package engine

import (
	"context"
	"errors"
	"fmt"
	"strings"
	"sync"
	"sync/atomic"

	"git.frostfs.info/TrueCloudLab/frostfs-node/internal/logs"
	"git.frostfs.info/TrueCloudLab/frostfs-node/pkg/core/container"
	"git.frostfs.info/TrueCloudLab/frostfs-node/pkg/core/object"
	"git.frostfs.info/TrueCloudLab/frostfs-node/pkg/local_object_storage/pilorama"
	"git.frostfs.info/TrueCloudLab/frostfs-node/pkg/local_object_storage/shard"
	"git.frostfs.info/TrueCloudLab/frostfs-node/pkg/local_object_storage/util/logicerr"
	tracingPkg "git.frostfs.info/TrueCloudLab/frostfs-node/pkg/tracing"
	"git.frostfs.info/TrueCloudLab/frostfs-node/pkg/util"
	"git.frostfs.info/TrueCloudLab/frostfs-observability/tracing"
	"git.frostfs.info/TrueCloudLab/frostfs-sdk-go/client"
	cid "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/container/id"
	objectSDK "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/object"
	oid "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/object/id"
	"git.frostfs.info/TrueCloudLab/hrw"
	"go.opentelemetry.io/otel/attribute"
	"go.opentelemetry.io/otel/trace"
	"go.uber.org/zap"
	"golang.org/x/sync/errgroup"
)

const (
	// containerWorkerCountDefault is a default value of the count of
	// concurrent container evacuation workers.
	containerWorkerCountDefault = 10
	// objectWorkerCountDefault is a default value of the count of
	// concurrent object evacuation workers.
	objectWorkerCountDefault = 10
)

var (
	ErrMustBeReadOnly = logicerr.New("shard must be in read-only mode")

	evacuationOperationLogField = zap.String("operation", "evacuation")
)

// EvacuateScope is an evacuation scope. Keep in sync with pkg/services/control/service.proto.
type EvacuateScope uint32

var (
	EvacuateScopeObjects EvacuateScope = 1
	EvacuateScopeTrees   EvacuateScope = 2
)

func (s EvacuateScope) String() string {
	var sb strings.Builder
	first := true
	if s&EvacuateScopeObjects == EvacuateScopeObjects {
		if !first {
			sb.WriteString(";")
		}
		sb.WriteString("objects")
		first = false
	}
	if s&EvacuateScopeTrees == EvacuateScopeTrees {
		if !first {
			sb.WriteString(";")
		}
		sb.WriteString("trees")
	}
	return sb.String()
}

func (s EvacuateScope) WithObjects() bool {
	return s&EvacuateScopeObjects == EvacuateScopeObjects
}

func (s EvacuateScope) WithTrees() bool {
	return s&EvacuateScopeTrees == EvacuateScopeTrees
}

func (s EvacuateScope) TreesOnly() bool {
	return s == EvacuateScopeTrees
}

// EvacuateShardPrm represents parameters for the EvacuateShard operation.
type EvacuateShardPrm struct {
	ShardID        []*shard.ID
	ObjectsHandler func(context.Context, oid.Address, *objectSDK.Object) (bool, error)
	TreeHandler    func(context.Context, cid.ID, string, pilorama.Forest) (bool, string, error)
	IgnoreErrors   bool
	Async          bool
	Scope          EvacuateScope
	RepOneOnly     bool

	ContainerWorkerCount uint32
	ObjectWorkerCount    uint32
}

// EvacuateShardRes represents result of the EvacuateShard operation.
type EvacuateShardRes struct {
	objEvacuated *atomic.Uint64
	objTotal     *atomic.Uint64
	objFailed    *atomic.Uint64
	objSkipped   *atomic.Uint64

	trEvacuated *atomic.Uint64
	trTotal     *atomic.Uint64
	trFailed    *atomic.Uint64
}

