/*
 * hunt-time: A time library for D programming language.
 *
 * Copyright (C) 2015-2018 HuntLabs
 *
 * Website: https://www.huntlabs.net/
 *
 * Licensed under the Apache-2.0 License.
 *
 */

module hunt.time.chrono.ChronoZonedDateTime;

import hunt.time.temporal.ChronoField;
import hunt.time.temporal.ChronoUnit;

import hunt.stream.Common;
import hunt.time.Exceptions;
import hunt.time.Instant;
import hunt.time.LocalTime;
import hunt.time.ZoneId;
import hunt.time.ZoneOffset;
import hunt.time.ZonedDateTime;
// import hunt.time.format.DateTimeFormatter;
import hunt.time.temporal.ChronoField;
import hunt.time.temporal.ChronoUnit;
import hunt.time.temporal.Temporal;
import hunt.time.temporal.TemporalAccessor;
import hunt.time.temporal.TemporalAdjuster;
import hunt.time.temporal.TemporalAmount;
import hunt.time.temporal.TemporalField;
import hunt.time.temporal.TemporalQueries;
import hunt.time.temporal.TemporalQuery;
import hunt.time.temporal.TemporalUnit;
import hunt.time.Exceptions;
import hunt.time.temporal.ValueRange;
import hunt.util.Common;
import hunt.util.Comparator;
import hunt.time.chrono.ChronoLocalDate;
import hunt.Functions;
import hunt.time.chrono.ChronoLocalDateTime;
import hunt.time.chrono.Chronology;
import hunt.time.util.QueryHelper;

/**
 * A date-time with a time-zone _in an arbitrary chronology,
 * intended for advanced globalization use cases.
 * !(p)
 * !(b)Most applications should declare method signatures, fields and variables
 * as {@link ZonedDateTime}, not this interface.</b>
 * !(p)
 * A {@code ChronoZonedDateTime} is the abstract representation of an offset date-time
 * where the {@code Chronology chronology}, or calendar system, is pluggable.
 * The date-time is defined _in terms of fields expressed by {@link TemporalField},
 * where most common implementations are defined _in {@link ChronoField}.
 * The chronology defines how the calendar system operates and the meaning of
 * the standard fields.
 *
 * !(h3)When to use this interface</h3>
 * The design of the API encourages the use of {@code ZonedDateTime} rather than this
 * interface, even _in the case where the application needs to deal with multiple
 * calendar systems. The rationale for this is explored _in detail _in {@link ChronoLocalDate}.
 * !(p)
 * Ensure that the discussion _in {@code ChronoLocalDate} has been read and understood
 * before using this interface.
 *
 * @implSpec
 * This interface must be implemented with care to ensure other classes operate correctly.
 * All implementations that can be instantiated must be final, immutable and thread-safe.
 * Subclasses should be Serializable wherever possible.
 *
 * @param !(D) the concrete type for the date of this date-time
 * @since 1.8
 */
public interface ChronoZonedDateTime(D = ChronoLocalDate)  if(is(D : ChronoLocalDate))
        : Temporal, Comparable!(ChronoZonedDateTime!(D)) { 

    /**
     * Gets a comparator that compares {@code ChronoZonedDateTime} _in
     * time-line order ignoring the chronology.
     * !(p)
     * This comparator differs from the comparison _in {@link #compareTo} _in that it
     * only compares the underlying instant and not the chronology.
     * This allows dates _in different calendar systems to be compared based
     * on the position of the date-time on the instant time-line.
     * The underlying comparison is equivalent to comparing the epoch-second and nano-of-second.
     *
     * @return a comparator that compares _in time-line order ignoring the chronology
     * @see #isAfter
     * @see #isBefore
     * @see #isEqual
     */
    static Comparator!(ChronoZonedDateTime!(ChronoLocalDate)) timeLineOrder() {
        return new class Comparator!(ChronoZonedDateTime!(ChronoLocalDate)) {
            int compare(ChronoZonedDateTime!(ChronoLocalDate) dateTime1, 
                ChronoZonedDateTime!(ChronoLocalDate) dateTime2) nothrow {
                try {
                    int cmp = hunt.util.Comparator.compare(dateTime1.toEpochSecond(), dateTime2.toEpochSecond());
                    if (cmp == 0) {
                        cmp = hunt.util.Comparator.compare(dateTime1.toLocalTime().getNano(), dateTime2.toLocalTime().getNano());
                    }
                    return cmp;
                } catch(Exception) {
                    // FIXME: Needing refactor or cleanup -@zxp at 12/29/2018, 11:30:49 PM
                    // 
                    return 0;
                }
            };
        };
    }

