import java.applet.Applet;
import java.awt.Canvas;
import java.awt.Image;
import java.awt.Point;
import java.awt.Graphics;
import java.awt.Color;
import java.util.Vector;
import java.awt.Event;
import java.net.URL;

/**
 * a Canvas subclass that accepts multiple
 * image specs, loads them, and displays 
 * one of them at a time.   (Note that a lot of
 * this code is a little looser than I would
 * normally write, to try to keep the resulting
 * .class file a little smaller)
 */
public class MultiImageDisplay extends Canvas
{
  // fields -- accessible to this package
  int currentImage;
  Vector images;
 
  boolean drawlocations;
  Vector locations;
  Color  pointColor;
  Color  specialColor;
  Location specialLocation;

  static int MARGINS   = 2;
  static int POINTSIZE = 6;
  static int TOLERANCE = 4;

  /**
   * constructor, accepts an integer telling
   * about how many images to expect.  Giving
   * 0 means use default.
   */
  public MultiImageDisplay(int expectNo)
  {
        currentImage = -1;
        if (expectNo == 0) expectNo = 6;
        images = new Vector(expectNo);
        locations = new Vector(expectNo); 
        drawlocations = true;
        specialLocation = null;
        pointColor = Color.red;
        specialColor = new Color(60,75,255);
  }

  /**
   * paint function, paint the image and 
   * maybe paint the locations also.
   */
  public void paint(Graphics g)
  {
    Object co;

    super.paint(g);
    if (currentImage < 0 || currentImage >= images.size()) 
      return;

    co = images.elementAt(currentImage);
    if (!(co instanceof Image)) return;

    if (g.drawImage((Image)co, MARGINS, MARGINS, this)) {
        drawLocationPoints(g);
    }
    return;
  }

  public boolean imageUpdate(Image img, int flags,
                int x, int y, int w, int h)
  {
    boolean ret = super.imageUpdate(img,flags,x,y,w,h);
    if ((flags & ALLBITS) != 0) {
        drawLocationPoints(null);
    }
    return ret;
  }


  /**
   * draw location points as dots, if the 
   * boolean flag drawlocations is set.
   */
  public void drawLocationPoints(Graphics g)
  {
    Object lo;
    if (drawlocations == false) return; 
    if (currentImage < 0 || currentImage >= images.size()) 
      return;
    lo = locations.elementAt(currentImage);
    if (!(lo instanceof Vector)) return;
    Vector points = (Vector)lo; 
    if (points.size() == 0) return;

    if (g == null) g = getGraphics();

    int len = points.size();
    for(int ix = 0; ix < len; ix++) {
        Location loc = (Location)(points.elementAt(ix));
        if (loc == specialLocation) g.setColor(specialColor);
        else g.setColor(pointColor);
        if (loc.w() > 0 && loc.h() > 0) {
          g.drawRect(loc.x() + MARGINS, loc.y() + MARGINS, 
                        loc.w(), loc.h());
        } else {
          g.fillOval((loc.x() - POINTSIZE/2) + MARGINS, 
                     (loc.y() - POINTSIZE/2) + MARGINS, 
                     POINTSIZE, POINTSIZE);
        }
    }
    return;
  }


  /**
   * look through the current list of Locations and
   * find first point near the given Point.
   */
  public Location findLocationNear(Point p, int tol)
  {
    Object lo;
    Location ret;
    if (currentImage < 0 || currentImage >= images.size()) 
      return null;
    lo = locations.elementAt(currentImage);
    if (!(lo instanceof Vector)) return null;

    Vector points = (Vector)lo; 
    int len = points.size();

    for(int ix = 0; ix < len; ix++) {
      ret = (Location)(points.elementAt(ix));
      if (ret.within(p,tol))
        return ret;
    }
    return null;
  }

  /**
   * this adds a new image to this MultiImageDisplay
   * canvas.  The new image is supplied as a URL string,
   * which we translate into a URL and then load as an
   * image.  We return the image object, or null if
   * any errors occurred.  Note that the image will
   * we loaded in its own thread, so we cannot assume
   * that the height and width are correct at first.
   */
  public Image addImage(Applet applet, String urlstr)
  {
    Image ret = null;
    URL url;

    try {
        url = new URL(applet.getDocumentBase(), urlstr);
        ret = applet.getImage(url);
    } 
    catch (Exception e) {
        url = null;
        ret = null;
    }

    if (ret != null) {
        images.addElement(ret);
        if (currentImage < 0) {
          currentImage = 0;
          repaint();
        }
        locations.addElement(new Vector(10));
    }

    return ret;
  }


  /**
   * this adds a supplied Location to the current
   * image location vector, creating the vector if
   * necessary.  we return the new Location object
   * so that the caller can set a name and description.
   */
  public Location addLocation(String xy)
  {
    Object lo;
    if (currentImage < 0 || currentImage >= images.size()) 
      return null;
    lo = locations.elementAt(currentImage);
    if (!(lo instanceof Vector)) return null;
    // this line might throw a NumberFormatException
    Location ret = new Location(xy);
    Vector points = (Vector)lo; 
    points.addElement(ret);
  
    return ret;
  }


  /**
   * this method handles mouse down events by
   * calling action with the Location under the 
   * mouse as an argument object.
   */
  public boolean mouseDown(Event evt, int x, int y)
  {
    Location clicked = 
        findLocationNear(new Point(x - MARGINS,y - MARGINS), 
                         TOLERANCE);
    return getParent().action(evt, clicked);
  }
   


};