/*
    *  Licensed to the Apache Software Foundation (ASF) under one
    *  or more contributor license agreements.  See the NOTICE file
    *  distributed with this work for additional information
    *  regarding copyright ownership.  The ASF licenses this file
    *  to you under the Apache License, Version 2.0 (the
    *  "License"); you may not use this file except in compliance
    *  with the License.  You may obtain a copy of the License at
    *  
   *    http://www.apache.org/licenses/LICENSE-2.0
   *  
   *  Unless required by applicable law or agreed to in writing,
   *  software distributed under the License is distributed on an
   *  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
   *  KIND, either express or implied.  See the License for the
   *  specific language governing permissions and limitations
   *  under the License. 
   *  
   */
  package org.apache.directory.server.xdbm.search.cursor;
  
  
  import java.io.IOException;
  import java.util.ArrayList;
  import java.util.Collections;
  import java.util.List;
  
  import org.apache.directory.api.ldap.model.constants.Loggers;
  import org.apache.directory.api.ldap.model.cursor.Cursor;
  import org.apache.directory.api.ldap.model.cursor.CursorException;
  import org.apache.directory.api.ldap.model.cursor.InvalidCursorPositionException;
  import org.apache.directory.api.ldap.model.exception.LdapException;
  import org.apache.directory.api.ldap.model.filter.ExprNode;
  import org.apache.directory.server.core.api.partition.PartitionTxn;
  import org.apache.directory.server.i18n.I18n;
  import org.apache.directory.server.xdbm.AbstractIndexCursor;
  import org.apache.directory.server.xdbm.IndexEntry;
  import org.apache.directory.server.xdbm.search.Evaluator;
  import org.apache.directory.server.xdbm.search.impl.ScanCountComparator;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  
  /**
   * A Cursor returning candidates satisfying a logical conjunction expression.
   *
   * @author <a href="mailto:dev@directory.apache.org">Apache Directory Project</a>
   */
  public class AndCursor<V> extends AbstractIndexCursor<V>
  {
      /** A dedicated log for cursors */
      private static final Logger LOG_CURSOR = LoggerFactory.getLogger( Loggers.CURSOR_LOG.getName() );
  
      /** Speedup for logs */
      private static final boolean IS_DEBUG = LOG_CURSOR.isDebugEnabled();
  
      /** The message for unsupported operations */
      private static final String UNSUPPORTED_MSG = I18n.err( I18n.ERR_707 );
  
      /** */
      private final Cursor<IndexEntry<V, String>> wrapped;
  
      /** The evaluators used for the members of the And filter */
      private final List<Evaluator<? extends ExprNode>> evaluators;
  
  
      /**
       * Creates an instance of a AndCursor. It wraps an index cursor and the list
       * of evaluators associated with all the elements connected by the And.
       * 
       * @param partitionTxn The transaction to use
       * @param wrapped The encapsulated IndexCursor
       * @param evaluators The list of evaluators associated with the elements
       */
      public AndCursor( PartitionTxn partitionTxn, Cursor<IndexEntry<V, String>> wrapped,
          List<Evaluator<? extends ExprNode>> evaluators )
      {
          if ( IS_DEBUG )
          {
              LOG_CURSOR.debug( "Creating AndCursor {}", this );
          }
  
          this.wrapped = wrapped;
          this.evaluators = optimize( evaluators );
          this.partitionTxn = partitionTxn;
      }
  
  
      /**
       * {@inheritDoc}
       */
      protected String getUnsupportedMessage()
      {
          return UNSUPPORTED_MSG;
      }
  
  
      /**
       * {@inheritDoc}
      */
     public void beforeFirst() throws LdapException, CursorException
     {
         checkNotClosed();
         wrapped.beforeFirst();
         setAvailable( false );
     }
 
 
     /**
      * {@inheritDoc}
      */
     public void afterLast() throws LdapException, CursorException
     {
         checkNotClosed();
         wrapped.afterLast();
         setAvailable( false );
     }
 