// NewEvacuateShardRes creates new EvacuateShardRes instance.
func NewEvacuateShardRes() *EvacuateShardRes {
	return &EvacuateShardRes{
		objEvacuated: new(atomic.Uint64),
		objTotal:     new(atomic.Uint64),
		objFailed:    new(atomic.Uint64),
		objSkipped:   new(atomic.Uint64),
		trEvacuated:  new(atomic.Uint64),
		trTotal:      new(atomic.Uint64),
		trFailed:     new(atomic.Uint64),
	}
}

// ObjectsEvacuated returns amount of evacuated objects.
// Objects for which handler returned no error are also assumed evacuated.
func (p *EvacuateShardRes) ObjectsEvacuated() uint64 {
	if p == nil {
		return 0
	}
	return p.objEvacuated.Load()
}

// ObjectsTotal returns total count objects to evacuate.
func (p *EvacuateShardRes) ObjectsTotal() uint64 {
	if p == nil {
		return 0
	}
	return p.objTotal.Load()
}

// ObjectsFailed returns count of failed objects to evacuate.
func (p *EvacuateShardRes) ObjectsFailed() uint64 {
	if p == nil {
		return 0
	}
	return p.objFailed.Load()
}

// ObjectsSkipped returns count of skipped objects.
func (p *EvacuateShardRes) ObjectsSkipped() uint64 {
	if p == nil {
		return 0
	}
	return p.objSkipped.Load()
}

// TreesEvacuated returns amount of evacuated trees.
func (p *EvacuateShardRes) TreesEvacuated() uint64 {
	if p == nil {
		return 0
	}
	return p.trEvacuated.Load()
}

// TreesTotal returns total count trees to evacuate.
func (p *EvacuateShardRes) TreesTotal() uint64 {
	if p == nil {
		return 0
	}
	return p.trTotal.Load()
}

// TreesFailed returns count of failed trees to evacuate.
func (p *EvacuateShardRes) TreesFailed() uint64 {
	if p == nil {
		return 0
	}
	return p.trFailed.Load()
}

// DeepCopy returns deep copy of result instance.
func (p *EvacuateShardRes) DeepCopy() *EvacuateShardRes {
	if p == nil {
		return nil
	}

	res := &EvacuateShardRes{
		objEvacuated: new(atomic.Uint64),
		objTotal:     new(atomic.Uint64),
		objFailed:    new(atomic.Uint64),
		objSkipped:   new(atomic.Uint64),
		trEvacuated:  new(atomic.Uint64),
		trTotal:      new(atomic.Uint64),
		trFailed:     new(atomic.Uint64),
	}

	res.objEvacuated.Store(p.objEvacuated.Load())
	res.objTotal.Store(p.objTotal.Load())
	res.objFailed.Store(p.objFailed.Load())
	res.objSkipped.Store(p.objSkipped.Load())
	res.trTotal.Store(p.trTotal.Load())
	res.trEvacuated.Store(p.trEvacuated.Load())
	res.trFailed.Store(p.trFailed.Load())
	return res
}

type pooledShard struct {
	hashedShard
	pool util.WorkerPool
}

var errMustHaveTwoShards = errors.New("must have at least 1 spare shard")

// Evacuate moves data from one shard to the others.
// The shard being moved must be in read-only mode.
func (e *StorageEngine) Evacuate(ctx context.Context, prm EvacuateShardPrm) (*EvacuateShardRes, error) {
	select {
	case <-ctx.Done():
		return nil, ctx.Err()
	default:
	}

	shardIDs := make([]string, len(prm.ShardID))
	for i := range prm.ShardID {
		shardIDs[i] = prm.ShardID[i].String()
	}

	ctx, span := tracing.StartSpanFromContext(ctx, "StorageEngine.Evacuate",
		trace.WithAttributes(
			attribute.StringSlice("shardIDs", shardIDs),
			attribute.Bool("async", prm.Async),
			attribute.Bool("ignoreErrors", prm.IgnoreErrors),
			attribute.Stringer("scope", prm.Scope),
		))
	defer span.End()

	shards, err := e.getActualShards(shardIDs, prm)
	if err != nil {
		return nil, err
	}

