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/*
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 * License version 2 only, as published by the Free Software Foundation.
 * However, the following notice accompanied the original version of this
 * file:
 *
 * Copyright (c) 2007-2012, Stephen Colebourne & Michael Nascimento Santos
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package java.time.temporal;

import static java.time.temporal.ChronoField.OFFSET_SECONDS;

import java.time.ZoneId;
import java.time.ZoneOffset;

/**
 * Common implementations of {@code TemporalQuery}.
 * <p>
 * This class provides common implementations of {@link TemporalQuery}.
 * These queries are primarily used as optimizations, allowing the internals
 * of other objects to be extracted effectively. Note that application code
 * can also use the {@code from(TemporalAccessor)} method on most temporal
 * objects as a method reference matching the query interface, such as
 * {@code LocalDate::from} and {@code ZoneId::from}.
 * <p>
 * There are two equivalent ways of using a {@code TemporalQuery}.
 * The first is to invoke the method on the interface directly.
 * The second is to use {@link TemporalAccessor#query(TemporalQuery)}:
 * <pre>
 *   // these two lines are equivalent, but the second approach is recommended
 *   dateTime = query.queryFrom(dateTime);
 *   dateTime = dateTime.query(query);
 * </pre>
 * It is recommended to use the second approach, {@code query(TemporalQuery)},
 * as it is a lot clearer to read in code.
 *
 * <h3>Specification for implementors</h3>
 * This is a thread-safe utility class.
 * All returned adjusters are immutable and thread-safe.
 *
 * @since 1.8
 */
public final class Queries {
    // note that it is vital that each method supplies a constant, not a
    // calculated value, as they will be checked for using ==
    // it is also vital that each constant is different (due to the == checking)
    // as such, alterations to use lambdas must be done with extreme care

    /**
     * Private constructor since this is a utility class.
     */
    private Queries() {
    }

    //-----------------------------------------------------------------------
    // special constants should be used to extract information from a TemporalAccessor
    // that cannot be derived in other ways
    // Javadoc added here, so as to pretend they are more normal than they really are

    /**
     * A strict query for the {@code ZoneId}.
     * <p>
     * This queries a {@code TemporalAccessor} for the zone.
     * The zone is only returned if the date-time conceptually contains a {@code ZoneId}.
     * It will not be returned if the date-time only conceptually has an {@code ZoneOffset}.
     * Thus a {@link java.time.ZonedDateTime ZonedDateTime} will return the result of
     * {@code getZone()}, but an {@link java.time.temporal.OffsetDateTime OffsetDateTime} will
     * return null.
     * <p>
     * In most cases, applications should use {@link #ZONE} as this query is too strict.
     * <p>
     * The result from JDK classes implementing {@code TemporalAccessor} is as follows:<br>
     * {@code LocalDate} returns null<br>
     * {@code LocalTime} returns null<br>
     * {@code LocalDateTime} returns null<br>
     * {@code ZonedDateTime} returns the associated zone<br>
     * {@code OffsetDate} returns null<br>
     * {@code OffsetTime} returns null<br>
     * {@code OffsetDateTime} returns null<br>
     * {@code ChronoLocalDate} returns null<br>
     * {@code ChronoLocalDateTime} returns null<br>
     * {@code ChronoZonedDateTime} returns the associated zone<br>
     * {@code Era} returns null<br>
     * {@code DayOfWeek} returns null<br>
     * {@code Month} returns null<br>
     * {@code Year} returns null<br>
     * {@code YearMonth} returns null<br>
     * {@code MonthDay} returns null<br>
     * {@code ZoneOffset} returns null<br>
     * {@code Instant} returns null<br>
     * @return a ZoneId, may be null
     */
    public static final TemporalQuery<ZoneId> zoneId() {
        return ZONE_ID;
    }
    static final TemporalQuery<ZoneId> ZONE_ID = new TemporalQuery<ZoneId>() {
        @Override
        public ZoneId queryFrom(TemporalAccessor temporal) {
            return temporal.query(this);
        }
    };

    /**
     * A query for the {@code Chrono}.
     * <p>
     * This queries a {@code TemporalAccessor} for the chronology.
     * If the target {@code TemporalAccessor} represents a date, or part of a date,
     * then it should return the chronology that the date is expressed in.
     * As a result of this definition, objects only representing time, such as
     * {@code LocalTime}, will return null.
     * <p>
     * The result from JDK classes implementing {@code TemporalAccessor} is as follows:<br>
     * {@code LocalDate} returns {@code ISOChrono.INSTANCE}<br>
     * {@code LocalTime} returns null (does not represent a date)<br>
     * {@code LocalDateTime} returns {@code ISOChrono.INSTANCE}<br>
     * {@code ZonedDateTime} returns {@code ISOChrono.INSTANCE}<br>
     * {@code OffsetDate} returns {@code ISOChrono.INSTANCE}<br>
     * {@code OffsetTime} returns null (does not represent a date)<br>
     * {@code OffsetDateTime} returns {@code ISOChrono.INSTANCE}<br>
     * {@code ChronoLocalDate} returns the associated chronology<br>
     * {@code ChronoLocalDateTime} returns the associated chronology<br>
     * {@code ChronoZonedDateTime} returns the associated chronology<br>
     * {@code Era} returns the associated chronology<br>
     * {@code DayOfWeek} returns null (shared across chronologies)<br>
     * {@code Month} returns {@code ISOChrono.INSTANCE}<br>
     * {@code Year} returns {@code ISOChrono.INSTANCE}<br>
     * {@code YearMonth} returns {@code ISOChrono.INSTANCE}<br>
     * {@code MonthDay} returns null {@code ISOChrono.INSTANCE}<br>
     * {@code ZoneOffset} returns null (does not represent a date)<br>
     * {@code Instant} returns null (does not represent a date)<br>
     * <p>
     * The method {@link Chrono#from(TemporalAccessor)} can be used as a
     * {@code TemporalQuery} via a method reference, {@code Chrono::from}.
     * That method is equivalent to this query, except that it throws an
     * exception if a chronology cannot be obtained.
     * @return a Chrono, may be null
     */
    public static final TemporalQuery<Chrono<?>> chrono() {
        return CHRONO;
    }
    static final TemporalQuery<Chrono<?>> CHRONO = new TemporalQuery<Chrono<?>>() {
        @Override
        public Chrono<?> queryFrom(TemporalAccessor temporal) {
            return temporal.query(this);
        }
    };

