content: package act.event;
  
  /*-
   * #%L
   * ACT Framework
   * %%
   * Copyright (C) 2014 - 2017 ActFramework
   * %%
   * 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.
   * #L%
   */
  
  import org.osgl.$;
  
  import java.util.EventObject;
  import java.util.IdentityHashMap;
  import java.util.Map;
  
  /**
   * An {@code ActEvent} is a generic version of {@link EventObject}
   * @param <T> the generic type (the sub class type) of the event source
   */
  public class ActEvent<T> extends EventObject {
  
      protected static final Object SOURCE_PLACEHODER = new Object();
  
      private final long ts;
  
      private Class<? extends ActEvent<T>> eventType;
  
      /**
       * This constructor allows sub class to construct a Self source event, e.g.
       * the source can be the event instance itself.
       *
       * **Note** if sub class needs to use this constructor the {@link #getSource()} ()}
       * method must be overwritten
       */
      protected ActEvent() {
          super(SOURCE_PLACEHODER);
          ts = $.ms();
          eventType = $.cast(referType(getClass()));
      }
  
      /**
       * Construct an `ActEvent` with source instance
       * @param source The object on which the Event initially occurred.
       *               or any payload the developer want to attach to the event
       */
      public ActEvent(T source) {
          super(source);
          ts = $.ms();
          eventType = $.cast(referType(getClass()));
      }
  
      /**
       * Unlike the {@link Object#getClass()} method, which always return
       * the java class of the current instance. This {@code eventType()}
       * method allow a certain implementation of the class terminate the
       * return value of the method. For example, suppose you have a event
       * class {@code MyEvent} and you might have some anonymous class
       * of {@code MyEvent}. If you implement the {@code eventType()} of
       * {@code MyEvent} class as follows:
       * <pre>
       *     public class&lt;MyEvent&gt; eventType() {
       *         return MyEvent.class;
       *     }
       * </pre>
       * Then all the anonymous sub class will return the {@code MyEvent.class}
       * instead of their own class.
       * <p>This allows the ActFramework properly handle the event class registration</p>
       * @return the type of the event
       */
      public Class<? extends ActEvent<T>> eventType() {
          return eventType;
      }
  
      public final T source() {
          return $.cast(getSource());
      }
  
      /**
       * Return the timestamp of the event
       * @return the timestamp
       * @see System#currentTimeMillis()
       */
      public final long timestamp() {
          return ts;
      }
  
      public static Class<? extends ActEvent<?>>  typeOf(ActEvent<?> event) {
          return event.eventType();
      }
  
      public static Class<? extends EventObject> typeOf(EventObject eventObject) {
          if (eventObject instanceof ActEvent) {
              return ((ActEvent<?>) eventObject).eventType();
          } else {
              return referType(eventObject.getClass());
          }
      }
  
      private static Map<Class, Class> referTypes = new IdentityHashMap<>();
  
      private static Class<? extends EventObject> referType(Class<? extends EventObject> eventType) {
          Class<? extends EventObject> referType = referTypes.get(eventType);
          if (null == referType) {
              referType = eventType.isAnonymousClass() ? referType((Class<? extends EventObject>) eventType.getSuperclass()) : eventType;
              referTypes.put(eventType, referType);
          }
          return referType;
      }
  
  }
  