EvolverTools.java

/*
 * Copyright (C) 2011 Laurent Caillette
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation, either
 * version 3 of the License, or (at your option) any later version.
 *
 * This program 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 this program.  If not, see <http://www.gnu.org/licenses/>.
 */

package org.novelang.common.tree;

import com.google.common.base.Preconditions;

/**
 * (Hopefully) useful implementations of {@link org.novelang.common.tree.Tree.Evolver}.
 *
 * @author Laurent Caillette
 */
public class EvolverTools {
  
  private EvolverTools() { }

  public static< T > Tree.Evolver< T > firstElementRemover() {
    return new RemoveFirst< T >() ;
  }

  public static< T > Tree.Evolver< T > lastElementRemover() {
    return new RemoveLast< T >() ;
  }

  public static< T > Tree.Evolver< T > elementAtIndexRemover( final int index ) {
    return new RemoveAtIndex< T >( index ) ;
  }

  public static class RemoveFirst< T > implements Tree.Evolver< T > {
    @Override
    public T apply( final int index, final T original, final int listSize ) {
      return index <= 0 ? null : original ;
    }
  }

  public static class RemoveLast< T > implements Tree.Evolver< T > {
    @Override
    public T apply( final int index, final T original, final int listSize ) {
      return index == listSize - 1 ? null : original ;
    }
  }

  public static class RemoveAtIndex< T > implements Tree.Evolver< T > {
    private final int indexForRemoval ;

    public RemoveAtIndex( final int indexForRemoval ) {
      Preconditions.checkArgument( indexForRemoval >= 0 ) ;
      this.indexForRemoval = indexForRemoval ;
    }

    @Override
    public T apply( final int index, final T original, final int listSize ) {
      if( listSize < indexForRemoval + 1 ) {
        throw new IllegalArgumentException(
            "Expected to remove at index " + indexForRemoval + " but list size is " + listSize ) ;
      }
      return index == indexForRemoval ? null : original ;
    }
  }


}