/*
    * ====================================================================
    * 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.
   * ====================================================================
   *
   * This software consists of voluntary contributions made by many
   * individuals on behalf of the Apache Software Foundation.  For more
   * information on the Apache Software Foundation, please see
   * <http://www.apache.org/>.
   *
   */
  
  package org.apache.http.nio.protocol;
  
  import java.io.Closeable;
  import java.io.IOException;
  import java.util.ArrayList;
  import java.util.List;
  import java.util.Queue;
  import java.util.concurrent.ConcurrentLinkedQueue;
  import java.util.concurrent.Future;
  import java.util.concurrent.atomic.AtomicBoolean;
  import java.util.concurrent.atomic.AtomicReference;
  
  import org.apache.http.ConnectionClosedException;
  import org.apache.http.ConnectionReuseStrategy;
  import org.apache.http.HttpException;
  import org.apache.http.HttpRequest;
  import org.apache.http.HttpResponse;
  import org.apache.http.concurrent.BasicFuture;
  import org.apache.http.concurrent.FutureCallback;
  import org.apache.http.impl.DefaultConnectionReuseStrategy;
  import org.apache.http.nio.ContentDecoder;
  import org.apache.http.nio.ContentEncoder;
  import org.apache.http.nio.IOControl;
  import org.apache.http.nio.NHttpClientConnection;
  import org.apache.http.protocol.HttpContext;
  import org.apache.http.protocol.HttpCoreContext;
  import org.apache.http.protocol.HttpProcessor;
  import org.apache.http.util.Args;
  import org.apache.http.util.Asserts;
  
  /**
   * Pipelining implementation of {@link org.apache.http.nio.protocol.HttpAsyncClientExchangeHandler}
   * that executes a series of pipelined HTTP requests.
   *
   * @param <T> the result type of request execution.
   * @since 4.4
   */
  @Pipelined()
  public class PipeliningClientExchangeHandler<T> implements HttpAsyncClientExchangeHandler {
  
      private final Queue<HttpAsyncRequestProducer> requestProducerQueue;
      private final Queue<HttpAsyncResponseConsumer<T>> responseConsumerQueue;
      private final Queue<HttpRequest> requestQueue;
      private final Queue<T> resultQueue;
      private final BasicFuture<List<T>> future;
      private final HttpContext localContext;
      private final NHttpClientConnection conn;
      private final HttpProcessor httpPocessor;
      private final ConnectionReuseStrategy connReuseStrategy;
  
      private final AtomicReference<HttpAsyncRequestProducer> requestProducerRef;
      private final AtomicReference<HttpAsyncResponseConsumer<T>> responseConsumerRef;
      private final AtomicBoolean keepAlive;
      private final AtomicBoolean closed;
  
      /**
       * Creates new instance of {@code PipeliningClientExchangeHandler}.
       *
       * @param requestProducers the request producers.
       * @param responseConsumers the response consumers.
       * @param callback the future callback invoked when the operation is completed.
       * @param localContext the local execution context.
       * @param conn the actual connection.
       * @param httpPocessor the HTTP protocol processor.
       * @param connReuseStrategy the connection re-use strategy.
       */
      public PipeliningClientExchangeHandler(
              final List<? extends HttpAsyncRequestProducer> requestProducers,
              final List<? extends HttpAsyncResponseConsumer<T>> responseConsumers,
              final FutureCallback<List<T>> callback,
              final HttpContext localContext,
              final NHttpClientConnection conn,
             final HttpProcessor httpPocessor,
             final ConnectionReuseStrategy connReuseStrategy) {
         super();
         Args.notEmpty(requestProducers, "Request producer list");
         Args.notEmpty(responseConsumers, "Response consumer list");
         Args.check(requestProducers.size() == responseConsumers.size(),
                 "Number of request producers does not match that of response consumers");
         this.requestProducerQueue = new ConcurrentLinkedQueue<HttpAsyncRequestProducer>(requestProducers);
         this.responseConsumerQueue = new ConcurrentLinkedQueue<HttpAsyncResponseConsumer<T>>(responseConsumers);
         this.requestQueue = new ConcurrentLinkedQueue<HttpRequest>();
         this.resultQueue = new ConcurrentLinkedQueue<T>();
         this.future = new BasicFuture<List<T>>(callback);
         this.localContext = Args.notNull(localContext, "HTTP context");
         this.conn = Args.notNull(conn, "HTTP connection");
         this.httpPocessor = Args.notNull(httpPocessor, "HTTP processor");
         this.connReuseStrategy = connReuseStrategy != null ? connReuseStrategy :
             DefaultConnectionReuseStrategy.INSTANCE;
         this.localContext.setAttribute(HttpCoreContext.HTTP_CONNECTION, this.conn);
         this.requestProducerRef = new AtomicReference<HttpAsyncRequestProducer>(null);
         this.responseConsumerRef = new AtomicReference<HttpAsyncResponseConsumer<T>>(null);
         this.keepAlive = new AtomicBoolean(false);
         this.closed = new AtomicBoolean(false);
     }
 
