// prepareToSnapshot changes the type of the tablet to backup (when
// the original type is master, it will proceed only if
// forceMasterSnapshot is true). It returns a function that will
// restore the original state.
func (wr *Wrangler) prepareToSnapshot(ti *topo.TabletInfo, forceMasterSnapshot bool) (restoreAfterSnapshot func() error, err error) {
	originalType := ti.Tablet.Type

	if ti.Tablet.Type == topo.TYPE_MASTER && forceMasterSnapshot {
		// In this case, we don't bother recomputing the serving graph.
		// All queries will have to fail anyway.
		log.Infof("force change type master -> backup: %v", ti.Alias)
		// There is a legitimate reason to force in the case of a single
		// master.
		ti.Tablet.Type = topo.TYPE_BACKUP
		err = topo.UpdateTablet(wr.ts, ti)
	} else {
		err = wr.ChangeType(ti.Alias, topo.TYPE_BACKUP, false)
	}

	if err != nil {
		return
	}

	restoreAfterSnapshot = func() (err error) {
		log.Infof("change type after snapshot: %v %v", ti.Alias, originalType)

		if ti.Tablet.Parent.Uid == topo.NO_TABLET && forceMasterSnapshot {
			log.Infof("force change type backup -> master: %v", ti.Alias)
			ti.Tablet.Type = topo.TYPE_MASTER
			return topo.UpdateTablet(wr.ts, ti)
		}

		return wr.ChangeType(ti.Alias, originalType, false)
	}

	return
}

func (ta *TabletActor) multiRestore(actionNode *actionnode.ActionNode) (err error) {
	args := actionNode.Args.(*actionnode.MultiRestoreArgs)

	// read our current tablet, verify its state
	// we only support restoring to the master or spare replicas
	tablet, err := ta.ts.GetTablet(ta.tabletAlias)
	if err != nil {
		return err
	}
	if tablet.Type != topo.TYPE_MASTER && tablet.Type != topo.TYPE_SPARE && tablet.Type != topo.TYPE_REPLICA && tablet.Type != topo.TYPE_RDONLY {
		return fmt.Errorf("expected master, spare replica or rdonly type, not %v: %v", tablet.Type, ta.tabletAlias)
	}

	// get source tablets addresses
	sourceAddrs := make([]*url.URL, len(args.SrcTabletAliases))
	keyRanges := make([]key.KeyRange, len(args.SrcTabletAliases))
	for i, alias := range args.SrcTabletAliases {
		t, e := ta.ts.GetTablet(alias)
		if e != nil {
			return e
		}
		sourceAddrs[i] = &url.URL{Host: t.GetAddr(), Path: "/" + t.DbName()}
		keyRanges[i], e = key.KeyRangesOverlap(tablet.KeyRange, t.KeyRange)
		if e != nil {
			return e
		}
	}

	// change type to restore, no change to replication graph
	originalType := tablet.Type
	tablet.Type = topo.TYPE_RESTORE
	err = topo.UpdateTablet(ta.ts, tablet)
	if err != nil {
		return err
	}

	// run the action, scrap if it fails
	if err := ta.mysqld.MultiRestore(tablet.DbName(), keyRanges, sourceAddrs, args.Concurrency, args.FetchConcurrency, args.InsertTableConcurrency, args.FetchRetryCount, args.Strategy); err != nil {
		if e := Scrap(ta.ts, ta.tabletAlias, false); e != nil {
			log.Errorf("Failed to Scrap after failed RestoreFromMultiSnapshot: %v", e)
		}
		return err
	}

	// restore type back
	tablet.Type = originalType
	return topo.UpdateTablet(ta.ts, tablet)
}

// SnapshotSourceEnd restores the state of the server after a
// Snapshot(server_mode =true)
// Should be called under RpcWrapLockAction.
func (agent *ActionAgent) SnapshotSourceEnd(args *actionnode.SnapshotSourceEndArgs) error {
	tablet, err := agent.TopoServer.GetTablet(agent.TabletAlias)
	if err != nil {
		return err
	}
	if tablet.Type != topo.TYPE_SNAPSHOT_SOURCE {
		return fmt.Errorf("expected snapshot_source type, not %v", tablet.Type)
	}

	if err := agent.Mysqld.SnapshotSourceEnd(args.SlaveStartRequired, args.ReadOnly, true, agent.hookExtraEnv()); err != nil {
		log.Errorf("SnapshotSourceEnd failed, leaving tablet type alone: %v", err)
		return err
	}

