/**
 * 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 org.apache.jena.system;

import java.util.ArrayList ;
import java.util.List ;
import java.util.ServiceLoader ;

/** Implementation of {@link JenaSubsystemRegistry} for use in the simple 
 *  but common case of running Jena as a collection of jars
 *  on the classpath. 
 *  <p>
 *  Uses {@link ServiceLoader} to find sub-systems. 
 */
public class JenaSubsystemRegistryBasic implements JenaSubsystemRegistry {
    
    private List<JenaSubsystemLifecycle> registry = new ArrayList<>() ;
    private Object registryLock = new Object() ;

    public JenaSubsystemRegistryBasic() {
    }
     
    @Override
    public void load() {
        synchronized (registryLock) {
            // Find subsystems asking for initialization. 
            ServiceLoader<JenaSubsystemLifecycle> sl = 
                // Use this->classloader form : better for OSGi 
                ServiceLoader.load(JenaSubsystemLifecycle.class, this.getClass().getClassLoader()) ;
            sl.forEach(this::add) ;
        }
    }

    @Override
    public void add(JenaSubsystemLifecycle module) {
        synchronized (registryLock) {
            if ( ! registry.contains(module) )
                registry.add(module);
        }
    }

    @Override
    public boolean isRegistered(JenaSubsystemLifecycle module) {
        synchronized (registryLock) {
            return registry.contains(module);
        }
    }

    @Override
    public void remove(JenaSubsystemLifecycle module) {
        synchronized (registryLock) {
            registry.remove(module);
        }
    }

    @Override
    public int size() {
        synchronized (registryLock) {
            return registry.size();
        }
    }

    @Override
    public boolean isEmpty() {
        synchronized (registryLock) {
            return registry.isEmpty();
        }
    }
    
    @Override
    public List<JenaSubsystemLifecycle> snapshot() {
        synchronized (registryLock) {
            return new ArrayList<>(registry) ;
        }
    }
}