/*
    * ExtractorCSS
    *
    * $Id: ExtractorCSS.java 4653 2006-09-25 18:58:50Z paul_jack $
    *
    * Created on Jan 6, 2004
    *
    * Copyright (C) 2004 Internet Archive.
    *
   * This file is part of the Heritrix web crawler (crawler.archive.org).
   *
   * Heritrix is free software; you can redistribute it and/or modify
   * it under the terms of the GNU Lesser Public License as published by
   * the Free Software Foundation; either version 2.1 of the License, or
   * any later version.
   *
   * Heritrix is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   * GNU Lesser Public License for more details.
   *
   * You should have received a copy of the GNU Lesser Public License
   * along with Heritrix; if not, write to the Free Software
   * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
   */
  
  package org.archive.crawler.extractor;
  
  import java.io.IOException;
  import java.util.logging.Logger;
  import java.util.regex.Matcher;
  
  import org.apache.commons.httpclient.URIException;
  import org.archive.crawler.datamodel.CoreAttributeConstants;
  import org.archive.crawler.datamodel.CrawlURI;
  import org.archive.crawler.framework.CrawlController;
  import org.archive.io.ReplayCharSequence;
  import org.archive.net.UURI;
  import org.archive.util.DevUtils;
  import org.archive.util.TextUtils;
  
  /***
   * This extractor is parsing URIs from CSS type files.
   * The format of a CSS URL value is 'url(' followed by optional white space
   * followed by an optional single quote (') or double quote (") character
   * followed by the URL itself followed by an optional single quote (') or
   * double quote (") character followed by optional white space followed by ')'.
   * Parentheses, commas, white space characters, single quotes (') and double
   * quotes (") appearing in a URL must be escaped with a backslash:
   * '\(', '\)', '\,'. Partial URLs are interpreted relative to the source of
   * the style sheet, not relative to the document. <a href="http://www.w3.org/TR/REC-CSS1#url">
   * Source: www.w3.org</a>
   *
   * @author Igor Ranitovic
   *
   **/
  
  public class ExtractorCSS extends Extractor implements CoreAttributeConstants {
  
      private static final long serialVersionUID = -1540252885329424902L;
  
      private static Logger logger =
          Logger.getLogger("org.archive.crawler.extractor.ExtractorCSS");
  
      private static String ESCAPED_AMP = "&amp";
      // CSS escapes: "Parentheses, commas, whitespace characters, single 
      // quotes (') and double quotes (") appearing in a URL must be 
      // escaped with a backslash"
      static final String CSS_BACKSLASH_ESCAPE = "////([,'\"//(//)//s])";
      
      /***
       *  CSS URL extractor pattern.
       *
       *  This pattern extracts URIs for CSS files
       **/
  //    static final String CSS_URI_EXTRACTOR =
  //        "url[(]//s*([\"\']?)([^//\"//'].*?)//1//s*[)]";
      static final String CSS_URI_EXTRACTOR =    
      "(?i)(?:@import (?:url[(]|)|url[(])//s*([//\"\']?)" + // G1
      "([^//\"\'].{0,"+UURI.MAX_URL_LENGTH+"}?)//1//s*[);]"; // G2
      // GROUPS:
      // (G1) optional ' or "
      // (G2) URI
      
      private long numberOfCURIsHandled = 0;
      private long numberOfLinksExtracted = 0;
  
      /***
       * @param name
       */
      public ExtractorCSS(String name) {
          super(name, "CSS Extractor. Extracts links from Cascading Style" +
                  " Sheets (.css).");
      }
  
      /***
       * @param curi Crawl URI to process.
       */
      public void extract(CrawlURI curi) {
         if (!isHttpTransactionContentToProcess(curi)) {
             return;
         }
         String mimeType = curi.getContentType();
         if (mimeType == null) {
             return;
         }
         if ((mimeType.toLowerCase().indexOf("css") < 0) &&
                 (!curi.toString().toLowerCase().endsWith(".css"))) {
             return;
         }
         this.numberOfCURIsHandled++;
 
         ReplayCharSequence cs = null;
         try {
             cs = curi.getHttpRecorder().getReplayCharSequence();
         } catch (IOException e) {
             logger.severe("Failed getting ReplayCharSequence: " + e.getMessage());
         }
         if (cs == null) {
             logger.warning("Failed getting ReplayCharSequence: " +
                 curi.toString());
             return;
         }
         
         // We have a ReplayCharSequence open.  Wrap all in finally so we
         // for sure close it before we leave.
         try {
             this.numberOfLinksExtracted +=
                 processStyleCode(curi, cs, getController());
             // Set flag to indicate that link extraction is completed.
             curi.linkExtractorFinished();
         } finally {
             if (cs != null) {
                 try {
                     cs.close();
                 } catch (IOException ioe) {
                     logger.warning(TextUtils.exceptionToString(
                         "Failed close of ReplayCharSequence.", ioe));
                 }
             }
         }
     }
 
     public static long processStyleCode(CrawlURI curi, CharSequence cs,
             CrawlController controller) {
         long foundLinks = 0;
         Matcher uris = null;
         String cssUri;
         try {
             uris = TextUtils.getMatcher(CSS_URI_EXTRACTOR, cs);
             while (uris.find()) {
                 cssUri = uris.group(2);
                 // TODO: Escape more HTML Entities.
                 cssUri = TextUtils.replaceAll(ESCAPED_AMP, cssUri, "&");
                 // Remove backslashes when used as escape character in CSS URL
                 cssUri = TextUtils.replaceAll(CSS_BACKSLASH_ESCAPE, cssUri,
                         "$1");
                 foundLinks++;
                 try {
                     curi.createAndAddLinkRelativeToBase(cssUri,Link.EMBED_MISC,
                             Link.EMBED_HOP);
                 } catch (URIException e) {
                     // There may not be a controller (e.g. If we're being run
                     // by the extractor tool).
                     if (controller != null) {
                         controller.logUriError(e, curi.getUURI(), cssUri);
                     } else {
                         logger.info(curi + ", " + cssUri + ": " +
                             e.getMessage());
                     }
                 }
             }
         } catch (StackOverflowError e) {
             DevUtils.warnHandle(e, "ExtractorCSS StackOverflowError");
         } finally {
             TextUtils.recycleMatcher(uris);
         }
         return foundLinks;
     }
 
     public String report() {
         StringBuffer ret = new StringBuffer();
         ret.append("Processor: org.archive.crawler.extractor.ExtractorCSS\n");
         ret.append("  Function:          Link extraction on Cascading Style Sheets (.css)\n");
         ret.append("  CrawlURIs handled: " + numberOfCURIsHandled + "\n");
         ret.append("  Links extracted:   " + numberOfLinksExtracted + "\n\n");
 
         return ret.toString();
     }
 }