutes);
 int absSeconds = absTotalSeconds % SECONDS_PER_MINUTE;
 if (absSeconds != 0) {
 buf.append(absSeconds < 10 ? ":0" : ":").append(absSeconds);
 }
 return buf.toString();
 }
 }

 //-----------------------------------------------------------------------
 /**
 * Gets the total zone offset in seconds.
 * <p>
 * This is the primary way to access the offset amount.
 * It returns the total of the hours, minutes and seconds fields as a
 * single offset that can be added to a time.
 *
 * @return the total zone offset amount in seconds
 */
 public int getTotalSeconds() {
 return totalSeconds;
 }

 /**
 * Gets the normalized zone offset ID.
 * <p>
 * The ID is minor variation to the standard ISO-8601 formatted string
 * for the offset. There are three formats:
 * <ul>
 * <li>{@code Z} - for UTC (ISO-8601)
 * <li>{@code +hh:mm} or {@code -hh:mm} - if the seconds are zero (ISO-8601)
 * <li>{@code +hh:mm:ss} or {@code -hh:mm:ss} - if the seconds are non-zero (not ISO-8601)
 * </ul>
 *
 * @return the zone offset ID, not null
 */
 @Override
 public String getId() {
 return id;
 }

 /**
 * Gets the associated time-zone rules.
 * <p>
 * The rules will always return this offset when queried.
 * The implementation class is immutable, thread-safe and serializable.
 *
 * @return the rules, not null
 */
 @Override
 public ZoneRules getRules() {
 return ZoneRules.of(this);
 }

 //-----------------------------------------------------------------------
 /**
 * Checks if the specified field is supported.
 * <p>
 * This checks if this offset can be queried for the specified field.
 * If false, then calling the {@link #range(TemporalField) range} and
 * {@link #get(TemporalField) get} methods will throw an exception.
 * <p>
 * If the field is a {@link ChronoField} then the query is implemented here.
 * The {@code OFFSET_SECONDS} field returns true.
 * All other {@code ChronoField} instances will return false.
 * <p>
 * If the field is not a {@code ChronoField}, then the result of this method
 * is obtained by invoking {@code TemporalField.isSupportedBy(TemporalAccessor)}
 * passing {@code this} as the argument.
 * Whether the field is supported is determined by the field.
 *
 * @param field the field to check, null returns false
 * @return true if the field is supported on this offset, false if not
 */
 @Override
 public boolean isSupported(TemporalField field) {
 if (field instanceof ChronoField) {
 return field == OFFSET_SECONDS;
 }
 return field != null && field.isSupportedBy(this);
 }

 /**
 * Gets the range of valid values for the specified field.
 * <p>
 * The range object expresses the minimum and maximum valid values for a field.
 * This offset is used to enhance the accuracy of the returned range.
 * If it is not possible to return the range, because the field is not supported
 * or for some other reason, an exception is thrown.
 * <p>
 * If the field is a {@link ChronoField} then the query is implemented here.
 * The {@link #isSupported(TemporalField) supported fields} will return
 * appropriate range instances.
 * All other {@code ChronoField} instances will throw an {@code UnsupportedTemporalTypeException}.
 * <p>
 * If the field is not a {@code ChronoField}, then the result of this method
 * is obtained by invoking {@code TemporalField.rangeRefinedBy(TemporalAccessor)}
 * passing {@code this} as the argument.
 * Whether the range can be obtained is determined by the field.
 *
 * @param field the field to query the range for, not null
 * @return the range of valid values for the field, not null
 * @throws DateTimeException if the range for the field cannot be obtained
 * @throws UnsupportedTemporalTypeException if the field is not supported
 */
 @Override // override for Javadoc
 public ValueRange range(TemporalField field) {
 return TemporalAccessor.super.range(field);
 }

