/*
 * JBoss, Home of Professional Open Source
 * Copyright 2010, 2015, Red Hat, Inc., and individual contributors
 * by the @authors tag. See the copyright.txt in the distribution for a
 * full listing of individual contributors.
 *
 * 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.
 */

package jakarta.enterprise.event;

import java.lang.annotation.Annotation;
import java.util.concurrent.CompletionStage;
import java.util.concurrent.Executor;

import jakarta.enterprise.util.TypeLiteral;
import jakarta.enterprise.inject.Any;

/**
 * <p>
 * Allows the application to fire events of a particular type.
 * </p>
 * 
 * <p>
 * Beans fire events via an instance of the <code>Event</code> interface, which may be injected:
 * </p>
 * 
 * <pre>
 * &#064;Inject
 * &#064;Any
 * Event&lt;LoggedInEvent&gt; loggedInEvent;
 * </pre>
 * 
 * <p>
 * The <code>fire()</code> method accepts an event object:
 * </p>
 * 
 * <pre>
 * public void login() { 
 *    ...
 *    loggedInEvent.fire( new LoggedInEvent(user) );
 * }
 * </pre>
 * 
 * <p>
 * Any combination of qualifiers may be specified at the injection point:
 * </p>
 * 
 * <pre>
 * &#064;Inject
 * &#064;Admin
 * Event&lt;LoggedInEvent&gt; adminLoggedInEvent;
 * </pre>
 * 
 * <p>
 * Or, the {@link Any &#064;Any} qualifier may be used, allowing the application to specify qualifiers
 * dynamically:
 * </p>
 * 
 * <pre>
 * &#064;Inject
 * &#064;Any
 * Event&lt;LoggedInEvent&gt; loggedInEvent;
 * </pre>
 * 
 * <p>
 * For an injected <code>Event</code>:
 * </p>
 * 
 * <ul>
 * <li>the <em>specified type</em> is the type parameter specified at the injection point, and</li>
 * <li>the <em>specified qualifiers</em> are the qualifiers specified at the injection point.</li>
 * </ul>
 * 
 * <p>
 * Events may also be fired asynchronously with {@link #fireAsync(Object)} and {@link #fireAsync(Object, NotificationOptions)} methods
 * </p>
 * 
 * @author Gavin King
 * @author Pete Muir
 * @author David Allen
 * @author Antoine Sabot-Durand
 * 
 * @param <T> the type of the event object
 */

public interface Event<T> {

    /**
     * <p>
     * Fires an event with the specified qualifiers and notifies observers.
     * </p>
     * 
     * @param event the event object
     * @throws IllegalArgumentException if the runtime type of the event object contains a type variable
     * @throws ObserverException if a notified observer throws a checked exception, it will be wrapped and rethrown as an
     *         (unchecked) {@link ObserverException}
     */
    public void fire(T event);

    /**
     * <p>
     * Fires an event asynchronously with the specified qualifiers and notifies asynchronous observers.
     * </p>
     *
     * @param <U> event type
     * @param event the event object
     * @return a {@link CompletionStage} allowing further pipeline composition on the asynchronous operation.
     *         Default asynchronous execution facility is container specific.
     *         If any observer notified by this event throws an exception
     *         then the resulting CompletionStage is completed exceptionally with {@link java.util.concurrent.CompletionException}
     *         that wraps all the exceptions raised by observers as suppressed exception.
     *         If no exception is thrown by observers then the resulting CompletionStage is completed normally with the event payload.
     * @throws IllegalArgumentException if the runtime type of the event object contains a type variable
     *
     * @since 2.0
     */
    public <U extends T> CompletionStage<U> fireAsync(U event);

    /**
     * <p>
     * Fires an event asynchronously with the specified qualifiers and notifies asynchronous observers.
     * A custom {@link Executor} will be used to make asynchronous calls 
     * </p>
     *
     * @param <U> event type
     * @param event the event object
     * @param options the notification options
     * @return a {@link CompletionStage} allowing further pipeline composition on the asynchronous operation.
     *         Default asynchronous execution facility is container specific.
     *         If any observer notified by this event throws an exception
     *         then the resulting CompletionStage is completed exceptionally with {@link java.util.concurrent.CompletionException}
     *         that wraps all the exceptions raised by observers as suppressed exception.
     *         If no exception is thrown by observers then the resulting CompletionStage is completed normally with the event payload.
     * @throws IllegalArgumentException if the runtime type of the event object contains a type variable
     *
     * @since 2.0
     */
    public <U extends T> CompletionStage<U>  fireAsync(U event, NotificationOptions options);

    /**
     * <p>
     * Obtains a child <code>Event</code> for the given additional required qualifiers.
     * </p>
     * 
     * @param qualifiers the additional specified qualifiers
     * @return the child <code>Event</code>
     * @throws IllegalArgumentException if passed two instances of the same non repeating qualifier type, or an instance of an annotation that
     *         is not a qualifier type
     */
    public Event<T> select(Annotation... qualifiers);

    /**
     * <p>
     * Obtains a child <code>Event</code> for the given required type and additional required qualifiers.
     * </p>
     * 
     * @param <U> the specified type
     * @param subtype a {@link java.lang.Class} representing the specified type
     * @param qualifiers the additional specified qualifiers
     * @return the child <code>Event</code>
     * @throws IllegalArgumentException if passed two instances of the same non repeating qualifier type, or an instance of an annotation that
     *         is not a qualifier type
     */
    public <U extends T> Event<U> select(Class<U> subtype, Annotation... qualifiers);

    /**
     * <p>
     * Obtains a child <code>Event</code> for the given required type and additional required qualifiers.
     * </p>
     * 
     * @param <U> the specified type
     * @param subtype a {@link TypeLiteral} representing the specified type
     * @param qualifiers the additional specified qualifiers
     * @return the child <code>Event</code>
     * @throws IllegalArgumentException if passed two instances of the same non repeating qualifier type, or an instance of an annotation that
     *         is not a qualifier type
     */
    public <U extends T> Event<U> select(TypeLiteral<U> subtype, Annotation... qualifiers);

}