    /**
     * A query for the smallest supported unit.
     * <p>
     * This queries a {@code TemporalAccessor} for the time precision.
     * If the target {@code TemporalAccessor} represents a consistent or complete date-time,
     * date or time then this must return the smallest precision actually supported.
     * Note that fields such as {@code NANO_OF_DAY} and {@code NANO_OF_SECOND}
     * are defined to always return ignoring the precision, thus this is the only
     * way to find the actual smallest supported unit.
     * For example, were {@code GregorianCalendar} to implement {@code TemporalAccessor}
     * it would return a precision of {@code MILLIS}.
     * <p>
     * The result from JDK classes implementing {@code TemporalAccessor} is as follows:<br>
     * {@code LocalDate} returns {@code DAYS}<br>
     * {@code LocalTime} returns {@code NANOS}<br>
     * {@code LocalDateTime} returns {@code NANOS}<br>
     * {@code ZonedDateTime} returns {@code NANOS}<br>
     * {@code OffsetDate} returns {@code DAYS}<br>
     * {@code OffsetTime} returns {@code NANOS}<br>
     * {@code OffsetDateTime} returns {@code NANOS}<br>
     * {@code ChronoLocalDate} returns {@code DAYS}<br>
     * {@code ChronoLocalDateTime} returns {@code NANOS}<br>
     * {@code ChronoZonedDateTime} returns {@code NANOS}<br>
     * {@code Era} returns {@code ERAS}<br>
     * {@code DayOfWeek} returns {@code DAYS}<br>
     * {@code Month} returns {@code MONTHS}<br>
     * {@code Year} returns {@code YEARS}<br>
     * {@code YearMonth} returns {@code MONTHS}<br>
     * {@code MonthDay} returns null (does not represent a complete date or time)<br>
     * {@code ZoneOffset} returns null (does not represent a date or time)<br>
     * {@code Instant} returns {@code NANOS}<br>
     * @return a ChronoUnit, may be null
     */
    public static final TemporalQuery<ChronoUnit> precision() {
        return PRECISION;
    }
    static final TemporalQuery<ChronoUnit> PRECISION = new TemporalQuery<ChronoUnit>() {
        @Override
        public ChronoUnit queryFrom(TemporalAccessor temporal) {
            return temporal.query(this);
        }
    };

    //-----------------------------------------------------------------------
    // non-special constants are standard queries that derive information from other information
    /**
     * A lenient query for the {@code ZoneId}, falling back to the {@code ZoneOffset}.
     * <p>
     * This queries a {@code TemporalAccessor} for the zone.
     * It first tries to obtain the zone, using {@link #zoneId()}.
     * If that is not found it tries to obtain the {@link #offset()}.
     * <p>
     * In most cases, applications should use this query rather than {@code #zoneId()}.
     * <p>
     * This query examines the {@link java.time.temporal.ChronoField#OFFSET_SECONDS offset-seconds}
     * field and uses it to create a {@code ZoneOffset}.
     * <p>
     * The method {@link ZoneId#from(TemporalAccessor)} can be used as a
     * {@code TemporalQuery} via a method reference, {@code ZoneId::from}.
     * That method is equivalent to this query, except that it throws an
     * exception if a zone cannot be obtained.
     * @return a ZoneId, may be null
     */
    public static final TemporalQuery<ZoneId> zone() {
        return ZONE;
    }
    static final TemporalQuery<ZoneId> ZONE = new TemporalQuery<ZoneId>() {
        @Override
        public ZoneId queryFrom(TemporalAccessor temporal) {
            ZoneId zone = temporal.query(ZONE_ID);
            return (zone != null ? zone : temporal.query(OFFSET));
        }
    };

    /**
     * A query for the {@code ZoneOffset}.
     * <p>
     * This queries a {@code TemporalAccessor} for the offset.
     * <p>
     * This query examines the {@link java.time.temporal.ChronoField#OFFSET_SECONDS offset-seconds}
     * field and uses it to create a {@code ZoneOffset}.
     * <p>
     * The method {@link ZoneOffset#from(TemporalAccessor)} can be used as a
     * {@code TemporalQuery} via a method reference, {@code ZoneOffset::from}.
     * That method is equivalent to this query, except that it throws an
     * exception if an offset cannot be obtained.
     * @return a ZoneOffset, may be null
     */
    public static final TemporalQuery<ZoneOffset> offset() {
        return OFFSET;
    }
    static final TemporalQuery<ZoneOffset> OFFSET = new TemporalQuery<ZoneOffset>() {
        @Override
        public ZoneOffset queryFrom(TemporalAccessor temporal) {
            if (temporal.isSupported(OFFSET_SECONDS)) {
                return ZoneOffset.ofTotalSeconds(temporal.get(OFFSET_SECONDS));
            }
            return null;
        }
    };

}