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/*
 * Licensed to the University Corporation for Advanced Internet Development, 
 * Inc. (UCAID) under one or more contributor license agreements.  See the 
 * NOTICE file distributed with this work for additional information regarding
 * copyright ownership. The UCAID 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.opensaml.saml2.metadata.provider;

import java.util.Collections;
import java.util.List;
import java.util.concurrent.CopyOnWriteArrayList;

/**
 * An observable base implementation of metadata providers. An observer that clears the descriptor index kept by
 * {@link AbstractMetadataProvider} is registered during construction time.
 */
public abstract class AbstractObservableMetadataProvider extends AbstractMetadataProvider implements
        ObservableMetadataProvider {

    /** List of registered observers. */
    private List observers;

    /** Constructor. */
    public AbstractObservableMetadataProvider() {
        super();
        observers = new CopyOnWriteArrayList();
        observers.add(new DescriptorIndexClearingObserver());
    }

    /** {@inheritDoc} */
    public List getObservers() {
        return observers;
    }
    
    /** {@inheritDoc} */
    public synchronized void destroy() {
        observers = Collections.emptyList();

        super.destroy();        
    }

    /**
     * Helper method for calling
     * {@link org.opensaml.saml2.metadata.provider.ObservableMetadataProvider.Observer#onEvent(MetadataProvider)} on
     * every registered Observer passing in this provider.
     */
    protected void emitChangeEvent() {
        synchronized (observers) {
            for (Observer observer : observers) {
                if (observer != null) {
                    observer.onEvent(this);
                }
            }
        }
    }

    /**
     * Observer that clears the descriptor index of this provider.
     */
    private class DescriptorIndexClearingObserver implements Observer {

        /** {@inheritDoc} */
        public void onEvent(MetadataProvider provider) {
            ((AbstractMetadataProvider) provider).clearDescriptorIndex();
        }
    }
}