/*
 * 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.hadoop.hbase.coprocessor;

import java.io.IOException;
import java.util.List;
import java.util.Map;
import java.util.Set;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.hbase.ClusterMetrics;
import org.apache.hadoop.hbase.HBaseInterfaceAudience;
import org.apache.hadoop.hbase.MetaMutationAnnotation;
import org.apache.hadoop.hbase.NamespaceDescriptor;
import org.apache.hadoop.hbase.ServerName;
import org.apache.hadoop.hbase.TableName;
import org.apache.hadoop.hbase.client.BalanceRequest;
import org.apache.hadoop.hbase.client.BalanceResponse;
import org.apache.hadoop.hbase.client.MasterSwitchType;
import org.apache.hadoop.hbase.client.Mutation;
import org.apache.hadoop.hbase.client.RegionInfo;
import org.apache.hadoop.hbase.client.SnapshotDescription;
import org.apache.hadoop.hbase.client.TableDescriptor;
import org.apache.hadoop.hbase.master.RegionPlan;
import org.apache.hadoop.hbase.net.Address;
import org.apache.hadoop.hbase.quotas.GlobalQuotaSettings;
import org.apache.hadoop.hbase.replication.ReplicationPeerConfig;
import org.apache.hadoop.hbase.replication.SyncReplicationState;
import org.apache.hadoop.hbase.security.access.Permission;
import org.apache.hadoop.hbase.security.access.UserPermission;
import org.apache.yetus.audience.InterfaceAudience;
import org.apache.yetus.audience.InterfaceStability;

/**
 * Defines coprocessor hooks for interacting with operations on the
 * {@link org.apache.hadoop.hbase.master.HMaster} process. <br>
 * <br>
 * Since most implementations will be interested in only a subset of hooks, this class uses
 * 'default' functions to avoid having to add unnecessary overrides. When the functions are
 * non-empty, it's simply to satisfy the compiler by returning value of expected (non-void) type. It
 * is done in a way that these default definitions act as no-op. So our suggestion to implementation
 * would be to not call these 'default' methods from overrides. <br>
 * <br>
 * <h3>Exception Handling</h3> For all functions, exception handling is done as follows:
 * <ul>
 * <li>Exceptions of type {@link IOException} are reported back to client.</li>
 * <li>For any other kind of exception:
 * <ul>
 * <li>If the configuration {@link CoprocessorHost#ABORT_ON_ERROR_KEY} is set to true, then the
 * server aborts.</li>
 * <li>Otherwise, coprocessor is removed from the server and
 * {@link org.apache.hadoop.hbase.DoNotRetryIOException} is returned to the client.</li>
 * </ul>
 * </li>
 * </ul>
 */
@InterfaceAudience.LimitedPrivate(HBaseInterfaceAudience.COPROC)
@InterfaceStability.Evolving
public interface MasterObserver {

  /**
   * Called before we create the region infos for this table. Called as part of create table RPC
   * call.
   * @param ctx  the environment to interact with the framework and master
   * @param desc the TableDescriptor for the table
   * @return the TableDescriptor used to create the table. Default is the one passed in. Return
   *         {@code null} means cancel the creation.
   */
  default TableDescriptor preCreateTableRegionsInfos(
    final ObserverContext<MasterCoprocessorEnvironment> ctx, TableDescriptor desc)
    throws IOException {
    return desc;
  }

  /**
   * Called before a new table is created by {@link org.apache.hadoop.hbase.master.HMaster}. Called
   * as part of create table RPC call.
   * @param ctx     the environment to interact with the framework and master
   * @param desc    the TableDescriptor for the table
   * @param regions the initial regions created for the table
   */
  default void preCreateTable(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    TableDescriptor desc, RegionInfo[] regions) throws IOException {
  }

  /**
   * Called after the createTable operation has been requested. Called as part of create table RPC
   * call.
   * @param ctx     the environment to interact with the framework and master
   * @param desc    the TableDescriptor for the table
   * @param regions the initial regions created for the table
   */
  default void postCreateTable(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    TableDescriptor desc, RegionInfo[] regions) throws IOException {
  }

  /**
   * Called before a new table is created by {@link org.apache.hadoop.hbase.master.HMaster}. Called
   * as part of create table procedure and it is async to the create RPC call.
   * @param ctx     the environment to interact with the framework and master
   * @param desc    the TableDescriptor for the table
   * @param regions the initial regions created for the table
   */
  default void preCreateTableAction(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final TableDescriptor desc, final RegionInfo[] regions) throws IOException {
  }

  /**
   * Called after the createTable operation has been requested. Called as part of create table RPC
   * call. Called as part of create table procedure and it is async to the create RPC call.
   * @param ctx     the environment to interact with the framework and master
   * @param desc    the TableDescriptor for the table
   * @param regions the initial regions created for the table
   */
  default void postCompletedCreateTableAction(
    final ObserverContext<MasterCoprocessorEnvironment> ctx, final TableDescriptor desc,
    final RegionInfo[] regions) throws IOException {
  }

  /**
   * Called before {@link org.apache.hadoop.hbase.master.HMaster} deletes a table. Called as part of
   * delete table RPC call.
   * @param ctx       the environment to interact with the framework and master
   * @param tableName the name of the table
   */
  default void preDeleteTable(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    TableName tableName) throws IOException {
  }

  /**
   * Called after the deleteTable operation has been requested. Called as part of delete table RPC
   * call.
   * @param ctx       the environment to interact with the framework and master
   * @param tableName the name of the table
   */
  default void postDeleteTable(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    TableName tableName) throws IOException {
  }

  /**
   * Called before {@link org.apache.hadoop.hbase.master.HMaster} deletes a table. Called as part of
   * delete table procedure and it is async to the delete RPC call.
   * @param ctx       the environment to interact with the framework and master
   * @param tableName the name of the table
   */
  default void preDeleteTableAction(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final TableName tableName) throws IOException {
  }

  /**
   * Called after {@link org.apache.hadoop.hbase.master.HMaster} deletes a table. Called as part of
   * delete table procedure and it is async to the delete RPC call.
   * @param ctx       the environment to interact with the framework and master
   * @param tableName the name of the table
   */
  default void postCompletedDeleteTableAction(
    final ObserverContext<MasterCoprocessorEnvironment> ctx, final TableName tableName)
    throws IOException {
  }

  /**
   * Called before {@link org.apache.hadoop.hbase.master.HMaster} truncates a table. Called as part
   * of truncate table RPC call.
   * @param ctx       the environment to interact with the framework and master
   * @param tableName the name of the table
   */
  default void preTruncateTable(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    TableName tableName) throws IOException {
  }

  /**
   * Called after the truncateTable operation has been requested. Called as part of truncate table
   * RPC call. The truncate is synchronous, so this method will be called when the truncate
   * operation is terminated.
   * @param ctx       the environment to interact with the framework and master
   * @param tableName the name of the table
   */
  default void postTruncateTable(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    TableName tableName) throws IOException {
  }

  /**
   * Called before {@link org.apache.hadoop.hbase.master.HMaster} truncates a table. Called as part
   * of truncate table procedure and it is async to the truncate RPC call.
   * @param ctx       the environment to interact with the framework and master
   * @param tableName the name of the table
   */
  default void preTruncateTableAction(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final TableName tableName) throws IOException {
  }

  /**
   * Called after {@link org.apache.hadoop.hbase.master.HMaster} truncates a table. Called as part
   * of truncate table procedure and it is async to the truncate RPC call.
   * @param ctx       the environment to interact with the framework and master
   * @param tableName the name of the table
   */
  default void postCompletedTruncateTableAction(
    final ObserverContext<MasterCoprocessorEnvironment> ctx, final TableName tableName)
    throws IOException {
  }

