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 * file:
 *
 * Copyright (c) 2007-2012, Stephen Colebourne & Michael Nascimento Santos
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package java.time.temporal;

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

import java.time.LocalDate;
import java.time.LocalTime;
import java.time.ZoneId;
import java.time.ZoneOffset;
import java.time.chrono.Chronology;


Common implementations of TemporalQuery. 
 This class provides common implementations of TemporalQuery. These are defined here as they must be constants, and the definition of lambdas does not guarantee that. By assigning them once here, they become 'normal' Java constants. 

Queries are a key tool for extracting information from temporal objects.
They exist to externalize the process of querying, permitting different
approaches, as per the strategy design pattern.
Examples might be a query that checks if the date is the day before February 29th
in a leap year, or calculates the number of days to your next birthday.

 The TemporalField interface provides another mechanism for querying temporal objects. That interface is limited to returning a long. By contrast, queries can return any type. 
 There are two equivalent ways of using a TemporalQuery. The first is to invoke the method on this interface directly. The second is to use TemporalAccessor.query(TemporalQuery<Object>): 
  // these two lines are equivalent, but the second approach is recommended
  temporal = thisQuery.queryFrom(temporal);
  temporal = temporal.query(thisQuery);

 It is recommended to use the second approach, query(TemporalQuery), as it is a lot clearer to read in code. 
 The most common implementations are method references, such as LocalDate::from and ZoneId::from. Additional common queries are provided to return: 
    

  •  a Chronology,

  •  a LocalDate,

  •  a LocalTime,

  •  a ZoneOffset,

  •  a precision,

  •  a zone, or

  •  a zoneId.



Since:1.8
/**
 * Common implementations of {@code TemporalQuery}.
 * <p>
 * This class provides common implementations of {@link TemporalQuery}.
 * These are defined here as they must be constants, and the definition
 * of lambdas does not guarantee that. By assigning them once here,
 * they become 'normal' Java constants.
 * <p>
 * Queries are a key tool for extracting information from temporal objects.
 * They exist to externalize the process of querying, permitting different
 * approaches, as per the strategy design pattern.
 * Examples might be a query that checks if the date is the day before February 29th
 * in a leap year, or calculates the number of days to your next birthday.
 * <p>
 * The {@link TemporalField} interface provides another mechanism for querying
 * temporal objects. That interface is limited to returning a {@code long}.
 * By contrast, queries can return any type.
 * <p>
 * There are two equivalent ways of using a {@code TemporalQuery}.
 * The first is to invoke the method on this interface directly.
 * The second is to use {@link TemporalAccessor#query(TemporalQuery)}:
 * <pre>
 *   // these two lines are equivalent, but the second approach is recommended
 *   temporal = thisQuery.queryFrom(temporal);
 *   temporal = temporal.query(thisQuery);
 * </pre>
 * It is recommended to use the second approach, {@code query(TemporalQuery)},
 * as it is a lot clearer to read in code.
 * <p>
 * The most common implementations are method references, such as
 * {@code LocalDate::from} and {@code ZoneId::from}.
 * Additional common queries are provided to return:
 * <ul>
 * <li> a Chronology,
 * <li> a LocalDate,
 * <li> a LocalTime,
 * <li> a ZoneOffset,
 * <li> a precision,
 * <li> a zone, or
 * <li> a zoneId.
 * </ul>
 *
 * @since 1.8
 */
public final class TemporalQueries {
    // 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 this code must be done with care

    
Private constructor since this is a utility class.

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

    //-----------------------------------------------------------------------
    // 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 ZoneId. 
 This queries a TemporalAccessor for the zone. The zone is only returned if the date-time conceptually contains a ZoneId. It will not be returned if the date-time only conceptually has an ZoneOffset. Thus a ZonedDateTime will return the result of getZone(), but an OffsetDateTime will return null. 
 In most cases, applications should use zone() as this query is too strict. 
 The result from JDK classes implementing TemporalAccessor is as follows:
 LocalDate returns null
 LocalTime returns null
 LocalDateTime returns null
 ZonedDateTime returns the associated zone
 OffsetTime returns null
 OffsetDateTime returns null
 ChronoLocalDate returns null
 ChronoLocalDateTime returns null
 ChronoZonedDateTime returns the associated zone
 Era returns null
 DayOfWeek returns null
 Month returns null
 Year returns null
 YearMonth returns null
 MonthDay returns null
 ZoneOffset returns null
 Instant returns null


