/*
   Copyright (c) 2010, Chin Huang
   All rights reserved.
   
   Redistribution and use in source and binary forms, with or without
   modification, are permitted provided that the following conditions are met:
   
    * Redistributions of source code must retain the above copyright notice,
      this list of conditions and the following disclaimer.
   * Redistributions in binary form must reproduce the above copyright notice,
     this list of conditions and the following disclaimer in the documentation
     and/or other materials provided with the distribution.
  
  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
  ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
  WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
  DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
  ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
  (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
  LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
  ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
  SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
  package net.ramapuram.thomas.webapp.jsp;
  
  import java.beans.FeatureDescriptor;
  import java.util.Iterator;
  import javax.el.ELContext;
  import javax.el.ELException;
  import javax.el.ELResolver;
  import javax.el.PropertyNotFoundException;
  import javax.el.PropertyNotWritableException;
  
  /**
   * {@link ELResolver} which escapes XML in String values.
   */
  public class EscapeXmlELResolver extends ELResolver {
  
      private ELResolver originalResolver;
      private ThreadLocal<Boolean> gettingValue = new ThreadLocal<Boolean>() {
          @Override
          protected Boolean initialValue() {
              return Boolean.FALSE;
          }
      };
      
      private ELResolver getOriginalResolver(ELContext context) {
          if (originalResolver == null) {
              originalResolver = context.getELResolver();
          }
          return originalResolver;
      }
      
      @Override
      public Class<?> getCommonPropertyType(ELContext context, Object base) {
          return getOriginalResolver(context).getCommonPropertyType(context, base);
      }
  
      @Override
      public Iterator<FeatureDescriptor> getFeatureDescriptors(
              ELContext context, Object base)
      {
          return getOriginalResolver(context).getFeatureDescriptors(context, base);
      }
  
      @Override
      public Class<?> getType(ELContext context, Object base, Object property)
          throws NullPointerException, PropertyNotFoundException, ELException
      {
          return getOriginalResolver(context).getType(context, base, property);
      }
  
      @Override
      public Object getValue(ELContext context, Object base, Object property)
          throws NullPointerException, PropertyNotFoundException, ELException
      {
          if (gettingValue.get()) {
              return null;
          }
          
          // This resolver is in the original resolver chain.  When this resolver
          // invokes the original resolver chain, set a flag so when execution
          // reaches this resolver, act like this resolver is not in the chain.
          gettingValue.set(true);
          Object value =
                  getOriginalResolver(context).getValue(context, base, property);
          gettingValue.set(false);
  
          if (value instanceof String) {
              value = EscapeXml.escape((String) value);
          }
          return value;
      }
  
      @Override
      public boolean isReadOnly(ELContext context, Object base, Object property)
          throws NullPointerException, PropertyNotFoundException, ELException
      {
         return getOriginalResolver(context).isReadOnly(context, base, property);
     }
 
     @Override
     public void setValue(
             ELContext context, Object base, Object property, Object value)
         throws NullPointerException, PropertyNotFoundException, PropertyNotWritableException, ELException
     {
         getOriginalResolver(context).setValue(context, base, property, value);
     }
 }