/*
    *    Copyright 2009-2022 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
    *
    *       https://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.ibatis.scripting.xmltags;
  
  import java.util.Map;
  import java.util.concurrent.ConcurrentHashMap;
  
  import ognl.Ognl;
  import ognl.OgnlException;
  
  import org.apache.ibatis.builder.BuilderException;
  
  /**
   * Caches OGNL parsed expressions.
   *
   * @author Eduardo Macarron
   *
   * @see <a href='https://github.com/mybatis/old-google-code-issues/issues/342'>Issue 342</a>
   */
  public final class OgnlCache {
  
    private static final OgnlMemberAccess MEMBER_ACCESS = new OgnlMemberAccess();
    private static final OgnlClassResolver CLASS_RESOLVER = new OgnlClassResolver();
    private static final Map<String, Object> expressionCache = new ConcurrentHashMap<>();
  
    private OgnlCache() {
      // Prevent Instantiation of Static Class
    }
  
    public static Object getValue(String expression, Object root) {
      try {
        Map context = Ognl.createDefaultContext(root, MEMBER_ACCESS, CLASS_RESOLVER, null);
        return Ognl.getValue(parseExpression(expression), context, root);
      } catch (OgnlException e) {
        throw new BuilderException("Error evaluating expression '" + expression + "'. Cause: " + e, e);
      }
    }
  
    private static Object parseExpression(String expression) throws OgnlException {
      Object node = expressionCache.get(expression);
      if (node == null) {
        node = Ognl.parseExpression(expression);
        expressionCache.put(expression, node);
      }
      return node;
    }
  
  }