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/*
* Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
* or more contributor license agreements. Licensed under the Elastic License
* 2.0 and the Server Side Public License, v 1; you may not use this file except
* in compliance with, at your election, the Elastic License 2.0 or the Server
* Side Public License, v 1.
*/
package org.elasticsearch.common;
import java.time.Instant;
import java.time.ZoneId;
import java.time.temporal.ChronoField;
import java.time.zone.ZoneOffsetTransition;
import java.time.zone.ZoneOffsetTransitionRule;
import java.time.zone.ZoneRules;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Iterator;
import java.util.List;
import java.util.Locale;
/**
* Converts utc into local time and back again.
*
* "Local time" is defined by some time zone, specifically and {@link ZoneId}.
* At any point in time a particular time zone is at some offset from from
* utc. So converting from utc is as simple as adding the offset.
*
* Getting from local time back to utc is harder. Most local times happen once.
* But some local times happen twice (DST overlap).
* And some don't happen at all (DST gap). Take, for example,
* the time in my house. Most days I don't touch my clocks and I'm a
* constant offset from UTC. But once in the fall at 2am I roll my clock back.
* So at 5am utc my clocks say 1am. Then at 6am utc my clocks say 1am AGAIN.
* I do similarly terrifying things again in the spring when I skip my clocks
* straight from 1:59am to 3am.
*
* So there are two methods to convert from local time back to utc,
* {@link #localToUtc(long, Strategy)} and {@link #localToUtcInThisOffset(long)}.
* @see ZoneOffsetTransition#isGap()
* @see ZoneOffsetTransition#isOverlap()
*/
public abstract class LocalTimeOffset {
/**
* Lookup offsets for a provided zone. This can fail if
* there are many transitions and the provided lookup would be very large.
*
* @return a {@linkplain Lookup} or {@code null} if none could be built
*/
public static Lookup lookup(ZoneId zone, long minUtcMillis, long maxUtcMillis) {
if (minUtcMillis > maxUtcMillis) {
throw new IllegalArgumentException("[" + minUtcMillis + "] must be <= [" + maxUtcMillis + "]");
}
ZoneRules rules = zone.getRules();
{
LocalTimeOffset fixed = checkForFixedZone(zone, rules);
if (fixed != null) {
return new FixedLookup(zone, fixed);
}
}
List transitions = collectTransitions(zone, rules, minUtcMillis, maxUtcMillis);
if (transitions == null) {
// The range is too large for us to pre-build all the offsets
return null;
}
if (transitions.size() < 3) {
/*
* Its actually quite common that there are *very* few transitions.
* This case where there are only two transitions covers an entire
* year of data! In any case, it is slightly faster to do the
* "simpler" thing and compare the start times instead of perform
* a binary search when there are so few offsets to look at.
*/
return new LinkedListLookup(zone, minUtcMillis, maxUtcMillis, transitions);
}
return new TransitionArrayLookup(zone, minUtcMillis, maxUtcMillis, transitions);
}
/**
* Lookup offsets without any known min or max time. This will generally
* fail if the provided zone isn't fixed.
*
* @return a lookup function of {@code null} if none could be built
*/
public static LocalTimeOffset fixedOffset(ZoneId zone) {
return checkForFixedZone(zone, zone.getRules());
}
private final long millis;
private LocalTimeOffset(long millis) {
this.millis = millis;
}
/**
* Convert a time in utc into a the local time at this offset.
*/
public final long utcToLocalTime(long utcMillis) {
return utcMillis + millis;
}
/**
* Convert a time in local millis to utc millis using this offset.
*
* Important: Callers will rarely want to force
* using this offset and are instead instead interested in picking an appropriate
* offset for some local time that they have rounded down. In that case use
* {@link #localToUtc(long, Strategy)}.
*/
public final long localToUtcInThisOffset(long localMillis) {
return localMillis - millis;
}
/**
* Convert a local time that occurs during this offset or a previous
* offset to utc, providing a strategy for how to resolve "funny" cases.
* You can use this if you've converted from utc to local, rounded down,
* and then want to convert back to utc and you need fine control over
* how to handle the "funny" edges.
*
* This will not help you if you must convert a local time that you've
* rounded up. For that you are on your own. May God
* have mercy on your soul.
*/
public abstract long localToUtc(long localMillis, Strategy strat);
public interface Strategy {
/**
* Handle a local time that never actually happened because a "gap"
* jumped over it. This happens in many time zones when folks wind
* their clocks forwards in the spring.