    //-----------------------------------------------------------------------
    /**
     * Obtains an instance of {@code ChronoZonedDateTime} from a temporal object.
     * !(p)
     * This creates a zoned date-time based on the specified temporal.
     * A {@code TemporalAccessor} represents an arbitrary set of date and time information,
     * which this factory converts to an instance of {@code ChronoZonedDateTime}.
     * !(p)
     * The conversion extracts and combines the chronology, date, time and zone
     * from the temporal object. The behavior is equivalent to using
     * {@link Chronology#zonedDateTime(TemporalAccessor)} with the extracted chronology.
     * Implementations are permitted to perform optimizations such as accessing
     * those fields that are equivalent to the relevant objects.
     * !(p)
     * This method matches the signature of the functional interface {@link TemporalQuery}
     * allowing it to be used as a query via method reference, {@code ChronoZonedDateTime::from}.
     *
     * @param temporal  the temporal object to convert, not null
     * @return the date-time, not null
     * @throws DateTimeException if unable to convert to a {@code ChronoZonedDateTime}
     * @see Chronology#zonedDateTime(TemporalAccessor)
     */
    static ChronoZonedDateTime!(ChronoLocalDate) from(TemporalAccessor temporal) {
        if (cast(ChronoZonedDateTime)(temporal) !is null) {
            return cast(ChronoZonedDateTime!(ChronoLocalDate)) temporal;
        }
        assert(temporal, "temporal");
        Chronology chrono = QueryHelper.query!Chronology(temporal,TemporalQueries.chronology());
        if (chrono is null) {
            throw new DateTimeException("Unable to obtain ChronoZonedDateTime from TemporalAccessor: " ~ typeid(temporal).stringof);
        }
        return chrono.zonedDateTime(temporal);
    }

    //-----------------------------------------------------------------------
    ValueRange range(TemporalField field);
    // override
    //  ValueRange range(TemporalField field) {
    //     if (cast(ChronoField)(field) !is null) {
    //         if (field == INSTANT_SECONDS || field == OFFSET_SECONDS) {
    //             return field.range();
    //         }
    //         return toLocalDateTime().range(field);
    //     }
    //     return field.rangeRefinedBy(this);
    // }
    int get(TemporalField field);
    // override
    //  int get(TemporalField field) {
    //     if (cast(ChronoField)(field) !is null) {
    //         switch (cast(ChronoField) field) {
    //             case INSTANT_SECONDS:
    //                 throw new UnsupportedTemporalTypeException("Invalid field 'InstantSeconds' for get() method, use getLong() instead");
    //             case OFFSET_SECONDS:
    //                 return getOffset().getTotalSeconds();
    //         }
    //         return toLocalDateTime().get(field);
    //     }
    //     return /* Temporal. */super.get(field);
    // }
    long getLong(TemporalField field);
    // override
    //  long getLong(TemporalField field) {
    //     if (cast(ChronoField)(field) !is null) {
    //         switch (cast(ChronoField) field) {
    //             case INSTANT_SECONDS: return toEpochSecond();
    //             case OFFSET_SECONDS: return getOffset().getTotalSeconds();
    //         }
    //         return toLocalDateTime().getLong(field);
    //     }
    //     return field.getFrom(this);
    // }

    /**
     * Gets the local date part of this date-time.
     * !(p)
     * This returns a local date with the same year, month and day
     * as this date-time.
     *
     * @return the date part of this date-time, not null
     */
     D toLocalDate();
    //  D toLocalDate() {
    //     return toLocalDateTime().toLocalDate();
    // }

    /**
     * Gets the local time part of this date-time.
     * !(p)
     * This returns a local time with the same hour, minute, second and
     * nanosecond as this date-time.
     *
     * @return the time part of this date-time, not null
     */
     LocalTime toLocalTime();
    //  LocalTime toLocalTime() {
    //     return toLocalDateTime().toLocalTime();
    // }