	shardsToEvacuate := make(map[string]*shard.Shard)
	for i := range shardIDs {
		for j := range shards {
			if shards[j].ID().String() == shardIDs[i] {
				shardsToEvacuate[shardIDs[i]] = shards[j].Shard
			}
		}
	}

	res := NewEvacuateShardRes()
	ctx = ctxOrBackground(ctx, prm.Async)
	eg, egCtx, err := e.evacuateLimiter.TryStart(ctx, shardIDs, res)
	if err != nil {
		return nil, err
	}

	var mtx sync.RWMutex
	copyShards := func() []pooledShard {
		mtx.RLock()
		defer mtx.RUnlock()
		t := make([]pooledShard, len(shards))
		copy(t, shards)
		return t
	}
	eg.Go(func() error {
		return e.evacuateShards(egCtx, shardIDs, prm, res, copyShards, shardsToEvacuate)
	})

	if prm.Async {
		return nil, nil
	}

	return res, eg.Wait()
}

func ctxOrBackground(ctx context.Context, background bool) context.Context {
	if background {
		return context.Background()
	}
	return ctx
}

func (e *StorageEngine) evacuateShards(ctx context.Context, shardIDs []string, prm EvacuateShardPrm, res *EvacuateShardRes,
	shards func() []pooledShard, shardsToEvacuate map[string]*shard.Shard,
) error {
	var err error
	ctx, span := tracing.StartSpanFromContext(ctx, "StorageEngine.evacuateShards",
		trace.WithAttributes(
			attribute.StringSlice("shardIDs", shardIDs),
			attribute.Bool("async", prm.Async),
			attribute.Bool("ignoreErrors", prm.IgnoreErrors),
			attribute.Stringer("scope", prm.Scope),
			attribute.Bool("repOneOnly", prm.RepOneOnly),
		))

	defer func() {
		span.End()
		e.evacuateLimiter.Complete(err)
	}()

	e.log.Info(logs.EngineStartedShardsEvacuation, zap.Strings("shard_ids", shardIDs), evacuationOperationLogField,
		zap.String("trace_id", tracingPkg.GetTraceID(ctx)), zap.Stringer("scope", prm.Scope))

	err = e.getTotals(ctx, prm, shardsToEvacuate, res)
	if err != nil {
		e.log.Error(logs.EngineShardsEvacuationFailedToCount, zap.Strings("shard_ids", shardIDs), zap.Error(err), evacuationOperationLogField,
			zap.String("trace_id", tracingPkg.GetTraceID(ctx)), zap.Stringer("scope", prm.Scope))
		return err
	}

	ctx, cancel, egShard, egContainer, egObject := e.createErrorGroupsForEvacuation(ctx, prm)
	continueLoop := true
	for i := 0; continueLoop && i < len(shardIDs); i++ {
		select {
		case <-ctx.Done():
			continueLoop = false
		default:
			egShard.Go(func() error {
				err := e.evacuateShard(ctx, cancel, shardIDs[i], prm, res, shards, shardsToEvacuate, egContainer, egObject)
				if err != nil {
					cancel(err)
				}
				return err
			})
		}
	}
	err = egShard.Wait()
	if err != nil {
		err = fmt.Errorf("shard error: %w", err)
	}
	errContainer := egContainer.Wait()
	errObject := egObject.Wait()
	if errContainer != nil {
		err = errors.Join(err, fmt.Errorf("container error: %w", errContainer))
	}
	if errObject != nil {
		err = errors.Join(err, fmt.Errorf("object error: %w", errObject))
	}
	if err != nil {
		e.log.Error(logs.EngineFinishedWithErrorShardsEvacuation, zap.Error(err), zap.Strings("shard_ids", shardIDs), evacuationOperationLogField,
			zap.String("trace_id", tracingPkg.GetTraceID(ctx)), zap.Stringer("scope", prm.Scope))
		return err
	}