Returns:a query that can obtain the zone ID of a temporal, not null
/**
     * 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} will return the result of {@code getZone()},
     * but an {@link java.time.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 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 query that can obtain the zone ID of a temporal, not null
     */
    public static TemporalQuery<ZoneId> zoneId() {
        return TemporalQueries.ZONE_ID;
    }

    
A query for the Chronology. 
 This queries a TemporalAccessor for the chronology. If the target 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 LocalTime, will return null. 
 The result from JDK classes implementing TemporalAccessor is as follows:
 LocalDate returns IsoChronology.INSTANCE
 LocalTime returns null (does not represent a date)
 LocalDateTime returns IsoChronology.INSTANCE
 ZonedDateTime returns IsoChronology.INSTANCE
 OffsetTime returns null (does not represent a date)
 OffsetDateTime returns IsoChronology.INSTANCE
 ChronoLocalDate returns the associated chronology
 ChronoLocalDateTime returns the associated chronology
 ChronoZonedDateTime returns the associated chronology
 Era returns the associated chronology
 DayOfWeek returns null (shared across chronologies)
 Month returns IsoChronology.INSTANCE
 Year returns IsoChronology.INSTANCE
 YearMonth returns IsoChronology.INSTANCE
 MonthDay returns null IsoChronology.INSTANCE
 ZoneOffset returns null (does not represent a date)
 Instant returns null (does not represent a date)


 The method Chronology.from(TemporalAccessor) can be used as a TemporalQuery via a method reference, Chronology::from. That method is equivalent to this query, except that it throws an exception if a chronology cannot be obtained. 
Returns:a query that can obtain the chronology of a temporal, not null
/**
     * A query for the {@code Chronology}.
     * <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 IsoChronology.INSTANCE}<br>
     * {@code LocalTime} returns null (does not represent a date)<br>
     * {@code LocalDateTime} returns {@code IsoChronology.INSTANCE}<br>
     * {@code ZonedDateTime} returns {@code IsoChronology.INSTANCE}<br>
     * {@code OffsetTime} returns null (does not represent a date)<br>
     * {@code OffsetDateTime} returns {@code IsoChronology.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 IsoChronology.INSTANCE}<br>
     * {@code Year} returns {@code IsoChronology.INSTANCE}<br>
     * {@code YearMonth} returns {@code IsoChronology.INSTANCE}<br>
     * {@code MonthDay} returns null {@code IsoChronology.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 java.time.chrono.Chronology#from(TemporalAccessor)} can be used as a
     * {@code TemporalQuery} via a method reference, {@code Chronology::from}.
     * That method is equivalent to this query, except that it throws an
     * exception if a chronology cannot be obtained.
     *
     * @return a query that can obtain the chronology of a temporal, not null
     */
    public static TemporalQuery<Chronology> chronology() {
        return TemporalQueries.CHRONO;
    }

    
A query for the smallest supported unit.

 This queries a TemporalAccessor for the time precision. If the target 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 NANO_OF_DAY and 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 GregorianCalendar to implement TemporalAccessor it would return a precision of MILLIS. 
 The result from JDK classes implementing TemporalAccessor is as follows:
 LocalDate returns DAYS
 LocalTime returns NANOS
 LocalDateTime returns NANOS
 ZonedDateTime returns NANOS
 OffsetTime returns NANOS
 OffsetDateTime returns NANOS
 ChronoLocalDate returns DAYS
 ChronoLocalDateTime returns NANOS
 ChronoZonedDateTime returns NANOS
 Era returns ERAS
 DayOfWeek returns DAYS
 Month returns MONTHS
 Year returns YEARS
 YearMonth returns MONTHS
 MonthDay returns null (does not represent a complete date or time)
 ZoneOffset returns null (does not represent a date or time)
 Instant returns NANOS


Returns:a query that can obtain the precision of a temporal, not null
/**
     * 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 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 query that can obtain the precision of a temporal, not null
     */
    public static TemporalQuery<TemporalUnit> precision() {
        return TemporalQueries.PRECISION;
    }

    //-----------------------------------------------------------------------
    // non-special constants are standard queries that derive information from other information
    