  /**
   * Called prior to modifying a table's properties. Called as part of modify table RPC call.
   * @param ctx               the environment to interact with the framework and master
   * @param tableName         the name of the table
   * @param currentDescriptor current TableDescriptor of the table
   * @param newDescriptor     after modify operation, table will have this descriptor
   */
  default TableDescriptor preModifyTable(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final TableName tableName, TableDescriptor currentDescriptor, TableDescriptor newDescriptor)
    throws IOException {
    return newDescriptor;
  }

  /**
   * Called after the modifyTable operation has been requested. Called as part of modify table RPC
   * call.
   * @param ctx               the environment to interact with the framework and master
   * @param tableName         the name of the table
   * @param oldDescriptor     descriptor of table before modify operation happened
   * @param currentDescriptor current TableDescriptor of the table
   */
  default void postModifyTable(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final TableName tableName, TableDescriptor oldDescriptor, TableDescriptor currentDescriptor)
    throws IOException {
  }

  /**
   * Called prior to modifying a table's store file tracker. Called as part of modify table store
   * file tracker RPC call.
   * @param ctx       the environment to interact with the framework and master
   * @param tableName the name of the table
   * @param dstSFT    the store file tracker
   * @return the store file tracker
   */
  default String preModifyTableStoreFileTracker(
    final ObserverContext<MasterCoprocessorEnvironment> ctx, final TableName tableName,
    String dstSFT) throws IOException {
    return dstSFT;
  }

  /**
   * Called after modifying a table's store file tracker. Called as part of modify table store file
   * tracker RPC call.
   * @param ctx       the environment to interact with the framework and master
   * @param tableName the name of the table
   * @param dstSFT    the store file tracker
   */
  default void postModifyTableStoreFileTracker(
    final ObserverContext<MasterCoprocessorEnvironment> ctx, final TableName tableName,
    String dstSFT) throws IOException {
  }

  /**
   * Called prior to modifying a family's store file tracker. Called as part of modify family store
   * file tracker RPC call.
   * @param ctx       the environment to interact with the framework and master
   * @param tableName the name of the table
   * @param family    the column family
   * @param dstSFT    the store file tracker
   * @return the store file tracker
   */
  default String preModifyColumnFamilyStoreFileTracker(
    final ObserverContext<MasterCoprocessorEnvironment> ctx, final TableName tableName,
    final byte[] family, String dstSFT) throws IOException {
    return dstSFT;
  }

  /**
   * Called after modifying a family store file tracker. Called as part of modify family store file
   * tracker RPC call.
   * @param ctx       the environment to interact with the framework and master
   * @param tableName the name of the table
   * @param family    the column family
   * @param dstSFT    the store file tracker
   */
  default void postModifyColumnFamilyStoreFileTracker(
    final ObserverContext<MasterCoprocessorEnvironment> ctx, final TableName tableName,
    final byte[] family, String dstSFT) throws IOException {
  }

  /**
   * Called prior to modifying a table's properties. Called as part of modify table procedure and it
   * is async to the modify table RPC call.
   * @param ctx               the environment to interact with the framework and master
   * @param tableName         the name of the table
   * @param currentDescriptor current TableDescriptor of the table
   * @param newDescriptor     after modify operation, table will have this descriptor
   */
  default void preModifyTableAction(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final TableName tableName, final TableDescriptor currentDescriptor,
    final TableDescriptor newDescriptor) throws IOException {
  }

  /**
   * Called after to modifying a table's properties. Called as part of modify table procedure and it
   * is async to the modify table RPC call.
   * @param ctx               the environment to interact with the framework and master
   * @param tableName         the name of the table
   * @param oldDescriptor     descriptor of table before modify operation happened
   * @param currentDescriptor current TableDescriptor of the table
   */
  default void postCompletedModifyTableAction(
    final ObserverContext<MasterCoprocessorEnvironment> ctx, final TableName tableName,
    final TableDescriptor oldDescriptor, final TableDescriptor currentDescriptor)
    throws IOException {
  }

  /**
   * Called prior to enabling a table. Called as part of enable table RPC call.
   * @param ctx       the environment to interact with the framework and master
   * @param tableName the name of the table
   */
  default void preEnableTable(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final TableName tableName) throws IOException {
  }

  /**
   * Called after the enableTable operation has been requested. Called as part of enable table RPC
   * call.
   * @param ctx       the environment to interact with the framework and master
   * @param tableName the name of the table
   */
  default void postEnableTable(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final TableName tableName) throws IOException {
  }

  /**
   * Called prior to enabling a table. Called as part of enable table procedure and it is async to
   * the enable table RPC call.
   * @param ctx       the environment to interact with the framework and master
   * @param tableName the name of the table
   */
  default void preEnableTableAction(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final TableName tableName) throws IOException {
  }

  /**
   * Called after the enableTable operation has been requested. Called as part of enable table
   * procedure and it is async to the enable table RPC call.
   * @param ctx       the environment to interact with the framework and master
   * @param tableName the name of the table
   */
  default void postCompletedEnableTableAction(
    final ObserverContext<MasterCoprocessorEnvironment> ctx, final TableName tableName)
    throws IOException {
  }

  /**
   * Called prior to disabling a table. Called as part of disable table RPC call.
   * @param ctx       the environment to interact with the framework and master
   * @param tableName the name of the table
   */
  default void preDisableTable(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final TableName tableName) throws IOException {
  }

  /**
   * Called after the disableTable operation has been requested. Called as part of disable table RPC
   * call.
   * @param ctx       the environment to interact with the framework and master
   * @param tableName the name of the table
   */
  default void postDisableTable(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final TableName tableName) throws IOException {
  }

  /**
   * Called prior to disabling a table. Called as part of disable table procedure and it is asyn to
   * the disable table RPC call.
   * @param ctx       the environment to interact with the framework and master
   * @param tableName the name of the table
   */
  default void preDisableTableAction(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final TableName tableName) throws IOException {
  }

  /**
   * Called after the disableTable operation has been requested. Called as part of disable table
   * procedure and it is asyn to the disable table RPC call.
   * @param ctx       the environment to interact with the framework and master
   * @param tableName the name of the table
   */
  default void postCompletedDisableTableAction(
    final ObserverContext<MasterCoprocessorEnvironment> ctx, final TableName tableName)
    throws IOException {
  }

  /**
   * Called before a abortProcedure request has been processed.
   * @param ctx    the environment to interact with the framework and master
   * @param procId the Id of the procedure
   */
  default void preAbortProcedure(ObserverContext<MasterCoprocessorEnvironment> ctx,
    final long procId) throws IOException {
  }

  /**
   * Called after a abortProcedure request has been processed.
   * @param ctx the environment to interact with the framework and master
   */
  default void postAbortProcedure(ObserverContext<MasterCoprocessorEnvironment> ctx)
    throws IOException {
  }

  /**
   * Called before a getProcedures request has been processed.
   * @param ctx the environment to interact with the framework and master
   */
  default void preGetProcedures(ObserverContext<MasterCoprocessorEnvironment> ctx)
    throws IOException {
  }

  /**
   * Called after a getProcedures request has been processed.
   * @param ctx the environment to interact with the framework and master
   */
  default void postGetProcedures(ObserverContext<MasterCoprocessorEnvironment> ctx)
    throws IOException {
  }

  /**
   * Called before a getLocks request has been processed.
   * @param ctx the environment to interact with the framework and master
   * @throws IOException if something went wrong
   */
  default void preGetLocks(ObserverContext<MasterCoprocessorEnvironment> ctx) throws IOException {
  }