*
* @return the time in utc representing the local time
*/
long inGap(long localMillis, Gap gap);
/**
* Handle a local time that happened before the start of a gap.
*
* @return the time in utc representing the local time
*/
long beforeGap(long localMillis, Gap gap);
/**
* Handle a local time that happened twice because an "overlap"
* jumped behind it. This happens in many time zones when folks wind
* their clocks back in the fall.
*
* @return the time in utc representing the local time
*/
long inOverlap(long localMillis, Overlap overlap);
/**
* Handle a local time that happened before the start of an overlap.
*
* @return the time in utc representing the local time
*/
long beforeOverlap(long localMillis, Overlap overlap);
}
/**
* Does this offset contain the provided time?
*/
protected abstract boolean containsUtcMillis(long utcMillis);
/**
* Find the offset containing the provided time, first checking this
* offset, then its previous offset, the than one's previous offset, etc.
*/
protected abstract LocalTimeOffset offsetContaining(long utcMillis);
/**
* Does this transition or any previous transitions move back to the
* previous day? See {@link Lookup#anyMoveBackToPreviousDay()} for rules.
*/
protected abstract boolean anyMoveBackToPreviousDay();
@Override
public String toString() {
return toString(millis);
}
protected abstract String toString(long millis);
/**
* How to get instances of {@link LocalTimeOffset}.
*/
public abstract static class Lookup {
/**
* Lookup the offset at the provided millis in utc.
*/
public abstract LocalTimeOffset lookup(long utcMillis);
/**
* If the offset for a range is constant then return it, otherwise
* return {@code null}.
*/
public abstract LocalTimeOffset fixedInRange(long minUtcMillis, long maxUtcMillis);
/**
* Do any of the transitions move back to the previous day?
*
* Note: If an overlap occurs at, say, 1 am and jumps back to
* exactly midnight then it doesn't count because
* midnight is still counted as being in the "next" day.
*/
public abstract boolean anyMoveBackToPreviousDay();
/**
* The number of offsets in the lookup. Package private for testing.
*/
abstract int size();
}
private static class NoPrevious extends LocalTimeOffset {
NoPrevious(long millis) {
super(millis);
}
@Override
public long localToUtc(long localMillis, Strategy strat) {
return localToUtcInThisOffset(localMillis);
}
@Override
protected boolean containsUtcMillis(long utcMillis) {
return true;
}
@Override
protected LocalTimeOffset offsetContaining(long utcMillis) {
/*
* Since there isn't a previous offset this offset *must* contain
* the provided time.
*/
return this;
}
@Override
protected boolean anyMoveBackToPreviousDay() {
return false;
}
@Override
protected String toString(long millis) {
return Long.toString(millis);
}
}
public abstract static class Transition extends LocalTimeOffset {
private final LocalTimeOffset previous;
private final long startUtcMillis;
private Transition(long millis, LocalTimeOffset previous, long startUtcMillis) {
super(millis);
this.previous = previous;
this.startUtcMillis = startUtcMillis;
}
/**
* The offset before the this one.
*/
public LocalTimeOffset previous() {
return previous;
}
@Override
protected final boolean containsUtcMillis(long utcMillis) {
return utcMillis >= startUtcMillis;
}
@Override
protected final LocalTimeOffset offsetContaining(long utcMillis) {
if (containsUtcMillis(utcMillis)) {
return this;
}
return previous.offsetContaining(utcMillis);
}
/**
* The time that this offset started in milliseconds since epoch.
*/
public long startUtcMillis() {
return startUtcMillis;
}
}
public static class Gap extends Transition {
private final long firstMissingLocalTime;
private final long firstLocalTimeAfterGap;
private Gap(long millis, LocalTimeOffset previous, long startUtcMillis, long firstMissingLocalTime, long firstLocalTimeAfterGap) {
super(millis, previous, startUtcMillis);
this.firstMissingLocalTime = firstMissingLocalTime;
this.firstLocalTimeAfterGap = firstLocalTimeAfterGap;
assert firstMissingLocalTime < firstLocalTimeAfterGap;
}
@Override
public long localToUtc(long localMillis, Strategy strat) {
if (localMillis >= firstLocalTimeAfterGap) {
return localToUtcInThisOffset(localMillis);
}
if (localMillis >= firstMissingLocalTime) {
return strat.inGap(localMillis, this);
}
return strat.beforeGap(localMillis, this);
}
/**
* The first time that is missing from the local time because of this gap.