	e.log.Info(logs.EngineFinishedSuccessfullyShardsEvacuation,
		zap.Strings("shard_ids", shardIDs),
		evacuationOperationLogField,
		zap.Uint64("total_objects", res.ObjectsTotal()),
		zap.Uint64("evacuated_objects", res.ObjectsEvacuated()),
		zap.Uint64("failed_objects", res.ObjectsFailed()),
		zap.Uint64("skipped_objects", res.ObjectsSkipped()),
		zap.Uint64("total_trees", res.TreesTotal()),
		zap.Uint64("evacuated_trees", res.TreesEvacuated()),
		zap.Uint64("failed_trees", res.TreesFailed()),
	)
	return nil
}

func (e *StorageEngine) createErrorGroupsForEvacuation(ctx context.Context, prm EvacuateShardPrm) (
	context.Context, context.CancelCauseFunc, *errgroup.Group, *errgroup.Group, *errgroup.Group,
) {
	operationCtx, cancel := context.WithCancelCause(ctx)
	egObject, _ := errgroup.WithContext(operationCtx)
	objectWorkerCount := prm.ObjectWorkerCount
	if objectWorkerCount == 0 {
		objectWorkerCount = objectWorkerCountDefault
	}
	egObject.SetLimit(int(objectWorkerCount))
	egContainer, _ := errgroup.WithContext(operationCtx)
	containerWorkerCount := prm.ContainerWorkerCount
	if containerWorkerCount == 0 {
		containerWorkerCount = containerWorkerCountDefault
	}
	egContainer.SetLimit(int(containerWorkerCount))
	egShard, _ := errgroup.WithContext(operationCtx)

	return operationCtx, cancel, egShard, egContainer, egObject
}

func (e *StorageEngine) getTotals(ctx context.Context, prm EvacuateShardPrm, shardsToEvacuate map[string]*shard.Shard, res *EvacuateShardRes) error {
	ctx, span := tracing.StartSpanFromContext(ctx, "StorageEngine.getTotals")
	defer span.End()

	for _, sh := range shardsToEvacuate {
		if prm.Scope.WithObjects() {
			cnt, err := sh.LogicalObjectsCount(ctx)
			if err != nil {
				if errors.Is(err, shard.ErrDegradedMode) {
					continue
				}
				return err
			}
			res.objTotal.Add(cnt)
		}
		if prm.Scope.WithTrees() && sh.PiloramaEnabled() {
			cnt, err := pilorama.TreeCountAll(ctx, sh)
			if err != nil {
				return err
			}
			res.trTotal.Add(cnt)
		}
	}
	return nil
}

func (e *StorageEngine) evacuateShard(ctx context.Context, cancel context.CancelCauseFunc, shardID string, prm EvacuateShardPrm, res *EvacuateShardRes,
	shards func() []pooledShard, shardsToEvacuate map[string]*shard.Shard,
	egContainer *errgroup.Group, egObject *errgroup.Group,
) error {
	ctx, span := tracing.StartSpanFromContext(ctx, "StorageEngine.evacuateShard",
		trace.WithAttributes(
			attribute.String("shardID", shardID),
		))
	defer span.End()

	if prm.Scope.WithObjects() {
		if err := e.evacuateShardObjects(ctx, cancel, shardID, prm, res, shards, shardsToEvacuate, egContainer, egObject); err != nil {
			return err
		}
	}
	if prm.Scope.WithTrees() && shardsToEvacuate[shardID].PiloramaEnabled() {
		if err := e.evacuateShardTrees(ctx, shardID, prm, res, shards, shardsToEvacuate); err != nil {
			return err
		}
	}

