//
//  ========================================================================
//  Copyright (c) 1995-2020 Mort Bay Consulting Pty Ltd and others.
//  ------------------------------------------------------------------------
//  All rights reserved. This program and the accompanying materials
//  are made available under the terms of the Eclipse Public License v1.0
//  and Apache License v2.0 which accompanies this distribution.
//
//      The Eclipse Public License is available at
//      http://www.eclipse.org/legal/epl-v10.html
//
//      The Apache License v2.0 is available at
//      http://www.opensource.org/licenses/apache2.0.php
//
//  You may elect to redistribute this code under either of these licenses.
//  ========================================================================
//

package org.eclipse.jetty.servlets;

import java.io.IOException;

/**
 * <p>{@link EventSource} is the passive half of an event source connection, as defined by the
 * <a href="http://www.w3.org/TR/eventsource/">EventSource Specification</a>.</p>
 * <p>{@link EventSource.Emitter} is the active half of the connection and allows to operate on the connection.</p>
 * <p>{@link EventSource} allows applications to be notified of events happening on the connection;
 * two events are being notified: the opening of the event source connection, where method
 * {@link EventSource#onOpen(Emitter)} is invoked, and the closing of the event source connection,
 * where method {@link EventSource#onClose()} is invoked.</p>
 *
 * @see EventSourceServlet
 */
public interface EventSource
{
    /**
     * <p>Callback method invoked when an event source connection is opened.</p>
     *
     * @param emitter the {@link Emitter} instance that allows to operate on the connection
     * @throws IOException if the implementation of the method throws such exception
     */
    void onOpen(Emitter emitter) throws IOException;

    /**
     * <p>Callback method invoked when an event source connection is closed.</p>
     */
    void onClose();

    /**
     * <p>{@link Emitter} is the active half of an event source connection, and allows applications
     * to operate on the connection by sending events, data or comments, or by closing the connection.</p>
     * <p>An {@link Emitter} instance will be created for each new event source connection.</p>
     * <p>{@link Emitter} instances are fully thread safe and can be used from multiple threads.</p>
     */
    interface Emitter
    {
        /**
         * <p>Sends a named event with data to the client.</p>
         * <p>When invoked as: <code>event("foo", "bar")</code>, the client will receive the lines:</p>
         * <pre>
         * event: foo
         * data: bar
         * </pre>
         *
         * @param name the event name
         * @param data the data to be sent
         * @throws IOException if an I/O failure occurred
         * @see #data(String)
         */
        void event(String name, String data) throws IOException;

        /**
         * <p>Sends a default event with data to the client.</p>
         * <p>When invoked as: <code>data("baz")</code>, the client will receive the line:</p>
         * <pre>
         * data: baz
         * </pre>
         * <p>When invoked as: <code>data("foo\r\nbar\rbaz\nbax")</code>, the client will receive the lines:</p>
         * <pre>
         * data: foo
         * data: bar
         * data: baz
         * data: bax
         * </pre>
         *
         * @param data the data to be sent
         * @throws IOException if an I/O failure occurred
         */
        void data(String data) throws IOException;

        /**
         * <p>Sends a comment to the client.</p>
         * <p>When invoked as: <code>comment("foo")</code>, the client will receive the line:</p>
         * <pre>
         * : foo
         * </pre>
         *
         * @param comment the comment to send
         * @throws IOException if an I/O failure occurred
         */
        void comment(String comment) throws IOException;

        /**
         * <p>Closes this event source connection.</p>
         */
        void close();
    }
}