*/
public long firstMissingLocalTime() {
return firstMissingLocalTime;
}
@Override
protected boolean anyMoveBackToPreviousDay() {
return previous().anyMoveBackToPreviousDay();
}
@Override
protected String toString(long millis) {
return "Gap of " + millis + "@" + Instant.ofEpochMilli(startUtcMillis());
}
}
public static class Overlap extends Transition {
private final long firstOverlappingLocalTime;
private final long firstNonOverlappingLocalTime;
private final boolean movesBackToPreviousDay;
private Overlap(
long millis,
LocalTimeOffset previous,
long startUtcMillis,
long firstOverlappingLocalTime,
long firstNonOverlappingLocalTime,
boolean movesBackToPreviousDay
) {
super(millis, previous, startUtcMillis);
this.firstOverlappingLocalTime = firstOverlappingLocalTime;
this.firstNonOverlappingLocalTime = firstNonOverlappingLocalTime;
assert firstOverlappingLocalTime < firstNonOverlappingLocalTime;
this.movesBackToPreviousDay = movesBackToPreviousDay;
}
@Override
public long localToUtc(long localMillis, Strategy strat) {
if (localMillis >= firstNonOverlappingLocalTime) {
return localToUtcInThisOffset(localMillis);
}
if (localMillis >= firstOverlappingLocalTime) {
return strat.inOverlap(localMillis, this);
}
return strat.beforeOverlap(localMillis, this);
}
/**
* The first local time after the overlap stops.
*/
public long firstNonOverlappingLocalTime() {
return firstNonOverlappingLocalTime;
}
/**
* The first local time to be appear twice.
*/
public long firstOverlappingLocalTime() {
return firstOverlappingLocalTime;
}
@Override
protected boolean anyMoveBackToPreviousDay() {
return movesBackToPreviousDay || previous().anyMoveBackToPreviousDay();
}
@Override
protected String toString(long millis) {
return "Overlap of " + millis + "@" + Instant.ofEpochMilli(startUtcMillis());
}
}
private static class FixedLookup extends Lookup {
private final ZoneId zone;
private final LocalTimeOffset fixed;
private FixedLookup(ZoneId zone, LocalTimeOffset fixed) {
this.zone = zone;
this.fixed = fixed;
}
@Override
public LocalTimeOffset lookup(long utcMillis) {
return fixed;
}
@Override
public LocalTimeOffset fixedInRange(long minUtcMillis, long maxUtcMillis) {
return fixed;
}
@Override
int size() {
return 1;
}
@Override
public String toString() {
return String.format(Locale.ROOT, "FixedLookup[for %s at %s]", zone, fixed);
}
@Override
public boolean anyMoveBackToPreviousDay() {
return false;
}
}
/**
* Looks up transitions by checking whether the date is after the start
* of each transition. Simple so fast for small numbers of transitions.
*/
private static class LinkedListLookup extends AbstractManyTransitionsLookup {
private final LocalTimeOffset lastOffset;
private final int size;
LinkedListLookup(ZoneId zone, long minUtcMillis, long maxUtcMillis, List transitions) {
super(zone, minUtcMillis, maxUtcMillis);
int size = 1;
LocalTimeOffset last = buildNoPrevious(transitions.get(0));
for (ZoneOffsetTransition t : transitions) {
last = buildTransition(t, last);
size++;
}
this.lastOffset = last;
this.size = size;
}
@Override
public LocalTimeOffset innerLookup(long utcMillis) {
return lastOffset.offsetContaining(utcMillis);
}
@Override
int size() {
return size;
}
@Override
public boolean anyMoveBackToPreviousDay() {
return lastOffset.anyMoveBackToPreviousDay();
}
}
/**
* Builds an array that can be {@link Arrays#binarySearch(long[], long)}ed
* for the daylight savings time transitions.
*/
private static class TransitionArrayLookup extends AbstractManyTransitionsLookup {
private final LocalTimeOffset[] offsets;
private final long[] transitionOutUtcMillis;
private TransitionArrayLookup(ZoneId zone, long minUtcMillis, long maxUtcMillis, List transitions) {
super(zone, minUtcMillis, maxUtcMillis);
this.offsets = new LocalTimeOffset[transitions.size() + 1];
this.transitionOutUtcMillis = new long[transitions.size()];
this.offsets[0] = buildNoPrevious(transitions.get(0));
int i = 0;
for (ZoneOffsetTransition t : transitions) {
Transition transition = buildTransition(t, this.offsets[i]);
transitionOutUtcMillis[i] = transition.startUtcMillis();
i++;
this.offsets[i] = transition;
}
}
@Override
protected LocalTimeOffset innerLookup(long utcMillis) {
int index = Arrays.binarySearch(transitionOutUtcMillis, utcMillis);
if (index < 0) {
/*
* We're mostly not going to find the exact offset. Instead we'll
* end up at the "insertion point" for the utcMillis. We have no
* plans to insert utcMillis in the array, but the offset that
* contains utcMillis happens to be "insertion point" - 1.
