/*
    * 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.commons.resourcehandler.resource;
  
  import java.io.IOException;
  import java.io.InputStream;
  import java.io.PushbackInputStream;
  import java.util.ArrayList;
  import java.util.List;
  import java.util.logging.Level;
  import java.util.logging.Logger;
  
  import javax.el.ELContext;
  import javax.el.ELException;
  import javax.el.ValueExpression;
  import javax.faces.context.FacesContext;
  import javax.faces.event.ExceptionQueuedEvent;
  import javax.faces.event.ExceptionQueuedEventContext;
  
  public class ValueExpressionFilterInputStream extends InputStream
  {
      private PushbackInputStream delegate;
      private String libraryName;
      private String resourceName;
      
      public ValueExpressionFilterInputStream(InputStream in, String libraryName, String resourceName)
      {
          super();
          delegate = new PushbackInputStream(in,255);
      }
  
      @Override
      public int read() throws IOException
      {
          int c1 = delegate.read();
          
          if (c1 == -1) return -1;
          
          if ( ((char)c1) == '#')
          {
              int c2 = delegate.read();
              if (c2 == -1) return -1;
              if (((char)c2) == '{')
              {
                  //It is a value expression. We need
                  //to look for a occurrence of } to 
                  //extract the expression and evaluate it,
                  //the result should be unread.
                  List<Integer> expressionList = new ArrayList<Integer>();
                  int c3 = delegate.read();
                  while ( c3 != -1 && ((char)c3) != '}' )
                  {
                      expressionList.add(c3);
                      c3 = delegate.read();
                  }
                  
                  if (c3 == -1)
                  {
                      //get back the data, because we can't
                      //extract any value expression
                      for (int i = 0; i < expressionList.size(); i++)
                      {
                          delegate.unread(expressionList.get(i));
                      }
                      delegate.unread(c2);
                      return c1;
                  }
                  else
                  {
                      //EL expression found. Evaluate it and pushback
                      //the result into the stream
                      FacesContext context = FacesContext.getCurrentInstance();
                      ELContext elContext = context.getELContext();
                      try
                      {
                          ValueExpression ve = context.getApplication().
                              getExpressionFactory().createValueExpression(
                                      elContext,
                                      "#{"+convertToExpression(expressionList)+"}",
                                      String.class);
                          String value = (String) ve.getValue(elContext);
                          
                          for (int i = value.length()-1; i >= 0 ; i--)
                         {
                             delegate.unread((int) value.charAt(i));
                         }
                     }
                     catch(ELException e)
                     {
                         ExceptionQueuedEventContext equecontext = new ExceptionQueuedEventContext (context, e, null);
                         context.getApplication().publishEvent (context, ExceptionQueuedEvent.class, equecontext);
                         
                         Logger log = Logger.getLogger(ResourceImpl.class.getName());
                         if (log.isLoggable(Level.SEVERE))
                             log.severe("Cannot evaluate EL expression "+convertToExpression(expressionList)+ " in resource " + (libraryName == null ? "" : libraryName)+":"+resourceName);
                         
                         delegate.unread(c3);
                         for (int i = expressionList.size()-1; i >= 0; i--)
                         {
                             delegate.unread(expressionList.get(i));
                         }
                         delegate.unread(c2);
                         return c1;
                     }
                     
                     //read again
                     return delegate.read();
                 }
             }
             else
             {
                 delegate.unread(c2);
                 return c1;
             }
         }
         else
         {
             //just continue
             return c1;
         }
     }
     
     private String convertToExpression(List<Integer> expressionList)
     {
         char[] exprArray = new char[expressionList.size()];
         
         for (int i = 0; i < expressionList.size(); i++)
         {
             exprArray[i] = (char) expressionList.get(i).intValue();
         }
         return String.valueOf(exprArray);
     }
 }