import java.applet.Applet;
import java.awt.Frame;
import java.awt.Image;
import java.awt.MediaTracker;
import java.io.InputStream;
import java.io.IOException;
import java.net.URL;
import java.net.URLConnection;


/** 
 * Various utilities methods required for the applet.<br>
 * NOTE: the setup utility should be the first method called by the applet so that any subsequent classes can
 * use these utility methods without having to instantiate the object for themselves.
 */
public final class Utils extends Object {

 /**
  * used to track the loading of images
  */
  private static MediaTracker tracker;
  
 /**
  * the parent applet - used to load images
  */
  private static Applet parentApplet;
    
  static {
    tracker = new MediaTracker(new Frame()); 
  }

 /**
  * don't let anyone instantiate this class
  */
  private Utils() {
  }
  
 /**
  * the setup method should be called once at the beginning of the applet, so images can be loaded
  */
  public static final void setup(Applet parent) {
    parentApplet = parent;
  }

 /**
  * clean up our statics
  */
  public static final void cleanup() {
    tracker      = null;
    parentApplet = null;
  }
  
 /**
  * get an image specified by its name.  This image must be in the applet's codebase
  * (or a directory below the codebase)
  */
  public static final Image getImage(String imageName) throws InterruptedException {
    if (parentApplet == null)
      return null;
      
    Image i = parentApplet.getImage(parentApplet.getCodeBase(),imageName);
    
    tracker.addImage(i,0);
    
    tracker.waitForAll();
    
    return i;
    
  }
  
 /**
  * create an input stream from the specified fileName - used for retrieving a data file from the server
  */
  public static InputStream getFileFromServer(String fileName) throws IOException {
    URL url = null;
    URLConnection urlConn;
    InputStream in = null;
  
    try {
      url = new URL(fileName);
      if( url == null) {
        throw new IOException("Failed to create URL object for data.");
      }

      //open a url connection to the url
      urlConn = url.openConnection();

      in = urlConn.getInputStream();  

    }
    catch(Exception e) {
      throw new IOException("unable to load data file: " + e.getMessage());
    }
    finally {
      url = null;
      urlConn = null;
    }
  
    return in;
  }
  
}