    /**
     * Gets the local date-time part of this date-time.
     * !(p)
     * This returns a local date with the same year, month and day
     * as this date-time.
     *
     * @return the local date-time part of this date-time, not null
     */
    ChronoLocalDateTime!(D) toLocalDateTime();

    /**
     * Gets the chronology of this date-time.
     * !(p)
     * The {@code Chronology} represents the calendar system _in use.
     * The era and other fields _in {@link ChronoField} are defined by the chronology.
     *
     * @return the chronology, not null
     */
     Chronology getChronology();
    //  Chronology getChronology() {
    //     return toLocalDate().getChronology();
    // }

    /**
     * Gets the zone offset, such as '+01:00'.
     * !(p)
     * This is the offset of the local date-time from UTC/Greenwich.
     *
     * @return the zone offset, not null
     */
    ZoneOffset getOffset();

    /**
     * Gets the zone ID, such as 'Europe/Paris'.
     * !(p)
     * This returns the stored time-zone id used to determine the time-zone rules.
     *
     * @return the zone ID, not null
     */
    ZoneId getZone();

    //-----------------------------------------------------------------------
    /**
     * Returns a copy of this date-time changing the zone offset to the
     * earlier of the two valid offsets at a local time-line overlap.
     * !(p)
     * This method only has any effect when the local time-line overlaps, such as
     * at an autumn daylight savings cutover. In this scenario, there are two
     * valid offsets for the local date-time. Calling this method will return
     * a zoned date-time with the earlier of the two selected.
     * !(p)
     * If this method is called when it is not an overlap, {@code this}
     * is returned.
     * !(p)
     * This instance is immutable and unaffected by this method call.
     *
     * @return a {@code ChronoZonedDateTime} based on this date-time with the earlier offset, not null
     * @throws DateTimeException if no rules can be found for the zone
     * @throws DateTimeException if no rules are valid for this date-time
     */
    ChronoZonedDateTime!(D) withEarlierOffsetAtOverlap();

    /**
     * Returns a copy of this date-time changing the zone offset to the
     * later of the two valid offsets at a local time-line overlap.
     * !(p)
     * This method only has any effect when the local time-line overlaps, such as
     * at an autumn daylight savings cutover. In this scenario, there are two
     * valid offsets for the local date-time. Calling this method will return
     * a zoned date-time with the later of the two selected.
     * !(p)
     * If this method is called when it is not an overlap, {@code this}
     * is returned.
     * !(p)
     * This instance is immutable and unaffected by this method call.
     *
     * @return a {@code ChronoZonedDateTime} based on this date-time with the later offset, not null
     * @throws DateTimeException if no rules can be found for the zone
     * @throws DateTimeException if no rules are valid for this date-time
     */
    ChronoZonedDateTime!(D) withLaterOffsetAtOverlap();

    /**
     * Returns a copy of this date-time with a different time-zone,
     * retaining the local date-time if possible.
     * !(p)
     * This method changes the time-zone and retains the local date-time.
     * The local date-time is only changed if it is invalid for the new zone.
     * !(p)
     * To change the zone and adjust the local date-time,
     * use {@link #withZoneSameInstant(ZoneId)}.
     * !(p)
     * This instance is immutable and unaffected by this method call.
     *
     * @param zone  the time-zone to change to, not null
     * @return a {@code ChronoZonedDateTime} based on this date-time with the requested zone, not null
     */
    ChronoZonedDateTime!(D) withZoneSameLocal(ZoneId zone);

    /**
     * Returns a copy of this date-time with a different time-zone,
     * retaining the instant.
     * !(p)
     * This method changes the time-zone and retains the instant.
     * This normally results _in a change to the local date-time.
     * !(p)
     * This method is based on retaining the same instant, thus gaps and overlaps
     * _in the local time-line have no effect on the result.
     * !(p)
     * To change the offset while keeping the local time,
     * use {@link #withZoneSameLocal(ZoneId)}.
     *
     * @param zone  the time-zone to change to, not null
     * @return a {@code ChronoZonedDateTime} based on this date-time with the requested zone, not null
     * @throws DateTimeException if the result exceeds the supported date range
     */
    ChronoZonedDateTime!(D) withZoneSameInstant(ZoneId zone);