*/
index = -index - 1;
} else {
index++;
}
assert index < offsets.length : "binarySearch did something weird";
return offsets[index];
}
@Override
int size() {
return offsets.length;
}
@Override
public boolean anyMoveBackToPreviousDay() {
return offsets[offsets.length - 1].anyMoveBackToPreviousDay();
}
@Override
public String toString() {
return String.format(
Locale.ROOT,
"TransitionArrayLookup[for %s between %s and %s]",
zone,
Instant.ofEpochMilli(minUtcMillis),
Instant.ofEpochMilli(maxUtcMillis)
);
}
}
private abstract static class AbstractManyTransitionsLookup extends Lookup {
protected final ZoneId zone;
protected final long minUtcMillis;
protected final long maxUtcMillis;
AbstractManyTransitionsLookup(ZoneId zone, long minUtcMillis, long maxUtcMillis) {
this.zone = zone;
this.minUtcMillis = minUtcMillis;
this.maxUtcMillis = maxUtcMillis;
}
@Override
public final LocalTimeOffset lookup(long utcMillis) {
assert utcMillis >= minUtcMillis;
assert utcMillis <= maxUtcMillis;
return innerLookup(utcMillis);
}
protected abstract LocalTimeOffset innerLookup(long utcMillis);
@Override
public final LocalTimeOffset fixedInRange(long minUtcMillis, long maxUtcMillis) {
LocalTimeOffset offset = lookup(maxUtcMillis);
return offset.containsUtcMillis(minUtcMillis) ? offset : null;
}
protected static NoPrevious buildNoPrevious(ZoneOffsetTransition transition) {
return new NoPrevious(transition.getOffsetBefore().getTotalSeconds() * 1000);
}
protected static Transition buildTransition(ZoneOffsetTransition transition, LocalTimeOffset previous) {
long utcStart = transition.toEpochSecond() * 1000;
long offsetBeforeMillis = transition.getOffsetBefore().getTotalSeconds() * 1000;
long offsetAfterMillis = transition.getOffsetAfter().getTotalSeconds() * 1000;
assert (false == previous instanceof Transition) || ((Transition) previous).startUtcMillis < utcStart
: "transition list out of order at [" + previous + "] and [" + transition + "]";
assert previous.millis != offsetAfterMillis
: "transition list is has a duplicate at [" + previous + "] and [" + transition + "]";
if (transition.isGap()) {
long firstMissingLocalTime = utcStart + offsetBeforeMillis;
long firstLocalTimeAfterGap = utcStart + offsetAfterMillis;
return new Gap(offsetAfterMillis, previous, utcStart, firstMissingLocalTime, firstLocalTimeAfterGap);
}
long firstOverlappingLocalTime = utcStart + offsetAfterMillis;
long firstNonOverlappingLocalTime = utcStart + offsetBeforeMillis;
return new Overlap(
offsetAfterMillis,
previous,
utcStart,
firstOverlappingLocalTime,
firstNonOverlappingLocalTime,
movesBackToPreviousDay(transition)
);
}
private static boolean movesBackToPreviousDay(ZoneOffsetTransition transition) {
if (transition.getDateTimeBefore().getDayOfMonth() == transition.getDateTimeAfter().getDayOfMonth()) {
return false;
}
if (transition.getDateTimeBefore().getLong(ChronoField.NANO_OF_DAY) == 0L) {
// If we change *at* midnight this is ok.
return false;
}
return true;
}
}
private static LocalTimeOffset checkForFixedZone(ZoneId zone, ZoneRules rules) {
if (false == rules.isFixedOffset()) {
return null;
}
LocalTimeOffset fixedTransition = new NoPrevious(rules.getOffset(Instant.EPOCH).getTotalSeconds() * 1000);
return fixedTransition;
}
/**
* The maximum number of {@link ZoneOffsetTransition} to collect before
* giving up because the date range will be "too big". I picked this number
* fairly arbitrarily with the following goals:
*
* - Don't let {@code lookup(Long.MIN_VALUE, Long.MAX_VALUE)} consume all
* the memory in the JVM.
