package org.codehaus.plexus.interpolation;

/*
 * Copyright 2007 The Codehaus Foundation.
 *
 * 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.
 */

import org.codehaus.plexus.interpolation.reflection.ReflectionValueExtractor;

Wraps an object, providing reflective access to the object graph of which the
supplied object is the root. Expressions like 'child.name' will translate into
'rootObject.getChild().getName()' for non-boolean properties, and
'rootObject.getChild().isName()' for boolean properties.
/**
 * Wraps an object, providing reflective access to the object graph of which the
 * supplied object is the root. Expressions like 'child.name' will translate into
 * 'rootObject.getChild().getName()' for non-boolean properties, and
 * 'rootObject.getChild().isName()' for boolean properties.
 */
public class ObjectBasedValueSource
    extends AbstractValueSource
{

    private final Object root;

    
Construct a new value source, using the supplied object as the root from
which to start, and using expressions split at the dot ('.') to navigate
the object graph beneath this root.
Params:
root – the root of the graph./**
     * Construct a new value source, using the supplied object as the root from
     * which to start, and using expressions split at the dot ('.') to navigate
     * the object graph beneath this root.
     * @param root the root of the graph.
     */
    public ObjectBasedValueSource( Object root )
    {
        super( true );
        this.root = root;
    }

    
Split the expression into parts, tokenized on the dot ('.') character. Then,
starting at the root object contained in this value source, apply each part
to the object graph below this root, using either 'getXXX()' or 'isXXX()'
accessor types to resolve the value for each successive expression part.
Finally, return the result of the last expression part's resolution.
NOTE: The object-graph nagivation actually takes place via the ReflectionValueExtractor class.
/**
     * <p>Split the expression into parts, tokenized on the dot ('.') character. Then,
     * starting at the root object contained in this value source, apply each part
     * to the object graph below this root, using either 'getXXX()' or 'isXXX()'
     * accessor types to resolve the value for each successive expression part.
     * Finally, return the result of the last expression part's resolution.</p>
     * 
     * <p><b>NOTE:</b> The object-graph nagivation actually takes place via the
     * {@link ReflectionValueExtractor} class.</p>
     */
    public Object getValue( String expression )
    {
        if ( expression == null || expression.trim().length() < 1 )
        {
            return null;
        }
        
        try
        {
            return ReflectionValueExtractor.evaluate( expression, root, false );
        }
        catch ( Exception e )
        {
            addFeedback( "Failed to extract \'" + expression + "\' from: " + root, e );
        }

        return null;
    }

}