/*
    * 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);
             }
 
             StringBuffer err = new StringBuffer(sxp.toString());
             err.append("\n - ");
             err.append(sxp.getSystemId());
             err.append("; line: ");
             err.append(sxp.getLineNumber());
             err.append(", column: ");
             err.append(sxp.getColumnNumber());
             throw new NestedIOException(err.toString(), 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;
     }
 
 }