	// change the type back
	if args.OriginalType == topo.TYPE_MASTER {
		// force the master update
		tablet.Tablet.Type = topo.TYPE_MASTER
		err = topo.UpdateTablet(agent.TopoServer, tablet)
	} else {
		err = topotools.ChangeType(agent.TopoServer, tablet.Alias, args.OriginalType, make(map[string]string), true /*runHooks*/)
	}

	return err
}

func (wr *Wrangler) SnapshotSourceEnd(tabletAlias topo.TabletAlias, slaveStartRequired, readWrite bool, originalType topo.TabletType) (err error) {
	var ti *topo.TabletInfo
	ti, err = wr.ts.GetTablet(tabletAlias)
	if err != nil {
		return
	}

	var actionPath string
	actionPath, err = wr.ai.SnapshotSourceEnd(tabletAlias, &tm.SnapshotSourceEndArgs{slaveStartRequired, !readWrite})
	if err != nil {
		return
	}

	// wait for completion, and save the error
	err = wr.ai.WaitForCompletion(actionPath, wr.actionTimeout())
	if err != nil {
		log.Errorf("SnapshotSourceEnd failed (%v), leaving tablet type alone", err)
		return
	}

	if ti.Tablet.Parent.Uid == topo.NO_TABLET {
		ti.Tablet.Type = topo.TYPE_MASTER
		err = topo.UpdateTablet(wr.ts, ti)
	} else {
		err = wr.ChangeType(ti.Alias(), originalType, false)
	}

	return err
}

// ChangeType changes the type of the tablet and possibly also updates
// the health informaton for it. Make this external, since these
// transitions need to be forced from time to time.
//
// - if health is nil, we don't touch the Tablet's Health record.
// - if health is an empty map, we clear the Tablet's Health record.
// - if health has values, we overwrite the Tablet's Health record.
func ChangeType(ctx context.Context, ts topo.Server, tabletAlias topo.TabletAlias, newType topo.TabletType, health map[string]string) error {
	tablet, err := ts.GetTablet(ctx, tabletAlias)
	if err != nil {
		return err
	}

	if !topo.IsTrivialTypeChange(tablet.Type, newType) {
		return fmt.Errorf("cannot change tablet type %v -> %v %v", tablet.Type, newType, tabletAlias)
	}

	tablet.Type = newType
	if newType == topo.TYPE_IDLE {
		tablet.Keyspace = ""
		tablet.Shard = ""
		tablet.KeyRange = key.KeyRange{}
		tablet.Health = health
	}
	if health != nil {
		if len(health) == 0 {
			tablet.Health = nil
		} else {
			tablet.Health = health
		}
	}
	return topo.UpdateTablet(ctx, ts, tablet)
}

func SlaveWasRestarted(ts topo.Server, tabletAlias topo.TabletAlias, swrd *actionnode.SlaveWasRestartedArgs) error {
	tablet, err := ts.GetTablet(tabletAlias)
	if err != nil {
		return err
	}

	// Once this action completes, update authoritive tablet node first.
	tablet.Parent = swrd.Parent
	if tablet.Type == topo.TYPE_MASTER {
		tablet.Type = topo.TYPE_SPARE
		tablet.State = topo.STATE_READ_ONLY
	}
	err = topo.UpdateTablet(ts, tablet)
	if err != nil {
		return err
	}

