/*
    * Copyright 2007 Joachim Grueneis
    *
    * 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 org.exolab.castor.xml.util.resolvers;
  
  import java.io.IOException;
  import java.io.InputStream;
  import java.net.URL;
  import java.util.ArrayList;
  import java.util.Enumeration;
  import java.util.HashMap;
  import java.util.List;
  import java.util.Map;
  import java.util.Properties;
  
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  import org.exolab.castor.mapping.ClassDescriptor;
  import org.exolab.castor.xml.ResolverException;
  import org.exolab.castor.xml.XMLConstants;
  
  /**
   * Resolves a class by reading the package level class-descriptor-resolver file and loading all
   * descriptors mentioned inside.
   * 
   * @author <a href="mailto:jgrueneis AT gmail DOT com">Joachim Grueneis</a>
   * @author <a href="mailto:stevendolg AT gxm DOT at">Steven Dolg</a>
   * @version $Revision$ $Date$
   * @since 1.2
   */
  public class ByCDR extends AbstractResolverPackageCommand {
    private static final Log LOG = LogFactory.getLog(ByCDR.class);
  
    private List<String> _loadedPackages = new ArrayList<String>();
  
    /**
     * No specific stuff needed.
     */
    public ByCDR() {
      super();
    }
  
    /**
     * Creates a Properties object and initializes it with the contents of the given URL. The provided
     * URL must exist and be suitable for loading properties from.
     *
     * @param url The URL to load the properties from. This must not be null!
     * @return The loaded properties.
     * @throws IOException If loading the properties from the given ULR failed.
     *
     * @see Properties
     * @see Properties#load(InputStream)
     */
    private Properties getProperties(URL url) throws java.io.IOException {
      Properties cdrList = new Properties();
  
      java.io.InputStream stream = url.openStream();
      cdrList.load(stream);
      stream.close();
  
      return cdrList;
    }
  
    /**
     * Tries to load the CDR file for the given package name using the provided class loader. If the
     * CDR file is available and could be loaded properly the descriptors listed in it are added to
     * this cache. <br>
     * If a descriptor is listed in the CDR file for the given package but could not be loaded (e.g.
     * because the reference class file is not available) the descriptor is ignored but no exception
     * is thrown. <br>
     * If a CDR file is not available for the given package this method will not load any descriptors
     * and not throw any exceptions. <br>
     * Further calls to this method with the same package name will not be processed. <br>
     * {@inheritDoc}
     */
    protected Map<String, ClassDescriptor> internalResolve(final String packageName,
        final ClassLoader classLoader, final Map properties) throws ResolverException {
  
      Map<String, ClassDescriptor> results = new HashMap<String, ClassDescriptor>();
      if (!isEmptyPackageName(packageName) && _loadedPackages.contains(packageName)) {
        if (LOG.isDebugEnabled()) {
          LOG.debug("Package: " + packageName + " has already been loaded.");
        }
        return results;
      }
      if (!isEmptyPackageName(packageName)) {
        _loadedPackages.add(packageName);
      }
  
     URL url = classLoader.getResource(
         ResolveHelpers.getQualifiedFileName(XMLConstants.PKG_CDR_LIST_FILE, packageName));
     if (url == null) {
       return results;
     }
 
     try {
       Properties cdrList = this.getProperties(url);
 
       for (Object clazz : cdrList.keySet()) {
         String clazzName = (String) clazz;
         String descriptorClassName = (String) cdrList.get(clazzName);
         try {
           Class<?> descriptorClass = classLoader.loadClass(descriptorClassName);
           if (LOG.isDebugEnabled()) {
             LOG.debug("Found descriptor: " + descriptorClass);
           }
           if (descriptorClass != null) {
             ClassDescriptor instance = (ClassDescriptor) descriptorClass.newInstance();
             results.put(clazzName, instance);
           } else if (LOG.isDebugEnabled()) {
             LOG.debug("Loading of descriptor class: " + descriptorClassName + " for class: "
                 + clazzName + " has failed - continue without");
           }
         } catch (Exception e) {
           if (LOG.isDebugEnabled()) {
             LOG.debug(
                 "Ignored problem at loading of: " + descriptorClassName + " with exception: " + e);
           }
         }
       }
     } catch (IOException iox) {
       String message = "Failed to load package: " + packageName + " with exception: " + iox;
       LOG.warn(message);
       throw new ResolverException(message);
     }
     return results;
   }
 }