	return nil
}

func (e *StorageEngine) evacuateShardObjects(ctx context.Context, cancel context.CancelCauseFunc, shardID string, prm EvacuateShardPrm, res *EvacuateShardRes,
	shards func() []pooledShard, shardsToEvacuate map[string]*shard.Shard,
	egContainer *errgroup.Group, egObject *errgroup.Group,
) error {
	sh := shardsToEvacuate[shardID]
	var cntPrm shard.IterateOverContainersPrm
	cntPrm.Handler = func(ctx context.Context, name []byte, cnt cid.ID) error {
		select {
		case <-ctx.Done():
			return context.Cause(ctx)
		default:
		}
		egContainer.Go(func() error {
			var skip bool
			c, err := e.containerSource.Load().cs.Get(cnt)
			if err != nil {
				if client.IsErrContainerNotFound(err) {
					skip = true
				} else {
					return err
				}
			}
			if !skip && prm.RepOneOnly {
				skip = e.isNotRepOne(c)
			}
			if skip {
				countPrm := shard.CountAliveObjectsInBucketPrm{BucketName: name}
				count, err := sh.CountAliveObjectsInBucket(ctx, countPrm)
				if err != nil {
					return err
				}
				res.objSkipped.Add(count)
				return nil
			}
			var objPrm shard.IterateOverObjectsInContainerPrm
			objPrm.BucketName = name
			objPrm.Handler = func(ctx context.Context, objInfo *object.Info) error {
				select {
				case <-ctx.Done():
					return context.Cause(ctx)
				default:
				}
				egObject.Go(func() error {
					err := e.evacuateObject(ctx, shardID, objInfo, prm, res, shards, shardsToEvacuate)
					if err != nil {
						cancel(err)
					}
					return err
				})
				return nil
			}
			err = sh.IterateOverObjectsInContainer(ctx, objPrm)
			if err != nil {
				cancel(err)
			}
			return err
		})
		return nil
	}

	sh.SetEvacuationInProgress(true)
	err := sh.IterateOverContainers(ctx, cntPrm)
	if err != nil {
		cancel(err)
		e.log.Error(logs.EngineShardsEvacuationFailedToListObjects, zap.String("shard_id", shardID), zap.Error(err), evacuationOperationLogField,
			zap.String("trace_id", tracingPkg.GetTraceID(ctx)))
	}
	return err
}

func (e *StorageEngine) evacuateShardTrees(ctx context.Context, shardID string, prm EvacuateShardPrm, res *EvacuateShardRes,
	getShards func() []pooledShard, shardsToEvacuate map[string]*shard.Shard,
) error {
	sh := shardsToEvacuate[shardID]
	shards := getShards()

	var listPrm pilorama.TreeListTreesPrm
	first := true

	for len(listPrm.NextPageToken) > 0 || first {
		select {
		case <-ctx.Done():
			return ctx.Err()
		default:
		}

		first = false

		listRes, err := sh.TreeListTrees(ctx, listPrm)
		if err != nil {
			return err
		}
		listPrm.NextPageToken = listRes.NextPageToken
		if err := e.evacuateTrees(ctx, sh, listRes.Items, prm, res, shards, shardsToEvacuate); err != nil {
			return err
		}
	}
	return nil
}

func (e *StorageEngine) evacuateTrees(ctx context.Context, sh *shard.Shard, trees []pilorama.ContainerIDTreeID,
	prm EvacuateShardPrm, res *EvacuateShardRes, shards []pooledShard, shardsToEvacuate map[string]*shard.Shard,
) error {
	ctx, span := tracing.StartSpanFromContext(ctx, "StorageEngine.evacuateTrees",
		trace.WithAttributes(
			attribute.Int("trees_count", len(trees)),
		))
	defer span.End()

	for _, contTree := range trees {
		select {
		case <-ctx.Done():
			return ctx.Err()
		default:
		}

		success, shardID, err := e.tryEvacuateTreeLocal(ctx, sh, contTree, prm, shards, shardsToEvacuate)
		if err != nil {
			return err
		}
		if success {
			e.log.Debug(logs.EngineShardsEvacuationTreeEvacuatedLocal,
				zap.String("cid", contTree.CID.EncodeToString()), zap.String("tree_id", contTree.TreeID),
				zap.String("from_shard_id", sh.ID().String()), zap.String("to_shard_id", shardID),
				evacuationOperationLogField, zap.String("trace_id", tracingPkg.GetTraceID(ctx)))
			res.trEvacuated.Add(1)
			continue
		}

