/*
    *  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.filter.reqres;
  
  import java.util.ArrayList;
  import java.util.HashMap;
  import java.util.Iterator;
  import java.util.LinkedHashSet;
  import java.util.List;
  import java.util.Map;
  import java.util.Set;
  import java.util.concurrent.ScheduledExecutorService;
  import java.util.concurrent.ScheduledFuture;
  import java.util.concurrent.TimeUnit;
  
  import org.apache.mina.core.filterchain.IoFilterChain;
  import org.apache.mina.core.session.AttributeKey;
  import org.apache.mina.core.session.IoSession;
  import org.apache.mina.core.write.WriteRequest;
  import org.apache.mina.filter.util.WriteRequestFilter;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  /**
   * TODO Add documentation
   * 
   * @author The Apache MINA Project (dev@mina.apache.org)
   * @version $Rev: 672583 $, $Date: 2008-06-28 23:29:15 +0200 (sam, 28 jun 2008) $
   */
  public class RequestResponseFilter extends WriteRequestFilter {
  
      private final AttributeKey RESPONSE_INSPECTOR = new AttributeKey(getClass(), "responseInspector");
      private final AttributeKey REQUEST_STORE = new AttributeKey(getClass(), "requestStore");
      private final AttributeKey UNRESPONDED_REQUEST_STORE = new AttributeKey(getClass(), "unrespondedRequestStore");
  
      private final ResponseInspectorFactory responseInspectorFactory;
      private final ScheduledExecutorService timeoutScheduler;
  
      private final Logger logger = LoggerFactory.getLogger(getClass());
  
      public RequestResponseFilter(final ResponseInspector responseInspector,
              ScheduledExecutorService timeoutScheduler) {
          if (responseInspector == null) {
              throw new NullPointerException("responseInspector");
          }
          if (timeoutScheduler == null) {
              throw new NullPointerException("timeoutScheduler");
          }
          this.responseInspectorFactory = new ResponseInspectorFactory() {
              public ResponseInspector getResponseInspector() {
                  return responseInspector;
              }
          };
          this.timeoutScheduler = timeoutScheduler;
      }
  
      public RequestResponseFilter(
              ResponseInspectorFactory responseInspectorFactory,
              ScheduledExecutorService timeoutScheduler) {
          if (responseInspectorFactory == null) {
              throw new NullPointerException("responseInspectorFactory");
          }
          if (timeoutScheduler == null) {
              throw new NullPointerException("timeoutScheduler");
          }
          this.responseInspectorFactory = responseInspectorFactory;
          this.timeoutScheduler = timeoutScheduler;
      }
  
      @Override
      public void onPreAdd(IoFilterChain parent, String name,
              NextFilter nextFilter) throws Exception {
          if (parent.contains(this)) {
              throw new IllegalArgumentException(
                      "You can't add the same filter instance more than once.  Create another instance and add it.");
          }
  
          IoSession session = parent.getSession();
          session.setAttribute(RESPONSE_INSPECTOR, responseInspectorFactory
                  .getResponseInspector());
          session.setAttribute(REQUEST_STORE, createRequestStore(session));
          session.setAttribute(UNRESPONDED_REQUEST_STORE, createUnrespondedRequestStore(session));
     }
 
     @Override
     public void onPostRemove(IoFilterChain parent, String name,
             NextFilter nextFilter) throws Exception {
         IoSession session = parent.getSession();
 
         destroyUnrespondedRequestStore(getUnrespondedRequestStore(session));
         destroyRequestStore(getRequestStore(session));
 
         session.removeAttribute(UNRESPONDED_REQUEST_STORE);
         session.removeAttribute(REQUEST_STORE);
         session.removeAttribute(RESPONSE_INSPECTOR);
     }
 