  /**
   * Called after a getLocks request has been processed.
   * @param ctx the environment to interact with the framework and master
   * @throws IOException if something went wrong
   */
  default void postGetLocks(ObserverContext<MasterCoprocessorEnvironment> ctx) throws IOException {
  }

  /**
   * Called prior to moving a given region from one region server to another.
   * @param ctx        the environment to interact with the framework and master
   * @param region     the RegionInfo
   * @param srcServer  the source ServerName
   * @param destServer the destination ServerName
   */
  default void preMove(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final RegionInfo region, final ServerName srcServer, final ServerName destServer)
    throws IOException {
  }

  /**
   * Called after the region move has been requested.
   * @param ctx        the environment to interact with the framework and master
   * @param region     the RegionInfo
   * @param srcServer  the source ServerName
   * @param destServer the destination ServerName
   */
  default void postMove(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final RegionInfo region, final ServerName srcServer, final ServerName destServer)
    throws IOException {
  }

  /**
   * Called prior to assigning a specific region.
   * @param ctx        the environment to interact with the framework and master
   * @param regionInfo the regionInfo of the region
   */
  default void preAssign(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final RegionInfo regionInfo) throws IOException {
  }

  /**
   * Called after the region assignment has been requested.
   * @param ctx        the environment to interact with the framework and master
   * @param regionInfo the regionInfo of the region
   */
  default void postAssign(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final RegionInfo regionInfo) throws IOException {
  }

  /**
   * Called prior to unassigning a given region.
   * @param ctx the environment to interact with the framework and master
   */
  default void preUnassign(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final RegionInfo regionInfo) throws IOException {
  }

  /**
   * Called after the region unassignment has been requested.
   * @param ctx the environment to interact with the framework and master
   */
  default void postUnassign(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final RegionInfo regionInfo) throws IOException {
  }

  /**
   * Called prior to marking a given region as offline.
   * @param ctx the environment to interact with the framework and master
   */
  default void preRegionOffline(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final RegionInfo regionInfo) throws IOException {
  }

  /**
   * Called after the region has been marked offline.
   * @param ctx the environment to interact with the framework and master
   */
  default void postRegionOffline(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final RegionInfo regionInfo) throws IOException {
  }

  /**
   * Called prior to requesting rebalancing of the cluster regions, though after the initial checks
   * for regions in transition and the balance switch flag.
   * @param ctx     the environment to interact with the framework and master
   * @param request the request used to trigger the balancer
   */
  default void preBalance(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    BalanceRequest request) throws IOException {
  }

  /**
   * Called after the balancing plan has been submitted.
   * @param ctx     the environment to interact with the framework and master
   * @param request the request used to trigger the balance
   * @param plans   the RegionPlans which master has executed. RegionPlan serves as hint as for the
   *                final destination for the underlying region but may not represent the final
   *                state of assignment
   */
  default void postBalance(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    BalanceRequest request, List<RegionPlan> plans) throws IOException {
  }

  /**
   * Called prior to setting split / merge switch Supports Coprocessor 'bypass'.
   * @param ctx        the coprocessor instance's environment
   * @param newValue   the new value submitted in the call
   * @param switchType type of switch
   */
  default void preSetSplitOrMergeEnabled(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final boolean newValue, final MasterSwitchType switchType) throws IOException {
  }

  /**
   * Called after setting split / merge switch
   * @param ctx        the coprocessor instance's environment
   * @param newValue   the new value submitted in the call
   * @param switchType type of switch
   */
  default void postSetSplitOrMergeEnabled(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final boolean newValue, final MasterSwitchType switchType) throws IOException {
  }

  /**
   * Called before the split region procedure is called.
   * @param c         the environment to interact with the framework and master
   * @param tableName the table where the region belongs to
   * @param splitRow  split point
   */
  default void preSplitRegion(final ObserverContext<MasterCoprocessorEnvironment> c,
    final TableName tableName, final byte[] splitRow) throws IOException {
  }

  /**
   * Called before the region is split.
   * @param c         the environment to interact with the framework and master
   * @param tableName the table where the region belongs to
   * @param splitRow  split point
   */
  default void preSplitRegionAction(final ObserverContext<MasterCoprocessorEnvironment> c,
    final TableName tableName, final byte[] splitRow) throws IOException {
  }

  /**
   * Called before the region is truncated.
   * @param c          The environment to interact with the framework and master
   * @param regionInfo The Region being truncated
   */
  @SuppressWarnings("unused")
  default void preTruncateRegionAction(final ObserverContext<MasterCoprocessorEnvironment> c,
    final RegionInfo regionInfo) {
  }

  /**
   * Called before the truncate region procedure is called.
   * @param c          The environment to interact with the framework and master
   * @param regionInfo The Region being truncated
   */
  @SuppressWarnings("unused")
  default void preTruncateRegion(final ObserverContext<MasterCoprocessorEnvironment> c,
    RegionInfo regionInfo) {
  }

  /**
   * Called after the truncate region procedure is called.
   * @param c          The environment to interact with the framework and master
   * @param regionInfo The Region being truncated
   */
  @SuppressWarnings("unused")
  default void postTruncateRegion(final ObserverContext<MasterCoprocessorEnvironment> c,
    RegionInfo regionInfo) {
  }

  /**
   * Called post the region is truncated.
   * @param c          The environment to interact with the framework and master
   * @param regionInfo The Region To be truncated
   */
  @SuppressWarnings("unused")
  default void postTruncateRegionAction(final ObserverContext<MasterCoprocessorEnvironment> c,
    final RegionInfo regionInfo) {
  }

  /**
   * Called after the region is split.
   * @param c           the environment to interact with the framework and master
   * @param regionInfoA the left daughter region
   * @param regionInfoB the right daughter region
   */
  default void postCompletedSplitRegionAction(final ObserverContext<MasterCoprocessorEnvironment> c,
    final RegionInfo regionInfoA, final RegionInfo regionInfoB) throws IOException {
  }

  /**
   * This will be called before update META step as part of split transaction.
   * @param ctx the environment to interact with the framework and master
   */
  default void preSplitRegionBeforeMETAAction(
    final ObserverContext<MasterCoprocessorEnvironment> ctx, final byte[] splitKey,
    final List<Mutation> metaEntries) throws IOException {
  }

  /**
   * This will be called after update META step as part of split transaction
   * @param ctx the environment to interact with the framework and master
   */
  default void preSplitRegionAfterMETAAction(
    final ObserverContext<MasterCoprocessorEnvironment> ctx) throws IOException {
  }

  /**
   * This will be called after the roll back of the split region is completed
   * @param ctx the environment to interact with the framework and master
   */
  default void postRollBackSplitRegionAction(
    final ObserverContext<MasterCoprocessorEnvironment> ctx) throws IOException {
  }

  /**
   * Called before the regions merge.
   * @param ctx the environment to interact with the framework and master
   */
  default void preMergeRegionsAction(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final RegionInfo[] regionsToMerge) throws IOException {
  }

  /**
   * called after the regions merge.
   * @param ctx the environment to interact with the framework and master
   */
  default void postCompletedMergeRegionsAction(
    final ObserverContext<MasterCoprocessorEnvironment> ctx, final RegionInfo[] regionsToMerge,
    final RegionInfo mergedRegion) throws IOException {
  }

  /**
   * This will be called before update META step as part of regions merge transaction.
   * @param ctx         the environment to interact with the framework and master
   * @param metaEntries mutations to execute on hbase:meta atomically with regions merge updates.
   *                    Any puts or deletes to execute on hbase:meta can be added to the mutations.
   */
  default void preMergeRegionsCommitAction(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final RegionInfo[] regionsToMerge, @MetaMutationAnnotation List<Mutation> metaEntries)
    throws IOException {
  }

