/** Let's draw a polygon, and let the user add points, in a similar manner to
 *  how we moved a rectangle to a new x,y position in section 12.2.
 *  The steps we take are inspired by the "how to" section in chapter 10, pp. 414-417.
 *  There is a separate class called Point that's implements an ordered pair.
 */
import java.util.*;             // defines ArrayList
import java.applet.*;           // defines Applet class
import java.awt.*;              // defines Graphics[2D]
import javax.swing.*;           // defines JPanel
import java.awt.event.*;        // defines ActionListener interface (italics in API)

public class PolygonApplet extends Applet
{
  // data should be instance variables of the applet (or panel if we had a panel)
  // in this case, we want an ArrayList of Point objects.
  ArrayList vertices;

  // in applet constructor we need to give the user interface components
  // Create a panel, and add buttons & text fields to it.
  public PolygonApplet()
  {
    vertices = new ArrayList();
    JPanel panel = new JPanel();

    // now create text fields and button to add (see RectangleFrame class of prev example)
    // The text fields are accessed in inner class, so compiler wants them "final"
    final JTextField xField = new JTextField(5);
    final JTextField yField = new JTextField(5);
    JButton addButton = new JButton("Add");
    JLabel xLabel = new JLabel("x = ");
    JLabel yLabel = new JLabel("y = ");
    // we've already created a panel object, so now "add" into it in order:
    panel.add(xLabel);
    panel.add(xField);
    panel.add(yLabel);
    panel.add(yField);
    panel.add(addButton);

    // listener for the add button
    class AddPointListener implements ActionListener
    {
      public void actionPerformed(ActionEvent e)
      {
        int x = Integer.parseInt(xField.getText());
        int y = Integer.parseInt(yField.getText());
        Point p = new Point(x, y);
        vertices.add(p);
        repaint();              // see effect of adding new point w/o waiting for window manager
      }
    }
    ActionListener listener = new AddPointListener();
    addButton.addActionListener(listener);

    JFrame frame = new JFrame();
    // do we need the following:
    // getContentPane().add(panel, BorderLayout.SOUTH);
    frame.setContentPane(panel);
    frame.pack();
    frame.show();
  }

  // visual representation of data
  public void paint(Graphics g)
  {
    Graphics2D g2 = (Graphics2D) g;
    int numPoints = vertices.size();
    int [] x = new int[numPoints];
    int [] y = new int[numPoints];
    for (int i = 0; i < numPoints; ++i)
    {
      x[i] = ((Point)vertices.get(i)).getX();
      y[i] = ((Point)vertices.get(i)).getY();
    }
    Polygon p = new Polygon(x, y, numPoints);
    g2.draw(p);
  }
}