     @Override
     public void messageReceived(NextFilter nextFilter, IoSession session,
             Object message) throws Exception {
         ResponseInspector responseInspector = (ResponseInspector) session
                 .getAttribute(RESPONSE_INSPECTOR);
         Object requestId = responseInspector.getRequestId(message);
         if (requestId == null) {
             // Not a response message.  Ignore.
             nextFilter.messageReceived(session, message);
             return;
         }
 
         // Retrieve (or remove) the corresponding request.
         ResponseType type = responseInspector.getResponseType(message);
         if (type == null) {
             nextFilter.exceptionCaught(session, new IllegalStateException(
                     responseInspector.getClass().getName()
                             + "#getResponseType() may not return null."));
         }
 
         Map<Object, Request> requestStore = getRequestStore(session);
 
         Request request;
         switch (type) {
         case WHOLE:
         case PARTIAL_LAST:
             synchronized (requestStore) {
                 request = requestStore.remove(requestId);
             }
             break;
         case PARTIAL:
             synchronized (requestStore) {
                 request = requestStore.get(requestId);
             }
             break;
         default:
             throw new InternalError();
         }
 
         if (request == null) {
             // A response message without request. Swallow the event because
             // the response might have arrived too late.
             if (logger.isWarnEnabled()) {
                 logger.warn("Unknown request ID '" + requestId
                         + "' for the response message. Timed out already?: "
                         + message);
             }
         } else {
             // Found a matching request.
             // Cancel the timeout task if needed.
             if (type != ResponseType.PARTIAL) {
                 ScheduledFuture<?> scheduledFuture = request.getTimeoutFuture();
                 if (scheduledFuture != null) {
                     scheduledFuture.cancel(false);
                     Set<Request> unrespondedRequests = getUnrespondedRequestStore(session);
                     synchronized (unrespondedRequests) {
                         unrespondedRequests.remove(request);
                     }
                 }
             }
 
             // And forward the event.
             Response response = new Response(request, message, type);
             request.signal(response);
             nextFilter.messageReceived(session, response);
         }
     }
 
     @Override
     protected Object doFilterWrite(
             final NextFilter nextFilter, IoSession session, WriteRequest writeRequest) throws Exception {
         Object message = writeRequest.getMessage();
         if (!(message instanceof Request)) {
             return null;
         }
 
         final Request request = (Request) message;
         if (request.getTimeoutFuture() != null) {
             throw new IllegalArgumentException("Request can not be reused.");
         }
 
         Map<Object, Request> requestStore = getRequestStore(session);
         Object oldValue = null;
         Object requestId = request.getId();
         synchronized (requestStore) {
             oldValue = requestStore.get(requestId);
             if (oldValue == null) {
                 requestStore.put(requestId, request);
             }
         }
         if (oldValue != null) {
             throw new IllegalStateException(
                     "Duplicate request ID: " + request.getId());
         }
 
         // Schedule a task to be executed on timeout.
         TimeoutTask timeoutTask = new TimeoutTask(
                 nextFilter, request, session);
         ScheduledFuture<?> timeoutFuture = timeoutScheduler.schedule(
                 timeoutTask, request.getTimeoutMillis(),
                 TimeUnit.MILLISECONDS);
         request.setTimeoutTask(timeoutTask);
         request.setTimeoutFuture(timeoutFuture);
 
         // Add the timeout task to the unfinished task set.
         Set<Request> unrespondedRequests = getUnrespondedRequestStore(session);
         synchronized (unrespondedRequests) {
             unrespondedRequests.add(request);
         }
 
         return request.getMessage();
     }
 
     @Override
     public void sessionClosed(NextFilter nextFilter, IoSession session)
             throws Exception {
         // Copy the unfinished task set to avoid unnecessary lock acquisition.
         // Copying will be cheap because there won't be that many requests queued.
         Set<Request> unrespondedRequests = getUnrespondedRequestStore(session);
         List<Request> unrespondedRequestsCopy;
         synchronized (unrespondedRequests) {
             unrespondedRequestsCopy = new ArrayList<Request>(
                     unrespondedRequests);
             unrespondedRequests.clear();
         }
 
