packages/core/src/zone/ZoneRules.js
/*
* @copyright (c) 2016, Philipp Thürwächter & Pattrick Hüper
* @copyright (c) 2007-present, Stephen Colebourne & Michael Nascimento Santos
* @license BSD-3-Clause (see LICENSE in the root directory of this source tree)
*/
import { requireNonNull, abstractMethodFail } from '../assert';
import { Duration } from '../Duration';
import { Instant } from '../Instant';
export class ZoneRules {
/**
* Obtains an instance of {@link ZoneRules} that always uses the same offset.
*
* The returned rules always have the same offset.
*
* @param {ZoneOffset} offset - the offset, not null
* @return {ZoneRules} the zone rules, not null
*/
static of(offset) {
requireNonNull(offset, 'offset');
return new Fixed(offset);
}
//-----------------------------------------------------------------------
/**
* Checks of the zone rules are fixed, such that the offset never varies.
*
* @return {boolean} true if the time-zone is fixed and the offset never changes
*/
isFixedOffset(){
abstractMethodFail('ZoneRules.isFixedOffset');
}
//-----------------------------------------------------------------------
/**
*
* @param instantOrLocalDateTime
* @returns {ZoneOffset}
*/
offset(instantOrLocalDateTime){
if(instantOrLocalDateTime instanceof Instant){
return this.offsetOfInstant(instantOrLocalDateTime);
} else {
return this.offsetOfLocalDateTime(instantOrLocalDateTime);
}
}
/**
* Gets the offset applicable at the specified instant in these rules.
*
* The mapping from an instant to an offset is simple, there is only
* one valid offset for each instant.
* This method returns that offset.
*
* @param {Instant} instant - the instant to find the offset for, not null, but null
* may be ignored if the rules have a single offset for all instants
* @return {ZoneOffset} the offset, not null
*/
// eslint-disable-next-line no-unused-vars
offsetOfInstant(instant){
abstractMethodFail('ZoneRules.offsetInstant');
}
/**
* Gets the offset applicable at the specified epochMilli in these rules.
*
* The method is for javascript performance optimisation.
*
* @param {number} epochMilli - the epoch millisecond to find the offset for, not null, but null
* may be ignored if the rules have a single offset for all instants
* @return {ZoneOffset} the offset, not null
*/
// eslint-disable-next-line no-unused-vars
offsetOfEpochMilli(epochMilli){
abstractMethodFail('ZoneRules.offsetOfEpochMilli');
}
/**
* Gets a suitable offset for the specified local date-time in these rules.
*
* The mapping from a local date-time to an offset is not straightforward.
* There are three cases:
*
* * Normal, with one valid offset. For the vast majority of the year, the normal
* case applies, where there is a single valid offset for the local date-time.
* * Gap, with zero valid offsets. This is when clocks jump forward typically
* due to the spring daylight savings change from "winter" to "summer".
* In a gap there are local date-time values with no valid offset.
* * Overlap, with two valid offsets. This is when clocks are set back typically
* due to the autumn daylight savings change from "summer" to "winter".
* In an overlap there are local date-time values with two valid offsets.
*
* Thus, for any given local date-time there can be zero, one or two valid offsets.
* This method returns the single offset in the Normal case, and in the Gap or Overlap
* case it returns the offset before the transition.
*
* Since, in the case of Gap and Overlap, the offset returned is a "best" value, rather
* than the "correct" value, it should be treated with care. Applications that care
* about the correct offset should use a combination of this method,
* {@link getValidOffsets} and {@link getTransition}.
*
* @param {LocalDateTime} localDateTime - the local date-time to query, not null, but null
* may be ignored if the rules have a single offset for all instants
* @return {ZoneOffset} the best available offset for the local date-time, not null
*/
// eslint-disable-next-line no-unused-vars
offsetOfLocalDateTime(localDateTime){
abstractMethodFail('ZoneRules.offsetLocalDateTime');
}
/**
* Gets the offset applicable at the specified local date-time in these rules.
*
* The mapping from a local date-time to an offset is not straightforward.
* There are three cases:
*
* * Normal, with one valid offset. For the vast majority of the year, the normal
* case applies, where there is a single valid offset for the local date-time.
* * Gap, with zero valid offsets. This is when clocks jump forward typically
* due to the spring daylight savings change from "winter" to "summer".
* In a gap there are local date-time values with no valid offset.
* * Overlap, with two valid offsets. This is when clocks are set back typically
* due to the autumn daylight savings change from "summer" to "winter".
* In an overlap there are local date-time values with two valid offsets.
*
* Thus, for any given local date-time there can be zero, one or two valid offsets.
* This method returns that list of valid offsets, which is a list of size 0, 1 or 2.
* In the case where there are two offsets, the earlier offset is returned at index 0
* and the later offset at index 1.
