package pool

import (
	"bytes"
	"context"
	"crypto/ecdsa"
	"errors"
	"fmt"
	"io"
	"sync"
	"sync/atomic"
	"time"

	"git.frostfs.info/TrueCloudLab/frostfs-sdk-go/accounting"
	"git.frostfs.info/TrueCloudLab/frostfs-sdk-go/ape"
	sdkClient "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/client"
	apistatus "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/client/status"
	"git.frostfs.info/TrueCloudLab/frostfs-sdk-go/container"
	cid "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/container/id"
	"git.frostfs.info/TrueCloudLab/frostfs-sdk-go/netmap"
	"git.frostfs.info/TrueCloudLab/frostfs-sdk-go/object"
	"git.frostfs.info/TrueCloudLab/frostfs-sdk-go/session"
	"git.frostfs.info/TrueCloudLab/frostfs-sdk-go/user"
	"go.uber.org/zap"
	"go.uber.org/zap/zapcore"
	"google.golang.org/grpc"
)

// errPoolClientUnhealthy is an error to indicate that client in pool is unhealthy.
var errPoolClientUnhealthy = errors.New("pool client unhealthy")

// clientStatusMonitor count error rate and other statistics for connection.
type clientStatusMonitor struct {
	logger         *zap.Logger
	addr           string
	healthy        *atomic.Uint32
	errorThreshold uint32

	mu                sync.RWMutex // protect counters
	currentErrorCount uint32
	overallErrorCount uint64
	methods           []*MethodStatus

	// RLock means the client is being used for an operation.
	// Lock means the client is marked as closed.
	status sync.RWMutex
}

// values for healthy status of clientStatusMonitor.
const (
	// statusUnhealthyOnRequest is set when communication after dialing to the
	// endpoint is failed due to immediate or accumulated errors, connection is
	// available and pool should close it before re-establishing connection once again.
	statusUnhealthyOnRequest = iota

	// statusHealthy is set when connection is ready to be used by the pool.
	statusHealthy
)

// MethodIndex index of method in list of statuses in clientStatusMonitor.
type MethodIndex int

const (
	methodBalanceGet MethodIndex = iota
	methodContainerPut
	methodContainerGet
	methodContainerList
	methodContainerListStream
	methodContainerDelete
	methodEndpointInfo
	methodNetworkInfo
	methodNetMapSnapshot
	methodObjectPut
	methodObjectDelete
	methodObjectGet
	methodObjectHead
	methodObjectRange
	methodObjectPatch
	methodSessionCreate
	methodAPEManagerAddChain
	methodAPEManagerRemoveChain
	methodAPEManagerListChains
	methodLast
)

// String implements fmt.Stringer.
func (m MethodIndex) String() string {
	switch m {
	case methodBalanceGet:
		return "balanceGet"
	case methodContainerPut:
		return "containerPut"
	case methodContainerGet:
		return "containerGet"
	case methodContainerList:
		return "containerList"
	case methodContainerListStream:
		return "containerListStream"
	case methodContainerDelete:
		return "containerDelete"
	case methodEndpointInfo:
		return "endpointInfo"
	case methodNetworkInfo:
		return "networkInfo"
	case methodNetMapSnapshot:
		return "netMapSnapshot"
	case methodObjectPut:
		return "objectPut"
	case methodObjectPatch:
		return "objectPatch"
	case methodObjectDelete:
		return "objectDelete"
	case methodObjectGet:
		return "objectGet"
	case methodObjectHead:
		return "objectHead"
	case methodObjectRange:
		return "objectRange"
	case methodSessionCreate:
		return "sessionCreate"
	case methodAPEManagerAddChain:
		return "apeManagerAddChain"
	case methodAPEManagerRemoveChain:
		return "apeManagerRemoveChain"
	case methodAPEManagerListChains:
		return "apeManagerListChains"
	case methodLast:
		return "it's a system name rather than a method"
	default:
		return "unknown"
	}
}

func newClientStatusMonitor(logger *zap.Logger, addr string, errorThreshold uint32) clientStatusMonitor {
	methods := make([]*MethodStatus, methodLast)
	for i := methodBalanceGet; i < methodLast; i++ {
		methods[i] = &MethodStatus{name: i.String()}
	}

	healthy := new(atomic.Uint32)
	healthy.Store(statusHealthy)

	return clientStatusMonitor{
		logger:         logger,
		addr:           addr,
		healthy:        healthy,
		errorThreshold: errorThreshold,
		methods:        methods,
	}
}

