/**
    *    Copyright 2011 meltmedia
    *
    *    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.xchain.namespaces.core;
  
  import org.apache.commons.jxpath.JXPathContext;
  
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  import org.xchain.Command;
  import org.xchain.annotations.Attribute;
  import org.xchain.annotations.AttributeType;
  import org.xchain.annotations.Element;
  
  import org.xchain.framework.jxpath.Scope;
  import org.xchain.framework.jxpath.ScopedQNameVariables;
  
  import java.util.List;
  
  import javax.xml.namespace.QName;
  
  /**
   * <p>The <code>variable</code> command will declare and set a variable in the context.
   * The <code>name</code> attribute is the QName of the variable.
   * The <code>select</code>, <code>select-nodes</code>, or <code>select-single-node</code> attribute will be the value of the variable.
   * The <code>scope</code> attribute will determine the scope of the variable.  A 'chain' scope variable will only exist if the current
   * context.  A 'request' scope variable will exist for every context.  A request scope is assumed if no scope attribute is
   * provided.</p>
   *
   * <code class="source">
   * &lt;xchain:variable xmlns:xchain="http://www.xchain.org/core/1.0" name="/some/xpath" select="/some/xpath"/ scope="chain"/&gt;
   * </code>
   *
   * @author Christian Trimble
   * @author Devon Tackett
   * @author Josh Kennedy
   */
  @Element(localName="variable")
  public abstract class VariableCommand
    implements Command
  {
    public static Logger log = LoggerFactory.getLogger(VariableCommand.class);
  
    /**
     * The QName of the variable.
     */
    @Attribute(localName="name", type=AttributeType.QNAME)
    public abstract QName getName( JXPathContext context )
      throws Exception;
    public abstract boolean hasName();
  
    /**
     * The value of the variable. 
     */
    @Attribute(localName="select", type=AttributeType.JXPATH_VALUE)
    public abstract Object getSelect( JXPathContext context )
      throws Exception;
    public abstract boolean hasSelect();
  
    /**
     * The value of the variable. 
     */  
    @Attribute(localName="select-nodes", type=AttributeType.JXPATH_SELECT_NODES)
    public abstract List getSelectNodes( JXPathContext context )
      throws Exception;
    public abstract boolean hasSelectNodes();
  
    /**
     * The value of the variable. 
     */  
    @Attribute(localName="select-single-node", type=AttributeType.JXPATH_SELECT_SINGLE_NODE)
    public abstract Object getSelectSingleNode( JXPathContext context )
      throws Exception;
    public abstract boolean hasSelectSingleNode();
    
    /**
     * The scope of the variable.  Can either be the literal request, execution or chain. 
     */
    @Attribute(localName="scope", type=AttributeType.LITERAL, defaultValue="request")
    public abstract Scope getScope(JXPathContext context)
      throws Exception;
  
    public boolean execute( JXPathContext context )
      throws Exception
    {
      QName variableName = getName(context);
     Object variableValue = null;
 
     if( hasSelect() ) {
       variableValue = getSelect(context);
     }
     else if( hasSelectNodes() ) {
       variableValue = getSelectNodes(context);
     }
     else if( hasSelectSingleNode() ) {
       variableValue = getSelectSingleNode(context);
     }
     else {
       throw new Exception( "Variable '"+variableName+"' must have a select attribute (select, select-nodes, or select-single-node)" );
     }
 
     // get the scope.
     Scope scope = getScope(context);
 
     if( log.isDebugEnabled() ) {
       log.debug("Setting variable name '"+variableName+"' to value '"+variableValue+"' in scope '"+scope+"'.");
     }
 
     // declare the variable.
     ((ScopedQNameVariables)context.getVariables()).declareVariable( variableName, variableValue, scope );
 
     // return false and allow other chains to execute.
     return false;
   }
 }