/*
    * 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.myfaces.el;
  
  import java.beans.FeatureDescriptor;
  import java.util.ArrayList;
  import java.util.Collection;
  import java.util.Collections;
  import java.util.Iterator;
  import java.util.NoSuchElementException;
  
  import javax.el.ELContext;
  import javax.el.ELResolver;
  
  /**
   * @author Mathias Broekelmann (latest modification by $Author$)
   * @version $Revision$ $Date$
   */
  public class CompositeELResolver extends javax.el.CompositeELResolver
  {
      private Collection<ELResolver> _elResolvers;
  
      @Override
      public Iterator<FeatureDescriptor> getFeatureDescriptors(final ELContext context, final Object base)
      {
          Collection<ELResolver> resolvers = _elResolvers;
          if (resolvers == null)
          {
              resolvers = Collections.emptyList();
          }
          
          return new CompositeIterator(context, base, resolvers.iterator());
      }
  
      /**
       * @param elResolver
       */
      @Override
      public final synchronized void add(final ELResolver elResolver)
      {
          super.add(elResolver);
  
          if (_elResolvers == null)
          {
              _elResolvers = new ArrayList<ELResolver>();
          }
  
          _elResolvers.add(elResolver);
      }
  
      private static class CompositeIterator implements Iterator<FeatureDescriptor>
      {
          private final ELContext _context;
          private final Object _base;
          private final Iterator<ELResolver> _elResolvers;
  
          private FeatureDescriptor _nextFD;
  
          private Iterator<FeatureDescriptor> _currentFDIter;
  
          public CompositeIterator(final ELContext context, final Object base, final Iterator<ELResolver> elResolvers)
          {
              _context = context;
              _base = base;
              _elResolvers = elResolvers;
          }
  
          public boolean hasNext()
          {
              if (_nextFD != null)
              {
                  return true;
              }
              if (_currentFDIter != null)
              {
                  while (_nextFD == null && _currentFDIter.hasNext())
                  {
                      _nextFD = _currentFDIter.next();
                  }
              }
              if (_nextFD == null)
              {
                  if (_elResolvers.hasNext())
                 {
                     _currentFDIter = _elResolvers.next().getFeatureDescriptors(_context, _base);
                 }
                 else
                 {
                     return false;
                 }
             }
             return hasNext();
         }
 
         public FeatureDescriptor next()
         {
             if (!hasNext())
             {
                 throw new NoSuchElementException();
             }
             FeatureDescriptor next = _nextFD;
             _nextFD = null;
             return next;
         }
 
         public void remove()
         {
             throw new UnsupportedOperationException();
         }
 
     }
 }