  /**
   * This will be called after META step as part of regions merge transaction.
   * @param ctx the environment to interact with the framework and master
   */
  default void postMergeRegionsCommitAction(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final RegionInfo[] regionsToMerge, final RegionInfo mergedRegion) throws IOException {
  }

  /**
   * This will be called after the roll back of the regions merge.
   * @param ctx the environment to interact with the framework and master
   */
  default void postRollBackMergeRegionsAction(
    final ObserverContext<MasterCoprocessorEnvironment> ctx, final RegionInfo[] regionsToMerge)
    throws IOException {
  }

  /**
   * Called prior to modifying the flag used to enable/disable region balancing.
   * @param ctx the coprocessor instance's environment
   */
  default void preBalanceSwitch(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final boolean newValue) throws IOException {
  }

  /**
   * Called after the flag to enable/disable balancing has changed.
   * @param ctx      the coprocessor instance's environment
   * @param oldValue the previously set balanceSwitch value
   * @param newValue the newly set balanceSwitch value
   */
  default void postBalanceSwitch(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final boolean oldValue, final boolean newValue) throws IOException {
  }

  /**
   * Called prior to shutting down the full HBase cluster, including this
   * {@link org.apache.hadoop.hbase.master.HMaster} process.
   */
  default void preShutdown(final ObserverContext<MasterCoprocessorEnvironment> ctx)
    throws IOException {
  }

  /**
   * Called immediately prior to stopping this {@link org.apache.hadoop.hbase.master.HMaster}
   * process.
   */
  default void preStopMaster(final ObserverContext<MasterCoprocessorEnvironment> ctx)
    throws IOException {
  }

  /**
   * Called immediately after an active master instance has completed initialization. Will not be
   * called on standby master instances unless they take over the active role.
   */
  default void postStartMaster(final ObserverContext<MasterCoprocessorEnvironment> ctx)
    throws IOException {
  }

  /**
   * Call before the master initialization is set to true.
   * {@link org.apache.hadoop.hbase.master.HMaster} process.
   */
  default void preMasterInitialization(final ObserverContext<MasterCoprocessorEnvironment> ctx)
    throws IOException {
  }

  /**
   * Called before a new snapshot is taken. Called as part of snapshot RPC call.
   * @param ctx             the environment to interact with the framework and master
   * @param snapshot        the SnapshotDescriptor for the snapshot
   * @param tableDescriptor the TableDescriptor of the table to snapshot
   */
  default void preSnapshot(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final SnapshotDescription snapshot, final TableDescriptor tableDescriptor) throws IOException {
  }

  /**
   * Called after the snapshot operation has been requested. Called as part of snapshot RPC call.
   * @param ctx             the environment to interact with the framework and master
   * @param snapshot        the SnapshotDescriptor for the snapshot
   * @param tableDescriptor the TableDescriptor of the table to snapshot
   */
  default void postSnapshot(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final SnapshotDescription snapshot, final TableDescriptor tableDescriptor) throws IOException {
  }

  /**
   * Called after the snapshot operation has been completed.
   * @param ctx             the environment to interact with the framework and master
   * @param snapshot        the SnapshotDescriptor for the snapshot
   * @param tableDescriptor the TableDescriptor of the table to snapshot
   */
  default void postCompletedSnapshotAction(ObserverContext<MasterCoprocessorEnvironment> ctx,
    SnapshotDescription snapshot, TableDescriptor tableDescriptor) throws IOException {
  }

  /**
   * Called before listSnapshots request has been processed.
   * @param ctx      the environment to interact with the framework and master
   * @param snapshot the SnapshotDescriptor of the snapshot to list
   */
  default void preListSnapshot(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final SnapshotDescription snapshot) throws IOException {
  }

  /**
   * Called after listSnapshots request has been processed.
   * @param ctx      the environment to interact with the framework and master
   * @param snapshot the SnapshotDescriptor of the snapshot to list
   */
  default void postListSnapshot(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final SnapshotDescription snapshot) throws IOException {
  }

  /**
   * Called before a snapshot is cloned. Called as part of restoreSnapshot RPC call.
   * @param ctx             the environment to interact with the framework and master
   * @param snapshot        the SnapshotDescriptor for the snapshot
   * @param tableDescriptor the TableDescriptor of the table to create
   */
  default void preCloneSnapshot(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final SnapshotDescription snapshot, final TableDescriptor tableDescriptor) throws IOException {
  }

  /**
   * Called after a snapshot clone operation has been requested. Called as part of restoreSnapshot
   * RPC call.
   * @param ctx             the environment to interact with the framework and master
   * @param snapshot        the SnapshotDescriptor for the snapshot
   * @param tableDescriptor the v of the table to create
   */
  default void postCloneSnapshot(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final SnapshotDescription snapshot, final TableDescriptor tableDescriptor) throws IOException {
  }

  /**
   * Called before a snapshot is restored. Called as part of restoreSnapshot RPC call.
   * @param ctx             the environment to interact with the framework and master
   * @param snapshot        the SnapshotDescriptor for the snapshot
   * @param tableDescriptor the TableDescriptor of the table to restore
   */
  default void preRestoreSnapshot(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final SnapshotDescription snapshot, final TableDescriptor tableDescriptor) throws IOException {
  }

  /**
   * Called after a snapshot restore operation has been requested. Called as part of restoreSnapshot
   * RPC call.
   * @param ctx             the environment to interact with the framework and master
   * @param snapshot        the SnapshotDescriptor for the snapshot
   * @param tableDescriptor the TableDescriptor of the table to restore
   */
  default void postRestoreSnapshot(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final SnapshotDescription snapshot, final TableDescriptor tableDescriptor) throws IOException {
  }

  /**
   * Called before a snapshot is deleted. Called as part of deleteSnapshot RPC call.
   * @param ctx      the environment to interact with the framework and master
   * @param snapshot the SnapshotDescriptor of the snapshot to delete
   */
  default void preDeleteSnapshot(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final SnapshotDescription snapshot) throws IOException {
  }

  /**
   * Called after the delete snapshot operation has been requested. Called as part of deleteSnapshot
   * RPC call.
   * @param ctx      the environment to interact with the framework and master
   * @param snapshot the SnapshotDescriptor of the snapshot to delete
   */
  default void postDeleteSnapshot(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final SnapshotDescription snapshot) throws IOException {
  }

  /**
   * Called before a getTableDescriptors request has been processed.
   * @param ctx            the environment to interact with the framework and master
   * @param tableNamesList the list of table names, or null if querying for all
   * @param descriptors    an empty list, can be filled with what to return in coprocessor
   * @param regex          regular expression used for filtering the table names
   */
  default void preGetTableDescriptors(ObserverContext<MasterCoprocessorEnvironment> ctx,
    List<TableName> tableNamesList, List<TableDescriptor> descriptors, String regex)
    throws IOException {
  }

  /**
   * Called after a getTableDescriptors request has been processed.
   * @param ctx            the environment to interact with the framework and master
   * @param tableNamesList the list of table names, or null if querying for all
   * @param descriptors    the list of descriptors about to be returned
   * @param regex          regular expression used for filtering the table names
   */
  default void postGetTableDescriptors(ObserverContext<MasterCoprocessorEnvironment> ctx,
    List<TableName> tableNamesList, List<TableDescriptor> descriptors, String regex)
    throws IOException {
  }

  /**
   * Called before a getTableNames request has been processed.
   * @param ctx         the environment to interact with the framework and master
   * @param descriptors an empty list, can be filled with what to return by coprocessor
   * @param regex       regular expression used for filtering the table names
   */
  default void preGetTableNames(ObserverContext<MasterCoprocessorEnvironment> ctx,
    List<TableDescriptor> descriptors, String regex) throws IOException {
  }