	// Update the new tablet location in the replication graph now that
	// we've updated the tablet.
	err = topo.CreateTabletReplicationData(ts, tablet.Tablet)
	if err != nil && err != topo.ErrNodeExists {
		return err
	}

	return nil
}

func (ta *TabletActor) updateReplicationGraphForPromotedSlave(tablet *topo.TabletInfo, actionNode *ActionNode) error {
	// Remove tablet from the replication graph if this is not already the master.
	if tablet.Parent.Uid != topo.NO_TABLET {
		err := ta.ts.DeleteReplicationPath(tablet.Keyspace, tablet.Shard, tablet.ReplicationPath())
		if err != nil && err != topo.ErrNoNode {
			return err
		}
	}
	// Update tablet regardless - trend towards consistency.
	tablet.State = topo.STATE_READ_WRITE
	tablet.Type = topo.TYPE_MASTER
	tablet.Parent.Cell = ""
	tablet.Parent.Uid = topo.NO_TABLET
	err := topo.UpdateTablet(ta.ts, tablet)
	if err != nil {
		return err
	}
	// NOTE(msolomon) A serving graph update is required, but in order for the
	// shard to be consistent the master must be scrapped first. That is
	// externally coordinated by the wrangler reparent action.

	// Insert the new tablet location in the replication graph now that
	// we've updated the tablet.
	err = ta.ts.CreateReplicationPath(tablet.Keyspace, tablet.Shard, tablet.ReplicationPath())
	if err != nil && err != topo.ErrNodeExists {
		return err
	}

	return nil
}

func updateReplicationGraphForPromotedSlave(ts topo.Server, tablet *topo.TabletInfo) error {
	// Remove tablet from the replication graph if this is not already the master.
	if tablet.Parent.Uid != topo.NO_TABLET {
		if err := topo.DeleteTabletReplicationData(ts, tablet.Tablet); err != nil && err != topo.ErrNoNode {
			return err
		}
	}

	// Update tablet regardless - trend towards consistency.
	tablet.State = topo.STATE_READ_WRITE
	tablet.Type = topo.TYPE_MASTER
	tablet.Parent.Cell = ""
	tablet.Parent.Uid = topo.NO_TABLET
	tablet.Health = nil
	err := topo.UpdateTablet(ts, tablet)
	if err != nil {
		return err
	}
	// NOTE(msolomon) A serving graph update is required, but in
	// order for the shard to be consistent the old master must be
	// scrapped first. That is externally coordinated by the
	// wrangler reparent action.

	// Insert the new tablet location in the replication graph now that
	// we've updated the tablet.
	err = topo.CreateTabletReplicationData(ts, tablet.Tablet)
	if err != nil && err != topo.ErrNodeExists {
		return err
	}

	return nil
}

// Make this external, since these transitions need to be forced from time to time.
func SetBlacklistedTables(ts topo.Server, tabletAlias topo.TabletAlias, tables []string) error {
	tablet, err := ts.GetTablet(tabletAlias)
	if err != nil {
		return err
	}

	tablet.BlacklistedTables = tables
	return topo.UpdateTablet(ts, tablet)
}

// Make this external, since these transitions need to be forced from time to time.
func ChangeType(ts topo.Server, tabletAlias topo.TabletAlias, newType topo.TabletType, runHooks bool) error {
	tablet, err := ts.GetTablet(tabletAlias)
	if err != nil {
		return err
	}

	if !topo.IsTrivialTypeChange(tablet.Type, newType) || !topo.IsValidTypeChange(tablet.Type, newType) {
		return fmt.Errorf("cannot change tablet type %v -> %v %v", tablet.Type, newType, tabletAlias)
	}

	if runHooks {
		// Only run the preflight_serving_type hook when
		// transitioning from non-serving to serving.
		if !topo.IsInServingGraph(tablet.Type) && topo.IsInServingGraph(newType) {
			if err := hook.NewSimpleHook("preflight_serving_type").ExecuteOptional(); err != nil {
				return err
			}
		}
	}