// clientWrapper is used by default, alternative implementations are intended for testing purposes only.
type clientWrapper struct {
	clientMutex sync.RWMutex
	client      *sdkClient.Client
	dialed      bool
	prm         wrapperPrm

	clientStatusMonitor
}

// wrapperPrm is params to create clientWrapper.
type wrapperPrm struct {
	logger                  *zap.Logger
	address                 string
	key                     ecdsa.PrivateKey
	dialTimeout             time.Duration
	streamTimeout           time.Duration
	errorThreshold          uint32
	responseInfoCallback    func(sdkClient.ResponseMetaInfo) error
	poolRequestInfoCallback func(RequestInfo)
	dialOptions             []grpc.DialOption

	gracefulCloseOnSwitchTimeout time.Duration
}

// setAddress sets endpoint to connect in FrostFS network.
func (x *wrapperPrm) setAddress(address string) {
	x.address = address
}

// setKey sets sdkClient.Client private key to be used for the protocol communication by default.
func (x *wrapperPrm) setKey(key ecdsa.PrivateKey) {
	x.key = key
}

// setLogger sets sdkClient.Client logger.
func (x *wrapperPrm) setLogger(logger *zap.Logger) {
	x.logger = logger
}

// setDialTimeout sets the timeout for connection to be established.
func (x *wrapperPrm) setDialTimeout(timeout time.Duration) {
	x.dialTimeout = timeout
}

// setStreamTimeout sets the timeout for individual operations in streaming RPC.
func (x *wrapperPrm) setStreamTimeout(timeout time.Duration) {
	x.streamTimeout = timeout
}

// setErrorThreshold sets threshold after reaching which connection is considered unhealthy
// until Pool.startRebalance routing updates its status.
func (x *wrapperPrm) setErrorThreshold(threshold uint32) {
	x.errorThreshold = threshold
}

// setGracefulCloseOnSwitchTimeout specifies the timeout after which unhealthy client be closed during rebalancing
// if it will become healthy back.
//
// See also setErrorThreshold.
func (x *wrapperPrm) setGracefulCloseOnSwitchTimeout(timeout time.Duration) {
	x.gracefulCloseOnSwitchTimeout = timeout
}

// setPoolRequestCallback sets callback that will be invoked after every pool response.
func (x *wrapperPrm) setPoolRequestCallback(f func(RequestInfo)) {
	x.poolRequestInfoCallback = f
}

// setResponseInfoCallback sets callback that will be invoked after every response.
func (x *wrapperPrm) setResponseInfoCallback(f func(sdkClient.ResponseMetaInfo) error) {
	x.responseInfoCallback = f
}

// setGRPCDialOptions sets the gRPC dial options for new gRPC client connection.
func (x *wrapperPrm) setGRPCDialOptions(opts []grpc.DialOption) {
	x.dialOptions = opts
}

// newWrapper creates a clientWrapper that implements the client interface.
func newWrapper(prm wrapperPrm) *clientWrapper {
	var cl sdkClient.Client
	prmInit := sdkClient.PrmInit{
		Key:                  prm.key,
		ResponseInfoCallback: prm.responseInfoCallback,
	}

	cl.Init(prmInit)

	res := &clientWrapper{
		client:              &cl,
		clientStatusMonitor: newClientStatusMonitor(prm.logger, prm.address, prm.errorThreshold),
		prm:                 prm,
	}

	return res
}

// dial establishes a connection to the server from the FrostFS network.
// Returns an error describing failure reason. If failed, the client
// SHOULD NOT be used.
func (c *clientWrapper) dial(ctx context.Context) error {
	cl, err := c.getClient()
	if err != nil {
		return err
	}

	prmDial := sdkClient.PrmDial{
		Endpoint:        c.prm.address,
		DialTimeout:     c.prm.dialTimeout,
		StreamTimeout:   c.prm.streamTimeout,
		GRPCDialOptions: c.prm.dialOptions,
	}

	err = cl.Dial(ctx, prmDial)
	c.setDialed(err == nil)
	if err != nil {
		return err
	}

	return nil
}

// restart recreates and redial inner sdk client.
func (c *clientWrapper) restart(ctx context.Context) error {
	var cl sdkClient.Client
	prmInit := sdkClient.PrmInit{
		Key:                  c.prm.key,
		ResponseInfoCallback: c.prm.responseInfoCallback,
	}

	cl.Init(prmInit)

	prmDial := sdkClient.PrmDial{
		Endpoint:        c.prm.address,
		DialTimeout:     c.prm.dialTimeout,
		StreamTimeout:   c.prm.streamTimeout,
		GRPCDialOptions: c.prm.dialOptions,
	}

