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.applib.events;
  
  import java.util.Optional;
  import java.util.function.Supplier;
  
  import org.jspecify.annotations.Nullable;
  
  import org.apache.causeway.commons.functional.Try;
  import org.apache.causeway.commons.internal.base._Casts;
  import org.apache.causeway.commons.internal.reflection._Reflect;
  
  import static org.apache.causeway.commons.internal.reflection._Reflect.predicates.paramCount;
  
  /**
   * @since 2.0 {@index}
   */
  public abstract class EventObjectBase<T> {
  
      // -- FACTORIES
  
      /**
       * Optionally returns a new event instance,
       * based on whether the eventType has a public no-arg constructor.
       * <p>
       * Initializes the event's source with given {@code source}.
       */
      public static <T, E extends EventObjectBase<T>> Optional<E> getInstanceWithSource(
              final Class<E> eventType, final @Nullable T source) {
          return getInstanceWithSourceSupplier(eventType, (Supplier<T>) ()->source);
      }
  
      /**
       * Optionally returns a new event instance,
       * based on whether the eventType has a public no-arg constructor.
       * <p>
       * Initializes the event's source lazily, that is using given {@code eventSourceSupplier}.
       */
      public static <T, E extends EventObjectBase<T>> Optional<E> getInstanceWithSourceSupplier(
              final Class<E> eventType, final @Nullable Supplier<T> eventSourceSupplier) {
          return _Reflect.getPublicConstructors(eventType)
              .filter(paramCount(0))
              .getFirst()
              .map(_Reflect::invokeConstructor)
              .flatMap(Try::getValue)
              .map(evnt->{
                  final E event = _Casts.uncheckedCast(evnt);
                  event.sourceSupplier = eventSourceSupplier;
                  return event;
              });
      }
  
      // --
  
      /**
       * Provides the object on which the Event initially occurred.
       */
      protected transient Supplier<T> sourceSupplier = null;
  
      /**
       * Constructs a prototypical Event.
       *
       * @param source object on which the Event initially occurred (nullable)
       */
      protected EventObjectBase(final @Nullable T source) {
          this.sourceSupplier = source!=null
                  ? ()->source
                  : null;
      }
  
      /**
       * Returns the object on which the Event initially occurred.
       */
      public @Nullable T getSource() {
          return sourceSupplier!=null
                  ? sourceSupplier.get()
                  : null;
      }
  
      /**
       * Returns a String representation of this EventObject.
       */
      @Override
      public String toString() {
          return getClass().getName() + "[source=" + getSource() + "]";
      }
  
  }
  