*
- It should be much larger than the number of offsets I'm bound to
* collect.
*
* {@code 5_000} collects about 2_500 years worth offsets which feels like
* quite a few!
*/
private static final int MAX_TRANSITIONS = 5000;
/**
* Collect transitions from the provided rules for the provided date range
* into a list we can reason about. If we'd collect more than
* {@link #MAX_TRANSITIONS} rules we'll abort, returning {@code null}
* signaling that {@link LocalTimeOffset} is probably not the implementation
* to use in this case.
*
* {@link ZoneRules} gives us access to the local time transition database
* with two method: {@link ZoneRules#getTransitions()} for "fully defined"
* transitions and {@link ZoneRules#getTransitionRules()}. This first one
* is a list of transitions and when the they happened. To get the full
* picture of transitions you pick up from where that one leaves off using
* the rules, which are basically factories that you give the year in local
* time to build a transition for that year.
*
* This method collects all of the {@link ZoneRules#getTransitions()} that
* are relevant for the date range and, if our range extends past the last
* transition, calls
* {@link #buildTransitionsFromRules(List, ZoneId, ZoneRules, long, long)}
* to build the remaining transitions to fully describe the range.
*/
private static List collectTransitions(ZoneId zone, ZoneRules rules, long minUtcMillis, long maxUtcMillis) {
long minSecond = minUtcMillis / 1000;
long maxSecond = maxUtcMillis / 1000;
List transitions = new ArrayList<>();
ZoneOffsetTransition t = null;
Iterator itr = rules.getTransitions().iterator();
// Skip all transitions that are before our start time
while (itr.hasNext() && (t = itr.next()).toEpochSecond() < minSecond) {
}
if (false == itr.hasNext()) {
if (minSecond < t.toEpochSecond() && t.toEpochSecond() < maxSecond) {
transitions.add(t);
/*
* Sometimes the rules duplicate the transitions. And
* duplicates confuse us. So we have to skip past them.
*/
minSecond = t.toEpochSecond() + 1;
}
transitions = buildTransitionsFromRules(transitions, zone, rules, minSecond, maxSecond);
if (transitions != null && transitions.isEmpty()) {
/*
* If there aren't any rules and we haven't accumulated
* any transitions then we grab the last one we saw so we
* have some knowledge of the offset.
*/
transitions.add(t);
}
return transitions;
}
transitions.add(t);
while (itr.hasNext()) {
t = itr.next();
if (t.toEpochSecond() > maxSecond) {
return transitions;
}
transitions.add(t);
if (transitions.size() > MAX_TRANSITIONS) {
return null;
}
}
return buildTransitionsFromRules(transitions, zone, rules, t.toEpochSecond() + 1, maxSecond);
}
/**
* Build transitions for every year in our range from the rules
* stored in {@link ZoneRules#getTransitionRules()}.
*/
private static List buildTransitionsFromRules(
List transitions,
ZoneId zone,
ZoneRules rules,
long minSecond,
long maxSecond
) {
List transitionRules = rules.getTransitionRules();
if (transitionRules.isEmpty()) {
/*
* Zones like Asia/Kathmandu don't have any rules so we don't
* need to do any of this.
*/
return transitions;
}
int minYear = Instant.ofEpochSecond(minSecond).atZone(zone).toLocalDate().getYear();
int maxYear = Instant.ofEpochSecond(maxSecond).atZone(zone).toLocalDate().getYear();
/*
* Record only the rules from the current year that are greater
* than the minSecond so we don't go back in time when coming from
* a fixed transition.
*/
ZoneOffsetTransition lastTransitionFromMinYear = null;
for (ZoneOffsetTransitionRule rule : transitionRules) {
lastTransitionFromMinYear = rule.createTransition(minYear);
if (lastTransitionFromMinYear.toEpochSecond() < minSecond) {
continue;
}
transitions.add(lastTransitionFromMinYear);
if (transitions.size() > MAX_TRANSITIONS) {
return null;
}
}
if (minYear == maxYear) {
if (transitions.isEmpty()) {
// Make sure we have *some* transition to work with.
transitions.add(lastTransitionFromMinYear);
}
return transitions;
}
// Now build transitions for all of the remaining years.
minYear++;
if (transitions.size() + (maxYear - minYear) * transitionRules.size() > MAX_TRANSITIONS) {
return null;
}
for (int year = minYear; year <= maxYear; year++) {
for (ZoneOffsetTransitionRule rule : transitionRules) {
transitions.add(rule.createTransition(year));
}
}
return transitions;
}
}