  /**
   * Called after a getTableNames request has been processed.
   * @param ctx         the environment to interact with the framework and master
   * @param descriptors the list of descriptors about to be returned
   * @param regex       regular expression used for filtering the table names
   */
  default void postGetTableNames(ObserverContext<MasterCoprocessorEnvironment> ctx,
    List<TableDescriptor> descriptors, String regex) throws IOException {
  }

  /**
   * Called before a new namespace is created by {@link org.apache.hadoop.hbase.master.HMaster}.
   * @param ctx the environment to interact with the framework and master
   * @param ns  the NamespaceDescriptor for the table
   */
  default void preCreateNamespace(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    NamespaceDescriptor ns) throws IOException {
  }

  /**
   * Called after the createNamespace operation has been requested.
   * @param ctx the environment to interact with the framework and master
   * @param ns  the NamespaceDescriptor for the table
   */
  default void postCreateNamespace(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    NamespaceDescriptor ns) throws IOException {
  }

  /**
   * Called before {@link org.apache.hadoop.hbase.master.HMaster} deletes a namespace
   * @param ctx       the environment to interact with the framework and master
   * @param namespace the name of the namespace
   */
  default void preDeleteNamespace(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    String namespace) throws IOException {
  }

  /**
   * Called after the deleteNamespace operation has been requested.
   * @param ctx       the environment to interact with the framework and master
   * @param namespace the name of the namespace
   */
  default void postDeleteNamespace(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    String namespace) throws IOException {
  }

  /**
   * Called prior to modifying a namespace's properties.
   * @param ctx                 the environment to interact with the framework and master
   * @param currentNsDescriptor current NamespaceDescriptor of the namespace
   * @param newNsDescriptor     after modify operation, namespace will have this descriptor
   */
  default void preModifyNamespace(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    NamespaceDescriptor currentNsDescriptor, NamespaceDescriptor newNsDescriptor)
    throws IOException {
  }

  /**
   * Called after the modifyNamespace operation has been requested.
   * @param ctx                 the environment to interact with the framework and master
   * @param oldNsDescriptor     descriptor of namespace before modify operation happened
   * @param currentNsDescriptor current NamespaceDescriptor of the namespace
   */
  default void postModifyNamespace(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    NamespaceDescriptor oldNsDescriptor, NamespaceDescriptor currentNsDescriptor)
    throws IOException {
  }

  /**
   * Called before a getNamespaceDescriptor request has been processed.
   * @param ctx       the environment to interact with the framework and master
   * @param namespace the name of the namespace
   */
  default void preGetNamespaceDescriptor(ObserverContext<MasterCoprocessorEnvironment> ctx,
    String namespace) throws IOException {
  }

  /**
   * Called after a getNamespaceDescriptor request has been processed.
   * @param ctx the environment to interact with the framework and master
   * @param ns  the NamespaceDescriptor
   */
  default void postGetNamespaceDescriptor(ObserverContext<MasterCoprocessorEnvironment> ctx,
    NamespaceDescriptor ns) throws IOException {
  }

  /**
   * Called before a listNamespaces request has been processed.
   * @param ctx        the environment to interact with the framework and master
   * @param namespaces an empty list, can be filled with what to return if bypassing
   * @throws IOException if something went wrong
   */
  default void preListNamespaces(ObserverContext<MasterCoprocessorEnvironment> ctx,
    List<String> namespaces) throws IOException {
  }

  /**
   * Called after a listNamespaces request has been processed.
   * @param ctx        the environment to interact with the framework and master
   * @param namespaces the list of namespaces about to be returned
   * @throws IOException if something went wrong
   */
  default void postListNamespaces(ObserverContext<MasterCoprocessorEnvironment> ctx,
    List<String> namespaces) throws IOException {
  };

  /**
   * Called before a listNamespaceDescriptors request has been processed.
   * @param ctx         the environment to interact with the framework and master
   * @param descriptors an empty list, can be filled with what to return by coprocessor
   */
  default void preListNamespaceDescriptors(ObserverContext<MasterCoprocessorEnvironment> ctx,
    List<NamespaceDescriptor> descriptors) throws IOException {
  }

  /**
   * Called after a listNamespaceDescriptors request has been processed.
   * @param ctx         the environment to interact with the framework and master
   * @param descriptors the list of descriptors about to be returned
   */
  default void postListNamespaceDescriptors(ObserverContext<MasterCoprocessorEnvironment> ctx,
    List<NamespaceDescriptor> descriptors) throws IOException {
  }

  /**
   * Called before the table memstore is flushed to disk.
   * @param ctx       the environment to interact with the framework and master
   * @param tableName the name of the table
   */
  default void preTableFlush(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final TableName tableName) throws IOException {
  }

  /**
   * Called after the table memstore is flushed to disk.
   * @param ctx       the environment to interact with the framework and master
   * @param tableName the name of the table
   */
  default void postTableFlush(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final TableName tableName) throws IOException {
  }

  /**
   * Called before the master local region memstore is flushed to disk.
   * @param ctx the environment to interact with the framework and master
   */
  default void preMasterStoreFlush(final ObserverContext<MasterCoprocessorEnvironment> ctx)
    throws IOException {
  }

  /**
   * Called after the master local region memstore is flushed to disk.
   * @param ctx the environment to interact with the framework and master
   */
  default void postMasterStoreFlush(final ObserverContext<MasterCoprocessorEnvironment> ctx)
    throws IOException {
  }

  /**
   * Called before the quota for the user is stored.
   * @param ctx      the environment to interact with the framework and master
   * @param userName the name of user
   * @param quotas   the current quota for the user
   */
  default void preSetUserQuota(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final String userName, final GlobalQuotaSettings quotas) throws IOException {
  }

  /**
   * Called after the quota for the user is stored.
   * @param ctx      the environment to interact with the framework and master
   * @param userName the name of user
   * @param quotas   the resulting quota for the user
   */
  default void postSetUserQuota(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final String userName, final GlobalQuotaSettings quotas) throws IOException {
  }

  /**
   * Called before the quota for the user on the specified table is stored.
   * @param ctx       the environment to interact with the framework and master
   * @param userName  the name of user
   * @param tableName the name of the table
   * @param quotas    the current quota for the user on the table
   */
  default void preSetUserQuota(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final String userName, final TableName tableName, final GlobalQuotaSettings quotas)
    throws IOException {
  }

  /**
   * Called after the quota for the user on the specified table is stored.
   * @param ctx       the environment to interact with the framework and master
   * @param userName  the name of user
   * @param tableName the name of the table
   * @param quotas    the resulting quota for the user on the table
   */
  default void postSetUserQuota(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final String userName, final TableName tableName, final GlobalQuotaSettings quotas)
    throws IOException {
  }

  /**
   * Called before the quota for the user on the specified namespace is stored.
   * @param ctx       the environment to interact with the framework and master
   * @param userName  the name of user
   * @param namespace the name of the namespace
   * @param quotas    the current quota for the user on the namespace
   */
  default void preSetUserQuota(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final String userName, final String namespace, final GlobalQuotaSettings quotas)
    throws IOException {
  }

  /**
   * Called after the quota for the user on the specified namespace is stored.
   * @param ctx       the environment to interact with the framework and master
   * @param userName  the name of user
   * @param namespace the name of the namespace
   * @param quotas    the resulting quota for the user on the namespace
   */
  default void postSetUserQuota(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final String userName, final String namespace, final GlobalQuotaSettings quotas)
    throws IOException {
  }

  /**
   * Called before the quota for the table is stored.
   * @param ctx       the environment to interact with the framework and master
   * @param tableName the name of the table
   * @param quotas    the current quota for the table
   */
  default void preSetTableQuota(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final TableName tableName, final GlobalQuotaSettings quotas) throws IOException {
  }

