/*
 *  Copyright 2001-2014 Stephen Colebourne
 *
 *  Licensed under the Apache License, Version 2.0 (the "License");
 *  you may not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */
package org.joda.time.chrono;

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
import java.util.concurrent.ConcurrentHashMap;

import org.joda.time.Chronology;
import org.joda.time.DateTimeFieldType;
import org.joda.time.DateTimeZone;
import org.joda.time.field.DividedDateTimeField;
import org.joda.time.field.RemainderDateTimeField;

Implements a chronology that follows the rules of the ISO8601 standard,
which is compatible with Gregorian for all modern dates.
When ISO does not define a field, but it can be determined (such as AM/PM)
it is included.
 With the exception of century related fields, ISOChronology is exactly the same as GregorianChronology. In this chronology, centuries and year of century are zero based. For all years, the century is determined by dropping the last two digits of the year, ignoring sign. The year of century is the value of the last two year digits. 

ISOChronology is thread-safe and immutable.
Author:
Stephen Colebourne, Brian S O'Neill
Since:
1.0/**
 * Implements a chronology that follows the rules of the ISO8601 standard,
 * which is compatible with Gregorian for all modern dates.
 * When ISO does not define a field, but it can be determined (such as AM/PM)
 * it is included.
 * <p>
 * With the exception of century related fields, ISOChronology is exactly the
 * same as {@link GregorianChronology}. In this chronology, centuries and year
 * of century are zero based. For all years, the century is determined by
 * dropping the last two digits of the year, ignoring sign. The year of century
 * is the value of the last two year digits.
 * <p>
 * ISOChronology is thread-safe and immutable.
 *
 * @author Stephen Colebourne
 * @author Brian S O'Neill
 * @since 1.0
 */
public final class ISOChronology extends AssembledChronology {

    
Serialization lock /** Serialization lock */
    private static final long serialVersionUID = -6212696554273812441L;

    
Singleton instance of a UTC ISOChronology /** Singleton instance of a UTC ISOChronology */
    private static final ISOChronology INSTANCE_UTC;

    
Cache of zone to chronology /** Cache of zone to chronology */
    private static final ConcurrentHashMap<DateTimeZone, ISOChronology> cCache = new ConcurrentHashMap<DateTimeZone, ISOChronology>();
    static {
        INSTANCE_UTC = new ISOChronology(GregorianChronology.getInstanceUTC());
        cCache.put(DateTimeZone.UTC, INSTANCE_UTC);
    }

    
Gets an instance of the ISOChronology.
The time zone of the returned instance is UTC.
Returns:
a singleton UTC instance of the chronology/**
     * Gets an instance of the ISOChronology.
     * The time zone of the returned instance is UTC.
     * 
     * @return a singleton UTC instance of the chronology
     */
    public static ISOChronology getInstanceUTC() {
        return INSTANCE_UTC;
    }

    
Gets an instance of the ISOChronology in the default time zone.
Returns:
a chronology in the default time zone/**
     * Gets an instance of the ISOChronology in the default time zone.
     * 
     * @return a chronology in the default time zone
     */
    public static ISOChronology getInstance() {
        return getInstance(DateTimeZone.getDefault());
    }

    
Gets an instance of the ISOChronology in the given time zone.
Params:
zone –  the time zone to get the chronology in, null is default
Returns:
a chronology in the specified time zone/**
     * Gets an instance of the ISOChronology in the given time zone.
     * 
     * @param zone  the time zone to get the chronology in, null is default
     * @return a chronology in the specified time zone
     */
    public static ISOChronology getInstance(DateTimeZone zone) {
        if (zone == null) {
            zone = DateTimeZone.getDefault();
        }
        ISOChronology chrono = cCache.get(zone);
        if (chrono == null) {
            chrono = new ISOChronology(ZonedChronology.getInstance(INSTANCE_UTC, zone));
            ISOChronology oldChrono = cCache.putIfAbsent(zone, chrono);
            if (oldChrono != null) {
                chrono = oldChrono;
            }
        }
        return chrono;
    }