 
     /**
      * {@inheritDoc}
      */
     public boolean first() throws LdapException, CursorException
     {
         beforeFirst();
 
         return next();
     }
 
 
     /**
      * {@inheritDoc}
      */
     public boolean last() throws LdapException, CursorException
     {
         afterLast();
 
         return previous();
     }
 
 
     /**
      * {@inheritDoc}
      */
     public boolean previous( PartitionTxn partitionTxn ) throws LdapException, CursorException
     {
         while ( wrapped.previous() )
         {
             checkNotClosed();
 
             IndexEntry<V, String> candidate = wrapped.get();
 
             if ( matches( partitionTxn, candidate ) )
             {
                 return setAvailable( true );
             }
         }
 
         return setAvailable( false );
     }
 
 
     /**
      * {@inheritDoc}
      */
     public boolean next( PartitionTxn partitionTxn ) throws LdapException, CursorException
     {
         while ( wrapped.next() )
         {
             checkNotClosed();
             IndexEntry<V, String> candidate = wrapped.get();
 
             if ( matches( partitionTxn, candidate ) )
             {
                 return setAvailable( true );
             }
         }
 
         return setAvailable( false );
     }
 
 
     /**
      * {@inheritDoc}
      */
     public IndexEntry<V, String> get() throws CursorException
     {
         checkNotClosed();
 
         if ( available() )
         {
             return wrapped.get();
         }
 
         throw new InvalidCursorPositionException( I18n.err( I18n.ERR_708 ) );
     }
 
 
     /**
      * {@inheritDoc}
      */
     @Override
     public void close() throws IOException
     {
         if ( IS_DEBUG )
         {
             LOG_CURSOR.debug( "Closing AndCursor {}", this );
         }
 
         super.close();
         wrapped.close();
     }
 
 
     /**
      * {@inheritDoc}
      */
     @Override
     public void close( Exception cause ) throws IOException
     {
         if ( IS_DEBUG )
         {
             LOG_CURSOR.debug( "Closing AndCursor {}", this );
         }
 
         super.close( cause );
         wrapped.close( cause );
     }
 
 
     /**
      * Takes a set of Evaluators and copies then sorts them in a new list with
      * increasing scan counts on their expression nodes.  This is done to have
      * the Evaluators with the least scan count which have the highest
      * probability of rejecting a candidate first.  That will increase the
      * chance of shorting the checks on evaluators early so extra lookups and
      * comparisons are avoided.
      *
      * @param unoptimized the unoptimized list of Evaluators
      * @return optimized Evaluator list with increasing scan count ordering
      */
     private List<Evaluator<? extends ExprNode>> optimize(
         List<Evaluator<? extends ExprNode>> unoptimized )
     {
         List<Evaluator<? extends ExprNode>> optimized = new ArrayList<>(
             unoptimized.size() );
         optimized.addAll( unoptimized );
 
         Collections.sort( optimized, new ScanCountComparator() );
 
         return optimized;
     }
 
 
     /**
      * Checks if the entry is a valid candidate by using the evaluators.
      */
     private boolean matches( PartitionTxn partitionTxn, IndexEntry<V, String> indexEntry ) throws LdapException
     {
         for ( Evaluator<?> evaluator : evaluators )
         {
             if ( !evaluator.evaluate( partitionTxn, indexEntry ) )
             {
                 return false;
             }
         }
 
         return true;
     }
 
 
     /**
      * Dumps the evaluators
      */
     private String dumpEvaluators( String tabs )
     {
         StringBuilder sb = new StringBuilder();
 
         for ( Evaluator<? extends ExprNode> evaluator : evaluators )
         {
             sb.append( evaluator.toString( tabs + "  >>" ) );
         }
 
         return sb.toString();
     }
 
 
     /**
      * @see Object#toString()
      */
     @Override
     public String toString( String tabs )
     {
         StringBuilder sb = new StringBuilder();
 
         sb.append( tabs ).append( "AndCursor (" );
 
         if ( available() )
         {
             sb.append( "available) :\n" );
         }
         else
         {
             sb.append( "absent) :\n" );
         }
 
         if ( ( evaluators != null ) && !evaluators.isEmpty() )
         {
             sb.append( dumpEvaluators( tabs ) );
         }
 
         sb.append( wrapped.toString( tabs + "  " ) );
 
         return sb.toString();
     }
 
 
     /**
      * @see Object#toString()
      */
     public String toString()
     {
         return toString( "" );
     }
 }