import java.awt.*;
import javax.swing.*;
import java.awt.image.BufferedImage;


/**
 * A component for displaying a mirror-reversed line of text.
 * The text will be centered in the available space.  This component
 * is defined as a subclass of JPanel.  It respects any background 
 * color, foreground color, and font that are set for the JPanel.
 * The setText(String) method can be used to change the displayed
 * text.  Changing the text will also call revalidate() on this
 * component.
 */
public class MirrorText extends JPanel {

    private String text; // The text displayed by this component.
                         // The value is non-null.  If a null value is
                         // specified, it is changed to an empty string.

    private BufferedImage OSC; // Holds an un-reversed picture of the text.

    /**
     * Construct a MirrorText component that will display the specified
     * text in mirror-reversed form.
     */
    public MirrorText(String text) {
        if (text == null)
            text = "";
        this.text = text;
    }


    /**
     * Change the text that is displayed on the label.
     * @param text the new text to display
     */
    public void setText(String text) {
        if (text == null)
            text = "";
        if ( ! text.equals(this.text) ) {
            this.text = text;  // Change the instance variable.
            revalidate();      // Tell container to recompute its layout.
            repaint();         // Make sure component is redrawn.
        }
    }


    /**
     * Return the text that is displayed on this component.
     * The return value is non-null but can be an empty string.
     */
    public String getText() {
        return text;
    }


    /**
     * The paintComponent method makes a new off-screen canvas, if necessary, writes
     * the text to the off-screen canvas, then copies the canvas onto the screen
     * in mirror-reversed form.
     */
    public void paintComponent(Graphics g) {
        int width = getWidth();
        int height = getHeight();
        if (OSC == null || width != OSC.getWidth() 
                || height != OSC.getHeight()) {
            OSC = new BufferedImage(width,height,BufferedImage.TYPE_INT_RGB);
        }
        Graphics OSG = OSC.getGraphics();
        OSG.setColor(getBackground());
        OSG.fillRect(0, 0, width, height);
        OSG.setColor(getForeground()); 
        OSG.setFont(getFont());
        FontMetrics fm = OSG.getFontMetrics(getFont());
        int x = (width - fm.stringWidth(text)) / 2;
        int y = (height + fm.getAscent() - fm.getDescent()) / 2;
        OSG.drawString(text, x, y);
        OSG.dispose();
        g.drawImage(OSC, width, 0, 0, height, 0, 0, width, height, null);
    }


    /**
     * Compute a preferred size that includes the size of the text, plus
     * a boundary of 5 pixels on each edge.
     */
    public Dimension getPreferredSize() {
        FontMetrics fm = getFontMetrics(getFont());
        return new Dimension(fm.stringWidth(text) + 10, 
                fm.getAscent() + fm.getDescent() + 10);
    }

}  // end MirrorText