    /**
     * Checks if the specified field is supported.
     * !(p)
     * This checks if the specified field can be queried on this date-time.
     * If false, then calling the {@link #range(TemporalField) range},
     * {@link #get(TemporalField) get} and {@link #_with(TemporalField, long)}
     * methods will throw an exception.
     * !(p)
     * The set of supported fields is defined by the chronology and normally includes
     * all {@code ChronoField} fields.
     * !(p)
     * If the field is not a {@code ChronoField}, then the result of this method
     * is obtained by invoking {@code TemporalField.isSupportedBy(TemporalAccessor)}
     * passing {@code this} as the argument.
     * Whether the field is supported is determined by the field.
     *
     * @param field  the field to check, null returns false
     * @return true if the field can be queried, false if not
     */
    override
    bool isSupported(TemporalField field);

    /**
     * Checks if the specified unit is supported.
     * !(p)
     * This checks if the specified unit can be added to or subtracted from this date-time.
     * If false, then calling the {@link #plus(long, TemporalUnit)} and
     * {@link #minus(long, TemporalUnit) minus} methods will throw an exception.
     * !(p)
     * The set of supported units is defined by the chronology and normally includes
     * all {@code ChronoUnit} units except {@code FOREVER}.
     * !(p)
     * If the unit is not a {@code ChronoUnit}, then the result of this method
     * is obtained by invoking {@code TemporalUnit.isSupportedBy(Temporal)}
     * passing {@code this} as the argument.
     * Whether the unit is supported is determined by the unit.
     *
     * @param unit  the unit to check, null returns false
     * @return true if the unit can be added/subtracted, false if not
     */
     bool isSupported(TemporalUnit unit);
    // override
    //  bool isSupported(TemporalUnit unit) {
    //     if (cast(ChronoUnit)(unit) !is null) {
    //         return unit != FOREVER;
    //     }
    //     return unit !is null && unit.isSupportedBy(this);
    // }

    //-----------------------------------------------------------------------
    // override for covariant return type
    /**
     * {@inheritDoc}
     * @throws DateTimeException {@inheritDoc}
     * @throws ArithmeticException {@inheritDoc}
     */
     ChronoZonedDateTime!(D) _with(TemporalAdjuster adjuster);
    // override
    //  ChronoZonedDateTime!(D) _with(TemporalAdjuster adjuster) {
    //     return ChronoZonedDateTimeImpl.ensureValid(getChronology(), /* Temporal. */super._with(adjuster));
    // }

    /**
     * {@inheritDoc}
     * @throws DateTimeException {@inheritDoc}
     * @throws ArithmeticException {@inheritDoc}
     */
    override
    ChronoZonedDateTime!(D) _with(TemporalField field, long newValue);

    /**
     * {@inheritDoc}
     * @throws DateTimeException {@inheritDoc}
     * @throws ArithmeticException {@inheritDoc}
     */
      ChronoZonedDateTime!(D) plus(TemporalAmount amount);
    // override
    //  ChronoZonedDateTime!(D) plus(TemporalAmount amount) {
    //     return ChronoZonedDateTimeImpl.ensureValid(getChronology(), /* Temporal. */super.plus(amount));
    // }

    /**
     * {@inheritDoc}
     * @throws DateTimeException {@inheritDoc}
     * @throws ArithmeticException {@inheritDoc}
     */
    override
    ChronoZonedDateTime!(D) plus(long amountToAdd, TemporalUnit unit);

    /**
     * {@inheritDoc}
     * @throws DateTimeException {@inheritDoc}
     * @throws ArithmeticException {@inheritDoc}
     */
     ChronoZonedDateTime!(D) minus(TemporalAmount amount);
    // override
    //  ChronoZonedDateTime!(D) minus(TemporalAmount amount) {
    //     return ChronoZonedDateTimeImpl.ensureValid(getChronology(), /* Temporal. */super.minus(amount));
    // }

    /**
     * {@inheritDoc}
     * @throws DateTimeException {@inheritDoc}
     * @throws ArithmeticException {@inheritDoc}
     */
     override
     ChronoZonedDateTime!(D) minus(long amountToSubtract, TemporalUnit unit);
    // override
    //  ChronoZonedDateTime!(D) minus(long amountToSubtract, TemporalUnit unit) {
    //     return ChronoZonedDateTimeImpl.ensureValid(getChronology(), /* Temporal. */super.minus(amountToSubtract, unit));
    // }