A lenient query for the ZoneId, falling back to the ZoneOffset. 
 This queries a TemporalAccessor for the zone. It first tries to obtain the zone, using zoneId(). If that is not found it tries to obtain the offset(). Thus a ZonedDateTime will return the result of getZone(), while an OffsetDateTime will return the result of getOffset(). 
 In most cases, applications should use this query rather than #zoneId(). 
 The method ZoneId.from(TemporalAccessor) can be used as a TemporalQuery via a method reference, ZoneId::from. That method is equivalent to this query, except that it throws an exception if a zone cannot be obtained. 
Returns:a query that can obtain the zone ID or offset of a temporal, not null
/**
     * 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()}.
     * Thus a {@link java.time.ZonedDateTime} will return the result of {@code getZone()},
     * while an {@link java.time.OffsetDateTime} will return the result of {@code getOffset()}.
     * <p>
     * In most cases, applications should use this query rather than {@code #zoneId()}.
     * <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 query that can obtain the zone ID or offset of a temporal, not null
     */
    public static TemporalQuery<ZoneId> zone() {
        return TemporalQueries.ZONE;
    }

    
A query for ZoneOffset returning null if not found. 
 This returns a TemporalQuery that can be used to query a temporal object for the offset. The query will return null if the temporal object cannot supply an offset. 
 The query implementation examines the OFFSET_SECONDS field and uses it to create a ZoneOffset. 
 The method ZoneOffset.from(TemporalAccessor) can be used as a TemporalQuery via a method reference, ZoneOffset::from. This query and ZoneOffset::from will return the same result if the temporal object contains an offset. If the temporal object does not contain an offset, then the method reference will throw an exception, whereas this query will return null. 
Returns:a query that can obtain the offset of a temporal, not null
/**
     * A query for {@code ZoneOffset} returning null if not found.
     * <p>
     * This returns a {@code TemporalQuery} that can be used to query a temporal
     * object for the offset. The query will return null if the temporal
     * object cannot supply an offset.
     * <p>
     * The query implementation examines the {@link ChronoField#OFFSET_SECONDS OFFSET_SECONDS}
     * field and uses it to create a {@code ZoneOffset}.
     * <p>
     * The method {@link java.time.ZoneOffset#from(TemporalAccessor)} can be used as a
     * {@code TemporalQuery} via a method reference, {@code ZoneOffset::from}.
     * This query and {@code ZoneOffset::from} will return the same result if the
     * temporal object contains an offset. If the temporal object does not contain
     * an offset, then the method reference will throw an exception, whereas this
     * query will return null.
     *
     * @return a query that can obtain the offset of a temporal, not null
     */
    public static TemporalQuery<ZoneOffset> offset() {
        return TemporalQueries.OFFSET;
    }

    
A query for LocalDate returning null if not found. 
 This returns a TemporalQuery that can be used to query a temporal object for the local date. The query will return null if the temporal object cannot supply a local date. 
 The query implementation examines the EPOCH_DAY field and uses it to create a LocalDate. 
 The method ZoneOffset.from(TemporalAccessor) can be used as a TemporalQuery via a method reference, LocalDate::from. This query and LocalDate::from will return the same result if the temporal object contains a date. If the temporal object does not contain a date, then the method reference will throw an exception, whereas this query will return null. 
Returns:a query that can obtain the date of a temporal, not null
/**
     * A query for {@code LocalDate} returning null if not found.
     * <p>
     * This returns a {@code TemporalQuery} that can be used to query a temporal
     * object for the local date. The query will return null if the temporal
     * object cannot supply a local date.
     * <p>
     * The query implementation examines the {@link ChronoField#EPOCH_DAY EPOCH_DAY}
     * field and uses it to create a {@code LocalDate}.
     * <p>
     * The method {@link ZoneOffset#from(TemporalAccessor)} can be used as a
     * {@code TemporalQuery} via a method reference, {@code LocalDate::from}.
     * This query and {@code LocalDate::from} will return the same result if the
     * temporal object contains a date. If the temporal object does not contain
     * a date, then the method reference will throw an exception, whereas this
     * query will return null.
     *
     * @return a query that can obtain the date of a temporal, not null
     */
    public static TemporalQuery<LocalDate> localDate() {
        return TemporalQueries.LOCAL_DATE;
    }

