/*
 *  Copyright 2001-2011 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.base;

import java.util.Calendar;
import java.util.GregorianCalendar;
import java.util.Locale;

import org.joda.time.DateTimeFieldType;
import org.joda.time.DateTimeZone;
import org.joda.time.ReadableDateTime;
import org.joda.time.format.DateTimeFormat;

/**
 * AbstractDateTime provides the common behaviour for datetime classes.
 * <p>
 * This class should generally not be used directly by API users.
 * The {@link ReadableDateTime} interface should be used when different 
 * kinds of date/time objects are to be referenced.
 * <p>
 * Whenever you want to implement <code>ReadableDateTime</code> you should
 * extend this class.
 * <p>
 * AbstractDateTime subclasses may be mutable and not thread-safe.
 *
 * @author Brian S O'Neill
 * @author Stephen Colebourne
 * @since 1.0
 */
public abstract class AbstractDateTime
        extends AbstractInstant
        implements ReadableDateTime {

    /**
     * Constructor.
     */
    protected AbstractDateTime() {
        super();
    }

    //-----------------------------------------------------------------------
    /**
     * Get the value of one of the fields of a datetime.
     * <p>
     * This method uses the chronology of the datetime to obtain the value.
     * It is essentially a generic way of calling one of the get methods.
     *
     * @param type  a field type, usually obtained from DateTimeFieldType
     * @return the value of that field
     * @throws IllegalArgumentException if the field type is null
     */
    public int get(DateTimeFieldType type) {
        if (type == null) {
            throw new IllegalArgumentException("The DateTimeFieldType must not be null");
        }
        return type.getField(getChronology()).get(getMillis());
    }

    //-----------------------------------------------------------------------
    /**
     * Get the era field value.
     * 
     * @return the era
     */
    public int getEra() {
        return getChronology().era().get(getMillis());
    }

    /**
     * Get the year of era field value.
     * 
     * @return the year of era
     */
    public int getCenturyOfEra() {
        return getChronology().centuryOfEra().get(getMillis());
    }

    /**
     * Get the year of era field value.
     * 
     * @return the year of era
     */
    public int getYearOfEra() {
        return getChronology().yearOfEra().get(getMillis());
    }

    /**
     * Get the year of century field value.
     * 
     * @return the year of century
     */
    public int getYearOfCentury() {
        return getChronology().yearOfCentury().get(getMillis());
    }

    /**
     * Get the year field value.
     * 
     * @return the year
     */
    public int getYear() {
        return getChronology().year().get(getMillis());
    }

    /**
     * Get the weekyear field value.
     * <p>
     * The weekyear is the year that matches with the weekOfWeekyear field.
     * In the standard ISO8601 week algorithm, the first week of the year
     * is that in which at least 4 days are in the year. As a result of this
     * definition, day 1 of the first week may be in the previous year.
     * The weekyear allows you to query the effective year for that day.
     * 
     * @return the year of a week based year
     */
    public int getWeekyear() {
        return getChronology().weekyear().get(getMillis());
    }

    /**
     * Get the month of year field value.
     * 
     * @return the month of year
     */
    public int getMonthOfYear() {
        return getChronology().monthOfYear().get(getMillis());
    }

    /**
     * Get the week of weekyear field value.
     * <p>
     * This field is associated with the "weekyear" via {@link #getWeekyear()}.
     * In the standard ISO8601 week algorithm, the first week of the year
     * is that in which at least 4 days are in the year. As a result of this
     * definition, day 1 of the first week may be in the previous year.
     * 
     * @return the week of a week based year
     */
    public int getWeekOfWeekyear() {
        return getChronology().weekOfWeekyear().get(getMillis());
    }

    /**
     * Get the day of year field value.
     * 
     * @return the day of year
     */
    public int getDayOfYear() {
        return getChronology().dayOfYear().get(getMillis());
    }

    /**
     * Get the day of month field value.
     * <p>
     * The values for the day of month are defined in {@link org.joda.time.DateTimeConstants}.
     * 
     * @return the day of month
     */
    public int getDayOfMonth() {
        return getChronology().dayOfMonth().get(getMillis());
    }