    //-----------------------------------------------------------------------
    /**
     * Queries this date-time using the specified query.
     * !(p)
     * This queries this date-time using the specified query strategy object.
     * The {@code TemporalQuery} object defines the logic to be used to
     * obtain the result. Read the documentation of the query to understand
     * what the result of this method will be.
     * !(p)
     * The result of this method is obtained by invoking the
     * {@link TemporalQuery#queryFrom(TemporalAccessor)} method on the
     * specified query passing {@code this} as the argument.
     *
     * @param !(R) the type of the result
     * @param query  the query to invoke, not null
     * @return the query result, null may be returned (defined by the query)
     * @throws DateTimeException if unable to query (defined by the query)
     * @throws ArithmeticException if numeric overflow occurs (defined by the query)
     */
    /*@SuppressWarnings("unchecked")*/
    override
     R query(R)(TemporalQuery!(R) query);
    // override
    //  R query(R)(TemporalQuery!(R) query) {
    //     if (query == TemporalQueries.zone() || query == TemporalQueries.zoneId()) {
    //         return cast(R) getZone();
    //     } else if (query == TemporalQueries.offset()) {
    //         return cast(R) getOffset();
    //     } else if (query == TemporalQueries.localTime()) {
    //         return cast(R) toLocalTime();
    //     } else if (query == TemporalQueries.chronology()) {
    //         return cast(R) getChronology();
    //     } else if (query == TemporalQueries.precision()) {
    //         return cast(R) NANOS;
    //     }
    //     // inline TemporalAccessor.super.query(query) as an optimization
    //     // non-JDK classes are not permitted to make this optimization
    //     return query.queryFrom(this);
    // }

    /**
     * Formats this date-time using the specified formatter.
     * !(p)
     * This date-time will be passed to the formatter to produce a string.
     * !(p)
     * The  implementation must behave as follows:
     * !(pre)
     *  return formatter.format(this);
     * </pre>
     *
     * @param formatter  the formatter to use, not null
     * @return the formatted date-time string, not null
     * @throws DateTimeException if an error occurs during printing
     */
    //  string format(DateTimeFormatter formatter);
    //  string format(DateTimeFormatter formatter) {
    //     assert(formatter, "formatter");
    //     return formatter.format(this);
    // }

    //-----------------------------------------------------------------------
    /**
     * Converts this date-time to an {@code Instant}.
     * !(p)
     * This returns an {@code Instant} representing the same point on the
     * time-line as this date-time. The calculation combines the
     * {@linkplain #toLocalDateTime() local date-time} and
     * {@linkplain #getOffset() offset}.
     *
     * @return an {@code Instant} representing the same instant, not null
     */
     Instant toInstant();
    //  Instant toInstant() {
    //     return Instant.ofEpochSecond(toEpochSecond(), toLocalTime().getNano());
    // }

    /**
     * Converts this date-time to the number of seconds from the epoch
     * of 1970-01-01T00:00:00Z.
     * !(p)
     * This uses the {@linkplain #toLocalDateTime() local date-time} and
     * {@linkplain #getOffset() offset} to calculate the epoch-second value,
     * which is the number of elapsed seconds from 1970-01-01T00:00:00Z.
     * Instants on the time-line after the epoch are positive, earlier are negative.
     *
     * @return the number of seconds from the epoch of 1970-01-01T00:00:00Z
     */
     long toEpochSecond();
    //  long toEpochSecond() {
    //     long epochDay = toLocalDate().toEpochDay();
    //     long secs = epochDay * 86400 + toLocalTime().toSecondOfDay();
    //     secs -= getOffset().getTotalSeconds();
    //     return secs;
    // }

    //-----------------------------------------------------------------------
    /**
     * Compares this date-time to another date-time, including the chronology.
     * !(p)
     * The comparison is based first on the instant, then on the local date-time,
     * then on the zone ID, then on the chronology.
     * It is "consistent with equals", as defined by {@link Comparable}.
     * !(p)
     * If all the date-time objects being compared are _in the same chronology, then the
     * additional chronology stage is not required.
     * !(p)
     * This  implementation performs the comparison defined above.
     *
     * @param other  the other date-time to compare to, not null
     * @return the comparator value, negative if less, positive if greater
     */
    //  override
     int compareTo(ChronoZonedDateTime!(ChronoLocalDate) other);
    // override
    //  int compareTo(ChronoZonedDateTime!(ChronoLocalDate) other) {
    //     int cmp = Long.compare(toEpochSecond(), other.toEpochSecond());
    //     if (cmp == 0) {
    //         cmp = toLocalTime().getNano() - other.toLocalTime().getNano();
    //         if (cmp == 0) {
    //             cmp = toLocalDateTime().compareTo(other.toLocalDateTime());
    //             if (cmp == 0) {
    //                 cmp = getZone().getId().compareTo(other.getZone().getId());
    //                 if (cmp == 0) {
    //                     cmp = getChronology().compareTo(other.getChronology());
    //                 }
    //             }
    //         }
    //     }
    //     return cmp;
    // }

