/**
 *#########################################################################
 *
 * A component of the Gatherer application, part of the Greenstone digital
 * library suite from the New Zealand Digital Library Project at the
 * University of Waikato, New Zealand.
 *
 * <BR><BR>
 *
 * Principal Author: John Thompson, NZDL Project, University of Waikato
 *
 * <BR><BR>
 *
 * Copyright (C) 1999 New Zealand Digital Library Project
 *
 * <BR><BR>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * <BR><BR>
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * <BR><BR>
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 *########################################################################
 */
package org.greenstone.gatherer.help;

import java.awt.*;
import java.io.*;
import java.net.*;
import java.util.*;
import javax.swing.*;
import javax.swing.event.*;
import javax.swing.tree.*;
import org.apache.xerces.parsers.DOMParser;
import org.greenstone.gatherer.Dictionary;
import org.greenstone.gatherer.Gatherer;
import org.greenstone.gatherer.util.StaticStrings;
import org.greenstone.gatherer.util.Utility;
import org.w3c.dom.*;

/**
 * This class provides a nice help facility. It is a separate frame that can be positioned
 * as the user wishes, and provides a contents page and the help information.
 * @author Michael Dewsnip, NZDL Project
 */
public class HelpFrame 
    extends JFrame {

    static private final String NULL_STRING = "<null>";
    /** The size of the frame */
    static private final Dimension SIZE = new Dimension(760, 560);

    /** The HTML rendering pane */
    private JEditorPane view = null;
    /** The contents tree model */
    private ContentsModel model = null;
    /** A contents tree for the top of the frame */
    private JTree contents = null;

    private JSplitPane split_pane = null;



    public HelpFrame()
    {
	setDefaultCloseOperation(HIDE_ON_CLOSE);
	setSize(SIZE);
	Dictionary.registerText(this, "Help.Title");

	view = new JEditorPane();
	view.setEditable(false);
	view.addHyperlinkListener(new ViewHyperlinkListener());

	HelpItem rootNode = new HelpItem(Dictionary.get("Help.Contents"), NULL_STRING);
	model = new ContentsModel(rootNode);
	contents = new JTree((DefaultTreeModel) model);
	contents.addTreeSelectionListener(new ContentsListener());
	contents.setExpandsSelectedPaths(true);

	// Creation
	JPanel content_pane = (JPanel) this.getContentPane();
	split_pane = new JSplitPane(JSplitPane.VERTICAL_SPLIT);
	JScrollPane index_scroll = new JScrollPane(contents);
	JScrollPane view_scroll = new JScrollPane(view);

	// Layout
	split_pane.add(index_scroll, JSplitPane.LEFT);
	split_pane.add(view_scroll, JSplitPane.RIGHT);
	content_pane.setLayout(new BorderLayout());
	content_pane.add(split_pane, BorderLayout.CENTER);

	// Center
	Dimension screen_size = Toolkit.getDefaultToolkit().getScreenSize();
	setLocation((screen_size.width - SIZE.width) / 2, (screen_size.height - SIZE.height) / 2);		  
    }

    private class ViewHyperlinkListener
	implements HyperlinkListener {
	public void hyperlinkUpdate(HyperlinkEvent e) {
	    if(e.getEventType() == HyperlinkEvent.EventType.ACTIVATED) {
		try {
		    view.setPage(e.getURL());
		}
		catch(Exception exception) {
		    Gatherer.printStackTrace(exception);
		}
	    }
	}
    }

    public void destroy()
    {
	view = null;
	contents = null;
    }


    public void setView(String sectionName)
    {
	// Find the node in the tree with the specified sectionName
	HelpItem node = model.getHelpItemNamed(sectionName);

	// Ensure the node is selected and visible
	TreePath path = new TreePath(node.getPath());
	contents.setSelectionPath(path);
	contents.scrollPathToVisible(path);

	// Display the selected page
	URL url = node.getURL();
	if (url != null) {
	    try {
		view.setPage(url);
	    }
	    catch (Exception exception) {
		Gatherer.printStackTrace(exception);
	    }
	}

	// Make the help frame visible
	show();
	split_pane.setDividerLocation(0.2);
    }


    private class ContentsModel
	extends DefaultTreeModel {

	public ContentsModel(MutableTreeNode rootNode) {
	    super(rootNode);

	    // Load the XML help file and build the contents structure from it
	    try {
		DOMParser parser = new DOMParser();
		parser.parse(Utility.getHelpFolder() + StaticStrings.HELP_INDEX_FILENAME);
		Document document = parser.getDocument();

