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/*

 * This file is available under and governed by the GNU General Public

 * License version 2 only, as published by the Free Software Foundation.

 * However, the following notice accompanied the original version of this

 * file:

 *

 * Copyright (c) 2012, Stephen Colebourne & Michael Nascimento Santos

 *

 * All rights reserved.

 *

 * Redistribution and use in source and binary forms, with or without

 * modification, are permitted provided that the following conditions are met:

 *

 *  * Redistributions of source code must retain the above copyright notice,

 *    this list of conditions and the following disclaimer.

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package java.time.temporal;

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

import static java.time.temporal.ChronoUnit.DAYS;

import static java.time.temporal.ChronoUnit.FOREVER;

import java.io.InvalidObjectException;

import java.io.Serializable;

import java.time.DateTimeException;

import java.time.LocalDate;

import java.time.format.DateTimeBuilder;

/**

 * A set of date fields that provide access to Julian Days.

 * <p>

 * The Julian Day is a standard way of expressing date and time commonly used in the scientific community.

 * It is expressed as a decimal number of whole days where days start at midday.

 * This class represents variations on Julian Days that count whole days from midnight.

 *

 * <h3>Specification for implementors</h3>

 * This is an immutable and thread-safe class.

 *

 * @since 1.8

 */

public final class JulianFields {

    /**

     * The offset from Julian to EPOCH DAY.

     */

    private static final long JULIAN_DAY_OFFSET = 2440588L;

    /**

     * Julian Day field.

     * <p>

     * This is an integer-based version of the Julian Day Number.

     * Julian Day is a well-known system that represents the count of whole days since day 0,

     * which is defined to be January 1, 4713 BCE in the Julian calendar, and -4713-11-24 Gregorian.

     * The field  has "JulianDay" as 'name', and 'DAYS' as 'baseUnit'.

     * The field always refers to the local date-time, ignoring the offset or zone.

     * <p>

     * For date-times, 'JULIAN_DAY.doGet()' assumes the same value from

     * midnight until just before the next midnight.

     * When 'JULIAN_DAY.doWith()' is applied to a date-time, the time of day portion remains unaltered.

     * 'JULIAN_DAY.doWith()' and 'JULIAN_DAY.doGet()' only apply to {@code Temporal} objects that

     * can be converted into {@link ChronoField#EPOCH_DAY}.

     * A {@link DateTimeException} is thrown for any other type of object.

     * <p>

     * <h3>Astronomical and Scientific Notes</h3>

     * The standard astronomical definition uses a fraction to indicate the time-of-day,

     * thus 3.25 would represent the time 18:00, since days start at midday.

     * This implementation uses an integer and days starting at midnight.

     * The integer value for the Julian Day Number is the astronomical Julian Day value at midday

     * of the date in question.

     * This amounts to the astronomical Julian Day, rounded to an integer {@code JDN = floor(JD + 0.5)}.

     * <p>

     * <pre>

     *  | ISO date          |  Julian Day Number | Astronomical Julian Day |

     *  | 1970-01-01T00:00  |         2,440,588  |         2,440,587.5     |

     *  | 1970-01-01T06:00  |         2,440,588  |         2,440,587.75    |

     *  | 1970-01-01T12:00  |         2,440,588  |         2,440,588.0     |

     *  | 1970-01-01T18:00  |         2,440,588  |         2,440,588.25    |

     *  | 1970-01-02T00:00  |         2,440,589  |         2,440,588.5     |

     *  | 1970-01-02T06:00  |         2,440,589  |         2,440,588.75    |

     *  | 1970-01-02T12:00  |         2,440,589  |         2,440,589.0     |

     * </pre>

     * <p>

     * Julian Days are sometimes taken to imply Universal Time or UTC, but this

     * implementation always uses the Julian Day number for the local date,

     * regardless of the offset or time-zone.

     */

    public static final TemporalField JULIAN_DAY = new Field("JulianDay", DAYS, FOREVER, JULIAN_DAY_OFFSET);

    /**

     * Modified Julian Day field.

     * <p>

     * This is an integer-based version of the Modified Julian Day Number.

     * Modified Julian Day (MJD) is a well-known system that counts days continuously.

     * It is defined relative to astronomical Julian Day as  {@code MJD = JD - 2400000.5}.

     * Each Modified Julian Day runs from midnight to midnight.

     * The field always refers to the local date-time, ignoring the offset or zone.

     * <p>

     * For date-times, 'MODIFIED_JULIAN_DAY.doGet()' assumes the same value from

     * midnight until just before the next midnight.

     * When 'MODIFIED_JULIAN_DAY.doWith()' is applied to a date-time, the time of day portion remains unaltered.

     * 'MODIFIED_JULIAN_DAY.doWith()' and 'MODIFIED_JULIAN_DAY.doGet()' only apply to {@code Temporal} objects

     * that can be converted into {@link ChronoField#EPOCH_DAY}.

     * A {@link DateTimeException} is thrown for any other type of object.

     * <p>

     * This implementation is an integer version of MJD with the decimal part rounded to floor.

