/*
    * This file is part of ***  M y C o R e  ***
    * See http://www.mycore.de/ for details.
    *
    * MyCoRe is free software: you can redistribute it and/or modify
    * it under the terms of the GNU General Public License as published by
    * the Free Software Foundation, either version 3 of the License, or
    * (at your option) any later version.
    *
   * MyCoRe 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 General Public License for more details.
   *
   * You should have received a copy of the GNU General Public License
   * along with MyCoRe.  If not, see <http://www.gnu.org/licenses/>.
   */
  
  package org.mycore.frontend.export;
  
  import org.apache.logging.log4j.LogManager;
  import org.apache.logging.log4j.Logger;
  import org.mycore.common.content.MCRContent;
  import org.mycore.common.content.transformer.MCRContentTransformer;
  import org.mycore.frontend.basket.MCRBasket;
  import org.mycore.frontend.basket.MCRBasketManager;
  import org.mycore.frontend.servlets.MCRServlet;
  import org.mycore.frontend.servlets.MCRServletJob;
  
  import jakarta.servlet.http.HttpServletRequest;
  
  /**
   * Provides functionality to export content. 
   * The content to export can be selected by specifying one or more 
   * URIs to read from, or by giving the ID of a basket to export. 
   * The selected content is collected as MCRExportCollection thats
   * root element name can be specified. 
   * The content is then transformed using an MCRContentTransformer instance
   * and forwarded to the requesting client.
   * 
   * Request Parameters:
   *   uri=... 
   *     can be repeated to include content from one or more URIs to read XML from
   *   basket=...
   *     the ID of a basket to read XML from  
   *   root=...
   *     optional, name of the root element that wraps the selected content
   *   ns=...
   *     optional, URI of the namespace of the root element
   *   transformer=...
   *     the ID of the transformer to use to export the selected content.
   *          
   * @see MCRExportCollection
   * @see MCRContentTransformer
   * 
   * @author Frank L\u00FCtzenkirchen
   */
  public class MCRExportServlet extends MCRServlet {
  
      private static final Logger LOGGER = LogManager.getLogger(MCRExportServlet.class);
  
      /** URIs beginning with these prefixes are forbidden for security reasons */
      private static final String[] FORBIDDEN_URIS = { "file", "webapp", "resource" };
  
      @Override
      public void doGetPost(MCRServletJob job) throws Exception {
          MCRExportCollection collection = createCollection(job.getRequest());
          fillCollection(job.getRequest(), collection);
          MCRContent content2export = collection.getContent();
  
          String filename = getProperty(job.getRequest(), "filename");
          if (filename == null) {
              filename = "export-" + System.currentTimeMillis();
          }
          job.getResponse().setHeader("Content-Disposition", "inline;filename=\"" + filename + "\"");
  
          String transformerID = job.getRequest().getParameter("transformer");
          job.getRequest().setAttribute("XSL.Transformer", transformerID);
          getLayoutService().doLayout(job.getRequest(), job.getResponse(), content2export);
      }
  
      /**
       * Fills the collection with the XML data requested by URIs or basket ID.
       */
      private void fillCollection(HttpServletRequest req, MCRExportCollection collection) throws Exception {
          String basketID = req.getParameter("basket");
          if (basketID != null) {
              MCRBasket basket = MCRBasketManager.getOrCreateBasketInSession(basketID);
              collection.add(basket);
              LOGGER.info("exporting basket {} via {}", basketID, req.getParameter("transformer"));
          }
  
          if (req.getParameter("uri") != null) {
              for (String uri : req.getParameterValues("uri")) {
                  if (isAllowed(uri)) {
                      collection.add(uri);
                      LOGGER.info("exporting {} via {}", uri, req.getParameter("transformer"));
                  }
              }
         }
     }
 
     private boolean isAllowed(String uri) {
         for (String prefix : FORBIDDEN_URIS) {
             if (uri.startsWith(prefix)) {
                 LOGGER.warn("URI {} is not allowed for security reasons", uri);
                 return false;
             }
         }
         return true;
     }
 
     /**
      * Creates a new, empty MCRExportCollection, optionally with the requested root element name and namespace.
      */
     private MCRExportCollection createCollection(HttpServletRequest req) {
         MCRExportCollection collection = new MCRExportCollection();
         String root = req.getParameter("root");
         String ns = req.getParameter("ns");
         if (!((root == null) || root.isEmpty())) {
             collection.setRootElement(root, ns);
         }
         return collection;
     }
 }