/*
    * Copyright 2007 Edward Kuns
    *
    * Licensed 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.
   *
   * $Id: XMLReader.java 0000 2007-01-11 00:00:00Z ekuns $
   */
  package org.castor.xmlctf.xmldiff.xml;
  
  import java.io.File;
  import java.io.FileReader;
  import java.net.MalformedURLException;
  
  import javax.xml.parsers.SAXParser;
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  import org.castor.core.util.Messages;
  import org.castor.xmlctf.xmldiff.xml.nodes.Root;
  import org.castor.xmlctf.xmldiff.xml.nodes.XMLNode;
  import org.exolab.castor.util.NestedIOException;
  import org.exolab.castor.xml.util.XMLParserUtils;
  import org.xml.sax.InputSource;
  import org.xml.sax.SAXException;
  import org.xml.sax.SAXParseException;
  import org.xml.sax.XMLReader;
  
  /**
   * A Utility class to read an XML document from a file into the XMLNode tree used by the XMLDiff
   * class.
   *
   * @author <a href="mailto:edward.kuns@aspect.com">Edward Kuns</a>
   * @version $Revision: 0000 $ $Date: 2007-01-11 00:00:00 -0600 (Thu, 11 Jan 2007) $
   * @see org.castor.xmlctf.xmldiff.XMLDiff
   * @since Castor 1.1
   */
  public class XMLFileReader {
  
    /**
     * The <a href="http://jakarta.apache.org/commons/logging/">Jakarta Commons Logging</a> instance
     * used for all logging.
     */
    private static final Log LOG = LogFactory.getLog(XMLFileReader.class);
  
    /** The file we are reading. */
    private final File _file;
    /** URL for the document to be parsed. */
    private final String _location;
    /** A handle to the SAX parser. */
    private XMLReader _parser;
  
    /**
     * Creates a new XMLReader for the given URILocation.
     *
     * @param filename the URILocation to create this reader for.
     */
    public XMLFileReader(final String filename) {
      if (filename == null) {
        throw new IllegalArgumentException("You must give a non-null fliename");
      }
      _file = new File(filename);
      if (!_file.exists()) {
        throw new IllegalArgumentException("File '" + filename + "' does not exist");
      }
  
      _location = getUrlFromFile();
  
      SAXParser saxParser = XMLParserUtils.getSAXParser(false, true);
      try {
        _parser = saxParser.getXMLReader();
      } catch (org.xml.sax.SAXException sx) {
        LOG.error(Messages.format("conf.configurationError", sx));
      }
  
      if (_parser == null) {
        _parser = XMLParserUtils.instantiateXMLReader("org.apache.xerces.parsers.SAXParser");
      }
    }
  
    /**
     * Reads an XML Document into an BaseNode from the provided file.
     *
     * @return the BaseNode
     * @throws java.io.IOException if any exception occurs during parsing
     */
    public XMLNode read() throws java.io.IOException {
      XMLNode node = null;
  
      try {
        InputSource source = new InputSource();
        source.setSystemId(_location);
        source.setCharacterStream(new FileReader(_file));
 
       XMLContentHandler builder = new XMLContentHandler();
 
       _parser.setContentHandler(builder);
       _parser.parse(source);
 
       node = builder.getRoot();
     } catch (SAXException sx) {
       Exception nested = sx.getException();
 
       SAXParseException sxp = null;
       if (sx instanceof SAXParseException) {
         sxp = (SAXParseException) sx;
       } else if (nested != null && (nested instanceof SAXParseException)) {
         sxp = (SAXParseException) nested;
       } else {
         throw new NestedIOException(sx);
       }
 
       String err = new StringBuilder(sxp.toString()).append("\n - ").append(sxp.getSystemId())
           .append("; line: ").append(sxp.getLineNumber()).append(", column: ")
           .append(sxp.getColumnNumber()).toString();
       throw new NestedIOException(err, sx);
     }
 
     Root root = (Root) node;
     return root;
   }
 
   /**
    * Returns the absolute URL as a string.
    * 
    * @param file The URL to resolve
    * @return the absolute URL as a string.
    */
   private String getUrlFromFile() {
     try {
       return _file.toURL().toString();
     } catch (MalformedURLException e) {
       // ignore -- cannot happen
     }
     return null;
   }
 
 }