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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 javax.faces.el.ValueBinding;

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 (Thu, 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);
    }
}