/*

  * $Id: ComposeStackUtil.java 1305937 2012-03-27 18:15:15Z nlebas $

  *

  * 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.template;

 import java.util.Deque;

 import java.util.LinkedList;

 import java.util.Map;

 import org.apache.tiles.request.Request;

 /**

  * Utilities to work with compose stacks.

  *

  * @version $Rev: 1305937 $ $Date: 2012-03-28 05:15:15 +1100 (Wed, 28 Mar 2012) $

  * @since 3.0.0

  */

 public final class ComposeStackUtil {

     /**

      * The name of the attribute that holds the compose stack.

      */

     public static final String COMPOSE_STACK_ATTRIBUTE_NAME = "org.apache.tiles.template.COMPOSE_STACK";

     /**

      * Private constructor to avoid instantiation.

      */

     private ComposeStackUtil() {

     }

     /**

      * Finds the first ancestor in the stack, that is assignable to the given class.

      *

      * @param composeStack The compose stack to evaluate.

      * @param clazz The class to check.

      * @return The first ancestor that is assignable to the class, or null if not found.

      * @since 3.0.0

      */

     public static Object findAncestorWithClass(Deque<Object> composeStack, Class<?> clazz) {

         for (Object obj : composeStack) {

             if (clazz.isAssignableFrom(obj.getClass())) {

                 return obj;

             }

         }

         return null;

     }

     /**

      * Returns the current compose stack, or creates a new one if not present.

      *

      * @param request The request.

      * @return The compose stack.

      * @since 3.0.0

      */

     @SuppressWarnings("unchecked")

     public static Deque<Object> getComposeStack(Request request) {

         Map<String, Object> requestScope = request.getContext("request");

         Deque<Object> composeStack = (Deque<Object>) requestScope

                 .get(COMPOSE_STACK_ATTRIBUTE_NAME);

         if (composeStack == null) {

             composeStack = new LinkedList<Object>();

             requestScope.put(ComposeStackUtil.COMPOSE_STACK_ATTRIBUTE_NAME, composeStack);

         }

         return composeStack;

     }

 }