/**
    * This file Copyright (c) 2008-2015 Magnolia International
    * Ltd.  (http://www.magnolia-cms.com). All rights reserved.
    *
    *
    * This file is dual-licensed under both the Magnolia
    * Network Agreement and the GNU General Public License.
    * You may elect to use one or the other of these licenses.
    *
   * This file is distributed in the hope that it will be
   * useful, but AS-IS and WITHOUT ANY WARRANTY; without even the
   * implied warranty of MERCHANTABILITY or FITNESS FOR A
   * PARTICULAR PURPOSE, TITLE, or NONINFRINGEMENT.
   * Redistribution, except as permitted by whichever of the GPL
   * or MNA you select, is prohibited.
   *
   * 1. For the GPL license (GPL), you can redistribute and/or
   * modify this file under the terms of the GNU General
   * Public License, Version 3, as published by the Free Software
   * Foundation.  You should have received a copy of the GNU
   * General Public License, Version 3 along with this program;
   * if not, write to the Free Software Foundation, Inc., 51
   * Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   *
   * 2. For the Magnolia Network Agreement (MNA), this file
   * and the accompanying materials are made available under the
   * terms of the MNA which accompanies this distribution, and
   * is available at http://www.magnolia-cms.com/mna.html
   *
   * Any modifications to this file must keep this entire header
   * intact.
   *
   */
  package info.magnolia.module.cache.util;
  
  import info.magnolia.cms.util.RequestHeaderUtil;
  import info.magnolia.module.cache.CacheModule;
  import info.magnolia.objectfactory.Components;
  
  import java.io.ByteArrayInputStream;
  import java.io.ByteArrayOutputStream;
  import java.io.IOException;
  import java.util.Arrays;
  import java.util.List;
  import java.util.zip.GZIPInputStream;
  import java.util.zip.GZIPOutputStream;
  
  import javax.servlet.http.HttpServletRequest;
  
  /**
   * Provide useful methods for working with gzip'd byte[]. Code originated
   * from net.sf.ehcache.constructs.web.PageInfo under the Apache License Version 2.0.
   *
   * @version $Revision: $ ($Author: $)
   */
  public class GZipUtil {
      private static final List GZIP_MIMETYPES = Arrays.asList(new String[]{
              "application/x-compressed",
              "application/x-gzip",
              "application/gnutar",
              "multipart/x-gzip"
      });
  
      private static final int FOUR_KB = 4196;
      private static final int GZIP_MAGIC_NUMBER_BYTE_1 = 31;
      private static final int GZIP_MAGIC_NUMBER_BYTE_2 = -117;
  
      public static byte[] gzip(byte[] ungzipped) throws IOException {
          if (isGZipped(ungzipped)) {
              throw new IllegalStateException("The byte[] is already gzipped. It should not be gzipped again.");
          }
          final ByteArrayOutputStream bytes = new ByteArrayOutputStream();
          final GZIPOutputStream gzipOutputStream = new GZIPOutputStream(bytes);
          gzipOutputStream.write(ungzipped);
          gzipOutputStream.close();
          return bytes.toByteArray();
      }
  
      public static byte[] ungzip(final byte[] gzipped) throws IOException {
          final GZIPInputStream inputStream = new GZIPInputStream(new ByteArrayInputStream(gzipped));
          final ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream(gzipped.length);
          final byte[] buffer = new byte[FOUR_KB];
          int bytesRead = 0;
          while (bytesRead != -1) {
              bytesRead = inputStream.read(buffer, 0, FOUR_KB);
              if (bytesRead != -1) {
                  byteArrayOutputStream.write(buffer, 0, bytesRead);
              }
          }
          byte[] ungzipped = byteArrayOutputStream.toByteArray();
          inputStream.close();
          byteArrayOutputStream.close();
          return ungzipped;
      }
  
      /**
       * Checks the first two bytes of the candidate byte array for the magic number 0x677a.
       */
      public static boolean isGZipped(byte[] candidate) {
         if (candidate == null || candidate.length < 2) {
             return false;
         } else {
             return (candidate[0] == GZIP_MAGIC_NUMBER_BYTE_1 && candidate[1] == GZIP_MAGIC_NUMBER_BYTE_2);
         }
     }
 
     public static boolean isGZipMimeType(String contentType) {
         return GZIP_MIMETYPES.contains(contentType);
     }
 
     /**
      * True if the response should be gzipped. Uses the compression configuration of the cache and checks if the client accepts gzip responses.
      */
     public static boolean isAcceptsGzip(HttpServletRequest request){
         CacheModule module = Components.getComponent(CacheModule.class);
         boolean compressionVote = module.getCompression().getVoters().vote(request)>0;
         boolean requestAcceptsGzip = RequestHeaderUtil.acceptsGzipEncoding(request);
         return requestAcceptsGzip && compressionVote;
     }
 
 }