/**
 * Copyright (C) 2014-2016 LinkedIn Corp. (pinot-core@linkedin.com)
 *
 * 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 com.linkedin.pinot.transport.common;

import java.util.List;

import com.linkedin.pinot.common.response.ServerInstance;


/**
 *
 * Replica selection Policy implementation. The options mentioned in {@link ReplicaSelectionPolicy}
 * are supported.
 *
 *
 */
public abstract class ReplicaSelection {

  /**
   *
   * Policy types for selecting a replica hosting a segmentId-group among
   * the candidate nodes
   */
  public enum ReplicaSelectionPolicy {
    UNKNOWN,
    /** Replica Selection Strategy not defined **/
    RANDOM,
    /** Replica will be independently selected at random  **/
    ROUND_ROBIN,
    /**
          Nodes are supposed to be arranged in deterministic
          (ascending) order and one picked in a round-robin
           fashion
    **/
    Hash,
    /**
          Nodes are supposed to be arranged in deterministic
          (ascending) order. A key ( in the request) is hashed
          to determine the replica
    **/

  };

  /**
   * This is a notification by the routing table provider that the set of servers
   * hosting the segmentId "p" has changed. The replica selection policy should
   * use this opportunity to cleanup any state for the segmentId.
   * @param p segmentId for which server set has changed.
   */
  public abstract void reset(SegmentId p);

  /**
   * This is a notification by the routing table provider that the set of servers
   * hosting the segmentId-group "p" has changed. The replica selection policy should
   * use this opportunity to cleanup any state for the segmentId-group.
   * @param p segmentId group for which server set has changed.
   */
  public abstract void reset(SegmentIdSet p);

  /**
   * Selects a server instance from the list of servers provided for the given segmentId. The list of servers
   * are expected to be ordered ( ascending or descending) to provide consistent selection
   * of servers. No additional ordering is done internally for performance reasons.
   *
   * This method is expected to be thread-safe as several request can call this method
   * concurrently.
   *
   * @param p The segmentId for which server selection needs to happen
   * @param orderedServers Ordered list of servers from which a server has to be selected
   * @param hashKey bucketKey whose {@link Object#hashCode()} provides hash-based selection
   * @return
   */
  public abstract ServerInstance selectServer(SegmentId p, List<ServerInstance> orderedServers, Object hashKey);

}