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JSF components and utilities that can be used with any JSF implementation. This library is based on the JSF1.1 version of Tomahawk, but with minor source code and build changes to take advantage of JSF2.1 features. A JSF2.1 implementation is required to use this version of the Tomahawk library.
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/*
 * 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.myfaces.custom.aliasbean;

import javax.el.ValueExpression;
import javax.faces.component.UIComponent;
import javax.faces.context.FacesContext;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

/**
 * A helper bean used by both AliasBean and AliasBeansScope components.
 * 
 * An Alias instance represents a single mapping from a "temporary" bean name
 * to the real bean that temporary name should reference. When this alias
 * is "activated" the temporary name is registered and when the alias is
 * "deactivated" the temporary name is removed.
 *
 * @author Sylvain Vieujot (latest modification by $Author: skitching $)
 * @version $Revision: 673833 $ $Date: 2008-07-03 16:58:05 -0500 (jue, 03 jul 2008) $
 */

class Alias {
    static final Log log = LogFactory.getLog(Alias.class);
    
    private transient UIComponent _aliasComponent;
    private String _aliasBeanExpression;
    private String _valueExpression;
    private transient boolean _active = false;
    
    private transient Object evaluatedExpression = null;

    Alias(AliasBean aliasComponent){
        this._aliasComponent = aliasComponent;
    }

    /**
     * Define the temporary/transient name that will exist while this alias
     * is "active" (in scope). This is usually a constant string.
     */
    void setAliasBeanExpression(String aliasBeanExpression){
        this._aliasBeanExpression = aliasBeanExpression;
    }
    
    /**
     * Define the object that will be referenced by the temporary/transient
     * name while it exists.
     * 
     * This can be a constant, but is more usually an EL expression. The value is
     * recalculated each time this alias is "activated".
     */
    void setValueExpression(String valueExpression){
        this._valueExpression = valueExpression;
    }
    
    String getValueExpression(){
        return _valueExpression;
    }
    
    boolean isActive(){
        return _active;
    }
    
    String[] saveState(){
        return new String[]{_aliasBeanExpression, _valueExpression};
    }
    
    void restoreState(Object state){
        String[] values = (String[]) state;
        _aliasBeanExpression = values[0];
        _valueExpression = values[1];
    }
    
    private void computeEvaluatedExpression(FacesContext facesContext){
        if( evaluatedExpression != null )
            return;
        
        ValueExpression valueVB = null;
        if (_valueExpression == null) {
            valueVB = _aliasComponent.getValueExpression("value");
            _valueExpression = valueVB.getExpressionString();
        }

        if( valueVB == null ){
            if( _valueExpression.startsWith("#{") ){
                valueVB = facesContext.getApplication().getExpressionFactory()
                    .createValueExpression(facesContext.getELContext(),                            
                            _valueExpression,
                            Object.class);
                evaluatedExpression = valueVB.getValue(facesContext.getELContext());
            }else{
                evaluatedExpression = _valueExpression;
            }
        }else{
            evaluatedExpression = valueVB.getValue(facesContext.getELContext());
        }
    }

    /**
     * Activate this alias (ie create the temporary name).
     */
    void make(FacesContext facesContext){
        if( _active )
            return;

        ValueExpression aliasVB;
        if (_aliasBeanExpression == null) {
            aliasVB = _aliasComponent.getValueExpression("alias");
            if( aliasVB == null )
                return;
            _aliasBeanExpression = aliasVB.getExpressionString();
            if( _aliasBeanExpression == null )
                return;
        } else {
            aliasVB = facesContext.getApplication().getExpressionFactory().
                createValueExpression(facesContext.getELContext(),_aliasBeanExpression,Object.class);
        }

        computeEvaluatedExpression( facesContext );
        
        aliasVB.setValue(facesContext.getELContext(), evaluatedExpression);
        _active = true;

        log.debug("makeAlias: " + _valueExpression + " = " + _aliasBeanExpression);
    }
    
    /**
     * Deactivate this alias (ie remove the temporary name).
     */
    void remove(FacesContext facesContext){
        _active = false;
        if( evaluatedExpression == null )
            return;
        
        evaluatedExpression = null;

        log.debug("removeAlias: " + _valueExpression + " != " + _aliasBeanExpression);
        ValueExpression aliasVB = _aliasComponent.getValueExpression("alias");
        if( aliasVB != null )
            aliasVB.setValue(facesContext.getELContext(), null);
    }
}