/* ===========================================================
 * JFreeChart : a free chart library for the Java(tm) platform
 * ===========================================================
 *
 * (C) Copyright 2000-2005, by Object Refinery Limited and Contributors.
 *
 * Project Info:  http://www.jfree.org/jfreechart/index.html
 *
 * This library is free software; you can redistribute it and/or modify it 
 * under the terms of the GNU Lesser General Public License as published by 
 * the Free Software Foundation; either version 2.1 of the License, or 
 * (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful, but 
 * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY 
 * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public 
 * License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, 
 * USA.  
 *
 * [Java is a trademark or registered trademark of Sun Microsystems, Inc. 
 * in the United States and other countries.]
 *
 * ---------
 * Week.java
 * ---------
 * (C) Copyright 2001-2004, by Object Refinery Limited and Contributors.
 *
 * Original Author:  David Gilbert (for Object Refinery Limited);
 * Contributor(s):   Aimin Han;
 *
 * $Id: Week.java,v 1.7.2.1 2005/10/25 21:35:24 mungady Exp $
 *
 * Changes
 * -------
 * 11-Oct-2001 : Version 1 (DG);
 * 18-Dec-2001 : Changed order of parameters in constructor (DG);
 * 19-Dec-2001 : Added a new constructor as suggested by Paul English (DG);
 * 29-Jan-2002 : Worked on the parseWeek() method (DG);
 * 13-Feb-2002 : Fixed bug in Week(Date) constructor (DG);
 * 26-Feb-2002 : Changed getStart(), getMiddle() and getEnd() methods to 
 *               evaluate with reference to a particular time zone (DG);
 * 05-Apr-2002 : Reinstated this class to the JCommon library (DG);
 * 24-Jun-2002 : Removed unnecessary main method (DG);
 * 10-Sep-2002 : Added getSerialIndex() method (DG);
 * 06-Oct-2002 : Fixed errors reported by Checkstyle (DG);
 * 18-Oct-2002 : Changed to observe 52 or 53 weeks per year, consistent with 
 *               GregorianCalendar. Thanks to Aimin Han for the code (DG);
 * 02-Jan-2003 : Removed debug code (DG);
 * 13-Mar-2003 : Moved to com.jrefinery.data.time package, and implemented 
 *               Serializable (DG);
 * 21-Oct-2003 : Added hashCode() method (DG);
 * 24-May-2004 : Modified getFirstMillisecond() and getLastMillisecond() to 
 *               take account of firstDayOfWeek setting in Java's Calendar 
 *               class (DG);
 * 30-Sep-2004 : Replaced getTime().getTime() with getTimeInMillis() (DG);
 * 04-Nov-2004 : Reverted change of 30-Sep-2004, because it won't work for 
 *               JDK 1.3 (DG);
 *
 */

package org.jfree.data.time;

import java.io.Serializable;
import java.util.Calendar;
import java.util.Date;
import java.util.TimeZone;

/**
 * A calendar week.  All years are considered to have 53 weeks, numbered from 1 
 * to 53, although in many cases the 53rd week is empty.  Most of the time, the
 * 1st week of the year *begins* in the previous calendar year, but it always 
 * finishes in the current year (this behaviour matches the workings of the 
 * <code>GregorianCalendar</code> class).
 * <P>
 * This class is immutable, which is a requirement for all 
 * {@link RegularTimePeriod} subclasses.
 */
public class Week extends RegularTimePeriod implements Serializable {

    /** For serialization. */
    private static final long serialVersionUID = 1856387786939865061L;
    
    /** Constant for the first week in the year. */
    public static final int FIRST_WEEK_IN_YEAR = 1;

    /** Constant for the last week in the year. */
    public static final int LAST_WEEK_IN_YEAR = 53;

    /** The year in which the week falls. */
    private Year year;

    /** The week (1-53). */
    private int week;

    /**
     * Creates a new time period for the week in which the current system 
     * date/time falls.
     */
    public Week() {
        this(new Date());
    }

    /**
     * Creates a time period representing the week in the specified year.
     *
     * @param week  the week (1 to 53).
     * @param year  the year (1900 to 9999).
     */
    public Week(int week, int year) {
        this(week, new Year(year));
    }

