/*
    *  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 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.schema.PrepareString;
  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.Index;
  import org.apache.directory.server.xdbm.IndexEntry;
  import org.apache.directory.server.xdbm.IndexNotFoundException;
  import org.apache.directory.server.xdbm.Store;
  import org.apache.directory.server.xdbm.search.evaluator.SubstringEvaluator;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  
  /**
   * A Cursor traversing candidates matching a Substring assertion expression.
   *
   * @author <a href="mailto:dev@directory.apache.org">Apache Directory Project</a>
   */
  public class SubstringCursor extends AbstractIndexCursor<String>
  {
      /** 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();
  
      private static final String UNSUPPORTED_MSG = I18n.err( I18n.ERR_725 );
      private final boolean hasIndex;
      private final Cursor<IndexEntry<String, String>> wrapped;
      private final SubstringEvaluator evaluator;
      private final IndexEntry<String, String> indexEntry = new IndexEntry<>();
  
  
      /**
       * Creates a new instance of an SubstringCursor
       * 
       * @param partitionTxn The transaction to use
       * @param store The store
       * @param substringEvaluator The SubstringEvaluator
       * @throws LdapException If the creation failed
       * @throws IndexNotFoundException If the index was not found
       */
      @SuppressWarnings("unchecked")
      public SubstringCursor( PartitionTxn partitionTxn, Store store, final SubstringEvaluator substringEvaluator )
          throws LdapException, IndexNotFoundException
      {
          if ( IS_DEBUG )
          {
              LOG_CURSOR.debug( "Creating SubstringCursor {}", this );
          }
  
          evaluator = substringEvaluator;
          this.partitionTxn = partitionTxn;
          hasIndex = store.hasIndexOn( evaluator.getExpression().getAttributeType() );
  
          if ( hasIndex )
          {
              wrapped = ( ( Index<String, String> ) store.getIndex( evaluator.getExpression().getAttributeType() ) )
                  .forwardCursor( partitionTxn );
          }
          else
          {
              /*
               * There is no index on the attribute here.  We have no choice but
               * to perform a full table scan but need to leverage an index for the
               * wrapped Cursor.  We know that all entries are listed under
               * the ndn index and so this will enumerate over all entries.  The
               * substringEvaluator is used in an assertion to constrain the
               * result set to only those entries matching the pattern.  The
               * substringEvaluator handles all the details of normalization and
              * knows to use it, when it itself detects the lack of an index on
              * the node's attribute.
              */
             wrapped = new AllEntriesCursor( partitionTxn, store );
         }
     }
 
 
     /**
      * {@inheritDoc}
      */
     protected String getUnsupportedMessage()
     {
         return UNSUPPORTED_MSG;
     }
 
 
     /**
      * {@inheritDoc}
      */
     public void beforeFirst() throws LdapException, CursorException
     {
         checkNotClosed();
         
         if ( evaluator.getExpression().getInitial() != null && hasIndex )
         {
             IndexEntry<String, String> beforeFirstIndexEntry = new IndexEntry<>();
             String normalizedKey = evaluator.getExpression().getAttributeType().getEquality().getNormalizer().normalize( 
                 evaluator.getExpression().getInitial(), PrepareString.AssertionType.SUBSTRING_INITIAL );
             beforeFirstIndexEntry.setKey( normalizedKey );
             wrapped.before( beforeFirstIndexEntry );
         }
         else
         {
             wrapped.beforeFirst();
         }
 
         clear();
     }
 
 
     private void clear()
     {
         setAvailable( false );
         indexEntry.setEntry( null );
         indexEntry.setId( null );
         indexEntry.setKey( null );
     }
 
 
     /**
      * {@inheritDoc}
      */
     public void afterLast() throws LdapException, CursorException
     {
         checkNotClosed();
 
         // to keep the cursor always *after* the last matched tuple
         // This fixes an issue if the last matched tuple is also the last record present in the
         // index. In this case the wrapped cursor is positioning on the last tuple instead of positioning after that
         wrapped.afterLast();
         clear();
     }
 
 
     /**
      * {@inheritDoc}
      */
     public boolean first() throws LdapException, CursorException
     {
         beforeFirst();
         return next();
     }
 
 
     private boolean evaluateCandidate( PartitionTxn partitionTxn, IndexEntry<String, String> indexEntry ) throws LdapException
     {
         if ( hasIndex )
         {
             String key = indexEntry.getKey();
             return evaluator.getPattern().matcher( key ).matches();
         }
         else
         {
             return evaluator.evaluate( partitionTxn, indexEntry );
         }
     }
 
 
     /**
      * {@inheritDoc}
      */
     public boolean last() throws LdapException, CursorException
     {
         afterLast();
 
         return previous();
     }
 
 
     /**
      * {@inheritDoc}
      */
     @Override
     public boolean previous() throws LdapException, CursorException
     {
         while ( wrapped.previous() )
         {
             checkNotClosed();
             IndexEntry<String, String> entry = wrapped.get();
 
             if ( evaluateCandidate( partitionTxn, entry ) )
             {
                 setAvailable( true );
                 this.indexEntry.setId( entry.getId() );
                 this.indexEntry.setKey( entry.getKey() );
                 this.indexEntry.setEntry( entry.getEntry() );
                 return true;
             }
         }
 
         clear();
         return false;
     }
 
 
     /**
      * {@inheritDoc}
      */
     @Override
     public boolean next() throws LdapException, CursorException
     {
         while ( wrapped.next() )
         {
             checkNotClosed();
             IndexEntry<String, String> entry = wrapped.get();
 
             if ( evaluateCandidate( partitionTxn, entry ) )
             {
                 setAvailable( true );
                 this.indexEntry.setId( entry.getId() );
                 this.indexEntry.setKey( entry.getKey() );
                 this.indexEntry.setEntry( entry.getEntry() );
 
                 return true;
             }
         }
 
         clear();
         return false;
     }
 
 
     /**
      * {@inheritDoc}
      */
     public IndexEntry<String, String> get() throws CursorException
     {
         checkNotClosed();
 
         if ( available() )
         {
             return indexEntry;
         }
 
         throw new InvalidCursorPositionException( I18n.err( I18n.ERR_708 ) );
     }
 
 
     /**
      * {@inheritDoc}
      */
     @Override
     public void close() throws IOException
     {
         if ( IS_DEBUG )
         {
             LOG_CURSOR.debug( "Closing SubstringCursor {}", this );
         }
 
         super.close();
         wrapped.close();
         clear();
     }
 
 
     /**
      * {@inheritDoc}
      */
     @Override
     public void close( Exception cause ) throws IOException
     {
         if ( IS_DEBUG )
         {
             LOG_CURSOR.debug( "Closing SubstringCursor {}", this );
         }
 
         super.close( cause );
         wrapped.close( cause );
         clear();
     }
 
 
     /**
      * @see Object#toString()
      */
     @Override
     public String toString( String tabs )
     {
         StringBuilder sb = new StringBuilder();
 
         sb.append( tabs ).append( "SubstringCursor (" );
 
         if ( available() )
         {
             sb.append( "available)" );
         }
         else
         {
             sb.append( "absent)" );
         }
 
         sb.append( "#index<" ).append( hasIndex ).append( "> :\n" );
 
         sb.append( tabs + "  >>" ).append( evaluator ).append( '\n' );
 
         sb.append( wrapped.toString( tabs + "    " ) );
 
         return sb.toString();
     }
 
 
     /**
      * @see Object#toString()
      */
     public String toString()
     {
         return toString( "" );
     }
 }