  /**
   * Called after the quota for the table is stored.
   * @param ctx       the environment to interact with the framework and master
   * @param tableName the name of the table
   * @param quotas    the resulting quota for the table
   */
  default void postSetTableQuota(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final TableName tableName, final GlobalQuotaSettings quotas) throws IOException {
  }

  /**
   * Called before the quota for the namespace is stored.
   * @param ctx       the environment to interact with the framework and master
   * @param namespace the name of the namespace
   * @param quotas    the current quota for the namespace
   */
  default void preSetNamespaceQuota(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final String namespace, final GlobalQuotaSettings quotas) throws IOException {
  }

  /**
   * Called after the quota for the namespace is stored.
   * @param ctx       the environment to interact with the framework and master
   * @param namespace the name of the namespace
   * @param quotas    the resulting quota for the namespace
   */
  default void postSetNamespaceQuota(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final String namespace, final GlobalQuotaSettings quotas) throws IOException {
  }

  /**
   * Called before the quota for the region server is stored.
   * @param ctx          the environment to interact with the framework and master
   * @param regionServer the name of the region server
   * @param quotas       the current quota for the region server
   */
  default void preSetRegionServerQuota(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final String regionServer, final GlobalQuotaSettings quotas) throws IOException {
  }

  /**
   * Called after the quota for the region server is stored.
   * @param ctx          the environment to interact with the framework and master
   * @param regionServer the name of the region server
   * @param quotas       the resulting quota for the region server
   */
  default void postSetRegionServerQuota(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final String regionServer, final GlobalQuotaSettings quotas) throws IOException {
  }

  /**
   * Called before merge regions request.
   * @param ctx            coprocessor environment
   * @param regionsToMerge regions to be merged
   */
  default void preMergeRegions(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final RegionInfo[] regionsToMerge) throws IOException {
  }

  /**
   * called after merge regions request.
   * @param c              coprocessor environment
   * @param regionsToMerge regions to be merged
   */
  default void postMergeRegions(final ObserverContext<MasterCoprocessorEnvironment> c,
    final RegionInfo[] regionsToMerge) throws IOException {
  }

  /**
   * Called before servers are moved to target region server group
   * @param ctx         the environment to interact with the framework and master
   * @param servers     set of servers to move
   * @param targetGroup destination group
   */
  default void preMoveServersAndTables(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    Set<Address> servers, Set<TableName> tables, String targetGroup) throws IOException {
  }

  /**
   * Called after servers are moved to target region server group
   * @param ctx         the environment to interact with the framework and master
   * @param servers     set of servers to move
   * @param targetGroup name of group
   */
  default void postMoveServersAndTables(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    Set<Address> servers, Set<TableName> tables, String targetGroup) throws IOException {
  }

  /**
   * Called before servers are moved to target region server group
   * @param ctx         the environment to interact with the framework and master
   * @param servers     set of servers to move
   * @param targetGroup destination group
   */
  default void preMoveServers(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    Set<Address> servers, String targetGroup) throws IOException {
  }

  /**
   * Called after servers are moved to target region server group
   * @param ctx         the environment to interact with the framework and master
   * @param servers     set of servers to move
   * @param targetGroup name of group
   */
  default void postMoveServers(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    Set<Address> servers, String targetGroup) throws IOException {
  }

  /**
   * Called before tables are moved to target region server group
   * @param ctx         the environment to interact with the framework and master
   * @param tables      set of tables to move
   * @param targetGroup name of group
   */
  default void preMoveTables(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    Set<TableName> tables, String targetGroup) throws IOException {
  }

  /**
   * Called after servers are moved to target region server group
   * @param ctx         the environment to interact with the framework and master
   * @param tables      set of tables to move
   * @param targetGroup name of group
   */
  default void postMoveTables(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    Set<TableName> tables, String targetGroup) throws IOException {
  }

  /**
   * Called before a new region server group is added
   * @param ctx  the environment to interact with the framework and master
   * @param name group name
   */
  default void preAddRSGroup(final ObserverContext<MasterCoprocessorEnvironment> ctx, String name)
    throws IOException {
  }

  /**
   * Called after a new region server group is added
   * @param ctx  the environment to interact with the framework and master
   * @param name group name
   */
  default void postAddRSGroup(final ObserverContext<MasterCoprocessorEnvironment> ctx, String name)
    throws IOException {
  }

  /**
   * Called before a region server group is removed
   * @param ctx  the environment to interact with the framework and master
   * @param name group name
   */
  default void preRemoveRSGroup(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    String name) throws IOException {
  }

  /**
   * Called after a region server group is removed
   * @param ctx  the environment to interact with the framework and master
   * @param name group name
   */
  default void postRemoveRSGroup(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    String name) throws IOException {
  }

  /**
   * Called before a region server group is removed
   * @param ctx       the environment to interact with the framework and master
   * @param groupName group name
   */
  default void preBalanceRSGroup(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    String groupName, BalanceRequest request) throws IOException {
  }

  /**
   * Called after a region server group is removed
   * @param ctx       the environment to interact with the framework and master
   * @param groupName group name
   * @param request   the request sent to the balancer
   * @param response  the response returned by the balancer
   */
  default void postBalanceRSGroup(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    String groupName, BalanceRequest request, BalanceResponse response) throws IOException {
  }

  /**
   * Called before servers are removed from rsgroup
   * @param ctx     the environment to interact with the framework and master
   * @param servers set of decommissioned servers to remove
   */
  default void preRemoveServers(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    Set<Address> servers) throws IOException {
  }

  /**
   * Called after servers are removed from rsgroup
   * @param ctx     the environment to interact with the framework and master
   * @param servers set of servers to remove
   */
  default void postRemoveServers(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    Set<Address> servers) throws IOException {
  }

  /**
   * Called before getting region server group info of the passed groupName.
   * @param ctx       the environment to interact with the framework and master
   * @param groupName name of the group to get RSGroupInfo for
   */
  default void preGetRSGroupInfo(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final String groupName) throws IOException {
  }

  /**
   * Called after getting region server group info of the passed groupName.
   * @param ctx       the environment to interact with the framework and master
   * @param groupName name of the group to get RSGroupInfo for
   */
  default void postGetRSGroupInfo(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final String groupName) throws IOException {
  }

  /**
   * Called before getting region server group info of the passed tableName.
   * @param ctx       the environment to interact with the framework and master
   * @param tableName name of the table to get RSGroupInfo for
   */
  default void preGetRSGroupInfoOfTable(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final TableName tableName) throws IOException {
  }

  /**
   * Called after getting region server group info of the passed tableName.
   * @param ctx       the environment to interact with the framework and master
   * @param tableName name of the table to get RSGroupInfo for
   */
  default void postGetRSGroupInfoOfTable(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final TableName tableName) throws IOException {
  }

  /**
   * Called before listing region server group information.
   * @param ctx the environment to interact with the framework and master
   */
  default void preListRSGroups(final ObserverContext<MasterCoprocessorEnvironment> ctx)
    throws IOException {
  }

  /**
   * Called after listing region server group information.
   * @param ctx the environment to interact with the framework and master
   */
  default void postListRSGroups(final ObserverContext<MasterCoprocessorEnvironment> ctx)
    throws IOException {
  }

  /**
   * Called before listing all tables in the region server group.
   * @param ctx       the environment to interact with the framework and master
   * @param groupName name of the region server group
   */
  default void preListTablesInRSGroup(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final String groupName) throws IOException {
  }

  /**
   * Called after listing all tables in the region server group.
   * @param ctx       the environment to interact with the framework and master
   * @param groupName name of the region server group
   */
  default void postListTablesInRSGroup(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final String groupName) throws IOException {
  }