*
* There are various ways to handle the conversion from a {@link LocalDateTime}.
* One technique, using this method, would be:
* <pre>
* List<ZoneOffset> validOffsets = rules.getOffset(localDT);
* if (validOffsets.size() == 1) {
* // Normal case: only one valid offset
* zoneOffset = validOffsets.get(0);
* } else {
* // Gap or Overlap: determine what to do from transition (which will be non-null)
* ZoneOffsetTransition trans = rules.getTransition(localDT);
* }
* </pre>
*
* In theory, it is possible for there to be more than two valid offsets.
* This would happen if clocks to be put back more than once in quick succession.
* This has never happened in the history of time-zones and thus has no special handling.
* However, if it were to happen, then the list would return more than 2 entries.
*
* @param {LocalDateTime} localDateTime - the local date-time to query for valid offsets, not null
* may be ignored if the rules have a single offset for all instants
* @return {ZoneOffset[]} the list of valid offsets, may be immutable, not null
*/
// eslint-disable-next-line no-unused-vars
validOffsets(localDateTime){
abstractMethodFail('ZoneRules.validOffsets');
}
/**
* Gets the offset transition applicable at the specified local date-time in these rules.
*
* The mapping from a local date-time to an offset is not straightforward.
* There are three cases:
*
* * Normal, with one valid offset. For the vast majority of the year, the normal
* case applies, where there is a single valid offset for the local date-time.
* * Gap, with zero valid offsets. This is when clocks jump forward typically
* due to the spring daylight savings change from "winter" to "summer".
* In a gap there are local date-time values with no valid offset.
* * Overlap, with two valid offsets. This is when clocks are set back typically
* due to the autumn daylight savings change from "summer" to "winter".
* In an overlap there are local date-time values with two valid offsets.
*
* A transition is used to model the cases of a Gap or Overlap.
* The Normal case will return null.
*
* There are various ways to handle the conversion from a {@link LocalDateTime}.
* One technique, using this method, would be:
* <pre>
* ZoneOffsetTransition trans = rules.getTransition(localDT);
* if (trans != null) {
* // Gap or Overlap: determine what to do from transition
* } else {
* // Normal case: only one valid offset
* zoneOffset = rule.getOffset(localDT);
* }
* </pre>
*
* @param {LocalDateTime} localDateTime the local date-time to query for offset transition, not null, but null
* may be ignored if the rules have a single offset for all instants
* @return {ZoneOffsetTransition} the offset transition, null if the local date-time is not in transition
*/
// eslint-disable-next-line no-unused-vars
transition(localDateTime){
abstractMethodFail('ZoneRules.transition');
}
//-----------------------------------------------------------------------
/**
* Gets the standard offset for the specified instant in this zone.
*
* This provides access to historic information on how the standard offset
* has changed over time.
* The standard offset is the offset before any daylight saving time is applied.
* This is typically the offset applicable during winter.
*
* @param {Instant} instant - the instant to find the offset information for, not null, but null
* may be ignored if the rules have a single offset for all instants
* @return {ZoneOffset} the standard offset, not null
*/
// eslint-disable-next-line no-unused-vars
standardOffset(instant){
abstractMethodFail('ZoneRules.standardOffset');
}
/**
* Gets the amount of daylight savings in use for the specified instant in this zone.
*
* This provides access to historic information on how the amount of daylight
* savings has changed over time.
* This is the difference between the standard offset and the actual offset.
* Typically the amount is zero during winter and one hour during summer.
* Time-zones are second-based, so the nanosecond part of the duration will be zero.
*
* @param {Instant} instant - the instant to find the daylight savings for, not null, but null
* may be ignored if the rules have a single offset for all instants
* @return {Duration} the difference between the standard and actual offset, not null
*/
// eslint-disable-next-line no-unused-vars
daylightSavings(instant){
abstractMethodFail('ZoneRules.daylightSavings');
// default {
// ZoneOffset standardOffset = getStandardOffset(instant);
// ZoneOffset actualOffset = getOffset(instant);
// return actualOffset.toDuration().minus(standardOffset.toDuration()).normalized();
// }
}
/**
* Checks if the specified instant is in daylight savings.
*
* This checks if the standard and actual offsets are the same at the specified instant.
*
* @param {Instant} instant - the instant to find the offset information for, not null, but null
* may be ignored if the rules have a single offset for all instants
* @return {boolean} the standard offset, not null
*/
// eslint-disable-next-line no-unused-vars
isDaylightSavings(instant) {
abstractMethodFail('ZoneRules.isDaylightSavings');
// default {
// return (getStandardOffset(instant).equals(getOffset(instant)) == false);
// }
}
/**
* Checks if the offset date-time is valid for these rules.