         // Generate timeout artificially.
         for (Request r : unrespondedRequestsCopy) {
             if (r.getTimeoutFuture().cancel(false)) {
                 r.getTimeoutTask().run();
             }
         }
 
         // Clear the request store just in case we missed something, though it's unlikely.
         Map<Object, Request> requestStore = getRequestStore(session);
         synchronized (requestStore) {
             requestStore.clear();
         }
 
         // Now tell the main subject.
         nextFilter.sessionClosed(session);
     }
 
     @SuppressWarnings("unchecked")
     private Map<Object, Request> getRequestStore(IoSession session) {
         return (Map<Object, Request>) session.getAttribute(REQUEST_STORE);
     }
 
     @SuppressWarnings("unchecked")
     private Set<Request> getUnrespondedRequestStore(IoSession session) {
         return (Set<Request>) session.getAttribute(UNRESPONDED_REQUEST_STORE);
     }
 
     /**
      * Returns a {@link Map} which stores {@code messageId}-{@link Request}
      * pairs whose {@link Response}s are not received yet.  Please override
      * this method if you need to use other {@link Map} implementation
      * than the default one ({@link HashMap}).
      */
     protected Map<Object, Request> createRequestStore(
             IoSession session) {
         return new HashMap<Object, Request>();
     }
 
     /**
      * Returns a {@link Set} which stores {@link Request} whose
      * {@link Response}s are not received yet. Please override
      * this method if you need to use other {@link Set} implementation
      * than the default one ({@link LinkedHashSet}).  Please note that
      * the {@link Iterator} of the returned {@link Set} have to iterate
      * its elements in the insertion order to ensure that
      * {@link RequestTimeoutException}s are thrown in the order which
      * {@link Request}s were written.  If you don't need to guarantee
      * the order of thrown exceptions, any {@link Set} implementation
      * can be used.
      */
     protected Set<Request> createUnrespondedRequestStore(
             IoSession session) {
         return new LinkedHashSet<Request>();
     }
 
     /**
      * Releases any resources related with the {@link Map} created by
      * {@link #createRequestStore(IoSession)}.  This method is useful
      * if you override {@link #createRequestStore(IoSession)}.
      *
      * @param requestStore what you returned in {@link #createRequestStore(IoSession)}
      */
     protected void destroyRequestStore(
             Map<Object, Request> requestStore) {
     }
 
     /**
      * Releases any resources related with the {@link Set} created by
      * {@link #createUnrespondedRequestStore(IoSession)}.  This method is
      * useful if you override {@link #createUnrespondedRequestStore(IoSession)}.
      *
      * @param unrespondedRequestStore what you returned in {@link #createUnrespondedRequestStore(IoSession)}
      */
     protected void destroyUnrespondedRequestStore(
             Set<Request> unrespondedRequestStore) {
     }
 
     private class TimeoutTask implements Runnable {
         private final NextFilter filter;
 
         private final Request request;
 
         private final IoSession session;
 
         private TimeoutTask(NextFilter filter, Request request,
                 IoSession session) {
             this.filter = filter;
             this.request = request;
             this.session = session;
         }
 
         public void run() {
             Set<Request> unrespondedRequests = getUnrespondedRequestStore(session);
             if (unrespondedRequests != null) {
                 synchronized (unrespondedRequests) {
                     unrespondedRequests.remove(request);
                 }
             }
 
             Map<Object, Request> requestStore = getRequestStore(session);
             Object requestId = request.getId();
             boolean timedOut;
             synchronized (requestStore) {
                 if (requestStore.get(requestId) == request) {
                     requestStore.remove(requestId);
                     timedOut = true;
                 } else {
                     timedOut = false;
                 }
             }
 
             if (timedOut) {
                 // Throw the exception only when it's really timed out.
                 RequestTimeoutException e = new RequestTimeoutException(request);
                 request.signal(e);
                 filter.exceptionCaught(session, e);
             }
         }
     }
 }