/*
    * 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.shared.context;
  
  import java.io.IOException;
  import java.util.ArrayList;
  import java.util.Collections;
  import java.util.LinkedList;
  import java.util.List;
  import java.util.Queue;
  import java.util.logging.Level;
  import java.util.logging.Logger;
  
  import javax.el.ELException;
  import javax.faces.FacesException;
  import javax.faces.context.ExceptionHandler;
  import javax.faces.context.ExternalContext;
  import javax.faces.context.FacesContext;
  import javax.faces.context.PartialResponseWriter;
  import javax.faces.context.PartialViewContext;
  import javax.faces.event.AbortProcessingException;
  import javax.faces.event.ExceptionQueuedEvent;
  import javax.faces.event.ExceptionQueuedEventContext;
  import javax.faces.event.SystemEvent;
  
  /**
   * 
   * Specialized Ajax Handler, according to JSF 2.0 rev A section 13.3.7.
   */
  public class AjaxExceptionHandlerImpl extends ExceptionHandler
  {
      //The spec says this related to exception handling in ajax requests:
      //
      //"... JavaServer Faces Ajax frameworks must ensure exception information 
      // is written to the response in the format: 
      //
      //<partial-response>
      //  <error>
      //    <error-name>...</error-name>
      //    <error-message>...</error-message>
      //  </error>
      //</partial-response>
      //
      //Implementations must ensure that an ExceptionHandler suitable for writing 
      //exceptions to the partial response is installed if the current request 
      //required an Ajax response (PartialViewContext.isAjaxRequest() returns true)
      //
      //Implementations may choose to include a specialized ExceptionHandler for 
      //Ajax that extends from javax.faces.context.ExceptionHandlerWrapper, and 
      //have the javax.faces.context.ExceptionHandlerFactory implementation 
      //install it if the environment requires it. ..."
      
      private static final Logger log = Logger.getLogger(AjaxExceptionHandlerImpl.class.getName());
      
      private Queue<ExceptionQueuedEvent> handled;
      private Queue<ExceptionQueuedEvent> unhandled;
      private ExceptionQueuedEvent handledAndThrown;
      
      public AjaxExceptionHandlerImpl()
      {
      }
      
      /**
       * {@inheritDoc}
       */
      @Override
      public ExceptionQueuedEvent getHandledExceptionQueuedEvent()
      {
          return handledAndThrown;
      }
  
      /**
       * {@inheritDoc}
       */
      @Override
      public Iterable<ExceptionQueuedEvent> getHandledExceptionQueuedEvents()
      {
          return handled == null ? Collections.<ExceptionQueuedEvent>emptyList() : handled;
      }
  
      /**
       * {@inheritDoc}
       */
     @Override
     public Throwable getRootCause(Throwable t)
     {
         if (t == null)
         {
             throw new NullPointerException("t");
         }
         
         while (t != null)
         {
             Class<?> clazz = t.getClass();
             if (!clazz.equals(FacesException.class) && !clazz.equals(ELException.class))
             {
                 return t;
             }
             
             t = t.getCause();
         }
         
         return null;
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     public Iterable<ExceptionQueuedEvent> getUnhandledExceptionQueuedEvents()
     {
         return unhandled == null ? Collections.<ExceptionQueuedEvent>emptyList() : unhandled;
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     public void handle() throws FacesException
     {
         if (unhandled != null && !unhandled.isEmpty())
         {
             if (handled == null)
             {
                 handled = new LinkedList<ExceptionQueuedEvent>();
             }
             
             List<Throwable> throwableList = new ArrayList<Throwable>();
             FacesContext facesContext = null;
             
             do
             {
                 // For each ExceptionEvent in the list
                 
                 // get the event to handle
                 ExceptionQueuedEvent event = unhandled.peek();
                 try
                 {
                     // call its getContext() method
                     ExceptionQueuedEventContext context = event.getContext();
 
                     if (facesContext == null)
                     {
                         facesContext = event.getContext().getContext();
                     }
                     
                     // and call getException() on the returned result
                     Throwable exception = context.getException();
                     
                     // Upon encountering the first such Exception that is not an instance of
                     // javax.faces.event.AbortProcessingException
                     if (!shouldSkip(exception))
                     {
                         // set handledAndThrown so that getHandledExceptionQueuedEvent() returns this event
                         handledAndThrown = event;
                         
                         Throwable rootCause = getRootCause(exception);
                         