	tablet.Type = newType
	if newType == topo.TYPE_IDLE {
		if tablet.Parent.IsZero() {
			si, err := ts.GetShard(tablet.Keyspace, tablet.Shard)
			if err != nil {
				return err
			}
			rec := concurrency.AllErrorRecorder{}
			wg := sync.WaitGroup{}
			for _, cell := range si.Cells {
				wg.Add(1)
				go func(cell string) {
					defer wg.Done()
					sri, err := ts.GetShardReplication(cell, tablet.Keyspace, tablet.Shard)
					if err != nil {
						log.Warningf("Cannot check cell %v for extra replication paths, assuming it's good", cell)
						return
					}
					for _, rl := range sri.ReplicationLinks {
						if rl.Parent == tabletAlias {
							rec.RecordError(fmt.Errorf("Still have a ReplicationLink in cell %v", cell))
						}
					}
				}(cell)
			}
			wg.Wait()
			if rec.HasErrors() {
				return rec.Error()
			}
		}
		tablet.Parent = topo.TabletAlias{}
		tablet.Keyspace = ""
		tablet.Shard = ""
		tablet.KeyRange = key.KeyRange{}
	}
	return topo.UpdateTablet(ts, tablet)
}

func (ta *TabletActor) SlaveWasRestarted(actionNode *ActionNode, masterAddr string) error {
	swrd := actionNode.args.(*SlaveWasRestartedData)

	tablet, err := ta.ts.GetTablet(ta.tabletAlias)
	if err != nil {
		return err
	}

	// Remove tablet from the replication graph.
	if err := topo.DeleteTabletReplicationData(ta.ts, tablet.Tablet); err != nil && err != topo.ErrNoNode {
		// FIXME(alainjobart) once we don't have replication paths
		// any more, remove this extra check
		if err == topo.ErrNotEmpty {
			log.Infof("Failed to delete master replication path, will be caught later")
		} else {
			return err
		}
	}

	// now we can check the reparent actually worked
	if masterAddr == "" {
		masterAddr, err = ta.mysqlDaemon.GetMasterAddr()
		if err != nil {
			return err
		}
	}
	if masterAddr != swrd.ExpectedMasterAddr && masterAddr != swrd.ExpectedMasterIpAddr {
		log.Errorf("slaveWasRestarted found unexpected master %v for %v (was expecting %v or %v)", masterAddr, ta.tabletAlias, swrd.ExpectedMasterAddr, swrd.ExpectedMasterIpAddr)
		if swrd.ScrapStragglers {
			return Scrap(ta.ts, tablet.Alias(), false)
		} else {
			return fmt.Errorf("Unexpected master %v for %v (was expecting %v or %v)", masterAddr, ta.tabletAlias, swrd.ExpectedMasterAddr, swrd.ExpectedMasterIpAddr)
		}
	}

	// Once this action completes, update authoritive tablet node first.
	tablet.Parent = swrd.Parent
	if tablet.Type == topo.TYPE_MASTER {
		tablet.Type = topo.TYPE_SPARE
		tablet.State = topo.STATE_READ_ONLY
	}
	err = topo.UpdateTablet(ta.ts, tablet)
	if err != nil {
		return err
	}

	// Insert the new tablet location in the replication graph now that
	// we've updated the tablet.
	err = topo.CreateTabletReplicationData(ta.ts, tablet.Tablet)
	if err != nil && err != topo.ErrNodeExists {
		return err
	}

	return nil
}

// SetMaster sets replication master, and waits for the
// reparent_journal table entry up to context timeout
func (agent *ActionAgent) SetMaster(ctx context.Context, parent topo.TabletAlias, timeCreatedNS int64, forceStartSlave bool) error {
	ti, err := agent.TopoServer.GetTablet(ctx, parent)
	if err != nil {
		return err
	}

	// See if we were replicating at all, and should be replicating
	wasReplicating := false
	shouldbeReplicating := false
	rs, err := agent.MysqlDaemon.SlaveStatus()
	if err == nil && (rs.SlaveIORunning || rs.SlaveSQLRunning) {
		wasReplicating = true
		shouldbeReplicating = true
	}
	if forceStartSlave {
		shouldbeReplicating = true
	}

	// Create the list of commands to set the master
	cmds := []string{}
	if wasReplicating {
		cmds = append(cmds, mysqlctl.SqlStopSlave)
	}
	smc, err := agent.MysqlDaemon.SetMasterCommands(ti.Hostname, ti.Portmap["mysql"])
	if err != nil {
		return err
	}
	cmds = append(cmds, smc...)
	if shouldbeReplicating {
		cmds = append(cmds, mysqlctl.SqlStartSlave)
	}
	if err := agent.MysqlDaemon.ExecuteSuperQueryList(cmds); err != nil {
		return err
	}

