/*
    * $Id: Expression.java 788032 2009-06-24 14:08:32Z apetrelli $
    *
    * 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.tiles;
  
  import static org.apache.tiles.CompareUtil.*;
  
  /**
   * It is an expression, along with the expression language (e.g. EL, MVEL, OGNL)
   * it is expressed with.
   *
   * @version $Rev: 788032 $ $Date: 2009-06-25 00:08:32 +1000 (Thu, 25 Jun 2009) $
   * @since 2.2.0
   */
  public class Expression {
  
      /**
       * The expression itself.
       */
      private String expression;
  
      /**
       * The language of the expression.
       */
      private String language;
  
      /**
       * Constructor.
       *
       * @param expression The expression itself.
       * @param language The language of the expression.
       * @since 2.2.0
       */
      public Expression(String expression, String language) {
          this.expression = expression;
          this.language = language;
      }
  
      /**
       * Constructor, using the default (i.e. <code>null</code>) language.
       *
       * @param expression The expression itself.
       * @since 2.2.0
       */
      public Expression(String expression) {
          this(expression, null);
      }
  
      /**
       * Copy constructor.
       *
       * @param toCopy The expression to copy.
       * @since 2.2.0
       */
      public Expression(Expression toCopy) {
          this.expression = toCopy.expression;
          this.language = toCopy.language;
      }
  
      /**
       * Creates an Expression object from a string in the form
       * <code>LANGUAGE:EXPRESSION</code>.
       *
       * @param describedExpression The expression in the form
       * <code>LANGUAGE:EXPRESSION</code>. The LANGUAGE part should be expressed
       * only with letters and numbers.
       * @return The created object, or <code>null</code> if the expression is null.
       * @since 2.2.0
       */
      public static Expression createExpressionFromDescribedExpression(String describedExpression) {
          if (describedExpression != null) {
              String language = null;
              String expression = describedExpression;
              if (describedExpression.matches("[a-zA-Z0-9]+:.+")) {
                  language = describedExpression.substring(0, describedExpression.indexOf(':'));
                  expression = describedExpression.substring(describedExpression.indexOf(':') + 1);
              }
              return new Expression(expression, language);
          }
  
          return null;
     }
 
     /**
      * Creates an Expression object from the expression and its language.
      *
      * @param expression The expression itself.
      * @param language The language of the expression.
      * @return The created object, or <code>null</code> if the expression is null.
      * @since 2.2.0
      */
     public static Expression createExpression(String expression, String language) {
         if (expression != null) {
             return new Expression(expression, language);
         }
 
         return null;
     }
 
     /**
      * Returns the expression string.
      *
      * @return The expression itself.
      * @since 2.2.0
      */
     public String getExpression() {
         return expression;
     }
 
     /**
      * Returns the language in which the expression is expressed.
      *
      * @return The expression language.
      * @since 2.2.0
      */
     public String getLanguage() {
         return language;
     }
 
     /** {@inheritDoc} */
     @Override
     public boolean equals(Object obj) {
         Expression exp = (Expression) obj;
         return nullSafeEquals(expression, exp.expression)
                 && nullSafeEquals(language, exp.language);
     }
 
     /** {@inheritDoc} */
     @Override
     public int hashCode() {
         return nullSafeHashCode(expression) + nullSafeHashCode(language);
     }
 
     /** {@inheritDoc} */
     @Override
     public String toString() {
         return (language == null ? "DEFAULT" : language) + ":" + expression;
     }
 }