/*
    * 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.api.ldap.model.cursor;
  
  
  import java.util.Comparator;
  
  import org.apache.directory.api.i18n.I18n;
  import org.apache.directory.api.ldap.model.constants.Loggers;
  import org.apache.directory.api.ldap.model.exception.LdapException;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  
  /**
   * A Cursor over a single element.
   *
   * @author <a href="mailto:dev@directory.apache.org">Apache Directory Project</a>
   * @param <E> The type of element on which this cursor will iterate
   */
  public class SingletonCursor<E> extends AbstractCursor<E>
  {
      /** 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();
  
      /** A flag to tell if the cursor is set before the first element */
      private boolean beforeFirst = true;
  
      /** A flag to tell if the cursor is set after the last element */
      private boolean afterLast;
  
      /** A flag to tell if the cursor is on the element */
      private boolean onSingleton;
  
      /** The comparator used for this cursor. */
      private final Comparator<E> comparator;
  
      /** The unique element stored in the cursor */
      private final E singleton;
  
  
      /**
       * Creates a new instance of SingletonCursor.
       *
       * @param singleton The unique element to store into this cursor
       */
      public SingletonCursor( E singleton )
      {
          this( singleton, null );
      }
  
  
      /**
       * Creates a new instance of SingletonCursor, with its associated
       * comparator
       *
       * @param singleton The unique element to store into this cursor
       * @param comparator The associated comparator
       */
      public SingletonCursor( E singleton, Comparator<E> comparator )
      {
          if ( IS_DEBUG )
          {
              LOG_CURSOR.debug( "Creating SingletonCursor {}", this );
          }
  
          this.singleton = singleton;
          this.comparator = comparator;
      }
  
  
      /**
       * {@inheritDoc}
       */
      public boolean available()
      {
          return onSingleton;
      }
  
  
     /**
      * {@inheritDoc}
      */
     public void before( E element ) throws LdapException, CursorException
     {
         checkNotClosed( "before()" );
 
         if ( comparator == null )
         {
             throw new UnsupportedOperationException( I18n.err( I18n.ERR_02010_NO_COMPARATOR_CANT_MOVE_BEFORE ) );
         }
 
         int comparison = comparator.compare( singleton, element );
 
         if ( comparison < 0 )
         {
             first();
         }
         else
         {
             beforeFirst();
         }
     }
 
 
     /**
      * {@inheritDoc}
      */
     public void after( E element ) throws LdapException, CursorException
     {
         checkNotClosed( "after()" );
 
         if ( comparator == null )
         {
             throw new UnsupportedOperationException( I18n.err( I18n.ERR_02011_NO_COMPARATOR_CANT_MOVE_AFTER ) );
         }
 
         int comparison = comparator.compare( singleton, element );
 
         if ( comparison > 0 )
         {
             first();
         }
         else
         {
             afterLast();
         }
     }
 
 
     /**
      * {@inheritDoc}
      */
     public void beforeFirst() throws LdapException, CursorException
     {
         checkNotClosed( "beforeFirst" );
         beforeFirst = true;
         afterLast = false;
         onSingleton = false;
     }
 
 
     /**
      * {@inheritDoc}
      */
     public void afterLast() throws LdapException, CursorException
     {
         checkNotClosed( "afterLast" );
         beforeFirst = false;
         afterLast = true;
         onSingleton = false;
     }
 
 
     /**
      * {@inheritDoc}
      */
     public boolean first() throws LdapException, CursorException
     {
         checkNotClosed( "first" );
         beforeFirst = false;
         onSingleton = true;
         afterLast = false;
 
         return true;
     }
 
 
     /**
      * {@inheritDoc}
      */
     public boolean last() throws LdapException, CursorException
     {
         checkNotClosed( "last" );
         beforeFirst = false;
         onSingleton = true;
         afterLast = false;
 
         return true;
     }
 
 
     /**
      * {@inheritDoc}
      */
     @Override
     public boolean isFirst()
     {
         return onSingleton;
     }
 
 
     /**
      * {@inheritDoc}
      */
     @Override
     public boolean isLast()
     {
         return onSingleton;
     }
 
 
     /**
      * {@inheritDoc}
      */
     @Override
     public boolean isAfterLast()
     {
         return afterLast;
     }
 
 
     /**
      * {@inheritDoc}
      */
     @Override
     public boolean isBeforeFirst()
     {
         return beforeFirst;
     }
 
 
     /**
      * {@inheritDoc}
      */
     public boolean previous() throws LdapException, CursorException
     {
         checkNotClosed( "previous" );
 
         if ( beforeFirst )
         {
             return false;
         }
 
         if ( afterLast )
         {
             beforeFirst = false;
             onSingleton = true;
             afterLast = false;
 
             return true;
         }
 
         // must be on the singleton
         beforeFirst = true;
         onSingleton = false;
         afterLast = false;
 
         return false;
     }
 
 
     /**
      * {@inheritDoc}
      */
     public boolean next() throws LdapException, CursorException
     {
         checkNotClosed( "next" );
 
         if ( beforeFirst )
         {
             beforeFirst = false;
             onSingleton = true;
             afterLast = false;
 
             return true;
         }
 
         if ( afterLast )
         {
             return false;
         }
 
         // must be on the singleton
         beforeFirst = false;
         onSingleton = false;
         afterLast = true;
 
         return false;
     }
 
 
     /**
      * {@inheritDoc}
      */
     public E get() throws CursorException
     {
         checkNotClosed( "get" );
 
         if ( onSingleton )
         {
             return singleton;
         }
 
         if ( beforeFirst )
         {
             throw new InvalidCursorPositionException( I18n.err( I18n.ERR_02012_CANNOT_ACCESS_IF_BEFORE_FIRST ) );
         }
         else
         {
             throw new InvalidCursorPositionException( I18n.err( I18n.ERR_02013_CANNOT_ACCESS_IF_AFTER_LAST ) );
         }
     }
 
 
     /**
      * {@inheritDoc}
      */
     @Override
     public void close()
     {
         if ( IS_DEBUG )
         {
             LOG_CURSOR.debug( "Closing SingletonCursor {}", this );
         }
 
         super.close();
     }
 
 
     /**
      * {@inheritDoc}
      */
     @Override
     public void close( Exception cause )
     {
         if ( IS_DEBUG )
         {
             LOG_CURSOR.debug( "Closing SingletonCursor {}", this );
         }
 
         super.close( cause );
     }
 }