                         throwableList.add(rootCause == null ? exception : rootCause);
                         
                         //break;
                     }
                     else
                     {
                         // Testing mojarra it logs a message and the exception
                         // however, this behaviour is not mentioned in the spec
                         log.log(Level.SEVERE, exception.getClass().getName() + " occured while processing " +
                                 (context.inBeforePhase() ? "beforePhase() of " : 
                                         (context.inAfterPhase() ? "afterPhase() of " : "")) + 
                                 "phase " + context.getPhaseId() + ": " +
                                 "UIComponent-ClientId=" + 
                                 (context.getComponent() != null ? 
                                         context.getComponent().getClientId(context.getContext()) : "") + ", " +
                                 "Message=" + exception.getMessage());
                         
                         log.log(Level.SEVERE, exception.getMessage(), exception);
                     }
                 }
                 finally
                 {
                     // if we will throw the Exception or if we just logged it,
                     // we handled it in either way --> add to handled
                     handled.add(event);
                     unhandled.remove(event);
                 }
             } while (!unhandled.isEmpty());
 
             if (!throwableList.isEmpty())
             {
                 PartialResponseWriter partialWriter = null;
                 boolean responseComplete = false;
 
                 //Retrieve the partial writer used to render the exception
                 if (facesContext == null)
                 {
                     facesContext = FacesContext.getCurrentInstance();
                 }
                 
                 facesContext = (facesContext == null) ? FacesContext.getCurrentInstance() : facesContext;
                 ExternalContext externalContext = facesContext.getExternalContext();
                 
                 //Clean up the response if by some reason something has been written before.
                 if (!facesContext.getExternalContext().isResponseCommitted())
                 {
                     facesContext.getExternalContext().responseReset();
                 }
                 
                 PartialViewContext partialViewContext = facesContext.getPartialViewContext();
                 partialWriter = partialViewContext.getPartialResponseWriter();
 
                 // ajax request --> xml error page 
                 externalContext.setResponseContentType("text/xml");
                 externalContext.setResponseCharacterEncoding("UTF-8");
                 externalContext.addResponseHeader("Cache-control", "no-cache");
                 
                 try
                 {
                     partialWriter.startDocument();
     
                     for (Throwable t : throwableList)
                     {
                         renderAjaxError(partialWriter, t);
                     }
                     
                     responseComplete = true;
                 }
                 catch (IOException e)
                 {
                     if (log.isLoggable(Level.SEVERE))
                     {
                         log.log(Level.SEVERE, "Cannot render exception on ajax request", e);
                     }
                 }
                 finally
                 {
                     if (responseComplete)
                     {
                         try
                         {
                             partialWriter.endDocument();
                             facesContext.responseComplete();
                         }
                         catch (IOException e1)
                         {
                             if (log.isLoggable(Level.SEVERE))
                             {
                                 log.log(Level.SEVERE, "Cannot render exception on ajax request", e1);
                             }
                         }
                     }
                 }
             }
         }
     }
     
     private void renderAjaxError(PartialResponseWriter partialWriter, Throwable ex) throws IOException
     {
         partialWriter.startError(ex.getClass().getName());
         if (ex.getCause() != null)
         {
             partialWriter.write(ex.getCause().toString());
         }
         else if (ex.getMessage() != null)
         {
             partialWriter.write(ex.getMessage());
         }
         partialWriter.endError();
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     public boolean isListenerForSource(Object source)
     {
         return source instanceof ExceptionQueuedEventContext;
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     public void processEvent(SystemEvent exceptionQueuedEvent) throws AbortProcessingException
     {
         if (unhandled == null)
         {
             unhandled = new LinkedList<ExceptionQueuedEvent>();
         }
         
         unhandled.add((ExceptionQueuedEvent)exceptionQueuedEvent);
     }
     
     protected Throwable getRethrownException(Throwable exception)
     {
         // Let toRethrow be either the result of calling getRootCause() on the Exception, 
         // or the Exception itself, whichever is non-null
         Throwable toRethrow = getRootCause(exception);
         if (toRethrow == null)
         {
             toRethrow = exception;
         }
         
         return toRethrow;
     }
     
     protected FacesException wrap(Throwable exception)
     {
         if (exception instanceof FacesException)
         {
             return (FacesException) exception;
         }
         return new FacesException(exception);
     }
     
     protected boolean shouldSkip(Throwable exception)
     {
         return exception instanceof AbortProcessingException;
     }
 
 }