// This example is from _Java Examples in a Nutshell_. (http://www.oreilly.com)
// Copyright (c) 1997 by David Flanagan
// This example is provided WITHOUT ANY WARRANTY either expressed or implied.
// You may study, use, modify, and distribute it for non-commercial purposes.
// For any commercial use, see http://www.davidflanagan.com/javaexamples

import java.io.*;
import java.net.*;
import java.applet.Applet;
import netscape.javascript.JSObject;    // A special class we need

/**
 * An output stream that sends HTML text to a newly created web browser window.
 * It relies on the netscape.javascript.JSObject class to send JavaScript
 * commands to the Web browser, and only works for applets running in 
 * the Netscape Navigator Web browser.
 **/
public class HTMLWriter extends Writer {
  JSObject main_window;        // the initial browser window
  JSObject window;             // the new window we create
  JSObject document;           // the document of that new window
  static int window_num = 0;   // used to give each new window a unique name
  
  /**
   * When you create a new HTMLWriter, it pops up a new, blank, Web browser
   * window to display the output in.  You must specify the applet
   * (this specifies the main browser window) and the desired size
   * for the new window.
   **/
  public HTMLWriter(Applet applet, int width, int height) {
    // Verify that we can find the JSObject class we need.  Warn if not.
    try { Class c = Class.forName("netscape.javascript.JSObject"); }
    catch (ClassNotFoundException e) {
      throw new NoClassDefFoundError("HTMLWriter requires " +
                                     "Netscape Navigator 4.0 or higher");
    }

    // Get a reference to the main browser window from the applet.
    main_window = JSObject.getWindow(applet);

    // Create a new window to display output in.
    window = (JSObject)
      main_window.eval("self.open(''," +
                       "'HTMLWriter" + window_num++ + "'," +
                       "'menubar,status,resizable,scrollbars," +
                       "width=" + width + ",height=" + height + "')");

    // Obtain the Document object of this new window, and open it.
    document = (JSObject) window.getMember("document");
    document.call("open", null);
  }
  
  /**
   * This is the write() method required for all Writer subclasses.
   * Writer defines all its other write() methods in terms of this one.
   **/
  public void write(char[] buf, int offset, int length) {
    // If no window or document, do nothing.   This occurs if the stream
    // has been closed, or if the code is not running in Navigator.
    if ((window == null) || (document == null)) return;
    // If the window has been closed by the user, do nothing
    if (((Boolean)window.getMember("closed")).booleanValue()) return;
    // Otherwise, create a string from the specified bytes
    String s = new String(buf, offset, length);
    // And pass it to the JS document.write() method to output the HTML
    document.call("write", new String[] { s });
  }
  
  /**
   * There is no general way to force JavaScript to flush all pending output,
   * so this method does nothing.  To flush, output a <P> tag or some other
   * HTML tag that forces a line break in the output.
   **/
  public void flush() {}

  /**
   * When the stream is closed, close the JavaScript Document object
   * (But don't close the window yet.)
   **/
  public void close() { document.call("close", null); document = null; }

  /**
   * If the browser window is still open, close it.
   * This method is unique to HTMLWriter.  
   **/
  public void closeWindow() {
    if (document != null) close();
    if (!((Boolean)window.getMember("closed")).booleanValue())
      window.call("close", null);
    window = null;
  }

  /** A finalizer method to close the window in case we forget. */
  public void finalize() { closeWindow(); }

  /**
   * This nested class is an applet that demonstrates the use of HTMLWriter.
   * It reads the contents of the URL specified in its url parameter and
   * writes them out to an HTMLWriter stream.  It will only work in 
   * Netscape 4.0 or later.  It requires an <APPLET> tag like this:
   *   <APPLET CODE="HTMLWriter$Test.class" WIDTH=10 HEIGHT=10 MAYSCRIPT>
   *   <PARAM NAME="url" VALUE="HTMLWriter.java">
   *   </APPLET>
   * Note that MAYSCRIPT attribute.  It is required to enable the applet
   * to invoke JavaScript.
   **/
  public static class Test extends Applet {
    HTMLWriter out;
    /** When the applet starts, read and display specified URL */
    public void init() {  
      try {
        // Get the URL specified in the <PARAM> tag
        URL url = new URL(this.getDocumentBase(), this.getParameter("url"));
        // Get a stream to read its contents
        Reader in = new InputStreamReader(url.openStream());
        // Create an HTMLWriter stream for out output
        out = new HTMLWriter(this, 400, 200);
        // Read buffers of characters and output them to the HTMLWriter 
        char[] buffer = new char[4096];
        int numchars;
        while((numchars = in.read(buffer)) != -1) 
          out.write(buffer, 0, numchars);
        // Close the streams
        in.close();
        out.close();
      }
      catch (IOException e) {}
    }
    /** When the applet terminates, close the window we created */
    public void destroy() { out.closeWindow(); }
  }
}