     /**
      * Creates new instance of {@code PipeliningClientExchangeHandler}.
      *
      * @param requestProducers the request producers.
      * @param responseConsumers the response consumers.
      * @param localContext the local execution context.
      * @param conn the actual connection.
      * @param httpPocessor the HTTP protocol processor.
      */
     public PipeliningClientExchangeHandler(
             final List<? extends HttpAsyncRequestProducer> requestProducers,
             final List<? extends HttpAsyncResponseConsumer<T>> responseConsumers,
             final HttpContext localContext,
             final NHttpClientConnection conn,
             final HttpProcessor httpPocessor) {
         this(requestProducers, responseConsumers, null, localContext, conn, httpPocessor, null);
     }
 
     public Future<List<T>> getFuture() {
         return this.future;
     }
 
     private static void closeQuietly(final Closeable closeable) {
         if (closeable != null) {
             try {
                 closeable.close();
             } catch (final IOException ex) {
             }
         }
     }
 
     private void releaseResources() {
         closeQuietly(this.requestProducerRef.getAndSet(null));
         closeQuietly(this.responseConsumerRef.getAndSet(null));
         while (!this.requestProducerQueue.isEmpty()) {
             closeQuietly(this.requestProducerQueue.remove());
         }
         while (!this.responseConsumerQueue.isEmpty()) {
             closeQuietly(this.responseConsumerQueue.remove());
         }
         this.requestQueue.clear();
         this.resultQueue.clear();
     }
 
     @Override
     public void close() throws IOException {
         if (this.closed.compareAndSet(false, true)) {
             releaseResources();
             if (!this.future.isDone()) {
                 this.future.cancel();
             }
         }
     }
 
     @Override
     public HttpRequest generateRequest() throws IOException, HttpException {
         Asserts.check(this.requestProducerRef.get() == null, "Inconsistent state: request producer is not null");
         final HttpAsyncRequestProducer requestProducer = this.requestProducerQueue.poll();
         if (requestProducer == null) {
             return null;
         }
         this.requestProducerRef.set(requestProducer);
         final HttpRequest request = requestProducer.generateRequest();
         this.httpPocessor.process(request, this.localContext);
         this.requestQueue.add(request);
         return request;
     }
 
     @Override
     public void produceContent(
             final ContentEncoder encoder, final IOControl ioControl) throws IOException {
         final HttpAsyncRequestProducer requestProducer = this.requestProducerRef.get();
         Asserts.check(requestProducer != null, "Inconsistent state: request producer is null");
         requestProducer.produceContent(encoder, ioControl);
     }
 
     @Override
     public void requestCompleted() {
         final HttpAsyncRequestProducer requestProducer = this.requestProducerRef.getAndSet(null);
         Asserts.check(requestProducer != null, "Inconsistent state: request producer is null");
         requestProducer.requestCompleted(this.localContext);
     }
 
     @Override
     public void responseReceived(final HttpResponse response) throws IOException, HttpException {
         Asserts.check(this.responseConsumerRef.get() == null, "Inconsistent state: response consumer is not null");
 
         final HttpAsyncResponseConsumer<T> responseConsumer = this.responseConsumerQueue.poll();
         Asserts.check(responseConsumer != null, "Inconsistent state: response consumer queue is empty");
         this.responseConsumerRef.set(responseConsumer);
 
         final HttpRequest request = this.requestQueue.poll();
         Asserts.check(request != null, "Inconsistent state: request queue is empty");
 
         this.localContext.setAttribute(HttpCoreContext.HTTP_REQUEST, request);
         this.localContext.setAttribute(HttpCoreContext.HTTP_RESPONSE, response);
         this.httpPocessor.process(response, this.localContext);
 
         responseConsumer.responseReceived(response);
         this.keepAlive.set(this.connReuseStrategy.keepAlive(response, this.localContext));
     }
 
     @Override
     public void consumeContent(
             final ContentDecoder decoder, final IOControl ioControl) throws IOException {
         final HttpAsyncResponseConsumer<T> responseConsumer = this.responseConsumerRef.get();
         Asserts.check(responseConsumer != null, "Inconsistent state: response consumer is null");
         responseConsumer.consumeContent(decoder, ioControl);
     }
 
     @Override
     public void responseCompleted() throws IOException {
         final HttpAsyncResponseConsumer<T> responseConsumer = this.responseConsumerRef.getAndSet(null);
         Asserts.check(responseConsumer != null, "Inconsistent state: response consumer is null");
         try {
             if (!this.keepAlive.get()) {
                 this.conn.close();
             }
             responseConsumer.responseCompleted(this.localContext);
             final T result = responseConsumer.getResult();
             final Exception ex = responseConsumer.getException();
             if (result != null) {
                 this.resultQueue.add(result);
             } else {
                 this.future.failed(ex);
                 this.conn.shutdown();
             }
             if (!conn.isOpen()) {
                 if (this.closed.compareAndSet(false, true)) {
                     releaseResources();
                 }
             }
             if (!this.future.isDone() && this.responseConsumerQueue.isEmpty()) {
                 this.future.completed(new ArrayList<T>(this.resultQueue));
                 this.resultQueue.clear();
             }
         } catch (final RuntimeException ex) {
             failed(ex);
             throw ex;
         }
     }
 
     @Override
     public void inputTerminated() {
         failed(new ConnectionClosedException());
     }
 
     @Override
     public void failed(final Exception ex) {
         if (this.closed.compareAndSet(false, true)) {
             try {
                 final HttpAsyncRequestProducer requestProducer = this.requestProducerRef.get();
                 if (requestProducer != null) {
                     requestProducer.failed(ex);
                 }
                 final HttpAsyncResponseConsumer<T> responseConsumer = this.responseConsumerRef.get();
                 if (responseConsumer != null) {
                     responseConsumer.failed(ex);
                 }
             } finally {
                 try {
                     this.future.failed(ex);
                 } finally {
                     releaseResources();
                 }
             }
         }
     }
 
     @Override
     public boolean cancel() {
         if (this.closed.compareAndSet(false, true)) {
             try {
                 try {
                     final HttpAsyncResponseConsumer<T> responseConsumer = this.responseConsumerRef.get();
                     return responseConsumer != null && responseConsumer.cancel();
                 } finally {
                     this.future.cancel();
                 }
             } finally {
                 releaseResources();
             }
         }
         return false;
     }
 
     @Override
     public boolean isDone() {
         return this.future.isDone();
     }
 
 }