/**
 * This class is a custom component that supports scribbling.  It also has
 * a popup menu that allows the scribble color to be set and provides access
 * to printing, cut-and-paste, and file loading and saving facilities.
 * Note that it extends Component rather than Canvas, making it "lightweight."
 */
class Scribble extends Component implements ActionListener {
  protected short last_x, last_y;                // Coordinates of last click.
  protected Vector lines = new Vector(256,256);  // Store the scribbles.
  protected Color current_color = Color.black;   // Current drawing color.
  protected int width, height;                   // The preferred size.
  protected PopupMenu popup;                     // The popup menu.
  protected Frame frame;         

/** This constructor requires a Frame and a desired size */
  public Scribble(Frame frame, int width, int height) {
    this.frame = frame;
    this.width = width;
    this.height = height;

    // We handle scribbling with low-level events, so we must specify which
    // events we are interested in. enableEvents: Enables the events defined
    // by the specified event mask parameter to be delivered to this component

    this.enableEvents(AWTEvent.MOUSE_EVENT_MASK);
      //variable in java.awt.AWTEvent:The event mask for selecting mouse events

    this.enableEvents(AWTEvent.MOUSE_MOTION_EVENT_MASK);
      //The event mask for selecting mouse motion events. 

    // Create the popup menu using a loop.  Note the separation of menu
    // "action command" string from menu label.  Good for internationalization.
    String[] labels = new String[] {
      "Clear", "Print", "Save", "Load", "Cut", "Copy", "Paste" };
    String[] commands = new String[] {
      "clear", "print", "save", "load", "cut", "copy", "paste" };
    popup = new PopupMenu();                   // Create the menu
    for(int i = 0; i < labels.length; i++) {
      MenuItem mi = new MenuItem(labels[i]);   // Create a menu item.
      mi.setActionCommand(commands[i]);        // Set its action command.
      mi.addActionListener(this);              // And its action listener.
      popup.add(mi);                           // Add item to the popup menu.
    }
    Menu colors = new Menu("Color");           // Create a submenu.
    popup.add(colors);                         // And add it to the popup.
    String[] colornames = new String[] { "Black", "Red", "Green", "Blue"};
    for(int i = 0; i < colornames.length; i++) {
      MenuItem mi = new MenuItem(colornames[i]);  // Create the submenu items
      mi.setActionCommand(colornames[i]);         // in the same way.
      mi.addActionListener(this);
      colors.add(mi);
    }
    // Finally, register the popup menu with the component it appears over
    this.add(popup);
  }



  /** Specifies big the component would like to be.  It always returns the
   *  preferred size passed to the Scribble() constructor */
  public Dimension getPreferredSize() { return new Dimension(width, height); }

  /** This is the ActionListener method invoked by the popup menu items */
   /* Event handling for the pop up menu - same as for pull-down menu items

  public void actionPerformed(ActionEvent event) {

    // Get the "action command" of the event, and dispatch based on that.
    // This method calls a lot of the interesting methods in this class.
    String command = event.getActionCommand();
    if (command.equals("clear")) clear();
    else if (command.equals("print")) print();
    else if (command.equals("save")) save();
    else if (command.equals("load")) load();
    else if (command.equals("cut")) cut();
    else if (command.equals("copy")) copy();
    else if (command.equals("paste")) paste();
    else if (command.equals("Black")) current_color = Color.black;
    else if (command.equals("Red")) current_color = Color.red;
    else if (command.equals("Green")) current_color = Color.green;
    else if (command.equals("Blue")) current_color = Color.blue;
  }

  /** Draw all the saved lines of the scribble, in the appropriate colors */
  public void paint(Graphics g) {
    for(int i = 0; i < lines.size(); i++) {
      Line l = (Line)lines.elementAt(i);
      g.setColor(l.color);
      g.drawLine(l.x1, l.y1, l.x2, l.y2);
    }
  }

  /**
   * In addition to creating and registering a popup menu, we need to arrange
   * for it to pop up at the appropriate time
   * This is the low-level event-handling method called on mouse events
   * that do not involve mouse motion.  Note the use of isPopupTrigger()
   * to check for the platform-dependent popup menu posting event, and of
   * the show() method to make the popup visible.  If the menu is not posted,
   * then this method saves the coordinates of a mouse click or invokes
   * the superclass method.
   */
  public void processMouseEvent(MouseEvent e) {
    if (e.isPopupTrigger())                               // If popup trigger,
      popup.show(this, e.getX(), e.getY());               // pop up the menu.
    else if (e.getID() == MouseEvent.MOUSE_PRESSED) {
      last_x = (short)e.getX(); last_y = (short)e.getY(); // Save position.
    }
    else super.processMouseEvent(e);  // Pass other event types on.
  }
}