*
* To be valid, the local date-time must not be in a gap and the offset
* must match the valid offsets.
*
* @param {LocalDateTime} localDateTime - the date-time to check, not null, but null
* may be ignored if the rules have a single offset for all instants
* @param {ZoneOffset} offset - the offset to check, null returns false
* @return {boolean} true if the offset date-time is valid for these rules
*/
// eslint-disable-next-line no-unused-vars
isValidOffset(localDateTime, offset){
abstractMethodFail('ZoneRules.isValidOffset');
}
//-----------------------------------------------------------------------
/**
* Gets the next transition after the specified instant.
*
* This returns details of the next transition after the specified instant.
* For example, if the instant represents a point where "Summer" daylight savings time
* applies, then the method will return the transition to the next "Winter" time.
*
* @param {Instant} instant - the instant to get the next transition after, not null, but null
* may be ignored if the rules have a single offset for all instants
* @return {ZoneOffsetTransition} the next transition after the specified instant, null if this is after the last transition
*/
// eslint-disable-next-line no-unused-vars
nextTransition(instant){
abstractMethodFail('ZoneRules.nextTransition');
}
/**
* Gets the previous transition before the specified instant.
*
* This returns details of the previous transition after the specified instant.
* For example, if the instant represents a point where "summer" daylight saving time
* applies, then the method will return the transition from the previous "winter" time.
*
* @param {Instant} instant - the instant to get the previous transition after, not null, but null
* may be ignored if the rules have a single offset for all instants
* @return {ZoneOffsetTransition} the previous transition after the specified instant, null if this is before the first transition
*/
// eslint-disable-next-line no-unused-vars
previousTransition(instant){
abstractMethodFail('ZoneRules.previousTransition');
}
/**
* Gets the complete list of fully defined transitions.
*
* The complete set of transitions for this rules instance is defined by this method
* and {@link getTransitionRules}. This method returns those transitions that have
* been fully defined. These are typically historical, but may be in the future.
*
* The list will be empty for fixed offset rules and for any time-zone where there has
* only ever been a single offset. The list will also be empty if the transition rules are unknown.
*
* @return {ZoneOffsetTransition[]} an immutable list of fully defined transitions, not null
*/
transitions(){
abstractMethodFail('ZoneRules.transitions');
}
/**
* Gets the list of transition rules for years beyond those defined in the transition list.
*
* The complete set of transitions for this rules instance is defined by this method
* and {@link getTransitions}. This method returns instances of {@link ZoneOffsetTransitionRule}
* that define an algorithm for when transitions will occur.
*
* For any given {@link ZoneRules}, this list contains the transition rules for years
* beyond those years that have been fully defined. These rules typically refer to future
* daylight saving time rule changes.
*
* If the zone defines daylight savings into the future, then the list will normally
* be of size two and hold information about entering and exiting daylight savings.
* If the zone does not have daylight savings, or information about future changes
* is uncertain, then the list will be empty.
*
* The list will be empty for fixed offset rules and for any time-zone where there is no
* daylight saving time. The list will also be empty if the transition rules are unknown.
*
* @return {ZoneOffsetTransitionRule[]} an immutable list of transition rules, not null
*/
transitionRules(){
abstractMethodFail('ZoneRules.transitionRules');
}
toString(){
abstractMethodFail('ZoneRules.toString');
}
/**
* toJSON() use by JSON.stringify
* delegates to toString()
*
* @return {string}
*/
toJSON() {
return this.toString();
}
}
class Fixed extends ZoneRules{
/**
*
* @param {ZoneOffset} offset
* @private
*/
constructor(offset){
super();
this._offset = offset;
}
isFixedOffset(){
return true;
}
offsetOfInstant(){
return this._offset;
}
offsetOfEpochMilli(){
return this._offset;
}
offsetOfLocalDateTime(){
return this._offset;
}
validOffsets(){
return [this._offset];
}
transition(){
return null;
}
standardOffset(){
return this._offset;
}
daylightSavings(){
return Duration.ZERO;
}
isDaylightSavings(){
return false;
}
/**
*
* @param {LocalDateTime} localDateTime
* @param {ZoneOffset} offset
* @return {boolean}
*/
isValidOffset(localDateTime, offset) {
return this._offset.equals(offset);
}
nextTransition(){
return null;
}
previousTransition(){
return null;
}
transitions(){
return [];
}
transitionRules(){
return [];
}
//-----------------------------------------------------------------------
/**
*
* @param {*} other
* @returns {boolean}
*/
equals(other) {
if (this === other) {
return true;
}
if (other instanceof Fixed) {
return this._offset.equals(other._offset);
}
return false;
}
/**
*
* @returns {string}
*/
toString() {
return `FixedRules:${this._offset.toString()}`;
}
}