 /**
 * Gets the value of the specified field from this offset as an {@code int}.
 * <p>
 * This queries this offset for the value of the specified field.
 * The returned value will always be within the valid range of values for the field.
 * If it is not possible to return the value, because the field is not supported
 * or for some other reason, an exception is thrown.
 * <p>
 * If the field is a {@link ChronoField} then the query is implemented here.
 * The {@code OFFSET_SECONDS} field returns the value of the offset.
 * All other {@code ChronoField} instances will throw an {@code UnsupportedTemporalTypeException}.
 * <p>
 * If the field is not a {@code ChronoField}, then the result of this method
 * is obtained by invoking {@code TemporalField.getFrom(TemporalAccessor)}
 * passing {@code this} as the argument. Whether the value can be obtained,
 * and what the value represents, is determined by the field.
 *
 * @param field the field to get, not null
 * @return the value for the field
 * @throws DateTimeException if a value for the field cannot be obtained or
 * the value is outside the range of valid values for the field
 * @throws UnsupportedTemporalTypeException if the field is not supported or
 * the range of values exceeds an {@code int}
 * @throws ArithmeticException if numeric overflow occurs
 */
 @Override // override for Javadoc and performance
 public int get(TemporalField field) {
 if (field == OFFSET_SECONDS) {
 return totalSeconds;
 } else if (field instanceof ChronoField) {
 throw new UnsupportedTemporalTypeException("Unsupported field: " + field);
 }
 return range(field).checkValidIntValue(getLong(field), field);
 }

 /**
 * Gets the value of the specified field from this offset as a {@code long}.
 * <p>
 * This queries this offset for the value of the specified field.
 * If it is not possible to return the value, because the field is not supported
 * or for some other reason, an exception is thrown.
 * <p>
 * If the field is a {@link ChronoField} then the query is implemented here.
 * The {@code OFFSET_SECONDS} field returns the value of the offset.
 * All other {@code ChronoField} instances will throw an {@code UnsupportedTemporalTypeException}.
 * <p>
 * If the field is not a {@code ChronoField}, then the result of this method
 * is obtained by invoking {@code TemporalField.getFrom(TemporalAccessor)}
 * passing {@code this} as the argument. Whether the value can be obtained,
 * and what the value represents, is determined by the field.
 *
 * @param field the field to get, not null
 * @return the value for the field
 * @throws DateTimeException if a value for the field cannot be obtained
 * @throws UnsupportedTemporalTypeException if the field is not supported
 * @throws ArithmeticException if numeric overflow occurs
 */
 @Override
 public long getLong(TemporalField field) {
 if (field == OFFSET_SECONDS) {
 return totalSeconds;
 } else if (field instanceof ChronoField) {
 throw new UnsupportedTemporalTypeException("Unsupported field: " + field);
 }
 return field.getFrom(this);
 }

 //-----------------------------------------------------------------------
 /**
 * Queries this offset using the specified query.
 * <p>
 * This queries this offset using the specified query strategy object.
 * The {@code TemporalQuery} object defines the logic to be used to
 * obtain the result. Read the documentation of the query to understand
 * what the result of this method will be.
 * <p>
 * The result of this method is obtained by invoking the
 * {@link TemporalQuery#queryFrom(TemporalAccessor)} method on the
 * specified query passing {@code this} as the argument.
 *
 * @param <R> the type of the result
 * @param query the query to invoke, not null
 * @return the query result, null may be returned (defined by the query)
 * @throws DateTimeException if unable to query (defined by the query)
 * @throws ArithmeticException if numeric overflow occurs (defined by the query)
 */
 @SuppressWarnings("unchecked")
 @Override
 public <R> R query(TemporalQuery<R> query) {
 if (query == TemporalQueries.offset() || query == TemporalQueries.zone()) {
 return (R) this;
 }
 return TemporalAccessor.super.query(query);
 }

