/**
    * Copyright (C) 2014-2015 Philip Helger (www.helger.com)
    * philip[at]helger[dot]com
    *
    * 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.
   */
  package com.helger.schematron;
  
  import java.io.InputStream;
  import java.io.Reader;
  import java.net.MalformedURLException;
  
  import javax.annotation.Nonnull;
  import javax.annotation.Nullable;
  import javax.annotation.concurrent.Immutable;
  import javax.xml.transform.Source;
  import javax.xml.transform.dom.DOMSource;
  import javax.xml.transform.stream.StreamSource;
  
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  import org.w3c.dom.Document;
  import org.w3c.dom.Node;
  import org.xml.sax.SAXException;
  
  import com.helger.commons.ValueEnforcer;
  import com.helger.commons.annotation.PresentForCodeCoverage;
  import com.helger.commons.io.resource.URLResource;
  import com.helger.commons.string.StringHelper;
  import com.helger.commons.xml.serialize.read.DOMReader;
  
  /**
   * This is a common utility class.
   *
   * @author Philip Helger
   */
  @Immutable
  public final class SchematronResourceHelper
  {
    private static final Logger s_aLogger = LoggerFactory.getLogger (SchematronResourceHelper.class);
  
    @PresentForCodeCoverage
    private static final SchematronResourceHelper s_aInstance = new SchematronResourceHelper ();
  
    private SchematronResourceHelper ()
    {}
  
    /**
     * Convert the passed transform source into a DOM node. Currently on
     * {@link DOMSource} and {@link StreamSource} can be handled.
     *
     * @param aSource
     *        The transform source to use. May not be <code>null</code>.
     * @return The DOM node and never <code>null</code>.
     * @throws SAXException
     *         In case XML parsing fails
     * @throws IllegalArgumentException
     *         in case an unsupported {@link Source} implementation is provided.
     */
    @Nullable
    public static Node getNodeOfSource (@Nonnull final Source aSource) throws SAXException
    {
      ValueEnforcer.notNull (aSource, "Source");
  
      if (aSource instanceof DOMSource)
      {
        // Node is already in DOMSource
        return ((DOMSource) aSource).getNode ();
      }
  
      if (aSource instanceof StreamSource)
      {
        // In StreamSource it can either be a byte stream or a character stream or
        // a system ID
        final StreamSource aStreamSource = (StreamSource) aSource;
  
        final InputStream aIS = aStreamSource.getInputStream ();
        if (aIS != null)
        {
          // Byte stream
          final Document aDoc = DOMReader.readXMLDOM (aIS);
          if (aDoc == null)
            throw new IllegalArgumentException ("Failed to read source " + aSource + " as XML from InputStream " + aIS);
          return aDoc;
        }
  
        final Reader aReader = aStreamSource.getReader ();
        if (aReader != null)
        {
         // CHaracter stream
         final Document aDoc = DOMReader.readXMLDOM (aReader);
         if (aDoc == null)
           throw new IllegalArgumentException ("Failed to read source " + aSource + " as XML from Reader " + aReader);
         return aDoc;
       }
 
       final String sSystemID = aStreamSource.getSystemId ();
       if (StringHelper.hasText (sSystemID))
       {
         // System ID
         try
         {
           final URLResource aURL = new URLResource (sSystemID);
           final Document aDoc = DOMReader.readXMLDOM (aURL);
           if (aDoc == null)
             throw new IllegalArgumentException ("Failed to read source " +
                                                 aSource +
                                                 " as XML from SystemID '" +
                                                 sSystemID +
                                                 "'");
           return aDoc;
         }
         catch (final MalformedURLException ex)
         {
           throw new IllegalArgumentException ("Failed to read source " +
                                               aSource +
                                               " as XML from SystemID '" +
                                               sSystemID +
                                               "': " +
                                               ex.getMessage ());
         }
       }
 
       // Neither InputStream nor Reader present
       s_aLogger.error ("StreamSource contains neither InputStream nor Reader nor SystemID - cannot handle!");
       return null;
     }
 
     final String sMsg = "Can only handle DOMSource and StreamSource - having " +
                         aSource +
                         " with system ID '" +
                         aSource.getSystemId () +
                         "'";
     s_aLogger.error (sMsg);
     throw new IllegalArgumentException (sMsg);
   }
 }