/*
    * 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.
   * <p>
   * 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.
       * <p>
       * 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);
     }
 }