		moved, nodePK, err := e.evacuateTreeToOtherNode(ctx, sh, contTree, prm)
		if err != nil {
			e.log.Error(logs.EngineShardsEvacuationFailedToMoveTree,
				zap.String("cid", contTree.CID.EncodeToString()), zap.String("tree_id", contTree.TreeID),
				zap.String("from_shard_id", sh.ID().String()), evacuationOperationLogField,
				zap.Error(err), zap.String("trace_id", tracingPkg.GetTraceID(ctx)))
			return err
		}
		if moved {
			e.log.Debug(logs.EngineShardsEvacuationTreeEvacuatedRemote,
				zap.String("cid", contTree.CID.EncodeToString()), zap.String("treeID", contTree.TreeID),
				zap.String("from_shardID", sh.ID().String()), zap.String("to_node", nodePK),
				evacuationOperationLogField, zap.String("trace_id", tracingPkg.GetTraceID(ctx)))
			res.trEvacuated.Add(1)
		} else if prm.IgnoreErrors {
			res.trFailed.Add(1)
			e.log.Warn(logs.EngineShardsEvacuationFailedToMoveTree,
				zap.String("cid", contTree.CID.EncodeToString()), zap.String("tree_id", contTree.TreeID),
				zap.String("from_shard_id", sh.ID().String()), evacuationOperationLogField,
				zap.Error(err), zap.String("trace_id", tracingPkg.GetTraceID(ctx)))
		} else {
			e.log.Error(logs.EngineShardsEvacuationFailedToMoveTree,
				zap.String("cid", contTree.CID.EncodeToString()), zap.String("tree_id", contTree.TreeID),
				zap.String("from_shard_id", sh.ID().String()), evacuationOperationLogField,
				zap.Error(err), zap.String("trace_id", tracingPkg.GetTraceID(ctx)))
			return fmt.Errorf("no remote nodes available to replicate tree '%s' of container %s", contTree.TreeID, contTree.CID)
		}
	}
	return nil
}

func (e *StorageEngine) evacuateTreeToOtherNode(ctx context.Context, sh *shard.Shard, tree pilorama.ContainerIDTreeID, prm EvacuateShardPrm) (bool, string, error) {
	if prm.TreeHandler == nil {
		return false, "", fmt.Errorf("failed to evacuate tree '%s' for container %s from shard %s: local evacuation failed, but no remote evacuation available", tree.TreeID, tree.CID, sh.ID())
	}

	return prm.TreeHandler(ctx, tree.CID, tree.TreeID, sh)
}

func (e *StorageEngine) tryEvacuateTreeLocal(ctx context.Context, sh *shard.Shard, tree pilorama.ContainerIDTreeID,
	prm EvacuateShardPrm, shards []pooledShard, shardsToEvacuate map[string]*shard.Shard,
) (bool, string, error) {
	target, found, err := e.findShardToEvacuateTree(ctx, tree, shards, shardsToEvacuate)
	if err != nil {
		return false, "", err
	}
	if !found {
		return false, "", nil
	}
	const readBatchSize = 1000
	source := make(chan *pilorama.Move, readBatchSize)
	ctx, cancel := context.WithCancel(ctx)
	defer cancel()
	var wg sync.WaitGroup

	wg.Add(1)
	var applyErr error
	go func() {
		defer wg.Done()

		applyErr = target.TreeApplyStream(ctx, tree.CID, tree.TreeID, source)
		if applyErr != nil {
			cancel()
		}
	}()

	var height uint64
	for {
		op, err := sh.TreeGetOpLog(ctx, tree.CID, tree.TreeID, height)
		if err != nil {
			cancel()
			wg.Wait()
			close(source) // close after cancel to ctx.Done() hits first
			if prm.IgnoreErrors {
				return false, "", nil
			}
			return false, "", err
		}

