/*-
 * ============LICENSE_START=======================================================
 * ONAP - SO
 * ================================================================================
 * Copyright (C) 2017 AT&T Intellectual Property. All rights reserved.
 * ================================================================================
 * 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.
 * ============LICENSE_END=========================================================
 */

package org.onap.so.client.dmaap;

import java.util.ServiceLoader;

public class DmaapPropertiesLoader {
    /* required to make ServiceLoader thread safe */
    private static final ThreadLocal<ServiceLoader<DmaapProperties>> services =
            new ThreadLocal<ServiceLoader<DmaapProperties>>() {
                @Override
                protected ServiceLoader<DmaapProperties> initialValue() {
                    return ServiceLoader.load(DmaapProperties.class);
                }
            };

    private DmaapPropertiesLoader() {}

    private static class Helper {
        private static final DmaapPropertiesLoader INSTANCE = new DmaapPropertiesLoader();
    }

    public static DmaapPropertiesLoader getInstance() {
        return Helper.INSTANCE;
    }

    public DmaapProperties getImpl() {
        return this.getImpl(false);
    }

    public DmaapProperties getNewImpl() {
        return this.getImpl(true);
    }

    private DmaapProperties getImpl(boolean forceNewInstance) {

        ServiceLoader<DmaapProperties> loader = this.services.get();
        for (DmaapProperties service : loader) {
            if (forceNewInstance) {
                try {
                    return service.getClass().newInstance();
                } catch (InstantiationException | IllegalAccessException e) {
                    /*
                     * all spi implementations must provide a public no argument constructor
                     */
                }
            } else {
                return service;
            }
        }

        return null;
    }
}