     * <p>

     * <h3>Astronomical and Scientific Notes</h3>

     * <pre>

     *  | ISO date          | Modified Julian Day |      Decimal MJD |

     *  | 1970-01-01T00:00  |             40,587  |       40,587.0   |

     *  | 1970-01-01T06:00  |             40,587  |       40,587.25  |

     *  | 1970-01-01T12:00  |             40,587  |       40,587.5   |

     *  | 1970-01-01T18:00  |             40,587  |       40,587.75  |

     *  | 1970-01-02T00:00  |             40,588  |       40,588.0   |

     *  | 1970-01-02T06:00  |             40,588  |       40,588.25  |

     *  | 1970-01-02T12:00  |             40,588  |       40,588.5   |

     * </pre>

     * <p>

     * Modified Julian Days are sometimes taken to imply Universal Time or UTC, but this

     * implementation always uses the Modified Julian Day for the local date,

     * regardless of the offset or time-zone.

     */

    public static final TemporalField MODIFIED_JULIAN_DAY = new Field("ModifiedJulianDay", DAYS, FOREVER, 40587L);

    /**

     * Rata Die field.

     * <p>

     * Rata Die counts whole days continuously starting day 1 at midnight at the beginning of 0001-01-01 (ISO).

     * The field always refers to the local date-time, ignoring the offset or zone.

     * <p>

     * For date-times, 'RATA_DIE.doGet()' assumes the same value from

     * midnight until just before the next midnight.

     * When 'RATA_DIE.doWith()' is applied to a date-time, the time of day portion remains unaltered.

     * 'MODIFIED_JULIAN_DAY.doWith()' and 'RATA_DIE.doGet()' only apply to {@code Temporal} objects

     * that can be converted into {@link ChronoField#EPOCH_DAY}.

     * A {@link DateTimeException} is thrown for any other type of object.

     */

    public static final TemporalField RATA_DIE = new Field("RataDie", DAYS, FOREVER, 719163L);

    /**

     * Restricted constructor.

     */

    private JulianFields() {

        throw new AssertionError("Not instantiable");

    }

    /**

     * implementation of JulianFields.  Each instance is a singleton.

     */

    private static class Field implements TemporalField, Serializable {

        private static final long serialVersionUID = -7501623920830201812L;

        private final String name;

        private final transient TemporalUnit baseUnit;

        private final transient TemporalUnit rangeUnit;

        private final transient ValueRange range;

        private final transient long offset;

        private Field(String name, TemporalUnit baseUnit, TemporalUnit rangeUnit, long offset) {

            this.name = name;

            this.baseUnit = baseUnit;

            this.rangeUnit = rangeUnit;

            this.range = ValueRange.of(-365243219162L + offset, 365241780471L + offset);

            this.offset = offset;

        }

        /**

         * Resolve the object from the stream to the appropriate singleton.

         * @return one of the singleton objects {@link #JULIAN_DAY},

         *     {@link #MODIFIED_JULIAN_DAY}, or {@link #RATA_DIE}.

         * @throws InvalidObjectException if the object in the stream is not one of the singletons.

         */

        private Object readResolve() throws InvalidObjectException {

            if (JULIAN_DAY.getName().equals(name)) {

                return JULIAN_DAY;

            } else if (MODIFIED_JULIAN_DAY.getName().equals(name)) {

                return MODIFIED_JULIAN_DAY;

            } else if (RATA_DIE.getName().equals(name)) {

                return RATA_DIE;

            } else {

                throw new InvalidObjectException("Not one of the singletons");

            }

        }

        //-----------------------------------------------------------------------

        @Override

        public String getName() {

            return name;

        }

        @Override

        public TemporalUnit getBaseUnit() {

            return baseUnit;

        }

        @Override

        public TemporalUnit getRangeUnit() {

            return rangeUnit;

        }

        @Override

        public ValueRange range() {

            return range;

        }

        //-----------------------------------------------------------------------

        @Override

        public boolean doIsSupported(TemporalAccessor temporal) {

            return temporal.isSupported(EPOCH_DAY);

        }

        @Override

        public ValueRange doRange(TemporalAccessor temporal) {

            if (doIsSupported(temporal) == false) {

                throw new DateTimeException("Unsupported field: " + this);

            }

            return range();

        }

        @Override

        public long doGet(TemporalAccessor temporal) {

            return temporal.getLong(EPOCH_DAY) + offset;

        }

        @Override

        public <R extends Temporal> R doWith(R temporal, long newValue) {

            if (range().isValidValue(newValue) == false) {

                throw new DateTimeException("Invalid value: " + name + " " + newValue);

            }

            return (R) temporal.with(EPOCH_DAY, Math.subtractExact(newValue, offset));

        }

        //-----------------------------------------------------------------------

        @Override

        public boolean resolve(DateTimeBuilder builder, long value) {

            boolean changed = false;

            changed = resolve0(JULIAN_DAY, builder, changed);

            changed = resolve0(MODIFIED_JULIAN_DAY, builder, changed);

            changed = resolve0(RATA_DIE, builder, changed);

            return changed;

        }

        private boolean resolve0(TemporalField field, DateTimeBuilder builder, boolean changed) {

            if (builder.containsFieldValue(field)) {

                builder.addCalendrical(LocalDate.ofEpochDay(Math.subtractExact(builder.getFieldValue(JULIAN_DAY), JULIAN_DAY_OFFSET)));

                builder.removeFieldValue(JULIAN_DAY);

                changed = true;

            }

            return changed;

        }

        //-----------------------------------------------------------------------

        @Override

        public String toString() {

            return getName();

        }

    }

}