		if op.Time == 0 { // completed get op log
			close(source)
			wg.Wait()
			if applyErr == nil {
				return true, target.ID().String(), nil
			}
			if prm.IgnoreErrors {
				return false, "", nil
			}
			return false, "", applyErr
		}

		select {
		case <-ctx.Done(): // apply stream failed or operation cancelled
			wg.Wait()
			if prm.IgnoreErrors {
				return false, "", nil
			}
			if applyErr != nil {
				return false, "", applyErr
			}
			return false, "", ctx.Err()
		case source <- &op:
		}

		height = op.Time + 1
	}
}

// findShardToEvacuateTree returns first shard according HRW or first shard with tree exists.
func (e *StorageEngine) findShardToEvacuateTree(ctx context.Context, tree pilorama.ContainerIDTreeID,
	shards []pooledShard, shardsToEvacuate map[string]*shard.Shard,
) (pooledShard, bool, error) {
	hrw.SortHasherSliceByValue(shards, hrw.StringHash(tree.CID.EncodeToString()))
	var result pooledShard
	var found bool
	for _, target := range shards {
		select {
		case <-ctx.Done():
			return pooledShard{}, false, ctx.Err()
		default:
		}

		if _, ok := shardsToEvacuate[target.ID().String()]; ok {
			continue
		}

		if !target.PiloramaEnabled() || target.GetMode().ReadOnly() {
			continue
		}

		if !found {
			result = target
			found = true
		}

		exists, err := target.TreeExists(ctx, tree.CID, tree.TreeID)
		if err != nil {
			continue
		}
		if exists {
			return target, true, nil
		}
	}
	return result, found, nil
}

func (e *StorageEngine) getActualShards(shardIDs []string, prm EvacuateShardPrm) ([]pooledShard, error) {
	e.mtx.RLock()
	defer e.mtx.RUnlock()

	for i := range shardIDs {
		sh, ok := e.shards[shardIDs[i]]
		if !ok {
			return nil, errShardNotFound
		}

		if !sh.GetMode().ReadOnly() {
			return nil, ErrMustBeReadOnly
		}

		if prm.Scope.TreesOnly() && !sh.PiloramaEnabled() {
			return nil, fmt.Errorf("shard %s doesn't have pilorama enabled", sh.ID())
		}
	}

	if len(e.shards)-len(shardIDs) < 1 && prm.ObjectsHandler == nil && prm.Scope.WithObjects() {
		return nil, errMustHaveTwoShards
	}

	if len(e.shards)-len(shardIDs) < 1 && prm.TreeHandler == nil && prm.Scope.WithTrees() {
		return nil, errMustHaveTwoShards
	}

	// We must have all shards, to have correct information about their
	// indexes in a sorted slice and set appropriate marks in the metabase.
	// Evacuated shard is skipped during put.
	shards := make([]pooledShard, 0, len(e.shards))
	for id := range e.shards {
		shards = append(shards, pooledShard{
			hashedShard: hashedShard(e.shards[id]),
			pool:        e.shardPools[id],
		})
	}
	return shards, nil
}

func (e *StorageEngine) evacuateObject(ctx context.Context, shardID string, objInfo *object.Info, prm EvacuateShardPrm, res *EvacuateShardRes,
	getShards func() []pooledShard, shardsToEvacuate map[string]*shard.Shard,
) error {
	ctx, span := tracing.StartSpanFromContext(ctx, "StorageEngine.evacuateObjects")
	defer span.End()

	select {
	case <-ctx.Done():
		return context.Cause(ctx)
	default:
	}

	shards := getShards()
	addr := objInfo.Address

	var getPrm shard.GetPrm
	getPrm.SetAddress(addr)
	getPrm.SkipEvacCheck(true)

	getRes, err := shardsToEvacuate[shardID].Get(ctx, getPrm)
	if err != nil {
		if prm.IgnoreErrors {
			res.objFailed.Add(1)
			return nil
		}
		e.log.Error(logs.EngineShardsEvacuationFailedToReadObject, zap.String("address", addr.EncodeToString()), zap.Error(err), evacuationOperationLogField,
			zap.String("trace_id", tracingPkg.GetTraceID(ctx)))
		return err
	}

