You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: balance_checker.go
    path of file: ./repos/milvus/internal/querycoordv2/checkers
    
    the code of the file until where you have to start completion: // Licensed to the LF AI & Data foundation 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 checkers

import (
	"context"
	"sort"
	"time"

	"github.com/samber/lo"
	"go.uber.org/zap"

	"github.com/milvus-io/milvus/internal/proto/querypb"
	"github.com/milvus-io/milvus/internal/querycoordv2/balance"
	"github.com/milvus-io/milvus/internal/querycoordv2/meta"
	. "github.com/milvus-io/milvus/internal/querycoordv2/params"
	"github.com/milvus-io/milvus/internal/querycoordv2/session"
	"github.com/milvus-io/milvus/internal/querycoordv2/task"
	"github.com/milvus-io/milvus/internal/querycoordv2/utils"
	"github.com/milvus-io/milvus/pkg/log"
	"github.com/milvus-io/milvus/pkg/util/typeutil"
)

// BalanceChecker checks the cluster distribution and generates balance tasks.
type BalanceChecker struct {
	*checkerActivation
	balance.Balance
	meta                                 *meta.Meta
	nodeManager                          *session.NodeManager
	normalBalanceCollectionsCurrentRound typeutil.UniqueSet
	scheduler                 
    
func (b *BalanceChecker) replicasToBalance() []int64 {
	ids := b.meta.GetAll()

	// all replicas belonging to loading collection will be skipped
	loadedCollections := lo.Filter(ids, func(cid int64, _ int) bool {
		collection := b.meta.GetCollection(cid)
		return collection != nil && collection.GetStatus() == querypb.LoadStatus_Loaded
	})
	sort.Slice(loadedCollections, func(i, j int) bool {
		return loadedCollections[i] < loadedCollections[j]
	})

	// balance collections influenced by stopping nodes
	stoppingReplicas := make([]int64, 0)
	for _, cid := range loadedCollections {
		// if target and meta isn't ready, skip balance this collection
		if !b.readyToCheck(cid) {
			continue
		}
		replicas := b.meta.ReplicaManager.GetByCollection(cid)
		for _, replica := range replicas {
			for _, nodeID := range replica.GetNodes() {
				isStopping, _ := b.nodeManager.IsStoppingNode(nodeID)
				if isStopping {
					stoppingReplicas = append(stoppingReplicas, replica.GetID())
					break
				}
			}
		}
	}
	// do stopping balance only in this round
	if len(stoppingReplicas) > 0 {
		return stoppingReplicas
	}

	// no stopping balance and auto balance is disabled, return empty collections for balance
	if !Params.QueryCoordCfg.AutoBalance.GetAsBool() {
		return nil
	}
	// scheduler is handling segment task, skip
	if b.scheduler.GetSegmentTaskNum() != 0 {
		return nil
	}

	// iterator one normal collection in one round
	normalReplicasToBalance := make([]int64, 0)
	hasUnbalancedCollection := false
	for _, cid := range loadedCollections {
		if b.normalBalanceCollectionsCurrentRound.Contain(cid) {
			log.Debug("ScoreBasedBalancer has balanced collection, skip balancing in this round",
				zap.Int64("collectionID", cid))
			continue
		}
		hasUnbalancedCollection = true
		b.normalBalanceCollectionsCurrentRound.Insert(cid)
		for _, replica := range b.meta.ReplicaManager.GetByCollection(cid) {
			normalReplicasToBalance = append(normalReplicasToBalance, replica.GetID())
		}
		break
	}

	if !hasUnbalancedCollection {
		b.normalBalanceCollectionsCurrentRound.Clear()
		log.RatedDebug(10, "ScoreBasedBalancer has balanced all "+
			"collections in one round, clear collectionIDs for this round")
	}
	return normalReplicasToBalance
}