/*
    *  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.evaluator;
  
  
  import java.util.ArrayList;
  import java.util.Collections;
  import java.util.List;
  
  import org.apache.directory.api.ldap.model.entry.Entry;
  import org.apache.directory.api.ldap.model.exception.LdapException;
  import org.apache.directory.api.ldap.model.filter.AndNode;
  import org.apache.directory.api.ldap.model.filter.ExprNode;
  import org.apache.directory.server.core.api.partition.PartitionTxn;
  import org.apache.directory.server.xdbm.IndexEntry;
  import org.apache.directory.server.xdbm.search.Evaluator;
  import org.apache.directory.server.xdbm.search.impl.ScanCountComparator;
  
  
  /**
   * An Evaluator for logical conjunction (AND) expressions.
   *
   * @author <a href="mailto:dev@directory.apache.org">Apache Directory Project</a>
   */
  public class AndEvaluator implements Evaluator<AndNode>
  {
      /** The list of evaluators associated with each of the children */
      private final List<Evaluator<? extends ExprNode>> evaluators;
  
      /** The AndNode */
      private final AndNode node;
  
  
      /**
       * Creates an instance of AndEvaluator
       * @param node The And Node
       * @param evaluators The list of evaluators for all the contaned nodes
       */
      public AndEvaluator( AndNode node, List<Evaluator<? extends ExprNode>> evaluators )
      {
          this.node = node;
          this.evaluators = optimize( evaluators );
      }
  
  
      /**
       * 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 )
      {
          switch ( unoptimized.size() )
          {
              case 0 :
              case 1 :
                  return unoptimized;
                  
              case 2 :
                  Object count1 = unoptimized.get( 0 ).getExpression().get( "count" );
                  Object count2 = unoptimized.get( 1 ).getExpression().get( "count" );
                  
                  if ( count1 == null )
                  {
                      if ( count2 != null )
                      {
                          unoptimized.add( unoptimized.remove( 0 ) );
                      }
                  }
                  else
                  {
                      if ( ( count2 != null ) && ( ( Long ) count1 > ( Long ) count2 ) )
                      {
                          unoptimized.add( unoptimized.remove( 0 ) );
                      }
                 }
                 
                 return unoptimized;
 
             default :
                 List<Evaluator<? extends ExprNode>> optimized = new ArrayList<>(
                     unoptimized.size() );
                 optimized.addAll( unoptimized );
 
                 Collections.sort( optimized, new ScanCountComparator() );
 
                 return optimized;
         }
         
         /* Potential speed up, for when we do'nt care about the evaluation itself.
     private List<Evaluator<? extends ExprNode>> optimize(
         List<Evaluator<? extends ExprNode>> evaluators )
     {
         long minCount = Long.MAX_VALUE;
         int pos = 0;
         int minPos = 0;
         
         for ( Evaluator<? extends ExprNode> evaluator : evaluators )
         {
             long count = ( Long ) evaluator.getExpression().get( "count" );
             
             if ( count < minCount )
             {
                 minCount = count;
                 minPos = pos;
             }
             
             pos++;
         }
         
         if ( minPos > 0 )
         {
             Evaluator<? extends ExprNode> minEvaluator = evaluators.remove( minPos );
             evaluators.set( 0,  minEvaluator );
             
         }
 
         return evaluators;
     }
 
          */
     }
 
 
     /**
      * {@inheritDoc}
      */
     public boolean evaluate( Entry entry ) throws LdapException
     {
         for ( Evaluator<?> evaluator : evaluators )
         {
             if ( !evaluator.evaluate( entry ) )
             {
                 return false;
             }
         }
 
         return true;
     }
 
 
     /**
      * {@inheritDoc}
      */
     public boolean evaluate( PartitionTxn partitionTxn, IndexEntry<?, String> indexEntry ) throws LdapException
     {
         for ( Evaluator<?> evaluator : evaluators )
         {
             if ( !evaluator.evaluate( partitionTxn, indexEntry ) )
             {
                 return false;
             }
         }
 
         return true;
     }
 
 
     /**
      * {@inheritDoc}
      */
     public AndNode getExpression()
     {
         return node;
     }
 
 
     /**
      * 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()
      */
     public String toString( String tabs )
     {
         StringBuilder sb = new StringBuilder();
 
         sb.append( tabs ).append( "AndEvaluator : " ).append( node ).append( "\n" );
 
         if ( ( evaluators != null ) && !evaluators.isEmpty() )
         {
             sb.append( dumpEvaluators( tabs + "  " ) ).append( "\n" );
         }
 
         return sb.toString();
     }
 
 
     /**
      * @see Object#toString()
      */
     public String toString()
     {
         return toString( "" );
     }
 }