	// if connection is dialed before, to avoid routine / connection leak,
	// pool has to close it and then initialize once again.
	if c.isDialed() {
		c.scheduleGracefulClose()
	}

	err := cl.Dial(ctx, prmDial)
	c.setDialed(err == nil)
	if err != nil {
		return err
	}

	c.clientMutex.Lock()
	c.client = &cl
	c.clientMutex.Unlock()

	return nil
}

func (c *clientWrapper) isDialed() bool {
	c.mu.RLock()
	defer c.mu.RUnlock()
	return c.dialed
}

func (c *clientWrapper) setDialed(dialed bool) {
	c.mu.Lock()
	c.dialed = dialed
	c.mu.Unlock()
}

func (c *clientWrapper) getClient() (*sdkClient.Client, error) {
	c.clientMutex.RLock()
	defer c.clientMutex.RUnlock()
	if c.isHealthy() {
		return c.client, nil
	}
	return nil, errPoolClientUnhealthy
}

func (c *clientWrapper) getClientRaw() *sdkClient.Client {
	c.clientMutex.RLock()
	defer c.clientMutex.RUnlock()
	return c.client
}

// balanceGet invokes sdkClient.BalanceGet parse response status to error and return result as is.
func (c *clientWrapper) balanceGet(ctx context.Context, prm PrmBalanceGet) (accounting.Decimal, error) {
	cl, err := c.getClient()
	if err != nil {
		return accounting.Decimal{}, err
	}

	cliPrm := sdkClient.PrmBalanceGet{
		Account: prm.account,
	}

	start := time.Now()
	res, err := cl.BalanceGet(ctx, cliPrm)
	c.incRequests(time.Since(start), methodBalanceGet)
	var st apistatus.Status
	if res != nil {
		st = res.Status()
	}
	if err = c.handleError(ctx, st, err); err != nil {
		return accounting.Decimal{}, fmt.Errorf("balance get on client: %w", err)
	}

	return res.Amount(), nil
}

// containerPut invokes sdkClient.ContainerPut parse response status to error and return result as is.
// It also waits for the container to appear on the network.
func (c *clientWrapper) containerPut(ctx context.Context, prm PrmContainerPut) (cid.ID, error) {
	cl, err := c.getClient()
	if err != nil {
		return cid.ID{}, err
	}

	start := time.Now()
	res, err := cl.ContainerPut(ctx, prm.ClientParams)
	c.incRequests(time.Since(start), methodContainerPut)
	var st apistatus.Status
	if res != nil {
		st = res.Status()
	}
	if err = c.handleError(ctx, st, err); err != nil {
		return cid.ID{}, fmt.Errorf("container put on client: %w", err)
	}

	if prm.WaitParams == nil {
		prm.WaitParams = defaultWaitParams()
	}
	if err = prm.WaitParams.CheckValidity(); err != nil {
		return cid.ID{}, fmt.Errorf("invalid wait parameters: %w", err)
	}

	idCnr := res.ID()

	getPrm := PrmContainerGet{
		ContainerID: idCnr,
		Session:     prm.ClientParams.Session,
	}

	err = waitForContainerPresence(ctx, c, getPrm, prm.WaitParams)
	if err = c.handleError(ctx, nil, err); err != nil {
		return cid.ID{}, fmt.Errorf("wait container presence on client: %w", err)
	}

	return idCnr, nil
}

// containerGet invokes sdkClient.ContainerGet parse response status to error and return result as is.
func (c *clientWrapper) containerGet(ctx context.Context, prm PrmContainerGet) (container.Container, error) {
	cl, err := c.getClient()
	if err != nil {
		return container.Container{}, err
	}

	cliPrm := sdkClient.PrmContainerGet{
		ContainerID: &prm.ContainerID,
		Session:     prm.Session,
	}

	start := time.Now()
	res, err := cl.ContainerGet(ctx, cliPrm)
	c.incRequests(time.Since(start), methodContainerGet)
	var st apistatus.Status
	if res != nil {
		st = res.Status()
	}
	if err = c.handleError(ctx, st, err); err != nil {
		return container.Container{}, fmt.Errorf("container get on client: %w", err)
	}

	return res.Container(), nil
}

// containerList invokes sdkClient.ContainerList parse response status to error and return result as is.
func (c *clientWrapper) containerList(ctx context.Context, prm PrmContainerList) ([]cid.ID, error) {
	cl, err := c.getClient()
	if err != nil {
		return nil, err
	}

	cliPrm := sdkClient.PrmContainerList{
		OwnerID: prm.OwnerID,
		Session: prm.Session,
	}