  /**
   * Called before rename rsgroup.
   * @param ctx     the environment to interact with the framework and master
   * @param oldName old rsgroup name
   * @param newName new rsgroup name
   */
  default void preRenameRSGroup(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final String oldName, final String newName) throws IOException {
  }

  /**
   * Called after rename rsgroup.
   * @param ctx     the environment to interact with the framework and master
   * @param oldName old rsgroup name
   * @param newName new rsgroup name
   */
  default void postRenameRSGroup(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final String oldName, final String newName) throws IOException {
  }

  /**
   * Called before update rsgroup config.
   * @param ctx           the environment to interact with the framework and master
   * @param groupName     the group name
   * @param configuration new configuration of the group name to be set
   */
  default void preUpdateRSGroupConfig(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final String groupName, final Map<String, String> configuration) throws IOException {
  }

  /**
   * Called after update rsgroup config.
   * @param ctx           the environment to interact with the framework and master
   * @param groupName     the group name
   * @param configuration new configuration of the group name to be set
   */
  default void postUpdateRSGroupConfig(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final String groupName, final Map<String, String> configuration) throws IOException {
  }

  /**
   * Called before getting the configured namespaces and tables in the region server group.
   * @param ctx       the environment to interact with the framework and master
   * @param groupName name of the region server group
   */
  default void preGetConfiguredNamespacesAndTablesInRSGroup(
    final ObserverContext<MasterCoprocessorEnvironment> ctx, final String groupName)
    throws IOException {
  }

  /**
   * Called after getting the configured namespaces and tables in the region server group.
   * @param ctx       the environment to interact with the framework and master
   * @param groupName name of the region server group
   */
  default void postGetConfiguredNamespacesAndTablesInRSGroup(
    final ObserverContext<MasterCoprocessorEnvironment> ctx, final String groupName)
    throws IOException {
  }

  /**
   * Called before getting region server group info of the passed server.
   * @param ctx    the environment to interact with the framework and master
   * @param server server to get RSGroupInfo for
   */
  default void preGetRSGroupInfoOfServer(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final Address server) throws IOException {
  }

  /**
   * Called after getting region server group info of the passed server.
   * @param ctx    the environment to interact with the framework and master
   * @param server server to get RSGroupInfo for
   */
  default void postGetRSGroupInfoOfServer(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final Address server) throws IOException {
  }

  /**
   * Called before add a replication peer
   * @param ctx        the environment to interact with the framework and master
   * @param peerId     a short name that identifies the peer
   * @param peerConfig configuration for the replication peer
   */
  default void preAddReplicationPeer(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    String peerId, ReplicationPeerConfig peerConfig) throws IOException {
  }

  /**
   * Called after add a replication peer
   * @param ctx        the environment to interact with the framework and master
   * @param peerId     a short name that identifies the peer
   * @param peerConfig configuration for the replication peer
   */
  default void postAddReplicationPeer(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    String peerId, ReplicationPeerConfig peerConfig) throws IOException {
  }

  /**
   * Called before remove a replication peer
   * @param peerId a short name that identifies the peer
   */
  default void preRemoveReplicationPeer(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    String peerId) throws IOException {
  }

  /**
   * Called after remove a replication peer
   * @param peerId a short name that identifies the peer
   */
  default void postRemoveReplicationPeer(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    String peerId) throws IOException {
  }

  /**
   * Called before enable a replication peer
   * @param peerId a short name that identifies the peer
   */
  default void preEnableReplicationPeer(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    String peerId) throws IOException {
  }

  /**
   * Called after enable a replication peer
   * @param peerId a short name that identifies the peer
   */
  default void postEnableReplicationPeer(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    String peerId) throws IOException {
  }

  /**
   * Called before disable a replication peer
   * @param peerId a short name that identifies the peer
   */
  default void preDisableReplicationPeer(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    String peerId) throws IOException {
  }

  /**
   * Called after disable a replication peer
   * @param peerId a short name that identifies the peer
   */
  default void postDisableReplicationPeer(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    String peerId) throws IOException {
  }

  /**
   * Called before get the configured ReplicationPeerConfig for the specified peer
   * @param peerId a short name that identifies the peer
   */
  default void preGetReplicationPeerConfig(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    String peerId) throws IOException {
  }

  /**
   * Called after get the configured ReplicationPeerConfig for the specified peer
   * @param peerId a short name that identifies the peer
   */
  default void postGetReplicationPeerConfig(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    String peerId) throws IOException {
  }

  /**
   * Called before update peerConfig for the specified peer
   * @param peerId a short name that identifies the peer
   */
  default void preUpdateReplicationPeerConfig(
    final ObserverContext<MasterCoprocessorEnvironment> ctx, String peerId,
    ReplicationPeerConfig peerConfig) throws IOException {
  }

  /**
   * Called after update peerConfig for the specified peer
   * @param ctx    the environment to interact with the framework and master
   * @param peerId a short name that identifies the peer
   */
  default void postUpdateReplicationPeerConfig(
    final ObserverContext<MasterCoprocessorEnvironment> ctx, String peerId,
    ReplicationPeerConfig peerConfig) throws IOException {
  }

  /**
   * Called before list replication peers.
   * @param ctx   the environment to interact with the framework and master
   * @param regex The regular expression to match peer id
   */
  default void preListReplicationPeers(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    String regex) throws IOException {
  }

  /**
   * Called after list replication peers.
   * @param ctx   the environment to interact with the framework and master
   * @param regex The regular expression to match peer id
   */
  default void postListReplicationPeers(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    String regex) throws IOException {
  }

  /**
   * Called before transit current cluster state for the specified synchronous replication peer
   * @param ctx    the environment to interact with the framework and master
   * @param peerId a short name that identifies the peer
   * @param state  the new state
   */
  default void preTransitReplicationPeerSyncReplicationState(
    final ObserverContext<MasterCoprocessorEnvironment> ctx, String peerId,
    SyncReplicationState state) throws IOException {
  }

  /**
   * Called after transit current cluster state for the specified synchronous replication peer
   * @param ctx    the environment to interact with the framework and master
   * @param peerId a short name that identifies the peer
   * @param from   the old state
   * @param to     the new state
   */
  default void postTransitReplicationPeerSyncReplicationState(
    final ObserverContext<MasterCoprocessorEnvironment> ctx, String peerId,
    SyncReplicationState from, SyncReplicationState to) throws IOException {
  }

  /**
   * Called before new LockProcedure is queued.
   * @param ctx the environment to interact with the framework and master
   */
  default void preRequestLock(ObserverContext<MasterCoprocessorEnvironment> ctx, String namespace,
    TableName tableName, RegionInfo[] regionInfos, String description) throws IOException {
  }

  /**
   * Called after new LockProcedure is queued.
   * @param ctx the environment to interact with the framework and master
   */
  default void postRequestLock(ObserverContext<MasterCoprocessorEnvironment> ctx, String namespace,
    TableName tableName, RegionInfo[] regionInfos, String description) throws IOException {
  }

  /**
   * Called before heartbeat to a lock.
   * @param ctx the environment to interact with the framework and master
   */
  default void preLockHeartbeat(ObserverContext<MasterCoprocessorEnvironment> ctx, TableName tn,
    String description) throws IOException {
  }

  /**
   * Called after heartbeat to a lock.
   * @param ctx the environment to interact with the framework and master
   */
  default void postLockHeartbeat(ObserverContext<MasterCoprocessorEnvironment> ctx)
    throws IOException {
  }

  /**
   * Called before get cluster status.
   */
  default void preGetClusterMetrics(ObserverContext<MasterCoprocessorEnvironment> ctx)
    throws IOException {
  }

