/*
 * Copyright 2016-2020 the original author or authors.
 *
 * 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
 *
 *      https://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.springframework.data.domain;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.List;

import org.springframework.data.annotation.Transient;
import org.springframework.util.Assert;

Convenience base class for aggregate roots that exposes a registerEvent(Object) to capture domain events and expose them via domainEvents(). The implementation is using the general event publication mechanism implied by DomainEvents and AfterDomainEventPublication. If in doubt or need to customize anything here, rather build your own base class and use the annotations directly. 
Author:
Oliver Gierke, Christoph Strobl
Since:
1.13/**
 * Convenience base class for aggregate roots that exposes a {@link #registerEvent(Object)} to capture domain events and
 * expose them via {@link #domainEvents()}. The implementation is using the general event publication mechanism implied
 * by {@link DomainEvents} and {@link AfterDomainEventPublication}. If in doubt or need to customize anything here,
 * rather build your own base class and use the annotations directly.
 *
 * @author Oliver Gierke
 * @author Christoph Strobl
 * @since 1.13
 */
public class AbstractAggregateRoot<A extends AbstractAggregateRoot<A>> {

	private transient final @Transient List<Object> domainEvents = new ArrayList<>();

	
Registers the given event object for publication on a call to a Spring Data repository's save methods.
Params:
event – must not be null.
See Also:
andEvent(Object)
Returns:
the event that has been added./**
	 * Registers the given event object for publication on a call to a Spring Data repository's save methods.
	 *
	 * @param event must not be {@literal null}.
	 * @return the event that has been added.
	 * @see #andEvent(Object)
	 */
	protected <T> T registerEvent(T event) {

		Assert.notNull(event, "Domain event must not be null!");

		this.domainEvents.add(event);
		return event;
	}

	
Clears all domain events currently held. Usually invoked by the infrastructure in place in Spring Data
repositories.
/**
	 * Clears all domain events currently held. Usually invoked by the infrastructure in place in Spring Data
	 * repositories.
	 */
	@AfterDomainEventPublication
	protected void clearDomainEvents() {
		this.domainEvents.clear();
	}

	
All domain events currently captured by the aggregate.
/**
	 * All domain events currently captured by the aggregate.
	 */
	@DomainEvents
	protected Collection<Object> domainEvents() {
		return Collections.unmodifiableList(domainEvents);
	}

	
Adds all events contained in the given aggregate to the current one.
Params:
aggregate – must not be null.
Returns:
the aggregate/**
	 * Adds all events contained in the given aggregate to the current one.
	 *
	 * @param aggregate must not be {@literal null}.
	 * @return the aggregate
	 */
	@SuppressWarnings("unchecked")
	protected final A andEventsFrom(A aggregate) {

		Assert.notNull(aggregate, "Aggregate must not be null!");

		this.domainEvents.addAll(aggregate.domainEvents());

		return (A) this;
	}

	
Adds the given event to the aggregate for later publication when calling a Spring Data repository's save-method. Does the same as registerEvent(Object) but returns the aggregate instead of the event. 
Params:
event – must not be null.
See Also:
registerEvent(Object)
Returns:
the aggregate/**
	 * Adds the given event to the aggregate for later publication when calling a Spring Data repository's save-method.
	 * Does the same as {@link #registerEvent(Object)} but returns the aggregate instead of the event.
	 *
	 * @param event must not be {@literal null}.
	 * @return the aggregate
	 * @see #registerEvent(Object)
	 */
	@SuppressWarnings("unchecked")
	protected final A andEvent(Object event) {

		registerEvent(event);

		return (A) this;
	}
}