import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Component;
import java.awt.Container;
import java.awt.FlowLayout;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.Calendar;
import java.util.GregorianCalendar;

import javax.swing.BorderFactory;
import javax.swing.JButton;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class Calender extends JPanel
{
  protected int yy;
  protected int mm, dd;

  /** The buttons to be displayed */
  protected JButton labs[][];

  /** The number of day squares to leave blank at the start of this month */
  protected int leadGap = 0;

  /** A Calendar object used throughout */
  Calendar calendar = new GregorianCalendar();

  /** Today's year */
  protected final int thisYear = calendar.get(Calendar.YEAR);

  /** Today's month */
  protected final int thisMonth = calendar.get(Calendar.MONTH);

  /** One of the buttons. We just keep its reference for getBackground(). */
  private JButton b0;

  /** The month choice */
  private JComboBox monthChoice;

  /** The year choice */
  private JComboBox yearChoice;

  /**
   * Construct a Cal, starting with today.
   */
  Calender()
  {
    super();
    setYYMMDD(calendar.get(Calendar.YEAR),
        calendar.get(Calendar.MONTH),
        calendar.get(Calendar.DAY_OF_MONTH));
    buildGUI();
    recompute();
  }

  /**
   * Construct a Cal, given the leading days and the total days
   * 
   * @exception IllegalArgumentException
   *                If year out of range
   */
  Calender(int year, int month, int today)
  {
    super();
    setYYMMDD(year, month, today);
    buildGUI();
    recompute();
  }

  private void setYYMMDD(int year, int month, int today)
  {
    yy = year;
    mm = month;
    dd = today;
  }

  String[] months = { "January", "February", "March", "April", "May", "June",
      "July", "August", "September", "October", "November", "December" };

  /** Build the GUI. Assumes that setYYMMDD has been called. */
  private void buildGUI()
  {
    getAccessibleContext().setAccessibleDescription(
        "Calendar not accessible yet. Sorry!");
    setBorder(BorderFactory.createEtchedBorder());

    setLayout(new BorderLayout());

    JPanel tp = new JPanel();
    tp.add(monthChoice = new JComboBox());
    for (int i = 0; i < months.length; i++)
      monthChoice.addItem(months[i]);
    monthChoice.setSelectedItem(months[mm]);
    monthChoice.addActionListener(new ActionListener()
    {
      public void actionPerformed(ActionEvent ae)
      {
        int i = monthChoice.getSelectedIndex();
        if (i >= 0) {
          mm = i;
          // System.out.println("Month=" + mm);
          recompute();
        }
      }
    });
    monthChoice.getAccessibleContext().setAccessibleName("Months");
    monthChoice.getAccessibleContext().setAccessibleDescription(
        "Choose a month of the year");

    tp.add(yearChoice = new JComboBox());
    yearChoice.setEditable(true);
    for (int i = yy - 5; i < yy + 5; i++)
      yearChoice.addItem(Integer.toString(i));
    yearChoice.setSelectedItem(Integer.toString(yy));
    yearChoice.addActionListener(new ActionListener()
    {
      public void actionPerformed(ActionEvent ae)
      {
        int i = yearChoice.getSelectedIndex();
        if (i >= 0) {
          yy = Integer.parseInt(yearChoice.getSelectedItem()
              .toString());
          //System.out.println("Year=" + yy);
          recompute();
        }
      }
    });
    add(BorderLayout.CENTER, tp);

    JPanel bp = new JPanel();
    bp.setLayout(new GridLayout(7, 7));
    labs = new JButton[6][7]; // first row is days

    bp.add(b0 = new JButton("S"));
    bp.add(new JButton("M"));
    bp.add(new JButton("T"));
    bp.add(new JButton("W"));
    bp.add(new JButton("R"));
    bp.add(new JButton("F"));
    bp.add(new JButton("S"));

    ActionListener dateSetter = new ActionListener()
    {
      public void actionPerformed(ActionEvent e)
      {
        String num = e.getActionCommand();
        if (!num.equals(""))
        {
          // set the current day highlighted
          setDayActive(Integer.parseInt(num));
          // When this becomes a Bean, you can
          // fire some kind of DateChanged event here.
          // Also, build a similar daySetter for day-of-week btns.
        }
      }
    };

