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.bifromq.plugin.eventcollector;
  
  import static java.lang.ThreadLocal.withInitial;
  
  import java.lang.reflect.Modifier;
  import java.util.HashSet;
  import java.util.IdentityHashMap;
  import java.util.Set;
  import lombok.SneakyThrows;
  import org.reflections.Reflections;
  
  public final class ThreadLocalEventPool {
      private static final Set<Class<? extends Event<?>>> EVENT_TYPES = new HashSet<>();
  
      private static final ThreadLocal<IdentityHashMap<Class<? extends Event<?>>, Event<?>>> THREAD_LOCAL_EVENTS;
  
      static {
          Reflections reflections = new Reflections(Event.class.getPackageName());
          for (Class<?> eventClass : reflections.getSubTypesOf(Event.class)) {
              if (!Modifier.isAbstract(eventClass.getModifiers())) {
                  EVENT_TYPES.add((Class<? extends Event<?>>) eventClass);
              }
          }
          THREAD_LOCAL_EVENTS = withInitial(ThreadLocalEventPool::init);
      }
  
      private static IdentityHashMap<Class<? extends Event<?>>, Event<?>> init() {
          IdentityHashMap<Class<? extends Event<?>>, Event<?>> events = new IdentityHashMap<>(EVENT_TYPES.size());
          EVENT_TYPES.forEach(t -> add(t, events));
          return events;
      }
  
      @SneakyThrows
      private static void add(Class<? extends Event<?>> eventClass,
                              IdentityHashMap<Class<? extends Event<?>>, Event<?>> eventMap) {
          Event<?> event = eventClass.getConstructor().newInstance();
          eventMap.put(eventClass, event);
      }
  
      public static <T extends Event<T>> T getLocal(Class<T> eventClass) {
          return (T) THREAD_LOCAL_EVENTS.get().get(eventClass);
      }
  }
  