    /**
     * Checks if the instant of this date-time is before that of the specified date-time.
     * !(p)
     * This method differs from the comparison _in {@link #compareTo} _in that it
     * only compares the instant of the date-time. This is equivalent to using
     * {@code dateTime1.toInstant().isBefore(dateTime2.toInstant());}.
     * !(p)
     * This  implementation performs the comparison based on the epoch-second
     * and nano-of-second.
     *
     * @param other  the other date-time to compare to, not null
     * @return true if this point is before the specified date-time
     */
     bool isBefore(ChronoZonedDateTime!(ChronoLocalDate) other);
    //  bool isBefore(ChronoZonedDateTime!(Object) other) {
    //     long thisEpochSec = toEpochSecond();
    //     long otherEpochSec = other.toEpochSecond();
    //     return thisEpochSec < otherEpochSec ||
    //         (thisEpochSec == otherEpochSec && toLocalTime().getNano() < other.toLocalTime().getNano());
    // }

    /**
     * Checks if the instant of this date-time is after that of the specified date-time.
     * !(p)
     * This method differs from the comparison _in {@link #compareTo} _in that it
     * only compares the instant of the date-time. This is equivalent to using
     * {@code dateTime1.toInstant().isAfter(dateTime2.toInstant());}.
     * !(p)
     * This  implementation performs the comparison based on the epoch-second
     * and nano-of-second.
     *
     * @param other  the other date-time to compare to, not null
     * @return true if this is after the specified date-time
     */
     bool isAfter(ChronoZonedDateTime!(ChronoLocalDate) other);
    //  bool isAfter(ChronoZonedDateTime!(Object) other) {
    //     long thisEpochSec = toEpochSecond();
    //     long otherEpochSec = other.toEpochSecond();
    //     return thisEpochSec > otherEpochSec ||
    //         (thisEpochSec == otherEpochSec && toLocalTime().getNano() > other.toLocalTime().getNano());
    // }

    /**
     * Checks if the instant of this date-time is equal to that of the specified date-time.
     * !(p)
     * This method differs from the comparison _in {@link #compareTo} and {@link #equals}
     * _in that it only compares the instant of the date-time. This is equivalent to using
     * {@code dateTime1.toInstant().equals(dateTime2.toInstant());}.
     * !(p)
     * This  implementation performs the comparison based on the epoch-second
     * and nano-of-second.
     *
     * @param other  the other date-time to compare to, not null
     * @return true if the instant equals the instant of the specified date-time
     */
     bool isEqual(ChronoZonedDateTime!(ChronoLocalDate) other);
    //  bool isEqual(ChronoZonedDateTime!(Object) other) {
    //     return toEpochSecond() == other.toEpochSecond() &&
    //             toLocalTime().getNano() == other.toLocalTime().getNano();
    // }

    //-----------------------------------------------------------------------
    /**
     * Checks if this date-time is equal to another date-time.
     * !(p)
     * The comparison is based on the offset date-time and the zone.
     * To compare for the same instant on the time-line, use {@link #compareTo}.
     * Only objects of type {@code ChronoZonedDateTime} are compared, other types return false.
     *
     * @param obj  the object to check, null returns false
     * @return true if this is equal to the other date-time
     */
    // override
    // bool opEquals(Object obj);

    /**
     * A hash code for this date-time.
     *
     * @return a suitable hash code
     */
    // override
    // size_t toHash() @trusted nothrow;

    //-----------------------------------------------------------------------
    /**
     * Outputs this date-time as a {@code string}.
     * !(p)
     * The output will include the full zoned date-time.
     *
     * @return a string representation of this date-time, not null
     */
    // override
    // string toString();

}