    // Construct all the buttons, and add them.
    for (int i = 0; i < 6; i++)
      for (int j = 0; j < 7; j++) {
        bp.add(labs[i][j] = new JButton(""));
        labs[i][j].addActionListener(dateSetter);
      }

    add(BorderLayout.SOUTH, bp);
  }

  public final static int dom[] = { 31, 28, 31, 30,31, 30, 31, 31,30, 31, 30, 31};

  /** Compute which days to put where, in the Cal panel */
  protected void recompute()
  {
    // System.out.println("Cal::recompute: " + yy + ":" + mm + ":" + dd);
    if (mm < 0 || mm > 11)
      throw new IllegalArgumentException("Month " + mm
          + " bad, must be 0-11");
    clearDayActive();
    calendar = new GregorianCalendar(yy, mm, dd);

    // Compute how much to leave before the first.
    // getDay() returns 0 for Sunday, which is just right.
    leadGap = new GregorianCalendar(yy, mm, 1).get(Calendar.DAY_OF_WEEK) - 1;
    // System.out.println("leadGap = " + leadGap);

    int daysInMonth = dom[mm];
    if (isLeap(calendar.get(Calendar.YEAR)) && mm > 1)
      ++daysInMonth;

    // Blank out the labels before 1st day of month
    for (int i = 0; i < leadGap; i++) {
      labs[0][i].setText("");
    }

    // Fill in numbers for the day of month.
    for (int i = 1; i <= daysInMonth; i++) {
      JButton b = labs[(leadGap + i - 1) / 7][(leadGap + i - 1) % 7];
      b.setText(Integer.toString(i));
    }

    // 7 days/week * up to 6 rows
    for (int i = leadGap + 1 + daysInMonth; i < 6 * 7; i++) {
      labs[(i) / 7][(i) % 7].setText("");
    }

    // Shade current day, only if current month
    if (thisYear == yy && mm == thisMonth)
      setDayActive(dd); // shade the box for today

    // Say we need to be drawn on the screen
    repaint();
  }

  /**
   * isLeap() returns true if the given year is a Leap Year.
   * 
   * "a year is a leap year if it is divisible by 4 but not by 100, except
   * that years divisible by 400 *are* leap years." -- Kernighan & Ritchie,
   * _The C Programming Language_, p 37.
   */
  public boolean isLeap(int year)
  {
    if (year % 4 == 0 && year % 100 != 0 || year % 400 == 0)
      return true;
    return false;
  }

  /** Set the year, month, and day */
  public void setDate(int yy, int mm, int dd)
  {
    // System.out.println("Cal::setDate");
    this.yy = yy;
    this.mm = mm; // starts at 0, like Date
    this.dd = dd;
    recompute();
  }

  /** Unset any previously highlighted day */
  private void clearDayActive()
  {
    JButton b;
    // First un-shade the previously-selected square, if any
    if (activeDay > 0)
    {
      b = labs[(leadGap + activeDay - 1) / 7][(leadGap + activeDay - 1) % 7];
      b.setBackground(b0.getBackground());
      b.repaint();
      activeDay = -1;
    }
  }

  private int activeDay = -1;

  /** Set just the day, on the current month */
  public void setDayActive(int newDay)
  {
    clearDayActive();
    // Set the new one
    if (newDay <= 0)
      dd = new GregorianCalendar().get(Calendar.DAY_OF_MONTH);
    else
      dd = newDay;
    // Now shade the correct square
    Component square = labs[(leadGap + newDay - 1) / 7][(leadGap + newDay - 1) % 7];
    square.setBackground(Color.red);
    square.repaint();
    activeDay = newDay;
  }

  /** For testing, a main program */
  public static void main(String[] av)
  {
    JFrame f = new JFrame("Calender");
    Container c = f.getContentPane();
    c.setLayout(new FlowLayout());
    // for this test driver, hardcode 1995/02/10.
//    c.add(new Calender(1995, 2 - 1, 10));
    // and beside it, the current month.
    c.add(new Calender());
    f.pack();
    f.setVisible(true);
  }
}