	evacuatedLocal, err := e.tryEvacuateObjectLocal(ctx, addr, getRes.Object(), shardsToEvacuate[shardID], shards, shardsToEvacuate, res)
	if err != nil {
		return err
	}

	if evacuatedLocal {
		return nil
	}

	if prm.ObjectsHandler == nil {
		// Do not check ignoreErrors flag here because
		// ignoring errors on put make this command kinda useless.
		return fmt.Errorf("%w: %s", errPutShard, objInfo)
	}

	moved, err := prm.ObjectsHandler(ctx, addr, getRes.Object())
	if err != nil {
		e.log.Error(logs.EngineShardsEvacuationFailedToMoveObject, zap.String("address", addr.EncodeToString()), zap.Error(err), evacuationOperationLogField,
			zap.String("trace_id", tracingPkg.GetTraceID(ctx)))
		return err
	}
	if moved {
		res.objEvacuated.Add(1)
	} else if prm.IgnoreErrors {
		res.objFailed.Add(1)
		e.log.Warn(logs.EngineShardsEvacuationFailedToMoveObject, zap.String("address", addr.EncodeToString()), zap.Error(err), evacuationOperationLogField,
			zap.String("trace_id", tracingPkg.GetTraceID(ctx)))
	} else {
		return fmt.Errorf("object %s was not replicated", addr)
	}
	return nil
}

func (e *StorageEngine) isNotRepOne(c *container.Container) bool {
	p := c.Value.PlacementPolicy()
	for i := range p.NumberOfReplicas() {
		if p.ReplicaDescriptor(i).NumberOfObjects() > 1 {
			return true
		}
	}
	return false
}

func (e *StorageEngine) tryEvacuateObjectLocal(ctx context.Context, addr oid.Address, object *objectSDK.Object, sh *shard.Shard,
	shards []pooledShard, shardsToEvacuate map[string]*shard.Shard, res *EvacuateShardRes,
) (bool, error) {
	hrw.SortHasherSliceByValue(shards, hrw.StringHash(addr.EncodeToString()))
	for j := range shards {
		select {
		case <-ctx.Done():
			return false, ctx.Err()
		default:
		}

		if _, ok := shardsToEvacuate[shards[j].ID().String()]; ok {
			continue
		}
		switch e.putToShard(ctx, shards[j].hashedShard, shards[j].pool, addr, object).status {
		case putToShardSuccess:
			res.objEvacuated.Add(1)
			e.log.Debug(logs.EngineObjectIsMovedToAnotherShard,
				zap.Stringer("from", sh.ID()),
				zap.Stringer("to", shards[j].ID()),
				zap.Stringer("addr", addr),
				evacuationOperationLogField,
				zap.String("trace_id", tracingPkg.GetTraceID(ctx)))
			return true, nil
		case putToShardExists, putToShardRemoved:
			res.objSkipped.Add(1)
			return true, nil
		default:
			continue
		}
	}

	return false, nil
}

func (e *StorageEngine) GetEvacuationState(ctx context.Context) (*EvacuationState, error) {
	select {
	case <-ctx.Done():
		return nil, ctx.Err()
	default:
	}

	return e.evacuateLimiter.GetState(), nil
}

func (e *StorageEngine) EnqueRunningEvacuationStop(ctx context.Context) error {
	select {
	case <-ctx.Done():
		return ctx.Err()
	default:
	}

	return e.evacuateLimiter.CancelIfRunning()
}

func (e *StorageEngine) ResetEvacuationStatus(ctx context.Context) error {
	select {
	case <-ctx.Done():
		return ctx.Err()
	default:
	}

	return e.evacuateLimiter.ResetEvacuationStatus()
}

func (e *StorageEngine) ResetEvacuationStatusForShards() {
	e.mtx.RLock()
	defer e.mtx.RUnlock()
	for _, sh := range e.shards {
		sh.SetEvacuationInProgress(false)
	}
}