  /**
   * Called after get cluster status.
   */
  default void postGetClusterMetrics(ObserverContext<MasterCoprocessorEnvironment> ctx,
    ClusterMetrics status) throws IOException {
  }

  /**
   * Called before clear dead region servers.
   */
  default void preClearDeadServers(ObserverContext<MasterCoprocessorEnvironment> ctx)
    throws IOException {
  }

  /**
   * Called after clear dead region servers.
   */
  default void postClearDeadServers(ObserverContext<MasterCoprocessorEnvironment> ctx,
    List<ServerName> servers, List<ServerName> notClearedServers) throws IOException {
  }

  /**
   * Called before decommission region servers.
   */
  default void preDecommissionRegionServers(ObserverContext<MasterCoprocessorEnvironment> ctx,
    List<ServerName> servers, boolean offload) throws IOException {
  }

  /**
   * Called after decommission region servers.
   */
  default void postDecommissionRegionServers(ObserverContext<MasterCoprocessorEnvironment> ctx,
    List<ServerName> servers, boolean offload) throws IOException {
  }

  /**
   * Called before list decommissioned region servers.
   */
  default void preListDecommissionedRegionServers(ObserverContext<MasterCoprocessorEnvironment> ctx)
    throws IOException {
  }

  /**
   * Called after list decommissioned region servers.
   */
  default void postListDecommissionedRegionServers(
    ObserverContext<MasterCoprocessorEnvironment> ctx) throws IOException {
  }

  /**
   * Called before recommission region server.
   */
  default void preRecommissionRegionServer(ObserverContext<MasterCoprocessorEnvironment> ctx,
    ServerName server, List<byte[]> encodedRegionNames) throws IOException {
  }

  /**
   * Called after recommission region server.
   */
  default void postRecommissionRegionServer(ObserverContext<MasterCoprocessorEnvironment> ctx,
    ServerName server, List<byte[]> encodedRegionNames) throws IOException {
  }

  /**
   * Called before switching rpc throttle enabled state.
   * @param ctx    the coprocessor instance's environment
   * @param enable the rpc throttle value
   */
  default void preSwitchRpcThrottle(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final boolean enable) throws IOException {
  }

  /**
   * Called after switching rpc throttle enabled state.
   * @param ctx      the coprocessor instance's environment
   * @param oldValue the previously rpc throttle value
   * @param newValue the newly rpc throttle value
   */
  default void postSwitchRpcThrottle(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final boolean oldValue, final boolean newValue) throws IOException {
  }

  /**
   * Called before getting if is rpc throttle enabled.
   * @param ctx the coprocessor instance's environment
   */
  default void preIsRpcThrottleEnabled(final ObserverContext<MasterCoprocessorEnvironment> ctx)
    throws IOException {
  }

  /**
   * Called after getting if is rpc throttle enabled.
   * @param ctx                the coprocessor instance's environment
   * @param rpcThrottleEnabled the rpc throttle enabled value
   */
  default void postIsRpcThrottleEnabled(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final boolean rpcThrottleEnabled) throws IOException {
  }

  /**
   * Called before switching exceed throttle quota state.
   * @param ctx    the coprocessor instance's environment
   * @param enable the exceed throttle quota value
   */
  default void preSwitchExceedThrottleQuota(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final boolean enable) throws IOException {
  }

  /**
   * Called after switching exceed throttle quota state.
   * @param ctx      the coprocessor instance's environment
   * @param oldValue the previously exceed throttle quota value
   * @param newValue the newly exceed throttle quota value
   */
  default void postSwitchExceedThrottleQuota(
    final ObserverContext<MasterCoprocessorEnvironment> ctx, final boolean oldValue,
    final boolean newValue) throws IOException {
  }

  /**
   * Called before granting user permissions.
   * @param ctx                      the coprocessor instance's environment
   * @param userPermission           the user and permissions
   * @param mergeExistingPermissions True if merge with previous granted permissions
   */
  default void preGrant(ObserverContext<MasterCoprocessorEnvironment> ctx,
    UserPermission userPermission, boolean mergeExistingPermissions) throws IOException {
  }

  /**
   * Called after granting user permissions.
   * @param ctx                      the coprocessor instance's environment
   * @param userPermission           the user and permissions
   * @param mergeExistingPermissions True if merge with previous granted permissions
   */
  default void postGrant(ObserverContext<MasterCoprocessorEnvironment> ctx,
    UserPermission userPermission, boolean mergeExistingPermissions) throws IOException {
  }

  /**
   * Called before revoking user permissions.
   * @param ctx            the coprocessor instance's environment
   * @param userPermission the user and permissions
   */
  default void preRevoke(ObserverContext<MasterCoprocessorEnvironment> ctx,
    UserPermission userPermission) throws IOException {
  }

  /**
   * Called after revoking user permissions.
   * @param ctx            the coprocessor instance's environment
   * @param userPermission the user and permissions
   */
  default void postRevoke(ObserverContext<MasterCoprocessorEnvironment> ctx,
    UserPermission userPermission) throws IOException {
  }

  /**
   * Called before getting user permissions.
   * @param ctx       the coprocessor instance's environment
   * @param userName  the user name, null if get all user permissions
   * @param namespace the namespace, null if don't get namespace permission
   * @param tableName the table name, null if don't get table permission
   * @param family    the table column family, null if don't get table family permission
   * @param qualifier the table column qualifier, null if don't get table qualifier permission
   * @throws IOException if something went wrong
   */
  default void preGetUserPermissions(ObserverContext<MasterCoprocessorEnvironment> ctx,
    String userName, String namespace, TableName tableName, byte[] family, byte[] qualifier)
    throws IOException {
  }

  /**
   * Called after getting user permissions.
   * @param ctx       the coprocessor instance's environment
   * @param userName  the user name, null if get all user permissions
   * @param namespace the namespace, null if don't get namespace permission
   * @param tableName the table name, null if don't get table permission
   * @param family    the table column family, null if don't get table family permission
   * @param qualifier the table column qualifier, null if don't get table qualifier permission
   * @throws IOException if something went wrong
   */
  default void postGetUserPermissions(ObserverContext<MasterCoprocessorEnvironment> ctx,
    String userName, String namespace, TableName tableName, byte[] family, byte[] qualifier)
    throws IOException {
  }

  /*
   * Called before checking if user has permissions.
   * @param ctx the coprocessor instance's environment
   * @param userName the user name
   * @param permissions the permission list
   */
  default void preHasUserPermissions(ObserverContext<MasterCoprocessorEnvironment> ctx,
    String userName, List<Permission> permissions) throws IOException {
  }

  /**
   * Called after checking if user has permissions.
   * @param ctx         the coprocessor instance's environment
   * @param userName    the user name
   * @param permissions the permission list
   */
  default void postHasUserPermissions(ObserverContext<MasterCoprocessorEnvironment> ctx,
    String userName, List<Permission> permissions) throws IOException {
  }

  /**
   * Called before reloading the HMaster's {@link Configuration} from disk
   * @param ctx           the coprocessor instance's environment
   * @param preReloadConf the {@link Configuration} in use prior to reload
   * @throws IOException if you need to signal an IO error
   */
  default void preUpdateMasterConfiguration(ObserverContext<MasterCoprocessorEnvironment> ctx,
    Configuration preReloadConf) throws IOException {
  }

  /**
   * Called after reloading the HMaster's {@link Configuration} from disk
   * @param ctx            the coprocessor instance's environment
   * @param postReloadConf the {@link Configuration} that was loaded
   * @throws IOException if you need to signal an IO error
   */
  default void postUpdateMasterConfiguration(ObserverContext<MasterCoprocessorEnvironment> ctx,
    Configuration postReloadConf) throws IOException {
  }
}