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  /*
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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 {@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 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 {@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 {@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 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.
       * <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 {@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 {@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 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 {@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 {@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 {@code ZoneId}.
       */
      static final TemporalQuery<ZoneId> ZONE_ID = (temporal) ->
          temporal.query(TemporalQueries.ZONE_ID);
  
      /**
       * A query for the {@code Chronology}.
       */
      static final TemporalQuery<Chronology> CHRONO = (temporal) ->
          temporal.query(TemporalQueries.CHRONO);
  
      /**
       * A query for the smallest supported unit.
       */
      static final TemporalQuery<TemporalUnit> PRECISION = (temporal) ->
          temporal.query(TemporalQueries.PRECISION);
  
      //-----------------------------------------------------------------------
      /**
       * A query for {@code ZoneOffset} returning null if not found.
       */
      static final TemporalQuery<ZoneOffset> OFFSET = (temporal) -> {
          if (temporal.isSupported(OFFSET_SECONDS)) {
              return ZoneOffset.ofTotalSeconds(temporal.get(OFFSET_SECONDS));
          }
          return null;
      };
  
      /**
       * A lenient query for the {@code ZoneId}, falling back to the {@code ZoneOffset}.
       */
      static final TemporalQuery<ZoneId> ZONE = (temporal) -> {
          ZoneId zone = temporal.query(ZONE_ID);
          return (zone != null ? zone : temporal.query(OFFSET));
      };
  
      /**
       * A query for {@code LocalDate} returning null if not found.
       */
      static final TemporalQuery<LocalDate> LOCAL_DATE = (temporal) -> {
          if (temporal.isSupported(EPOCH_DAY)) {
              return LocalDate.ofEpochDay(temporal.getLong(EPOCH_DAY));
          }
          return null;
      };
  
      /**
       * A query for {@code LocalTime} returning null if not found.
       */
      static final TemporalQuery<LocalTime> LOCAL_TIME = (temporal) -> {
          if (temporal.isSupported(NANO_OF_DAY)) {
              return LocalTime.ofNanoOfDay(temporal.getLong(NANO_OF_DAY));
          }
          return null;
      };
  
  }
  