	start := time.Now()
	res, err := cl.ContainerList(ctx, cliPrm)
	c.incRequests(time.Since(start), methodContainerList)
	var st apistatus.Status
	if res != nil {
		st = res.Status()
	}
	if err = c.handleError(ctx, st, err); err != nil {
		return nil, fmt.Errorf("container list on client: %w", err)
	}
	return res.Containers(), nil
}

func (c *clientStatusMonitor) incRequestCount() bool {
	return c.status.TryRLock()
}

func (c *clientStatusMonitor) decRequestCount() {
	c.status.RUnlock()
}

func (c *clientStatusMonitor) markClientClosed() {
	c.status.Lock()
}

// PrmListStream groups parameters of ListContainersStream operation.
type PrmListStream struct {
	OwnerID user.ID

	Session *session.Container
}

// ResListStream is designed to read list of object identifiers from FrostFS system.
//
// Must be initialized using Pool.ListContainersStream, any other usage is unsafe.
type ResListStream struct {
	r                   *sdkClient.ContainerListReader
	elapsedTimeCallback func(time.Duration)
	handleError         func(context.Context, apistatus.Status, error) error
}

// Read reads another list of the container identifiers.
func (x *ResListStream) Read(buf []cid.ID) (int, error) {
	start := time.Now()
	n, ok := x.r.Read(buf)
	x.elapsedTimeCallback(time.Since(start))
	if !ok {
		res, err := x.r.Close()
		if err == nil {
			return n, io.EOF
		}

		var status apistatus.Status
		if res != nil {
			status = res.Status()
		}
		err = x.handleError(nil, status, err)

		return n, err
	}

	return n, nil
}

// Iterate iterates over the list of found container identifiers.
// f can return true to stop iteration earlier.
//
// Returns an error if container can't be read.
func (x *ResListStream) Iterate(f func(cid.ID) bool) error {
	start := time.Now()
	err := x.r.Iterate(func(id cid.ID) bool {
		x.elapsedTimeCallback(time.Since(start))
		stop := f(id)
		start = time.Now()
		return stop
	})
	return err
}

// Close ends reading list of the matched containers and returns the result of the operation
// along with the final results. Must be called after using the ResListStream.
func (x *ResListStream) Close() {
	_, _ = x.r.Close()
}

// containerList invokes sdkClient.ContainerList parse response status to error and return result as is.
func (c *clientWrapper) containerListStream(ctx context.Context, prm PrmListStream) (ResListStream, error) {
	cl, err := c.getClient()
	if err != nil {
		return ResListStream{}, err
	}

	cliPrm := sdkClient.PrmContainerListStream{
		OwnerID: prm.OwnerID,
		Session: prm.Session,
	}

	start := time.Now()
	cnrRdr, err := cl.ContainerListInit(ctx, cliPrm)
	c.incRequests(time.Since(start), methodContainerListStream)
	if err = c.handleError(ctx, nil, err); err != nil {
		return ResListStream{}, fmt.Errorf("init container listing on client: %w", err)
	}
	return ResListStream{
		r: cnrRdr,
		elapsedTimeCallback: func(elapsed time.Duration) {
			c.incRequests(elapsed, methodContainerListStream)
		},
		handleError: c.handleError,
	}, nil
}

// containerDelete invokes sdkClient.ContainerDelete parse response status to error.
// It also waits for the container to be removed from the network.
func (c *clientWrapper) containerDelete(ctx context.Context, prm PrmContainerDelete) error {
	cl, err := c.getClient()
	if err != nil {
		return err
	}

	cliPrm := sdkClient.PrmContainerDelete{
		ContainerID: &prm.ContainerID,
		Session:     prm.Session,
	}

	start := time.Now()
	res, err := cl.ContainerDelete(ctx, cliPrm)
	c.incRequests(time.Since(start), methodContainerDelete)
	var st apistatus.Status
	if res != nil {
		st = res.Status()
	}
	if err = c.handleError(ctx, st, err); err != nil {
		return fmt.Errorf("container delete on client: %w", err)
	}

	if prm.WaitParams == nil {
		prm.WaitParams = defaultWaitParams()
	}
	if err := prm.WaitParams.CheckValidity(); err != nil {
		return fmt.Errorf("invalid wait parameters: %w", err)
	}

	getPrm := PrmContainerGet{
		ContainerID: prm.ContainerID,
		Session:     prm.Session,
	}

