/* Copyright (2007) Schibsted Søk AS
    * This file is part of SESAT.
    *
    *   SESAT is free software: you can redistribute it and/or modify
    *   it under the terms of the GNU Affero General Public License as published by
    *   the Free Software Foundation, either version 3 of the License, or
    *   (at your option) any later version.
    *
    *   SESAT 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 Affero General Public License for more details.
   *
   *   You should have received a copy of the GNU Affero General Public License
   *   along with SESAT.  If not, see <http://www.gnu.org/licenses/>.
   */
  package no.sesat.search.view.velocity;
  
  import java.io.IOException;
  import java.net.URL;
  import java.net.MalformedURLException;
  import java.io.InputStream;
  import java.util.regex.Matcher;
  import no.sesat.search.http.HTTPClient;
  import no.sesat.search.site.config.UrlResourceLoader;
  import no.sesat.search.site.Site;
  import org.apache.log4j.Logger;
  import org.apache.velocity.runtime.resource.Resource;
  import org.apache.velocity.runtime.resource.loader.ResourceLoader;
  import org.apache.velocity.exception.ResourceNotFoundException;
  import org.apache.commons.collections.ExtendedProperties;
  
  /** XXX This source file needs to be published to the internet as it is open-source code.
   *
   *
   * This is a simple URL-based loader.
   * ORIGINAL FROM http://svn.apache.org/repos/asf/jakarta/velocity/engine/trunk/whiteboard/geir/URLResourceLoader.java
   *
   * original version Id: URLResourceLoader.java,v 1.3 2004/03/19 17:13:40 dlr Exp
   *
   *
   *
   * MODIFIED TO SUIT SCHIBSTEDSØK's NEEDS.
   * There was a choice here to implement all the URL handling stuff from scratch or to plug into the existing
   * functionality found in no.schibstedsøk.front.search.configuration.loader
   * Since this class is hidden between the velocity API it made more sense to go from scratch to best
   * meet velocity's requirements...
   *
   *
   * @version $Id: URLResourceLoader.java,v 1.3 2004/03/19 17:13:40 dlr Exp $
   */
  public class URLResourceLoader extends ResourceLoader {
  
      public interface Context{
          boolean doesUrlExist(final URL url);
          URL getURL(final String resource, final Site site);
      }
  
      // Constants -----------------------------------------------------
  
      private static final Logger LOG = Logger.getLogger(URLResourceLoader.class);
  
      private static final String ERR_RESOURCE_NOT_FOUND = "Cannot find resource ";
      private static final String DEBUG_LOOKING_FOR = "Looking for ";
      private static final String DEBUG_EXISTS = "Positive HEAD on ";
      private static final String DEBUG_FULL_URL_IS = "Real URL is ";
      private static final String DEBUG_HOST_HEADER_IS = "URL's host-header is ";
      private static final String DEBUG_DOESNT_EXIST = "Using fallback URL";
  
  
      // Attributes ----------------------------------------------------
  
      private Site site;
  
  
      // Static --------------------------------------------------------
  
      private static Context context = new DefaultContext();
  
      // Allows the tests to switch the Velocity ResourceLoader over to a file based one.
      static void setContext(final Context context){
          URLResourceLoader.context = context;
      }
  
      // Constructors --------------------------------------------------
  
  
      // Public --------------------------------------------------------
  
      /** {@inheritDoc}
       */
      public void init(final ExtendedProperties configuration) {
          // the engine's properties actually come from the RuntimeServices *not* the ExtendedProperties
          site = (Site)rsvc.getProperty(Site.NAME_KEY);
      }
  
      /**
       * Get an InputStream so that the Runtime can build a
       * template with it.
      *
      * @param url  url of template to fetch bytestream of
      * @return InputStream containing the template
      * @throws ResourceNotFoundException if template not found
      *         in the file template path.
      */
      public /*synchronized*/ InputStream getResourceStream(final String url) throws ResourceNotFoundException{
 
         LOG.trace("start getResourceStream( " + url + " )");
         try{
             synchronized( url.intern() ){
                 return getStream(findUrl(url, site));
             }
 
         }catch( IOException e ){
             LOG.debug( ERR_RESOURCE_NOT_FOUND + url);
             throw new ResourceNotFoundException( ERR_RESOURCE_NOT_FOUND + url );
         }
     }
 
     /** {@inheritDoc}
      */
     public boolean isSourceModified(Resource resource){
 
         final boolean result =  getLastModified(resource) > resource.getLastModified();
         LOG.debug("isSourceModified( "+resource.getName()+" ): "+result);
         return result;
     }
 
     /** {@inheritDoc}
      */
     public long getLastModified(Resource resource){
         try{
             final URL url = findUrl(resource.getName(), site);
             final HTTPClient client = HTTPClient.instance(url, "localhost");
 
             return client.getLastModified("");
         }catch( ResourceNotFoundException e ){
             LOG.error( ERR_RESOURCE_NOT_FOUND + resource.getName() );
         }catch( IOException e ){
             LOG.error( ERR_RESOURCE_NOT_FOUND + resource.getName() );
         }
         return 0;
     }
 
 
     // Package protected ---------------------------------------------
 
     // Protected -----------------------------------------------------
 
     // Private -------------------------------------------------------
 
     private static URL findUrl(final String url, final Site currentSite) throws ResourceNotFoundException{
 
         try{
             LOG.trace(DEBUG_LOOKING_FOR + url );
             return findUrlImpl(url, currentSite);
 
         }catch( IOException e ){
             LOG.error( ERR_RESOURCE_NOT_FOUND + url, e );
             throw new ResourceNotFoundException( ERR_RESOURCE_NOT_FOUND + url );
         }
     }
 
     private static URL findUrlImpl(final String url, final Site currentSite)
             throws IOException, ResourceNotFoundException {
 
         final URL u = context.getURL(url, currentSite);
 
         if (context.doesUrlExist(u)) {
             return u;
         } else {
             final Site parent = currentSite.getParent();
 
             if (null == parent) {
                 throw new ResourceNotFoundException( ERR_RESOURCE_NOT_FOUND + url );
             }
 
             if (LOG.isTraceEnabled()) {
                 LOG.trace(DEBUG_DOESNT_EXIST + parent.getName());
             }
 
             // Recursively look for the resource in ancestor sites.
             return findUrlImpl(getFallbackURL(url, currentSite, parent), parent);
         }
     }
 
     private static String getFallbackURL(final String url, final Site currSite, final Site ancestorSite) {
 
         final String oldUrl = currSite.getName() + currSite.getConfigContext();
         final String newUrl = ancestorSite.getName() + ancestorSite.getConfigContext();
 
         return url.replaceFirst(Matcher.quoteReplacement(oldUrl), newUrl);
     }
 
 
     private static InputStream getStream(final URL url) throws IOException{
 
         final HTTPClient client = HTTPClient.instance(url, "localhost");
         try{
             return client.getBufferedStream("");
         }catch(IOException ioe){
             throw client.interceptIOException(ioe);
         }
     }
 
 
     // Inner classes -------------------------------------------------
 
     private static final class DefaultContext implements Context{
         public boolean doesUrlExist(final URL url) {
             return UrlResourceLoader.doesUrlExist(url);
         }
 
         public URL getURL(final String resource, final Site site) {
             try {
                 return new URL(resource);
             } catch (MalformedURLException e) {
                 throw new ResourceNotFoundException(e);
             }
         }
     }
 }