 /**
 * Adjusts the specified temporal object to have the same offset as this object.
 * <p>
 * This returns a temporal object of the same observable type as the input
 * with the offset changed to be the same as this.
 * <p>
 * The adjustment is equivalent to using {@link Temporal#with(TemporalField, long)}
 * passing {@link ChronoField#OFFSET_SECONDS} as the field.
 * <p>
 * In most cases, it is clearer to reverse the calling pattern by using
 * {@link Temporal#with(TemporalAdjuster)}:
 * <pre>
 * // these two lines are equivalent, but the second approach is recommended
 * temporal = thisOffset.adjustInto(temporal);
 * temporal = temporal.with(thisOffset);
 * </pre>
 * <p>
 * This instance is immutable and unaffected by this method call.
 *
 * @param temporal the target object to be adjusted, not null
 * @return the adjusted object, not null
 * @throws DateTimeException if unable to make the adjustment
 * @throws ArithmeticException if numeric overflow occurs
 */
 @Override
 public Temporal adjustInto(Temporal temporal) {
 return temporal.with(OFFSET_SECONDS, totalSeconds);
 }

 //-----------------------------------------------------------------------
 /**
 * Compares this offset to another offset in descending order.
 * <p>
 * The offsets are compared in the order that they occur for the same time
 * of day around the world. Thus, an offset of {@code +10:00} comes before an
 * offset of {@code +09:00} and so on down to {@code -18:00}.
 * <p>
 * The comparison is "consistent with equals", as defined by {@link Comparable}.
 *
 * @param other the other date to compare to, not null
 * @return the comparator value, negative if less, positive if greater
 * @throws NullPointerException if {@code other} is null
 */
 @Override
 public int compareTo(ZoneOffset other) {
 // abs(totalSeconds) <= MAX_SECONDS, so no overflow can happen here
 return other.totalSeconds - totalSeconds;
 }

 //-----------------------------------------------------------------------
 /**
 * Checks if this offset is equal to another offset.
 * <p>
 * The comparison is based on the amount of the offset in seconds.
 * This is equivalent to a comparison by ID.
 *
 * @param obj the object to check, null returns false
 * @return true if this is equal to the other offset
 */
 @Override
 public boolean equals(Object obj) {
 if (this == obj) {
 return true;
 }
 if (obj instanceof ZoneOffset) {
 return totalSeconds == ((ZoneOffset) obj).totalSeconds;
 }
 return false;
 }

 /**
 * A hash code for this offset.
 *
 * @return a suitable hash code
 */
 @Override
 public int hashCode() {
 return totalSeconds;
 }

 //-----------------------------------------------------------------------
 /**
 * Outputs this offset as a {@code String}, using the normalized ID.
 *
 * @return a string representation of this offset, not null
 */
 @Override
 public String toString() {
 return id;
 }

 // -----------------------------------------------------------------------
 /**
 * Writes the object using a
 * <a href="../../serialized-form.html#java.time.Ser">dedicated serialized form</a>.
 * @serialData
 * <pre>
 * out.writeByte(8); // identifies a ZoneOffset
 * int offsetByte = totalSeconds % 900 == 0 ? totalSeconds / 900 : 127;
 * out.writeByte(offsetByte);
 * if (offsetByte == 127) {
 * out.writeInt(totalSeconds);
 * }
 * </pre>
 *
 * @return the instance of {@code Ser}, not null
 */
 private Object writeReplace() {
 return new Ser(Ser.ZONE_OFFSET_TYPE, this);
 }

 /**
 * 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");
 }

 @Override
 void write(DataOutput out) throws IOException {
 out.writeByte(Ser.ZONE_OFFSET_TYPE);
 writeExternal(out);
 }

 void writeExternal(DataOutput out) throws IOException {
 final int offsetSecs = totalSeconds;
 int offsetByte = offsetSecs % 900 == 0 ? offsetSecs / 900 : 127; // compress to -72 to +72
 out.writeByte(offsetByte);
 if (offsetByte == 127) {
 out.writeInt(offsetSecs);
 }
 }

 static ZoneOffset readExternal(DataInput in) throws IOException {
 int offsetByte = in.readByte();
 return (offsetByte == 127 ? ZoneOffset.ofTotalSeconds(in.readInt()) : ZoneOffset.ofTotalSeconds(offsetByte * 900));
 }

}