	// change our type to spare if we used to be the master
	tablet, err := agent.TopoServer.GetTablet(ctx, agent.TabletAlias)
	if err != nil {
		return err
	}
	if tablet.Type == topo.TYPE_MASTER {
		tablet.Type = topo.TYPE_SPARE
		tablet.Health = nil
		if err := topo.UpdateTablet(ctx, agent.TopoServer, tablet); err != nil {
			return err
		}
	}

	// if needed, wait until we get the replicated row, or our
	// context times out
	if !shouldbeReplicating || timeCreatedNS == 0 {
		return nil
	}
	return agent.MysqlDaemon.WaitForReparentJournal(ctx, timeCreatedNS)
}

// Scrap will update the tablet type to 'Scrap', and remove it from
// the serving graph.
//
// 'force' means we are not on the tablet being scrapped, so it is
// probably dead. So if 'force' is true, we will also remove pending
// remote actions.  And if 'force' is false, we also run an optional
// hook.
func Scrap(ts topo.Server, tabletAlias topo.TabletAlias, force bool) error {
	tablet, err := ts.GetTablet(tabletAlias)
	if err != nil {
		return err
	}

	// If you are already scrap, skip updating replication data. It won't
	// be there anyway.
	wasAssigned := tablet.IsAssigned()
	tablet.Type = topo.TYPE_SCRAP
	tablet.Parent = topo.TabletAlias{}
	// Update the tablet first, since that is canonical.
	err = topo.UpdateTablet(ts, tablet)
	if err != nil {
		return err
	}

	// Remove any pending actions. Presumably forcing a scrap
	// means you don't want the agent doing anything and the
	// machine requires manual attention.
	if force {
		err := ts.PurgeTabletActions(tabletAlias, actionnode.ActionNodeCanBePurged)
		if err != nil {
			log.Warningf("purge actions failed: %v", err)
		}
	}

	if wasAssigned {
		err = topo.DeleteTabletReplicationData(ts, tablet.Tablet)
		if err != nil {
			if err == topo.ErrNoNode {
				log.V(6).Infof("no ShardReplication object for cell %v", tablet.Alias.Cell)
				err = nil
			}
			if err != nil {
				log.Warningf("remove replication data for %v failed: %v", tablet.Alias, err)
			}
		}
	}

	// run a hook for final cleanup, only in non-force mode.
	// (force mode executes on the vtctl side, not on the vttablet side)
	if !force {
		hk := hook.NewSimpleHook("postflight_scrap")
		ConfigureTabletHook(hk, tablet.Alias)
		if hookErr := hk.ExecuteOptional(); hookErr != nil {
			// we don't want to return an error, the server
			// is already in bad shape probably.
			log.Warningf("Scrap: postflight_scrap failed: %v", hookErr)
		}
	}

	return nil
}

func (ta *TabletActor) slaveWasRestarted(actionNode *ActionNode) error {
	swrd := actionNode.args.(*SlaveWasRestartedData)

	tablet, err := ta.ts.GetTablet(ta.tabletAlias)
	if err != nil {
		return err
	}

	// Remove tablet from the replication graph.
	err = ta.ts.DeleteReplicationPath(tablet.Keyspace, tablet.Shard, tablet.ReplicationPath())
	if err != nil && err != topo.ErrNoNode {
		return err
	}

	// now we can check the reparent actually worked
	masterAddr, err := ta.mysqld.GetMasterAddr()
	if err != nil {
		return err
	}
	if masterAddr != swrd.ExpectedMasterAddr && masterAddr != swrd.ExpectedMasterIpAddr {
		log.Errorf("slaveWasRestarted found unexpected master %v for %v (was expecting %v or %v)", masterAddr, ta.tabletAlias, swrd.ExpectedMasterAddr, swrd.ExpectedMasterIpAddr)
		if swrd.ScrapStragglers {
			return Scrap(ta.ts, tablet.Alias(), false)
		} else {
			return fmt.Errorf("Unexpected master %v for %v (was expecting %v or %v)", masterAddr, ta.tabletAlias, swrd.ExpectedMasterAddr, swrd.ExpectedMasterIpAddr)
		}
	}

