/*-
 * ============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;

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

public class RestPropertiesLoader {

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

    private RestPropertiesLoader() {}

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

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

    public <T> T getNewImpl(Class<? extends RestProperties> clazz) {
        return this.getImpl(clazz, true);
    }

    public <T> T getImpl(Class<? extends RestProperties> clazz) {
        return this.getImpl(clazz, false);
    }

    private <T> T getImpl(Class<? extends RestProperties> clazz, boolean forceNewInstance) {
        T result = null;
        ServiceLoader<RestProperties> loader = this.services.get();
        Iterator<RestProperties> propertyImpls = loader.iterator();
        RestProperties item;
        while (propertyImpls.hasNext()) {
            item = propertyImpls.next();
            if (clazz.isAssignableFrom(item.getClass())) {
                try {
                    if (forceNewInstance) {
                        result = (T) item.getClass().newInstance();
                    } else {
                        result = (T) item;
                    }
                } catch (InstantiationException | IllegalAccessException e) {
                    /*
                     * all spi implementations must provide a public no argument constructor
                     */

                }
                // break;
            }
        }

        return result;
    }
}