/*
    * ====================================================================
    * 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.client.methods;
  
  import java.io.File;
  import java.io.FileNotFoundException;
  import java.io.IOException;
  import java.io.RandomAccessFile;
  import java.nio.channels.FileChannel;
  
  import org.apache.http.Header;
  import org.apache.http.HttpEntity;
  import org.apache.http.HttpResponse;
  import org.apache.http.entity.ContentType;
  import org.apache.http.entity.FileEntity;
  import org.apache.http.nio.ContentDecoder;
  import org.apache.http.nio.ContentDecoderChannel;
  import org.apache.http.nio.FileContentDecoder;
  import org.apache.http.nio.IOControl;
  import org.apache.http.nio.protocol.AbstractAsyncResponseConsumer;
  import org.apache.http.protocol.HttpContext;
  import org.apache.http.util.Asserts;
  
  /**
   * {@link org.apache.http.nio.protocol.HttpAsyncResponseConsumer} implementation that
   * streams content entity enclosed in an HTTP response directly into a file
   * without an intermediate in-memory buffer.
   * <p>
   * This consumer can be useful for file downloads.
   *
   * @since 4.0
   */
  public abstract class ZeroCopyConsumer<T> extends AbstractAsyncResponseConsumer<T> {
  
      private final File file;
      private final RandomAccessFile accessfile;
  
      private HttpResponse response;
      private ContentType contentType;
      private Header contentEncoding;
      private FileChannel fileChannel;
      private long idx = -1;
  
      public ZeroCopyConsumer(final File file) throws FileNotFoundException {
          super();
          if (file == null) {
              throw new IllegalArgumentException("File may nor be null");
          }
          this.file = file;
          this.accessfile = new RandomAccessFile(this.file, "rw");
      }
  
      @Override
      protected void onResponseReceived(final HttpResponse response) {
          this.response = response;
      }
  
      @Override
      protected void onEntityEnclosed(
              final HttpEntity entity, final ContentType contentType) throws IOException {
          this.contentType = contentType;
          this.contentEncoding = entity.getContentEncoding();
          this.fileChannel = this.accessfile.getChannel();
          this.idx = 0;
      }
  
      @Override
      protected void onContentReceived(
              final ContentDecoder decoder, final IOControl ioControl) throws IOException {
          Asserts.notNull(this.fileChannel, "File channel");
          final long transferred;
          if (decoder instanceof FileContentDecoder) {
              transferred = ((FileContentDecoder)decoder).transfer(
                      this.fileChannel, this.idx, Integer.MAX_VALUE);
          } else {
             transferred = this.fileChannel.transferFrom(
                     new ContentDecoderChannel(decoder), this.idx, Integer.MAX_VALUE);
         }
         if (transferred > 0) {
             this.idx += transferred;
         }
         if (decoder.isCompleted()) {
             this.fileChannel.close();
         }
     }
 
     /**
      * Invoked to process received file.
      *
      * @param response original response head.
      * @param file file containing response content.
      * @param contentType the cotnent type.
      * @return result of the response processing
      */
     protected abstract T process(
             HttpResponse response, File file, ContentType contentType) throws Exception;
 
     @Override
     protected T buildResult(final HttpContext context) throws Exception {
         final FileEntity entity = new FileEntity(this.file, this.contentType);
         entity.setContentEncoding(this.contentEncoding);
         this.response.setEntity(entity);
         return process(this.response, this.file, this.contentType);
     }
 
     @Override
     protected void releaseResources() {
         try {
             this.accessfile.close();
         } catch (final IOException ignore) {
         }
     }
 
 }