	// Once this action completes, update authoritive tablet node first.
	tablet.Parent = swrd.Parent
	if tablet.Type == topo.TYPE_MASTER {
		tablet.Type = topo.TYPE_SPARE
		tablet.State = topo.STATE_READ_ONLY
	}
	err = topo.UpdateTablet(ta.ts, tablet)
	if err != nil {
		return err
	}

	// Insert the new tablet location in the replication graph now that
	// we've updated the tablet.
	err = ta.ts.CreateReplicationPath(tablet.Keyspace, tablet.Shard, tablet.ReplicationPath())
	if err != nil && err != topo.ErrNodeExists {
		return err
	}

	return nil
}

func (ta *TabletActor) demoteMaster() error {
	_, err := ta.mysqld.DemoteMaster()
	if err != nil {
		return err
	}

	tablet, err := ta.ts.GetTablet(ta.tabletAlias)
	if err != nil {
		return err
	}
	tablet.State = topo.STATE_READ_ONLY
	// NOTE(msolomon) there is no serving graph update - the master tablet will
	// be replaced. Even though writes may fail, reads will succeed. It will be
	// less noisy to simply leave the entry until well promote the master.
	return topo.UpdateTablet(ta.ts, tablet)
}

func (ta *TabletActor) setReadOnly(rdonly bool) error {
	err := ta.mysqld.SetReadOnly(rdonly)
	if err != nil {
		return err
	}

	tablet, err := ta.ts.GetTablet(ta.tabletAlias)
	if err != nil {
		return err
	}
	if rdonly {
		tablet.State = topo.STATE_READ_ONLY
	} else {
		tablet.State = topo.STATE_READ_WRITE
	}
	return topo.UpdateTablet(ta.ts, tablet)
}

// SetReadOnly makes the mysql instance read-only or read-write
// Should be called under RpcWrapLockAction.
func (agent *ActionAgent) SetReadOnly(rdonly bool) error {
	err := agent.Mysqld.SetReadOnly(rdonly)
	if err != nil {
		return err
	}

	tablet, err := agent.TopoServer.GetTablet(agent.TabletAlias)
	if err != nil {
		return err
	}
	if rdonly {
		tablet.State = topo.STATE_READ_ONLY
	} else {
		tablet.State = topo.STATE_READ_WRITE
	}
	return topo.UpdateTablet(agent.TopoServer, tablet)
}

func SlaveWasRestarted(ts topo.Server, mysqlDaemon mysqlctl.MysqlDaemon, tabletAlias topo.TabletAlias, swrd *actionnode.SlaveWasRestartedArgs) error {
	tablet, err := ts.GetTablet(tabletAlias)
	if err != nil {
		return err
	}

	// check the reparent actually worked
	masterAddr, err := mysqlDaemon.GetMasterAddr()
	if err != nil {
		return err
	}
	if masterAddr != swrd.ExpectedMasterAddr && masterAddr != swrd.ExpectedMasterIpAddr {
		log.Errorf("SlaveWasRestarted found unexpected master %v for %v (was expecting %v or %v)", masterAddr, tabletAlias, swrd.ExpectedMasterAddr, swrd.ExpectedMasterIpAddr)
		// Disabled for now
		// if swrd.ContinueOnUnexpectedMaster {
		//	log.Errorf("ContinueOnUnexpectedMaster is set, we keep going anyway")
		// } else
		if swrd.ScrapStragglers {
			return Scrap(ts, tablet.Alias, false)
		} else {
			return fmt.Errorf("Unexpected master %v for %v (was expecting %v or %v)", masterAddr, tabletAlias, swrd.ExpectedMasterAddr, swrd.ExpectedMasterIpAddr)
		}
	}

	// Once this action completes, update authoritive tablet node first.
	tablet.Parent = swrd.Parent
	if tablet.Type == topo.TYPE_MASTER {
		tablet.Type = topo.TYPE_SPARE
		tablet.State = topo.STATE_READ_ONLY
	}
	err = topo.UpdateTablet(ts, tablet)
	if err != nil {
		return err
	}

