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/*
 * 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.openjpa.slice;

import java.util.List;
import java.util.Random;


/**
 * Policy to select one of the physical databases referred as slice
 * in which a given persistent instance will be stored.
 *
 * The user application is required to implement this interface. Slice will
 * invoke the single method of this interface to determine the target slice for
 * a newly persistent or a detached instance being merged.
 *
 * @author Pinaki Poddar
 *
 */
public interface DistributionPolicy {
	/**
	 * Gets the name of the target slice where the given newly persistent or
	 * the detached, to-be-merged instance will be stored.
	 * 

	 * If the current state of the given instance is sufficient to determine
	 * the target slice, return null. In that case, the runtime will callback
	 * this method again before the instance being flushed to the datastore.
	 * By then, the policy must be able to determine the target slice.
	 *
	 * @param pc The newly persistent or to-be-merged object.
	 * @param slices list of names of the active slices. The ordering of
	 * the list is either explicit openjpa.slice.Names property
	 * or implicit i.e. alphabetic order of available identifiers if
	 * openjpa.slice.Names is unspecified.
     * @param context the generic persistence context managing the given
     * instance.
	 *
	 * @return identifier of the slice. This name must match one of the
	 * given slice names.
	 * @see DistributedConfiguration#getActiveSliceNames()
	 */
	String distribute(Object pc, List slices, Object context);

	/**
	 * Implements a default distribution policy to store the given
	 * instance to a randomly selected available slice.
	 *
	 */
	public static class Default implements DistributionPolicy {
		private static Random RNG = new Random();
        @Override
        public String distribute(Object pc, List slices, Object ctx) {
			return slices.get(RNG.nextInt(slices.size()));
		}
	}
}