package com.atlassian.gzipfilter.selector;
   
   import java.util.HashSet;
   import java.util.List;
   import java.util.Set;
   
   import javax.servlet.FilterConfig;
   import javax.servlet.http.HttpServletRequest;
   
  import static java.util.Arrays.asList;
  import static java.util.Collections.unmodifiableList;
  import static java.util.Collections.unmodifiableSet;
  
  /**
   * This factory will lok into user agent header to decide whenever to dogzip compressing or not
   * <p/>
   * By default gzip is on for defaultCompressableMimeTypes mime types and off for noCompressionUserAgents (IE 6 only)
   * <p/>
   * This is adjustable via COMPRESSABLE_MIME_TYPES_PARAM_NAME an NO_COMPRESSION_USER_AGENTS_PARAM_NAME init-params
   * respectively
   */
  public class UserAgentBasedGzipSelectorFactory implements GzipCompatibilitySelectorFactory
  {
  
      public static final String COMPRESSABLE_MIME_TYPES_PARAM_NAME = "compressableMimeTypes";
  
      public static final String NO_COMPRESSION_USER_AGENTS_PARAM_NAME = "noCompressionUserAgents";
  
      public static final String USER_AGENT_HEADER = "User-Agent";
  
      private static final GzipCompatibilitySelector NO_GZIP_SELECTOR = new NoGzipCompatibilitySelector();
  
      public static final Set<String> DEFAULT_COMPRESSABLE_MIME_TYPES = unmodifiableSet(new HashSet<String>(asList(
                              "text/html",
                              "text/xml",
                              "text/plain",
                              "text/javascript",
                              "text/css",
                              "application/javascript",
                              "application/x-javascript",
                              "application/xml",
                              "application/xhtml",
                              "application/xhtml+xml",
                              "application/json")));
  
      private static final List<String> DEFAULT_NO_COMPRESSION_USER_AGENTS = unmodifiableList(asList("MSIE 6"));
  
      private final Set<String> compressableMimeTypes;
      private final List<String> noCompressionUserAgents;
  
      public UserAgentBasedGzipSelectorFactory(FilterConfig filterConfig)
      {
          final String compressableMimeTypesString = filterConfig.getInitParameter(COMPRESSABLE_MIME_TYPES_PARAM_NAME);
          compressableMimeTypes = compressableMimeTypesString != null
                  ? unmodifiableSet(new HashSet<String>(split(compressableMimeTypesString)))
                  : DEFAULT_COMPRESSABLE_MIME_TYPES;
  
          final String noCompressionUserAgentsString = filterConfig.getInitParameter(NO_COMPRESSION_USER_AGENTS_PARAM_NAME);
          noCompressionUserAgents = noCompressionUserAgentsString != null
                  ? unmodifiableList(split(noCompressionUserAgentsString))
                  : DEFAULT_NO_COMPRESSION_USER_AGENTS;
  
      }
  
      public GzipCompatibilitySelector getSelector(final FilterConfig filterConfig, final HttpServletRequest request)
      {
          final String userAgentHeader = request.getHeader(USER_AGENT_HEADER);
          if (userAgentHeader != null)
          {
              for (String noCompressionUserAgent : noCompressionUserAgents)
              {
                  if (userAgentHeader.contains(noCompressionUserAgent))
                  {
                      return NO_GZIP_SELECTOR;
                  }
              }
          }
          return new MimeTypeBasedSelector(compressableMimeTypes);
      }
  
      private List<String> split(String string)
      {
          return asList(string.split(","));
      }
  }