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/*
 * Copyright (c) OSGi Alliance (2008, 2013). 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.
 */

package org.osgi.service.blueprint.reflect;

import java.util.Collection;

/**
 * Metadata for a reference to an OSGi service. This is the base type for
 * {@link ReferenceListMetadata} and {@link ReferenceMetadata}.
 * 
 * @ThreadSafe
 * @author $Id: 9aeb2ae92d89c4d0e82ba9a87c049adaa35df845 $
 */
public interface ServiceReferenceMetadata extends ComponentMetadata {

	/**
	 * A matching service is required at all times.
	 * 
	 * @see #getAvailability()
	 */
	static final int	AVAILABILITY_MANDATORY	= 1;

	/**
	 * A matching service is not required to be present.
	 * 
	 * @see #getAvailability()
	 */
	static final int	AVAILABILITY_OPTIONAL	= 2;

	/**
	 * Return whether or not a matching service is required at all times.
	 * 
	 * This is specified in the {@code availability} attribute of the service
	 * reference.
	 * 
	 * @return Whether or not a matching service is required at all times.
	 * @see #AVAILABILITY_MANDATORY
	 * @see #AVAILABILITY_OPTIONAL
	 */
	int getAvailability();

	/**
	 * Return the name of the interface type that a matching service must
	 * support.
	 * 
	 * This is specified in the {@code interface} attribute of the service
	 * reference.
	 * 
	 * @return The name of the interface type that a matching service must
	 *         support or {@code null} when no interface name is specified.
	 */
	String getInterface();

	/**
	 * Return the value of the {@code component-name} attribute of the service
	 * reference. This specifies the id of a component that is registered in the
	 * service registry. This will create an automatic filter, appended with the
	 * filter if set, to select this component based on its automatic {@code id}
	 * attribute.
	 * 
	 * @return The value of the {@code component-name} attribute of the service
	 *         reference or {@code null} if the attribute is not specified.
	 */
	String getComponentName();

	/**
	 * Return the filter expression that a matching service must match.
	 * 
	 * This is specified by the {@code filter} attribute of the service
	 * reference.
	 * 
	 * @return The filter expression that a matching service must match or
	 *         {@code null} if a filter is not specified.
	 */
	String getFilter();

	/**
	 * Return the reference listeners to receive bind and unbind events.
	 * 
	 * This is specified by the {@code reference-listener} elements of the
	 * service reference.
	 * 
	 * @return An immutable Collection of {@link ReferenceListener} objects to
	 *         receive bind and unbind events. The Collection is empty if no
	 *         reference listeners are specified for the service reference.
	 */
	Collection getReferenceListeners();
}