    /**
     * Creates a time period representing the week in the specified year.
     *
     * @param week  the week (1 to 53).
     * @param year  the year (1900 to 9999).
     */
    public Week(int week, Year year) {
        if ((week < FIRST_WEEK_IN_YEAR) && (week > LAST_WEEK_IN_YEAR)) {
            throw new IllegalArgumentException(
                "The 'week' argument must be in the range 1 - 53."
            );
        }
        this.week = week;
        this.year = year;
    }

    /**
     * Creates a time period for the week in which the specified date/time 
     * falls.
     *
     * @param time  the time (<code>null</code> not permitted).
     */
    public Week(Date time) {
        // defer argument checking...
        this(time, RegularTimePeriod.DEFAULT_TIME_ZONE);
    }

    /**
     * Creates a time period for the week in which the specified date/time 
     * falls, calculated relative to the specified time zone.
     *
     * @param time  the date/time (<code>null</code> not permitted).
     * @param zone  the time zone (<code>null</code> not permitted).
     */
    public Week(Date time, TimeZone zone) {
        if (time == null) {
            throw new IllegalArgumentException("Null 'time' argument.");   
        }
        if (zone == null) {
            throw new IllegalArgumentException("Null 'zone' argument.");   
        }
        Calendar calendar = Calendar.getInstance(zone);
        calendar.setTime(time);

        // sometimes the last few days of the year are considered to fall in 
        // the *first* week of the following year.  Refer to the Javadocs for 
        // GregorianCalendar.
        int tempWeek = calendar.get(Calendar.WEEK_OF_YEAR);
        if (tempWeek == 1 
                && calendar.get(Calendar.MONTH) == Calendar.DECEMBER) {
            this.week = 1;
            this.year =  new Year(calendar.get(Calendar.YEAR) + 1);
        }
        else {
            this.week = Math.min(tempWeek, LAST_WEEK_IN_YEAR);
            this.year = new Year(calendar.get(Calendar.YEAR));
        }

    }

    /**
     * Returns the year in which the week falls.
     *
     * @return The year (never <code>null</code>).
     */
    public Year getYear() {
        return this.year;
    }

    /**
     * Returns the year in which the week falls, as an integer value.
     *
     * @return The year.
     */
    public int getYearValue() {
        return this.year.getYear();
    }

    /**
     * Returns the week.
     *
     * @return The week.
     */
    public int getWeek() {
        return this.week;
    }

    /**
     * Returns the week preceding this one.  This method will return 
     * <code>null</code> for some lower limit on the range of weeks (currently 
     * week 1, 1900).  For week 1 of any year, the previous week is always week 
     * 53, but week 53 may not contain any days (you should check for this).
     *
     * @return The preceding week (possibly <code>null</code>).
     */
    public RegularTimePeriod previous() {

        Week result;
        if (this.week != FIRST_WEEK_IN_YEAR) {
            result = new Week(this.week - 1, this.year);
        }
        else {
            // we need to work out if the previous year has 52 or 53 weeks...
            Year prevYear = (Year) this.year.previous();
            if (prevYear != null) {
                int yy = prevYear.getYear();
                Calendar prevYearCalendar = Calendar.getInstance();
                prevYearCalendar.set(yy, Calendar.DECEMBER, 31);
                result = new Week(
                    prevYearCalendar.getActualMaximum(Calendar.WEEK_OF_YEAR), 
                    prevYear
                );
            }
            else {
                result = null;
            }
        }
        return result;

    }

    /**
     * Returns the week following this one.  This method will return 
     * <code>null</code> for some upper limit on the range of weeks (currently 
     * week 53, 9999).  For week 52 of any year, the following week is always 
     * week 53, but week 53 may not contain any days (you should check for 
     * this).
     *
     * @return The following week (possibly <code>null</code>).
     */
    public RegularTimePeriod next() {

        Week result;
        if (this.week < 52) {
            result = new Week(this.week + 1, this.year);
        }
        else {
            Calendar calendar = Calendar.getInstance();
            calendar.set(this.year.getYear(), Calendar.DECEMBER, 31);
            int actualMaxWeek 
                = calendar.getActualMaximum(Calendar.WEEK_OF_YEAR);
            if (this.week != actualMaxWeek) {
                result = new Week(this.week + 1, this.year);
            }
            else {
                Year nextYear = (Year) this.year.next();
                if (nextYear != null) {
                    result = new Week(FIRST_WEEK_IN_YEAR, nextYear);
                }
                else {
                    result = null;
                }
            }
        }
        return result;

    }

    /**
     * Returns a serial index number for the week.