package org.trails.descriptor.annotation;

 import ognl.Ognl;

 import ognl.OgnlException;

 import org.apache.commons.lang.Validate;

 import org.apache.commons.logging.Log;

 import org.apache.commons.logging.LogFactory;

 import org.trails.descriptor.IDescriptorExtension;

 import java.util.Map;

 public abstract class ExpressionExtension implements IDescriptorExtension

 {

         private static Log LOG = LogFactory.getLog(PossibleValuesDescriptorExtension.class);

         /**

          * Ognl expression that evaluated gets a list of possible values to use with

          * the current property, cannot be null.

          */

         private String expression;

         /**

          * Map of variables to put into the available namespace (scope) for OGNL expressions.

          */

         private Map context;

         /**

          * Creates a {@link ExpressionExtension}.

          *

          * @param theExpression Ognl expression that evaluated gets a list of possible

          *                      values to use with the current property, cannot be null.

          */

         public ExpressionExtension(final String theExpression)

         {

                 super();

                 Validate.notNull(theExpression, "The expression cannot be null");

                 expression = theExpression;

         }

         /**

          * Creates a {@link ExpressionExtension}.

          *

          * @param theExpression Ognl expression that evaluated gets a list of possible

          *                      values to use with the current property, cannot be null.

          * @param context

          */

         public ExpressionExtension(final String theExpression, Map context)

         {

                 this(theExpression);

                 this.context = context;

         }

         /**

          * Gets the Ognl expression that evaluated gets a list of possible values to

          * use with the current property.

          *

          * @return a String, never null.

          */

         /**

          * Method used to initialize the value of the filtering property using the

          * value of the filtered one (for example, initialize the country based on the

          * value of the state property.

          *

          * @param model the model used by the edit page, cannot be null.

          * @return

          * @throws ognl.OgnlException

          */

         public Object evaluateExpresion(final Object model) throws OgnlException

         {

                 Validate.notNull(model, "The model cannot be null");

                 try

                 {

                         if (context != null)

                         {

                                 return Ognl.getValue(expression, context, model);

                         } else

                         {

                                 return Ognl.getValue(expression, model);

                         }

                 } catch (OgnlException e)

                 {

                         LOG.warn("Exception thrown evaluationg " + expression, e);

                         throw e;

                 }

         }

 }