/*
 * 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 javax.websocket;

import java.util.Iterator;
import java.util.ServiceLoader;

/**
 * Use the {@link ServiceLoader} mechanism to provide instances of the WebSocket
 * client container.
 */
public abstract class ContainerProvider {

    private static final String DEFAULT_PROVIDER_CLASS_NAME =
            "org.apache.tomcat.websocket.WsWebSocketContainer";

    /**
     * Create a new container used to create outgoing WebSocket connections.
     */
    public static WebSocketContainer getWebSocketContainer() {
        WebSocketContainer result = null;

        ServiceLoader<ContainerProvider> serviceLoader =
                ServiceLoader.load(ContainerProvider.class);
        Iterator<ContainerProvider> iter = serviceLoader.iterator();
        while (result == null && iter.hasNext()) {
            result = iter.next().getContainer();
        }

        // Fall-back. Also used by unit tests
        if (result == null) {
            try {
                @SuppressWarnings("unchecked")
                Class<WebSocketContainer> clazz =
                        (Class<WebSocketContainer>) Class.forName(
                                DEFAULT_PROVIDER_CLASS_NAME);
                result = clazz.newInstance();
            } catch (ClassNotFoundException | InstantiationException |
                    IllegalAccessException e) {
                // No options left. Just return null.
            }
        }
        return result;
    }

    protected abstract WebSocketContainer getContainer();
}