    /**
     * Get the day of week field value.
     * <p>
     * The values for the day of week are defined in {@link org.joda.time.DateTimeConstants}.
     * 
     * @return the day of week
     */
    public int getDayOfWeek() {
        return getChronology().dayOfWeek().get(getMillis());
    }

    //-----------------------------------------------------------------------
    /**
     * Get the hour of day field value.
     *
     * @return the hour of day
     */
    public int getHourOfDay() {
        return getChronology().hourOfDay().get(getMillis());
    }

    /**
     * Get the minute of day field value.
     *
     * @return the minute of day
     */
    public int getMinuteOfDay() {
        return getChronology().minuteOfDay().get(getMillis());
    }

    /**
     * Get the minute of hour field value.
     *
     * @return the minute of hour
     */
    public int getMinuteOfHour() {
        return getChronology().minuteOfHour().get(getMillis());
    }

    /**
     * Get the second of day field value.
     *
     * @return the second of day
     */
    public int getSecondOfDay() {
        return getChronology().secondOfDay().get(getMillis());
    }

    /**
     * Get the second of minute field value.
     *
     * @return the second of minute
     */
    public int getSecondOfMinute() {
        return getChronology().secondOfMinute().get(getMillis());
    }

    /**
     * Get the millis of day field value.
     *
     * @return the millis of day
     */
    public int getMillisOfDay() {
        return getChronology().millisOfDay().get(getMillis());
    }

    /**
     * Get the millis of second field value.
     *
     * @return the millis of second
     */
    public int getMillisOfSecond() {
        return getChronology().millisOfSecond().get(getMillis());
    }

    //-----------------------------------------------------------------------
    /**
     * Get the date time as a <code>java.util.Calendar</code>, assigning
     * exactly the same millisecond instant.
     * The locale is passed in, enabling Calendar to select the correct
     * localized subclass.
     * <p>
     * The JDK and Joda-Time both have time zone implementations and these
     * differ in accuracy. Joda-Time's implementation is generally more up to
     * date and thus more accurate - for example JDK1.3 has no historical data.
     * The effect of this is that the field values of the <code>Calendar</code>
     * may differ from those of this object, even though the milliseond value
     * is the same. Most of the time this just means that the JDK field values
     * are wrong, as our time zone information is more up to date.
     *
     * @param locale  the locale to get the Calendar for, or default if null
     * @return a localized Calendar initialised with this datetime
     */
    public Calendar toCalendar(Locale locale) {
        if (locale == null) {
            locale = Locale.getDefault();
        }
        DateTimeZone zone = getZone();
        Calendar cal = Calendar.getInstance(zone.toTimeZone(), locale);
        cal.setTime(toDate());
        return cal;
    }

    /**
     * Get the date time as a <code>java.util.GregorianCalendar</code>,
     * assigning exactly the same millisecond instant.
     * <p>
     * The JDK and Joda-Time both have time zone implementations and these
     * differ in accuracy. Joda-Time's implementation is generally more up to
     * date and thus more accurate - for example JDK1.3 has no historical data.
     * The effect of this is that the field values of the <code>Calendar</code>
     * may differ from those of this object, even though the milliseond value
     * is the same. Most of the time this just means that the JDK field values
     * are wrong, as our time zone information is more up to date.
     *
     * @return a GregorianCalendar initialised with this datetime
     */
    public GregorianCalendar toGregorianCalendar() {
        DateTimeZone zone = getZone();
        GregorianCalendar cal = new GregorianCalendar(zone.toTimeZone());
        cal.setTime(toDate());
        return cal;
    }

    //-----------------------------------------------------------------------
    /**
     * Output the instant using the specified format pattern.
     *
     * @param pattern  the pattern specification, null means use <code>toString</code>
     * @see  org.joda.time.format.DateTimeFormat
     */
    public String toString(String pattern) {
        if (pattern == null) {
            return toString();
        }
        return DateTimeFormat.forPattern(pattern).print(this);
    }

    /**
     * Output the instant using the specified format pattern.
     *
     * @param pattern  the pattern specification, null means use <code>toString</code>
     * @param locale  Locale to use, null means default
     * @see  org.joda.time.format.DateTimeFormat
     */
    public String toString(String pattern, Locale locale) throws IllegalArgumentException {
        if (pattern == null) {
            return toString();
        }
        return DateTimeFormat.forPattern(pattern).withLocale(locale).print(this);
    }

}