/*
    * 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.servlets;
  
  import java.util.Collection;
  import java.util.Map;
  
  import org.jdom2.Element;
  import org.mycore.common.content.MCRJDOMContent;
  import org.mycore.datamodel.common.MCRLinkTableManager;
  import org.mycore.datamodel.metadata.MCRMetadataManager;
  import org.mycore.datamodel.metadata.MCRObject;
  import org.mycore.datamodel.metadata.MCRObjectID;
  import org.mycore.frontend.MCRFrontendUtil;
  
  /**
   * This servlet is used to display all parents of an mycore object and their
   * containing derivates. It returns a xml document which will be transformed
   * by derivateLinks-parentList.xsl.
   *  
   * @author Matthias Eichner
   */
  public class MCRDerivateLinkServlet extends MCRServlet {
  
      private static final long serialVersionUID = 1L;
  
      protected static String derivateLinkErrorPage = "error_derivatelink.xml";
  
      @Override
      protected void doGetPost(MCRServletJob job) throws Exception {
          @SuppressWarnings("unchecked")
          Map<String, String[]> pMap = job.getRequest().getParameterMap();
          String webpage = pMap.get("subselect.webpage")[0];
          String mcrId = getSubParameterValueOfBrowserAddressParameter(webpage, "mcrid");
          String parentId = getSubParameterValueOfBrowserAddressParameter(webpage, "parentID");
  
          // create a new root element
          Element rootElement = new Element("derivateLinks-parentList");
  
          MCRObjectID objId = MCRObjectID.getInstance(mcrId);
          if (MCRMetadataManager.exists(objId)) {
              /* mcr object exists in datastore -> add all parent with their
               * derivates to the jdom tree */
              addParentsToElement(rootElement, objId);
          } else if (parentId != null && MCRMetadataManager.exists(MCRObjectID.getInstance(parentId))) {
              /* mcr object doesnt exists in datastore -> use the parent id
               * to create the content */
              Element firstParent = getMyCoReObjectElement(MCRObjectID.getInstance(parentId));
              if (firstParent != null) {
                  rootElement.addContent(firstParent);
              }
              addParentsToElement(rootElement, MCRObjectID.getInstance(parentId));
          }
  
          // check if root element has content -> if not, show an error page
          if (rootElement.getContentSize() == 0) {
              job.getResponse().sendRedirect(
                  job.getResponse().encodeRedirectURL(MCRFrontendUtil.getBaseURL() + derivateLinkErrorPage));
              return;
          }
  
          // set some important attributes to the root element
          rootElement.setAttribute("session", pMap.get("subselect.session")[0]);
          rootElement.setAttribute("varpath", pMap.get("subselect.varpath")[0]);
          rootElement.setAttribute("webpage", webpage);
  
          // transform & display the generated xml document
          getLayoutService().doLayout(job.getRequest(), job.getResponse(), new MCRJDOMContent(rootElement));
      }
  
      /**
       * This method adds all parents and their derivates
       * iterative to the given element.
       * 
       * @param toElement the element where the parents and derivates will be added
       * @param objId the source object id
       */
      private void addParentsToElement(Element toElement, MCRObjectID objId) {
          MCRObjectID pId = objId;
          while ((pId = getParentId(pId)) != null) {
              Element parentElement = getMyCoReObjectElement(pId);
              if (parentElement != null) {
                  toElement.addContent(parentElement);
             }
         }
     }
 
     /**
      * Returns the parent object id of an mcr object.
      * 
      * @param objectId from which id
      * @return the parent id
      */
     private MCRObjectID getParentId(MCRObjectID objectId) {
         MCRObject obj = MCRMetadataManager.retrieveMCRObject(objectId);
         return obj.getStructure().getParentID();
     }
 
     /**
      * Creates a new mcrobject jdom element which contains all
      * derivates with their ids as children.
      * 
      * @param objectId id of the mcr object
      * @return a new jdom element
      */
     private Element getMyCoReObjectElement(MCRObjectID objectId) {
         Collection<String> derivates = MCRLinkTableManager.instance().getDestinationOf(objectId, "derivate");
         if (derivates.size() <= 0) {
             return null;
         }
         Element objElement = new Element("mycoreobject");
         objElement.setAttribute("id", objectId.toString());
         for (String derivate : derivates) {
             Element derElement = new Element("derivate");
             derElement.setAttribute("id", derivate);
             objElement.addContent(derElement);
         }
         return objElement;
     }
 
     /**
      * Returns the value of a parameter which is embedded in a parameter
      * of the browser address.
      * 
      * @param browserAddressParameter the separated parameter from the browser address
      * @param subParameter the sub parameter to search
      * @return the value of the sub parameter
      */
     private String getSubParameterValueOfBrowserAddressParameter(String browserAddressParameter, String subParameter) {
         String value = null;
         int index = browserAddressParameter.indexOf(subParameter);
         if (index != -1) {
             int startIndex = index + subParameter.length() + 1;
             int endIndex = browserAddressParameter.indexOf("&", index + 1);
             if (endIndex == -1) {
                 endIndex = browserAddressParameter.length();
             }
             value = browserAddressParameter.substring(startIndex, endIndex);
         }
         return value;
     }
 }