/*
    * Copyright 2004-2009 the original author or authors.
    *
    * 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.springmodules.validation.util.fel.parser;
  
  import ognl.Ognl;
  import ognl.OgnlException;
  import org.springmodules.validation.util.fel.FelEvaluationException;
  import org.springmodules.validation.util.fel.FelParseException;
  import org.springmodules.validation.util.fel.Function;
  import org.springmodules.validation.util.fel.FunctionExpressionParser;
  
  /**
   * A {@link FunctionExpressionParser} implementation that knows how to parse OGNL expressions and
   * return the appropriate function.
   *
   * @author Uri Boness
   */
  public class OgnlFunctionExpressionParser implements FunctionExpressionParser {
  
      public Function parse(String expression) {
          return new OgnlFunction(expression);
      }
  
      /**
       * A function that is associated with an OGNL expression and evaluates this expression on
       * the given object.
       */
      protected class OgnlFunction implements Function {
  
          private String expressionAsString;
  
          private Object ognlExpression;
  
          public OgnlFunction(String expressionAsString) {
              this.expressionAsString = expressionAsString;
              try {
                  this.ognlExpression = Ognl.parseExpression(expressionAsString);
              } catch (OgnlException oe) {
                  throw new FelParseException("Could not parse OGNL expression '" + expressionAsString + "'", oe);
              }
          }
  
          public Object evaluate(Object argument) {
              try {
                  return Ognl.getValue(ognlExpression, argument);
              } catch (OgnlException oe) {
                  throw new FelEvaluationException("Could not evaluate OGNL expression '" + expressionAsString +
                      "' on argument '" + String.valueOf(argument), oe);
              }
          }
      }
  
  }