/*
    *  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.mina.handler.demux;
  
  import java.util.Collections;
  import java.util.Map;
  import java.util.Set;
  import java.util.concurrent.ConcurrentHashMap;
  
  import org.apache.mina.core.service.IoHandler;
  import org.apache.mina.core.service.IoHandlerAdapter;
  import org.apache.mina.core.session.IoSession;
  import org.apache.mina.core.session.UnknownMessageTypeException;
  import org.apache.mina.util.IdentityHashSet;
  
  /**
   * A {@link IoHandler} that demuxes <code>messageReceived</code> events
   * to the appropriate {@link MessageHandler}.
   * <p>
   * You can freely register and deregister {@link MessageHandler}s using
   * {@link #addReceivedMessageHandler(Class, MessageHandler)} and
   * {@link #removeReceivedMessageHandler(Class)}.
   * <p>
   * When <code>message</code> is received through a call to
   * {@link #messageReceived(IoSession, Object)} the class of the
   * <code>message</code> object will be used to find a {@link MessageHandler} for
   * that particular message type. If no {@link MessageHandler} instance can be
   * found for the immediate class (i.e. <code>message.getClass()</code>) the
   * interfaces implemented by the immediate class will be searched in depth-first
   * order. If no match can be found for any of the interfaces the search will be
   * repeated recursively for the superclass of the immediate class
   * (i.e. <code>message.getClass().getSuperclass()</code>).
   * <p>
   * Consider the following type hierarchy (<code>Cx</code> are classes while
   * <code>Ix</code> are interfaces):
   * <pre>
   *     C3 - I7 - I9
   *      |    |   /\
   *      |   I8  I3 I4
   *      |
   *     C2 - I5 - I6
   *      |
   *     C1 - I1 - I2 - I4
   *      |         |
   *      |        I3
   *    Object
   * </pre>
   * When <code>message</code> is of type <code>C3</code> this hierarchy will be
   * searched in the following order:
   * <code>C3, I7, I8, I9, I3, I4, C2, I5, I6, C1, I1, I2, I3, I4, Object</code>.
   * <p>
   * For efficiency searches will be cached. Calls to
   * {@link #addReceivedMessageHandler(Class, MessageHandler)} and
   * {@link #removeReceivedMessageHandler(Class)} clear this cache.
   *
   * @author <a href="http://mina.apache.org">Apache MINA Project</a>
   */
  public class DemuxingIoHandler extends IoHandlerAdapter {
  
      private final Map<Class<?>, MessageHandler<?>> receivedMessageHandlerCache = new ConcurrentHashMap<>();
  
      private final Map<Class<?>, MessageHandler<?>> receivedMessageHandlers = new ConcurrentHashMap<>();
  
      private final Map<Class<?>, MessageHandler<?>> sentMessageHandlerCache = new ConcurrentHashMap<>();
  
      private final Map<Class<?>, MessageHandler<?>> sentMessageHandlers = new ConcurrentHashMap<>();
  
      private final Map<Class<?>, ExceptionHandler<?>> exceptionHandlerCache = new ConcurrentHashMap<>();
  
      private final Map<Class<?>, ExceptionHandler<?>> exceptionHandlers = new ConcurrentHashMap<>();
  
      /**
       * Creates a new instance with no registered {@link MessageHandler}s.
       */
      public DemuxingIoHandler() {
          // Do nothing
      }
  
      /**
       * Registers a {@link MessageHandler} that handles the received messages of
       * the specified <code>type</code>.
       * 
      * @param <E> The message handler's type
      * @param type The message's type
      * @param handler The message handler
      * @return the old handler if there is already a registered handler for
      *         the specified <tt>type</tt>.  <tt>null</tt> otherwise.
      */
     @SuppressWarnings("unchecked")
     public <E> MessageHandler<? super E> addReceivedMessageHandler(Class<E> type, MessageHandler<? super E> handler) {
         receivedMessageHandlerCache.clear();
         
         return (MessageHandler<? super E>) receivedMessageHandlers.put(type, handler);
     }
 