		// Traverse the document hierarchy, building a tree representing its structure
		Node documentNode = document.getFirstChild();

		int sectionNum = 0;
		NodeList children = documentNode.getChildNodes();
		for (int i = 0; i < children.getLength(); i++) {
		    Node child = children.item(i);
		    if (child.getNodeName().equals(StaticStrings.SECTION_ELEMENT)) {
			sectionNum++;
			buildContentsHierarchy(rootNode, sectionNum + StaticStrings.EMPTY_STR, child);
		    }
		}
	    }
	    catch (Exception ex) {
		ex.printStackTrace();
	    }
	}


	public void buildContentsHierarchy(MutableTreeNode parent, String pos, Node node)
	{
	    // Determine the section name
	    String sectionName = ((Element) node).getAttribute(StaticStrings.NAME_ATTRIBUTE);

	    // Determine the section title
	    String sectionTitle = "";
	    NodeList children = node.getChildNodes();
	    for (int i = 0; i < children.getLength(); i++) {
		Node child = children.item(i);
		if (child.getNodeName().equals(StaticStrings.TITLE_ELEMENT)) {
		    sectionTitle = pos + ": ";
		    if (child.getFirstChild() != null) {
			sectionTitle = sectionTitle + child.getFirstChild().getNodeValue();
		    }
		}
	    }

	    // Add the node into the tree
	    HelpItem item = new HelpItem(sectionTitle, sectionName);
	    insertNodeInto(item, parent, parent.getChildCount());

	    // Apply recursively to the children of this node
	    int sectionNum = 0;
	    for (int i = 0; i < children.getLength(); i++) {
		Node child = children.item(i);
		if (child.getNodeName().equals(StaticStrings.SECTION_ELEMENT)) {
		    sectionNum++;
		    buildContentsHierarchy(item, pos + StaticStrings.STOP_CHARACTER + sectionNum, child);
		}
	    }
	}


	public HelpItem getHelpItemNamed(String sectionName)
	{
	    // Find the node with name matching sectionName, somewhere in the tree
	    Enumeration descendants = ((DefaultMutableTreeNode) root).preorderEnumeration();
	    while (descendants.hasMoreElements()) {
		HelpItem node = (HelpItem) descendants.nextElement();
		if (node.name.equals(sectionName)) {
		    return node;
		}
	    }

	    // Couldn't be found, so just return the root (Contents) node
	    return (HelpItem) root;
	}
    }


    /** This listener is used to listen for selection changes in the contents tree, and
     * to show the appropriate page as required.
     */
    private class ContentsListener
	implements TreeSelectionListener {

	/** Any implementation of <i>TreeSelectionListener</i> must include this method so we can be informed when the tree selection changes.
	 * @param event A <strong>TreeSelectionEvent</strong> containing al the relevant information about the event itself.
	 */
	public void valueChanged(TreeSelectionEvent event)
	{
	    TreePath path = event.getPath();
	    HelpItem node = (HelpItem) path.getLastPathComponent();
	    URL url = node.getURL();
	    if (url != null) {
		//view.showHTMLDocument(url);
		try {
		    view.setPage(url);
		}
		catch (Exception exception) {
		    Gatherer.printStackTrace(exception);
		}
	    }
	}
    }


    /** This class provides a wrapper around a <strong>DefaultMutableTreeNode</strong> which
     * provides the ability to set an html page to be loaded when this node is selected.
     */
    private class HelpItem 
	extends DefaultMutableTreeNode {

	/** The unique name of the section (matches the HTML filename) */
	public String name = null;
	/** The title to be displayed for this tree node. */
	public String title = null;


	/** Constructor.
	 * @param title The title to be shown for this node as a <strong>String</strong>.
	 * @param name The name of the section as a <strong>String</strong>.
	 */
	public HelpItem(String title, String name)
	{
	    this.name = name;
	    this.title = title;
	}


	/** Method to create a url from the file name.
	 * @return A <strong>URL</strong> that points to the file's location.
	 */
	public URL getURL()
	{
	    if (name != null && !name.equals(NULL_STRING)) {
		try {
		    File file = new File(Utility.getHelpFolder() + name + StaticStrings.HTM_FILE_EXTENSION);
		    return file.toURL();
		}
		catch (Exception e) {
		}
	    }

	    return null;
	}


	public String toString()
	{
	    return title;
	}
    }
}