content: /*
   *  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.causeway.viewer.wicket.model.hints;
  
  import org.apache.wicket.event.IEvent;
  
  /**
   * Broadcast down by <tt>PageAbstract</tt> to all child components
   */
  public class CausewayEnvelopeEvent extends CausewayEventAbstract {
  
      private final CausewayEventLetterAbstract letter;
  
      public CausewayEnvelopeEvent(CausewayEventLetterAbstract ev) {
          super(ev.getTarget());
          this.letter = ev;
      }
  
      public CausewayEventLetterAbstract getLetter() {
          return letter;
      }
  
      /**
       * Opens the event, checks the event is an {@link org.apache.causeway.viewer.wicket.model.hints.CausewayEnvelopeEvent envelope} (event),
       * fetches the {@link org.apache.causeway.viewer.wicket.model.hints.CausewayEventLetterAbstract letter} (event) inside, and
       * returns if the letter is of the required type.
       *
       * <p>
       * Otherwise returns <tt>null</tt>.
       * </p>
       */
      public static <T> T openLetter(final IEvent<?> event, Class<T> letterEventClass) {
          if(!(event.getPayload() instanceof CausewayEnvelopeEvent)) {
              return null;
          }
          final CausewayEnvelopeEvent ev = (CausewayEnvelopeEvent) event.getPayload();
          final CausewayEventLetterAbstract letter = ev.getLetter();
          if(letter == null) {
              return null;
          }
          if(!letterEventClass.isAssignableFrom(letter.getClass())) {
              return null;
          }
          return letterEventClass.cast(letter);
      }
  
  }
  