     /**
      * Deregisters a {@link MessageHandler} that handles the received messages
      * of the specified <code>type</code>.
      *
      * @param <E> The message handler's type
      * @param type The message's type
      * @return the removed handler if successfully removed.  <tt>null</tt> otherwise.
      */
     @SuppressWarnings("unchecked")
     public <E> MessageHandler<? super E> removeReceivedMessageHandler(Class<E> type) {
         receivedMessageHandlerCache.clear();
         
         return (MessageHandler<? super E>) receivedMessageHandlers.remove(type);
     }
 
     /**
      * Registers a {@link MessageHandler} that handles the sent messages of the
      * specified <code>type</code>.
      *
      * @param <E> The message handler's type
      * @param type The message's type
      * @param handler The message handler
      * @return the old handler if there is already a registered handler for
      *         the specified <tt>type</tt>.  <tt>null</tt> otherwise.
      */
     @SuppressWarnings("unchecked")
     public <E> MessageHandler<? super E> addSentMessageHandler(Class<E> type, MessageHandler<? super E> handler) {
         sentMessageHandlerCache.clear();
         
         return (MessageHandler<? super E>) sentMessageHandlers.put(type, handler);
     }
 
     /**
      * Deregisters a {@link MessageHandler} that handles the sent messages of
      * the specified <code>type</code>.
      *
      * @param <E> The message handler's type
      * @param type The message's type
      * @return the removed handler if successfully removed.  <tt>null</tt> otherwise.
      */
     @SuppressWarnings("unchecked")
     public <E> MessageHandler<? super E> removeSentMessageHandler(Class<E> type) {
         sentMessageHandlerCache.clear();
         
         return (MessageHandler<? super E>) sentMessageHandlers.remove(type);
     }
 
     /**
      * Registers a {@link MessageHandler} that receives the messages of
      * the specified <code>type</code>.
      *
      * @param <E> The message handler's type
      * @param type The message's type
      * @param handler The Exception handler
      * @return the old handler if there is already a registered handler for
      *         the specified <tt>type</tt>.  <tt>null</tt> otherwise.
      */
     @SuppressWarnings("unchecked")
     public <E extends Throwable> ExceptionHandler<? super E> addExceptionHandler(Class<E> type,
             ExceptionHandler<? super E> handler) {
         exceptionHandlerCache.clear();
         
         return (ExceptionHandler<? super E>) exceptionHandlers.put(type, handler);
     }
 
     /**
      * Deregisters a {@link MessageHandler} that receives the messages of
      * the specified <code>type</code>.
      *
      * @param <E> The Exception Handler's type
      * @param type The message's type
      * @return the removed handler if successfully removed.  <tt>null</tt> otherwise.
      */
     @SuppressWarnings("unchecked")
     public <E extends Throwable> ExceptionHandler<? super E> removeExceptionHandler(Class<E> type) {
         exceptionHandlerCache.clear();
         
         return (ExceptionHandler<? super E>) exceptionHandlers.remove(type);
     }
 
     /**
      * @return the {@link MessageHandler} which is registered to process
      * the specified <code>type</code>.
      * @param <E> The message handler's type
      * @param type The message's type
      */
     @SuppressWarnings("unchecked")
     public <E> MessageHandler<? super E> getMessageHandler(Class<E> type) {
         return (MessageHandler<? super E>) receivedMessageHandlers.get(type);
     }
 
     /**
      * @return the {@link Map} which contains all messageType-{@link MessageHandler}
      * pairs registered to this handler for received messages.
      */
     public Map<Class<?>, MessageHandler<?>> getReceivedMessageHandlerMap() {
         return Collections.unmodifiableMap(receivedMessageHandlers);
     }
 
     /**
      * @return the {@link Map} which contains all messageType-{@link MessageHandler}
      * pairs registered to this handler for sent messages.
      */
     public Map<Class<?>, MessageHandler<?>> getSentMessageHandlerMap() {
         return Collections.unmodifiableMap(sentMessageHandlers);
     }
 
     /**
      * @return the {@link Map} which contains all messageType-{@link MessageHandler}
      * pairs registered to this handler.
      */
     public Map<Class<?>, ExceptionHandler<?>> getExceptionHandlerMap() {
         return Collections.unmodifiableMap(exceptionHandlers);
     }
 
     /**
      * Forwards the received events into the appropriate {@link MessageHandler}
      * which is registered by {@link #addReceivedMessageHandler(Class, MessageHandler)}.
      * 
      * <b>Warning !</b> If you are to overload this method, be aware that you 
      * _must_ call the messageHandler in your own method, otherwise it won't 
      * be called.
      * 
      * {@inheritDoc}
      */
     @Override
     public void messageReceived(IoSession session, Object message) throws Exception {
         MessageHandler<Object> handler = findReceivedMessageHandler(message.getClass());
         
         if (handler != null) {
             handler.handleMessage(session, message);
         } else {
             throw new UnknownMessageTypeException("No message handler found for message type: "
                     + message.getClass().getSimpleName());
         }
     }
 
