/*
    * 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 java.time.Instant;
  import java.util.Optional;
  import java.util.Random;
  
  import org.apache.logging.log4j.LogManager;
  import org.apache.logging.log4j.Logger;
  import org.mycore.oai.pmh.Header;
  import org.mycore.oai.pmh.MetadataFormat;
  import org.mycore.oai.set.MCRSet;
  
  /**
   * <p>Base class to query different types of data in the mycore system.
   * Implementations has to implement the query and the earliest time stamp
   * methods. The result of a query is a {@link MCROAIResult}.</p>
   * 
   * <p>Searchers have a unique id and a expiration time which increases
   * every time a query is fired.</p>
   * 
   * @author Matthias Eichner
   */
  public abstract class MCROAISearcher {
  
      protected static final Logger LOGGER = LogManager.getLogger(MCROAISearcher.class);
  
      protected MCROAIIdentify identify;
  
      protected MetadataFormat metadataFormat;
  
      /** The unique ID of this result set */
      protected final String id;
  
      protected long expire;
  
      /**
       * Increase every time a {@link #query(String)} is called
       */
      protected long runningExpirationTimer;
  
      protected int partitionSize;
  
      protected MCROAISetManager setManager;
  
      private MCROAIObjectManager objectManager;
  
      public MCROAISearcher() {
          Random random = new Random(System.currentTimeMillis());
          this.id = Long.toString(random.nextLong(), 36) + Long.toString(System.currentTimeMillis(), 36);
      }
  
      public void init(MCROAIIdentify identify, MetadataFormat format, long expire, int partitionSize,
          MCROAISetManager setManager, MCROAIObjectManager objectManager) {
          this.identify = identify;
          this.metadataFormat = format;
          this.expire = expire;
          this.partitionSize = partitionSize;
          this.setManager = setManager;
          this.objectManager = objectManager;
          updateRunningExpirationTimer();
      }
  
      public abstract Optional<Header> getHeader(String mcrId);
  
      public abstract MCROAIResult query(String cursor);
  
      public abstract MCROAIResult query(MCRSet set, Instant from, Instant until);
  
      /**
       * Returns the earliest created/modified record time stamp. If the earliest time stamp cannot be retrieved an
       * empty optional is returned.
       *
       * @return the earliest created/modified time stamp
       */
      public abstract Optional<Instant> getEarliestTimestamp();
  
      public boolean isExpired() {
          return System.currentTimeMillis() > runningExpirationTimer;
      }
  
      public Instant getExpirationTime() {
         return Instant.ofEpochMilli(runningExpirationTimer);
     }
 
     public MetadataFormat getMetadataFormat() {
         return metadataFormat;
     }
 
     public String getID() {
         return id;
     }
 
     public MCROAISetManager getSetManager() {
         return setManager;
     }
 
     public MCROAIObjectManager getObjectManager() {
         return objectManager;
     }
 
     protected String getConfigPrefix() {
         return this.identify.getConfigPrefix();
     }
 
     /**
      * Updates the running expiration timer.
      */
     protected void updateRunningExpirationTimer() {
         this.runningExpirationTimer = System.currentTimeMillis() + this.expire;
     }
 
     public int getPartitionSize() {
         return partitionSize;
     }
 
 }