	// Update the new tablet location in the replication graph now that
	// we've updated the tablet.
	err = topo.CreateTabletReplicationData(ts, tablet.Tablet)
	if err != nil && err != topo.ErrNodeExists {
		return err
	}

	return nil
}

// Scrap will update the tablet type to 'Scrap', and remove it from
// the serving graph.
//
// 'force' means we are not on the tablet being scrapped, so it is
// probably dead. So if 'force' is true, we will also remove pending
// remote actions.  And if 'force' is false, we also run an optional
// hook.
func Scrap(ctx context.Context, ts topo.Server, tabletAlias topo.TabletAlias, force bool) error {
	tablet, err := ts.GetTablet(ctx, tabletAlias)
	if err != nil {
		return err
	}

	// If you are already scrap, skip updating replication data. It won't
	// be there anyway.
	wasAssigned := tablet.IsAssigned()
	tablet.Type = topo.TYPE_SCRAP
	// Update the tablet first, since that is canonical.
	err = topo.UpdateTablet(ctx, ts, tablet)
	if err != nil {
		return err
	}

	if wasAssigned {
		err = topo.DeleteTabletReplicationData(ctx, ts, tablet.Tablet)
		if err != nil {
			if err == topo.ErrNoNode {
				log.V(6).Infof("no ShardReplication object for cell %v", tablet.Alias.Cell)
				err = nil
			}
			if err != nil {
				log.Warningf("remove replication data for %v failed: %v", tablet.Alias, err)
			}
		}
	}

	// run a hook for final cleanup, only in non-force mode.
	// (force mode executes on the vtctl side, not on the vttablet side)
	if !force {
		hk := hook.NewSimpleHook("postflight_scrap")
		ConfigureTabletHook(hk, tablet.Alias)
		if hookErr := hk.ExecuteOptional(); hookErr != nil {
			// we don't want to return an error, the server
			// is already in bad shape probably.
			log.Warningf("Scrap: postflight_scrap failed: %v", hookErr)
		}
	}

	return nil
}

// RestartSlavesExternal will tell all the slaves in the provided list
// that they have a new master, and also tell all the masters. The
// masters will be scrapped if they don't answer.
// We execute all the actions in parallel.
func RestartSlavesExternal(ts topo.Server, log logutil.Logger, slaveTabletMap, masterTabletMap map[topo.TabletAlias]*topo.TabletInfo, masterElectTabletAlias topo.TabletAlias, slaveWasRestarted func(*topo.TabletInfo, *actionnode.SlaveWasRestartedArgs) error) {
	wg := sync.WaitGroup{}

	swrd := actionnode.SlaveWasRestartedArgs{
		Parent: masterElectTabletAlias,
	}

	log.Infof("Updating individual tablets with the right master...")

	// do all the slaves
	for _, ti := range slaveTabletMap {
		wg.Add(1)
		go func(ti *topo.TabletInfo) {
			if err := slaveWasRestarted(ti, &swrd); err != nil {
				log.Warningf("Slave %v had an error: %v", ti.Alias, err)
			}
			wg.Done()
		}(ti)
	}

	// and do the old master and any straggler, if possible.
	for _, ti := range masterTabletMap {
		wg.Add(1)
		go func(ti *topo.TabletInfo) {
			err := slaveWasRestarted(ti, &swrd)
			if err != nil {
				// the old master can be annoying if left
				// around in the replication graph, so if we
				// can't restart it, we just scrap it.
				// We don't rebuild the Shard just yet though.
				log.Warningf("Old master %v is not restarting in time, forcing it to spare: %v", ti.Alias, err)

				ti.Type = topo.TYPE_SPARE
				ti.Parent = masterElectTabletAlias
				if err := topo.UpdateTablet(ts, ti); err != nil {
					log.Warningf("Failed to change old master %v to spare: %v", ti.Alias, err)
				}
			}
			wg.Done()
		}(ti)
	}
	wg.Wait()
}