import java.awt.*;

/**
 * The class ViewCanvas visualizes the threads in the monitor demonstration.
 * @author Stephan Fischli
 * @version 1.0
 */
public class ViewCanvas extends Canvas
{
   /**
   * The threads to visualize.
   */
   private DemoThread[] threads;

  /**
   * The width of the canvas.
   */
   private int width;

  /**
   * The height of the canvas.
   */
   private int height;

  /**
   * The offscreen image used for double buffering.
   */
   private Image image;

  /**
   * The graphics context of the offscreen image.
   */
   private Graphics graphics;

  /**
   * The current time in seconds.
   */
   private int time;

  /**
   * Creates a ViewCanvas object.
   * @param threads the threads to visualize
   */
   public ViewCanvas( DemoThread[] threads )
   {
        this.threads = threads;
        width = 540;
        height = 50*threads.length + 40;
        setSize( width, height );
   }

  /**
   * Updates the canvas.
   * @param g the graphics context to use
   */
   public void update( Graphics g )
   {
        // create image
        if ( image == null ) {
             image = createImage( width, height );
             graphics = image.getGraphics();
        }

        // clear image
        if ( time == 0 ) {
             graphics.setColor( Color.white );
             graphics.fillRect( 0, 0, width, height );
             graphics.setColor( Color.black );
             for ( int i = 0; i < threads.length; i++ )
             graphics.drawLine( 20, 71 + 50*i, 520, 71 + 50*i );
        }

        // draw activity of threads
        for ( int i = 0; i < threads.length; i++ ) {
             boolean running = false;
             Color color = Color.white;
             switch ( threads[i].getState() ) {
                  case DemoThread.RUNNING:
                       running = true; color = Color.green; break;
                  case DemoThread.ENTERING_MONITOR:
                       running = false; color = Color.green; break;
                  case DemoThread.RUNNING_MONITOR:
                       running = true; color = Color.red; break;
                  case DemoThread.WAITING_CONDITION:
                       running = false; color = Color.red; break;
             }
             graphics.setColor( color );
             graphics.drawLine( 20 + time, 70 + 50*i, 20 + time, 70 + 50*i - (running?40:0) );
        }

        // draw image
        g.drawImage( image, 0, 0, this );
        time = (time + 1) % 500;
   }

  /**
   * Paints the canvas.
   * @param g the graphics context to use
   */
   public void paint( Graphics g )
   {
        if ( image != null )
        g.drawImage( image, 0, 0, this );
   }
}