/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 * 
 *      http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.log4j.chainsaw;

import java.awt.event.ActionEvent;
import java.io.File;
import java.io.IOException;
import java.io.StringReader;
import javax.swing.AbstractAction;
import javax.swing.JFileChooser;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.parsers.SAXParserFactory;
import org.apache.log4j.Logger;
import org.xml.sax.InputSource;
import org.xml.sax.SAXException;
import org.xml.sax.XMLReader;

/**
 * Encapsulates the action to load an XML file.
 *
 * @author <a href="mailto:oliver@puppycrawl.com">Oliver Burn</a>
 * @version 1.0
 */
class LoadXMLAction extends AbstractAction {
    /** use to log messages **/
    private static final Logger LOG = Logger.getLogger(LoadXMLAction.class);

    /** the parent frame **/
    private final JFrame mParent;

    /**
     * the file chooser - configured to allow only the selection of a single file.
     */
    private final JFileChooser mChooser = new JFileChooser();
    {
	mChooser.setMultiSelectionEnabled(false);
	mChooser.setFileSelectionMode(JFileChooser.FILES_ONLY);
    }

    /** parser to read XML files **/
    private final XMLReader mParser;
    /** the content handler **/
    private final XMLFileHandler mHandler;

    /**
     * Creates a new <code>LoadXMLAction</code> instance.
     *
     * @param aParent the parent frame
     * @param aModel  the model to add events to
     * @exception SAXException if an error occurs
     * @throws ParserConfigurationException if an error occurs
     */
    LoadXMLAction(JFrame aParent, MyTableModel aModel) throws SAXException, ParserConfigurationException {
	mParent = aParent;
	mHandler = new XMLFileHandler(aModel);
	SAXParserFactory saxParserFactory = SAXParserFactory.newInstance();
	// prevent XXE attacks
	saxParserFactory.setFeature("http://xml.org/sax/features/external-general-entities", false);
	saxParserFactory.setFeature("http://xml.org/sax/features/external-parameter-entities", false);
	mParser = saxParserFactory.newSAXParser().getXMLReader();
	mParser.setContentHandler(mHandler);
    }

    /**
     * Prompts the user for a file to load events from.
     * 
     * @param aIgnore an <code>ActionEvent</code> value
     */
    public void actionPerformed(ActionEvent aIgnore) {
	LOG.info("load file called");
	if (mChooser.showOpenDialog(mParent) == JFileChooser.APPROVE_OPTION) {
	    LOG.info("Need to load a file");
	    final File chosen = mChooser.getSelectedFile();
	    LOG.info("loading the contents of " + chosen.getAbsolutePath());
	    try {
		final int num = loadFile(chosen.getAbsolutePath());
		JOptionPane.showMessageDialog(mParent, "Loaded " + num + " events.", "CHAINSAW",
			JOptionPane.INFORMATION_MESSAGE);
	    } catch (Exception e) {
		LOG.warn("caught an exception loading the file", e);
		JOptionPane.showMessageDialog(mParent, "Error parsing file - " + e.getMessage(), "CHAINSAW",
			JOptionPane.ERROR_MESSAGE);
	    }
	}
    }

    /**
     * Loads the contents of file into the model
     *
     * @param aFile the file to extract events from
     * @return the number of events loaded
     * @throws SAXException if an error occurs
     * @throws IOException  if an error occurs
     */
    private int loadFile(String aFile) throws SAXException, IOException {
	synchronized (mParser) {
	    // Create a dummy document to parse the file
	    final StringBuilder buf = new StringBuilder();
	    buf.append("<?xml version=\"1.0\" standalone=\"yes\"?>\n");
	    buf.append("<!DOCTYPE log4j:eventSet ");
	    buf.append("[<!ENTITY data SYSTEM \"file:///");
	    buf.append(aFile);
	    buf.append("\">]>\n");
	    buf.append("<log4j:eventSet xmlns:log4j=\"Claira\">\n");
	    buf.append("&data;\n");
	    buf.append("</log4j:eventSet>\n");

	    final InputSource is = new InputSource(new StringReader(buf.toString()));
	    mParser.parse(is);
	    return mHandler.getNumEvents();
	}
    }
}
