/*
    * 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.oai;
  
  import org.apache.logging.log4j.LogManager;
  import org.apache.logging.log4j.Logger;
  import org.jdom2.Element;
  import org.jdom2.output.Format;
  import org.jdom2.output.XMLOutputter;
  import org.mycore.common.config.MCRConfiguration2;
  import org.mycore.common.xml.MCRURIResolver;
  import org.mycore.datamodel.common.MCRXMLMetadataManager;
  import org.mycore.datamodel.metadata.MCRMetadataManager;
  import org.mycore.datamodel.metadata.MCRObjectID;
  import org.mycore.datamodel.metadata.history.MCRMetadataHistoryManager;
  import org.mycore.oai.pmh.Header;
  import org.mycore.oai.pmh.Header.Status;
  import org.mycore.oai.pmh.MetadataFormat;
  import org.mycore.oai.pmh.OAIConstants;
  import org.mycore.oai.pmh.Record;
  import org.mycore.oai.pmh.SimpleMetadata;
  
  /**
   * Provides an interface to the MyCoRe object engine.
   * 
   * @author Matthias Eichner
   */
  public class MCROAIObjectManager {
  
      protected static final Logger LOGGER = LogManager.getLogger(MCROAIObjectManager.class);
  
      protected MCROAIIdentify identify;
  
      protected String recordUriPattern;
  
      /**
       * Initialize the object manager. Its important to call this method before you
       * can retrieve records or headers!
       * 
       * @param identify oai repository identifier
       */
      public void init(MCROAIIdentify identify) {
          this.identify = identify;
          String configPrefix = this.identify.getConfigPrefix();
          this.recordUriPattern = MCRConfiguration2.getStringOrThrow(configPrefix + "Adapter.RecordURIPattern");
      }
  
      /**
       * Converts a oai identifier to a mycore id.
       * 
       * @param oaiId the oai identifier
       * @return the mycore identifier
       */
      public String getMyCoReId(String oaiId) {
          return oaiId.substring(oaiId.lastIndexOf(':') + 1);
      }
  
      /**
       * Converts a mycore id to a oai id.
       * 
       * @param mcrId mycore identifier
       */
      public String getOAIId(String mcrId) {
          return getOAIIDPrefix() + mcrId;
      }
  
      public Record getRecord(Header header, MetadataFormat format) {
          Element recordElement;
          if (header.isDeleted()) {
              return new Record(header);
          }
          try {
              recordElement = getJDOMRecord(getMyCoReId(header.getId()), format);
          } catch (Exception exc) {
              LOGGER.error("unable to get record {} ({})", header.getId(), format.getPrefix(), exc);
              return null;
          }
          Record record = new Record(header);
          if (recordElement.getNamespace().equals(OAIConstants.NS_OAI)) {
              Element metadataElement = recordElement.getChild("metadata", OAIConstants.NS_OAI);
              if (metadataElement != null && !metadataElement.getChildren().isEmpty()) {
                  Element metadataChild = metadataElement.getChildren().get(0);
                  record.setMetadata(new SimpleMetadata(metadataChild.detach()));
              }
             Element aboutElement = recordElement.getChild("about", OAIConstants.NS_OAI);
             if (aboutElement != null) {
                 for (Element aboutChild : aboutElement.getChildren()) {
                     record.getAboutList().add(aboutChild.detach());
                 }
             }
         } else {
             //handle as metadata
             record.setMetadata(new SimpleMetadata(recordElement));
         }
         return record;
     }
 
     /**
      * Returns a deleted record without metadata by given MyCoRe identifier or null, if the
      * record is not deleted.
      * 
      * @param mcrId id of the deleted record
      * @return deleted record
      */
     public Record getDeletedRecord(String mcrId) {
         try {
             // building the query
             return MCRMetadataHistoryManager.getLastDeletedDate(MCRObjectID.getInstance(mcrId))
                 .map(deletedDate -> new Record(
                     new Header(getOAIId(mcrId), deletedDate, Status.deleted)))
                 .orElse(null);
         } catch (Exception ex) {
             LOGGER.warn("Error while retrieving deleted record {}", mcrId, ex);
         }
         return null;
     }
 
     protected Element getJDOMRecord(String mcrId, MetadataFormat format) {
         String uri = formatURI(this.recordUriPattern, mcrId, format.getPrefix());
         return getURI(uri);
     }
 
     protected Element getURI(String uri) {
         Element e = MCRURIResolver.instance().resolve(uri).detach();
         if (LOGGER.isDebugEnabled()) {
             LOGGER.debug("get {}", uri);
             XMLOutputter out = new XMLOutputter(Format.getPrettyFormat());
             LOGGER.debug(out.outputString(e));
         }
         return e;
     }
 
     protected String formatURI(String uri, String id, String metadataPrefix) {
         MCRObjectID mcrID = MCRObjectID.isValid(id) ? MCRObjectID.getInstance(id) : null;
         boolean exists;
         String objectType;
         if (mcrID != null) {
             exists = MCRMetadataManager.exists(mcrID);
             objectType = mcrID.getTypeId();
         } else {
             //TODO remove this code path
             LOGGER.warn("MCRFileSystemNodes are not supported anymore! id: " + id);
             exists = false;
             objectType = "data_file";
         }
         return uri.replace("{id}", id).replace("{format}", metadataPrefix).replace("{objectType}", objectType).replace(
             ":{flag}", !exists ? ":deletedMcrObject" : "");
     }
 
     /**
      * Checks if a mycore object with the given oai identifier exists.
      * 
      * @param oaiId
      *            e.g. oai:www.mycore.de:Document_document_00000003
      * @return true if exists, otherwise false
      */
     protected boolean exists(String oaiId) {
         String mcrId = oaiId.substring(getOAIIDPrefix().length());
         try {
             MCRObjectID mcrObjId = MCRObjectID.getInstance(mcrId);
             return MCRXMLMetadataManager.instance().exists(mcrObjId);
         } catch (Exception ex) {
             return false;
         }
     }
 
     private String getOAIIDPrefix() {
         return "oai:" + this.identify.getIdentifierDescription().getRepositoryIdentifier() + ":";
     }
 
 }