import javax.swing.*;
import java.awt.*;
import java.awt.geom.*;

public class NgonView 
    extends JPanel
{
    private int nSides = 0;
    private Font ngonFont;
    
    static public final Dimension PREF_SIZE = new Dimension( 600, 700 );
    static public final float SCALE = 200.0F;
    static public final float tx = 1.5F;
    static public final float ty = 1.5F;
    static public final int warnX = 180;
    static public final int warnY = 600;
    static public final int areaX = 180;
    static public final int areaY = 600;
    
    public NgonView()
    {
        ngonFont = new Font( "SansSerif", Font.ITALIC, 16 );
    }
    
    public void setSides ( int n )
    {
        nSides = n;
        repaint();
    }
    
    public Dimension getPreferredSize()
    {
        return PREF_SIZE;
    }
    
    public void paintComponent( Graphics g )
    {
        Graphics2D g2 = (Graphics2D) g;
        float dtheta = (float) ( 2 * Math.PI ) / nSides;

        super.paintComponent( g );
        
        g2.setFont( ngonFont );
        g2.setPaint( Color.red );
        if ( nSides < 3 )
        {
            g2.drawString( "Elija un número de lados >= 3", warnX, warnY );
        }
        else
        {
            g2.drawString( "Área del polígono = " + getArea(), areaX, areaY );
        }
        
        g2.setStroke( new BasicStroke( 2 ) );
        Shape circle = new Ellipse2D.Float( transX ( -1.0F ), transY( -1.0F ),
                                            2.0F * SCALE, 2.0F * SCALE );
        g2.setPaint( Color.yellow );
        g2.fill( circle );
        g2.setPaint( Color.blue );
        g2.draw( circle );
        
        g2.setPaint( Color.green );
        GeneralPath ngon = new GeneralPath();
        ngon.moveTo( transX( 1.0F ), transY( 0.0F ) );
        for ( int i = 1; i < nSides; i++ )
        {
            float x = transX( (float) Math.cos( i * dtheta ));
            float y = transY( (float) Math.sin( i * dtheta ));
            ngon.lineTo( x, y );
        }
        ngon.closePath();
        g2.fill( ngon );
    }
    
    private double getArea()
    {
        double PIn = Math.PI / nSides;
        return nSides * Math.cos( PIn ) * Math.sin( PIn );
    }
    
    private float transX( float x )
    {
        return ( x + tx ) * SCALE;
    }
    
    private float transY( float y )
    {
        return ( y + ty ) * SCALE;
    }
}