    // Constructors and instance variables
    //-----------------------------------------------------------------------

    
Restricted constructor
/**
     * Restricted constructor
     */
    private ISOChronology(Chronology base) {
        super(base, null);
    }

    // Conversion
    //-----------------------------------------------------------------------
    
Gets the Chronology in the UTC time zone.
Returns:
the chronology in UTC/**
     * Gets the Chronology in the UTC time zone.
     * 
     * @return the chronology in UTC
     */
    public Chronology withUTC() {
        return INSTANCE_UTC;
    }

    
Gets the Chronology in a specific time zone.
Params:
zone –  the zone to get the chronology in, null is default
Returns:
the chronology/**
     * Gets the Chronology in a specific time zone.
     * 
     * @param zone  the zone to get the chronology in, null is default
     * @return the chronology
     */
    public Chronology withZone(DateTimeZone zone) {
        if (zone == null) {
            zone = DateTimeZone.getDefault();
        }
        if (zone == getZone()) {
            return this;
        }
        return getInstance(zone);
    }

    // Output
    //-----------------------------------------------------------------------
    
Gets a debugging toString.
Returns:
a debugging string/**
     * Gets a debugging toString.
     * 
     * @return a debugging string
     */
    public String toString() {
        String str = "ISOChronology";
        DateTimeZone zone = getZone();
        if (zone != null) {
            str = str + '[' + zone.getID() + ']';
        }
        return str;
    }

    protected void assemble(Fields fields) {
        if (getBase().getZone() == DateTimeZone.UTC) {
            // Use zero based century and year of century.
            fields.centuryOfEra = new DividedDateTimeField(
                ISOYearOfEraDateTimeField.INSTANCE, DateTimeFieldType.centuryOfEra(), 100);
            fields.centuries = fields.centuryOfEra.getDurationField();
            
            fields.yearOfCentury = new RemainderDateTimeField(
                (DividedDateTimeField) fields.centuryOfEra, DateTimeFieldType.yearOfCentury());
            fields.weekyearOfCentury = new RemainderDateTimeField(
                (DividedDateTimeField) fields.centuryOfEra, fields.weekyears, DateTimeFieldType.weekyearOfCentury());
        }
    }

    //-----------------------------------------------------------------------
    
Checks if this chronology instance equals another.
Params:
obj –  the object to compare to
Returns:
true if equal
Since:
1.6/**
     * Checks if this chronology instance equals another.
     * 
     * @param obj  the object to compare to
     * @return true if equal
     * @since 1.6
     */
    public boolean equals(Object obj) {
        if (this == obj) {
            return true;
        }
        if (obj instanceof ISOChronology) {
            ISOChronology chrono = (ISOChronology) obj;
            return getZone().equals(chrono.getZone());
        }
        return false;
    }

    
A suitable hash code for the chronology.
Returns:
the hash code
Since:
1.6/**
     * A suitable hash code for the chronology.
     * 
     * @return the hash code
     * @since 1.6
     */
    public int hashCode() {
        return "ISO".hashCode() * 11 + getZone().hashCode();
    }

    //-----------------------------------------------------------------------
    
Serialize ISOChronology instances using a small stub. This reduces the
serialized size, and deserialized instances come from the cache.
/**
     * Serialize ISOChronology instances using a small stub. This reduces the
     * serialized size, and deserialized instances come from the cache.
     */
    private Object writeReplace() {
        return new Stub(getZone());
    }

    private static final class Stub implements Serializable {
        private static final long serialVersionUID = -6212696554273812441L;

        private transient DateTimeZone iZone;

        Stub(DateTimeZone zone) {
            iZone = zone;
        }

        private Object readResolve() {
            return ISOChronology.getInstance(iZone);
        }

        private void writeObject(ObjectOutputStream out) throws IOException {
            out.writeObject(iZone);
        }

        private void readObject(ObjectInputStream in)
            throws IOException, ClassNotFoundException
        {
            iZone = (DateTimeZone)in.readObject();
        }
    }

}