//=============================================================================
// Copyright 2006-2010 Daniel W. Dyer
//
// Licensed 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.uncommons.watchmaker.examples.geneticprogramming;

import java.util.Random;
import org.uncommons.maths.random.Probability;

/**
 * Convenient base class for {@link Node}s that have no sub-trees.
 * @author Daniel Dyer
 */
abstract class LeafNode implements Node
{
    /**
     * The arity of a non-function node is always zero.
     * @return 0
     */
    public int getArity()
    {
        return 0;
    }

    
    /**
     * Leaf nodes always have a depth of 1 since they have no child nodes.
     * @return 1 
     */
    public int getDepth()
    {
        return 1;
    }


    /**
     * Leaf nodes always have a width of 1 since they have no child nodes.
     * @return 1
     */
    public int getWidth()
    {
        return 1;
    }

    
    /**
     * {@inheritDoc}
     */
    public int countNodes()
    {
        return 1;
    }


    public Node getNode(int index)
    {
        if (index != 0)
        {
            throw new IndexOutOfBoundsException("Invalid node index: " + index);
        }
        return this;
    }


    /**
     * {@inheritDoc}
     */
    public Node getChild(int index)
    {
        throw new IndexOutOfBoundsException("Leaf nodes have no children.");
    }


    public Node replaceNode(int index, Node newNode)
    {
        if (index != 0)
        {
            throw new IndexOutOfBoundsException("Invalid node index: " + index);
        }
        return newNode;        
    }

    
    /**
     * {@inheritDoc}
     */
    public Node mutate(Random rng, Probability mutationProbability, TreeFactory treeFactory)
    {
        if (mutationProbability.nextEvent(rng))
        {
            return treeFactory.generateRandomCandidate(rng);
        }
        else
        {
            // Node is unchanged.
            return this;
        }
    }


    @Override
    public String toString()
    {
        return print();
    }


    /**
     * Returns this node (leaf nodes cannot be simplified).
     * @return This node, unmodified.
     */
    public Node simplify()
    {
        return this;
    }
}