     /**
      * Invoked when a message written by IoSession.write(Object) is sent out.
      * 
      * <b>Warning !</b> If you are to overload this method, be aware that you 
      * _must_ call the messageHandler in your own method, otherwise it won't 
      * be called.
      * 
      * {@inheritDoc}
      */
     @Override
     public void messageSent(IoSession session, Object message) throws Exception {
         MessageHandler<Object> handler = findSentMessageHandler(message.getClass());
         
         if (handler != null) {
             handler.handleMessage(session, message);
         } else {
             throw new UnknownMessageTypeException("No handler found for message type: "
                     + message.getClass().getSimpleName());
         }
     }
 
     /**
      * Invoked when any exception is thrown by user IoHandler implementation 
      * or by MINA. If cause is an instance of IOException, MINA will close the 
      * connection automatically.
      *
      * <b>Warning !</b> If you are to overload this method, be aware that you 
      * _must_ call the messageHandler in your own method, otherwise it won't 
      * be called.
      * 
      * {@inheritDoc}
      */
     @Override
     public void exceptionCaught(IoSession session, Throwable cause) throws Exception {
         ExceptionHandler<Throwable> handler = findExceptionHandler(cause.getClass());
         
         if (handler != null) {
             handler.exceptionCaught(session, cause);
         } else {
             throw new UnknownMessageTypeException("No handler found for exception type: "
                     + cause.getClass().getSimpleName());
         }
     }
 
     protected MessageHandler<Object> findReceivedMessageHandler(Class<?> type) {
         return findReceivedMessageHandler(type, null);
     }
 
     protected MessageHandler<Object> findSentMessageHandler(Class<?> type) {
         return findSentMessageHandler(type, null);
     }
 
     protected ExceptionHandler<Throwable> findExceptionHandler(Class<? extends Throwable> type) {
         return findExceptionHandler(type, null);
     }
 
     @SuppressWarnings("unchecked")
     private MessageHandler<Object> findReceivedMessageHandler(Class<?> type, Set<Class<?>> triedClasses) {
         return (MessageHandler<Object>) findHandler(receivedMessageHandlers, receivedMessageHandlerCache, type,
                 triedClasses);
     }
 
     @SuppressWarnings("unchecked")
     private MessageHandler<Object> findSentMessageHandler(Class<?> type, Set<Class<?>> triedClasses) {
         return (MessageHandler<Object>) findHandler(sentMessageHandlers, sentMessageHandlerCache, type, triedClasses);
     }
 
     @SuppressWarnings("unchecked")
     private ExceptionHandler<Throwable> findExceptionHandler(Class<?> type, Set<Class<?>> triedClasses) {
         return (ExceptionHandler<Throwable>) findHandler(exceptionHandlers, exceptionHandlerCache, type, triedClasses);
     }
 
     @SuppressWarnings("unchecked")
     private Object findHandler(Map<Class<?>,?> handlers, Map handlerCache, Class<?> type, Set<Class<?>> triedClasses) {
         if ((triedClasses != null) && (triedClasses.contains(type))) {
             return null;
         }
 
         /*
          * Try the cache first.
          */
         Object handler = handlerCache.get(type);
         
         if (handler != null) {
             return handler;
         }
 
         /*
          * Try the registered handlers for an immediate match.
          */
         handler = handlers.get(type);
 
         if (handler == null) {
             /*
              * No immediate match could be found. Search the type's interfaces.
              */
 
             if (triedClasses == null) {
                 triedClasses = new IdentityHashSet<>();
             }
             
             triedClasses.add(type);
 
             Class<?>[] interfaces = type.getInterfaces();
             
             for (Class<?> element : interfaces) {
                 handler = findHandler(handlers, handlerCache, element, triedClasses);
                 
                 if (handler != null) {
                     break;
                 }
             }
         }
 
         if (handler == null) {
             /*
              * No match in type's interfaces could be found. Search the
              * superclass.
              */
             Class<?> superclass = type.getSuperclass();
             
             if (superclass != null) {
                 handler = findHandler(handlers, handlerCache, superclass, null);
             }
         }
 
         /*
          * Make sure the handler is added to the cache. By updating the cache
          * here all the types (superclasses and interfaces) in the path which
          * led to a match will be cached along with the immediate message type.
          */
         if (handler != null) {
             handlerCache.put(type, handler);
         }
 
         return handler;
     }
 }