    
A query for LocalTime returning null if not found. 
 This returns a TemporalQuery that can be used to query a temporal object for the local time. The query will return null if the temporal object cannot supply a local time. 
 The query implementation examines the NANO_OF_DAY field and uses it to create a LocalTime. 
 The method ZoneOffset.from(TemporalAccessor) can be used as a TemporalQuery via a method reference, LocalTime::from. This query and LocalTime::from will return the same result if the temporal object contains a time. If the temporal object does not contain a time, then the method reference will throw an exception, whereas this query will return null. 
Returns:a query that can obtain the time of a temporal, not null
/**
     * A query for {@code LocalTime} returning null if not found.
     * <p>
     * This returns a {@code TemporalQuery} that can be used to query a temporal
     * object for the local time. The query will return null if the temporal
     * object cannot supply a local time.
     * <p>
     * The query implementation examines the {@link ChronoField#NANO_OF_DAY NANO_OF_DAY}
     * field and uses it to create a {@code LocalTime}.
     * <p>
     * The method {@link ZoneOffset#from(TemporalAccessor)} can be used as a
     * {@code TemporalQuery} via a method reference, {@code LocalTime::from}.
     * This query and {@code LocalTime::from} will return the same result if the
     * temporal object contains a time. If the temporal object does not contain
     * a time, then the method reference will throw an exception, whereas this
     * query will return null.
     *
     * @return a query that can obtain the time of a temporal, not null
     */
    public static TemporalQuery<LocalTime> localTime() {
        return TemporalQueries.LOCAL_TIME;
    }

    //-----------------------------------------------------------------------
    
A strict query for the ZoneId. 
/**
     * A strict query for the {@code ZoneId}.
     */
    static final TemporalQuery<ZoneId> ZONE_ID = new TemporalQuery<>() {
        @Override
        public ZoneId queryFrom(TemporalAccessor temporal) {
            return temporal.query(TemporalQueries.ZONE_ID);
        }

        @Override
        public String toString() {
            return "ZoneId";
        }
    };

    
A query for the Chronology. 
/**
     * A query for the {@code Chronology}.
     */
    static final TemporalQuery<Chronology> CHRONO = new TemporalQuery<>() {
        @Override
        public Chronology queryFrom(TemporalAccessor temporal) {
            return temporal.query(TemporalQueries.CHRONO);
        }

        @Override
        public String toString() {
            return "Chronology";
        }
    };


    
A query for the smallest supported unit.

/**
     * A query for the smallest supported unit.
     */
    static final TemporalQuery<TemporalUnit> PRECISION = new TemporalQuery<>() {
        @Override
        public TemporalUnit queryFrom(TemporalAccessor temporal) {
            return temporal.query(TemporalQueries.PRECISION);
        }

        @Override
        public String toString() {
            return "Precision";
        }
    };

    //-----------------------------------------------------------------------
    
A query for ZoneOffset returning null if not found. 
/**
     * A query for {@code ZoneOffset} returning null if not found.
     */
    static final TemporalQuery<ZoneOffset> OFFSET = new TemporalQuery<>() {
        @Override
        public ZoneOffset queryFrom(TemporalAccessor temporal) {
            if (temporal.isSupported(OFFSET_SECONDS)) {
                return ZoneOffset.ofTotalSeconds(temporal.get(OFFSET_SECONDS));
            }
            return null;
        }

        @Override
        public String toString() {
            return "ZoneOffset";
        }
    };

    
A lenient query for the ZoneId, falling back to the ZoneOffset. 
/**
     * A lenient query for the {@code ZoneId}, falling back to the {@code ZoneOffset}.
     */
    static final TemporalQuery<ZoneId> ZONE = new TemporalQuery<>() {
        @Override
        public ZoneId queryFrom(TemporalAccessor temporal) {
            ZoneId zone = temporal.query(ZONE_ID);
            return (zone != null ? zone : temporal.query(OFFSET));
        }

        @Override
        public String toString() {
            return "Zone";
        }
    };

    
A query for LocalDate returning null if not found. 
/**
     * A query for {@code LocalDate} returning null if not found.
     */
    static final TemporalQuery<LocalDate> LOCAL_DATE = new TemporalQuery<>() {
        @Override
        public LocalDate queryFrom(TemporalAccessor temporal) {
            if (temporal.isSupported(EPOCH_DAY)) {
                return LocalDate.ofEpochDay(temporal.getLong(EPOCH_DAY));
            }
            return null;
        }

        @Override
        public String toString() {
            return "LocalDate";
        }
    };

    
A query for LocalTime returning null if not found. 
/**
     * A query for {@code LocalTime} returning null if not found.
     */
    static final TemporalQuery<LocalTime> LOCAL_TIME = new TemporalQuery<>() {
        @Override
        public LocalTime queryFrom(TemporalAccessor temporal) {
            if (temporal.isSupported(NANO_OF_DAY)) {
                return LocalTime.ofNanoOfDay(temporal.getLong(NANO_OF_DAY));
            }
            return null;
        }

        @Override
        public String toString() {
            return "LocalTime";
        }
    };

}