	return waitForContainerRemoved(ctx, c, getPrm, prm.WaitParams)
}

// apeManagerAddChain invokes sdkClient.APEManagerAddChain and parse response status to error.
func (c *clientWrapper) apeManagerAddChain(ctx context.Context, prm PrmAddAPEChain) error {
	cl, err := c.getClient()
	if err != nil {
		return err
	}

	cliPrm := sdkClient.PrmAPEManagerAddChain{
		ChainTarget: prm.Target,
		Chain:       prm.Chain,
	}

	start := time.Now()
	res, err := cl.APEManagerAddChain(ctx, cliPrm)
	c.incRequests(time.Since(start), methodAPEManagerAddChain)
	var st apistatus.Status
	if res != nil {
		st = res.Status()
	}
	if err = c.handleError(ctx, st, err); err != nil {
		return fmt.Errorf("add chain error: %w", err)
	}

	return nil
}

// apeManagerRemoveChain invokes sdkClient.APEManagerRemoveChain and parse response status to error.
func (c *clientWrapper) apeManagerRemoveChain(ctx context.Context, prm PrmRemoveAPEChain) error {
	cl, err := c.getClient()
	if err != nil {
		return err
	}

	cliPrm := sdkClient.PrmAPEManagerRemoveChain{
		ChainTarget: prm.Target,
		ChainID:     prm.ChainID,
	}

	start := time.Now()
	res, err := cl.APEManagerRemoveChain(ctx, cliPrm)
	c.incRequests(time.Since(start), methodAPEManagerRemoveChain)
	var st apistatus.Status
	if res != nil {
		st = res.Status()
	}
	if err = c.handleError(ctx, st, err); err != nil {
		return fmt.Errorf("remove chain error: %w", err)
	}

	return nil
}

// apeManagerListChains invokes sdkClient.APEManagerListChains. Returns chains and parsed response status to error.
func (c *clientWrapper) apeManagerListChains(ctx context.Context, prm PrmListAPEChains) ([]ape.Chain, error) {
	cl, err := c.getClient()
	if err != nil {
		return nil, err
	}

	cliPrm := sdkClient.PrmAPEManagerListChains{
		ChainTarget: prm.Target,
	}

	start := time.Now()
	res, err := cl.APEManagerListChains(ctx, cliPrm)
	c.incRequests(time.Since(start), methodAPEManagerListChains)
	var st apistatus.Status
	if res != nil {
		st = res.Status()
	}
	if err = c.handleError(ctx, st, err); err != nil {
		return nil, fmt.Errorf("list chains error: %w", err)
	}

	return res.Chains, nil
}

// endpointInfo invokes sdkClient.EndpointInfo parse response status to error and return result as is.
func (c *clientWrapper) endpointInfo(ctx context.Context, _ prmEndpointInfo) (netmap.NodeInfo, error) {
	cl, err := c.getClient()
	if err != nil {
		return netmap.NodeInfo{}, err
	}

	return c.endpointInfoRaw(ctx, cl)
}

func (c *clientWrapper) healthcheck(ctx context.Context) (netmap.NodeInfo, error) {
	cl := c.getClientRaw()
	return c.endpointInfoRaw(ctx, cl)
}

func (c *clientWrapper) endpointInfoRaw(ctx context.Context, cl *sdkClient.Client) (netmap.NodeInfo, error) {
	start := time.Now()
	res, err := cl.EndpointInfo(ctx, sdkClient.PrmEndpointInfo{})
	c.incRequests(time.Since(start), methodEndpointInfo)
	var st apistatus.Status
	if res != nil {
		st = res.Status()
	}
	if err = c.handleError(ctx, st, err); err != nil {
		return netmap.NodeInfo{}, fmt.Errorf("endpoint info on client: %w", err)
	}

	return res.NodeInfo(), nil
}

// networkInfo invokes sdkClient.NetworkInfo parse response status to error and return result as is.
func (c *clientWrapper) networkInfo(ctx context.Context, _ prmNetworkInfo) (netmap.NetworkInfo, error) {
	cl, err := c.getClient()
	if err != nil {
		return netmap.NetworkInfo{}, err
	}

	start := time.Now()
	res, err := cl.NetworkInfo(ctx, sdkClient.PrmNetworkInfo{})
	c.incRequests(time.Since(start), methodNetworkInfo)
	var st apistatus.Status
	if res != nil {
		st = res.Status()
	}
	if err = c.handleError(ctx, st, err); err != nil {
		return netmap.NetworkInfo{}, fmt.Errorf("network info on client: %w", err)
	}

	return res.Info(), nil
}

// networkInfo invokes sdkClient.NetworkInfo parse response status to error and return result as is.
func (c *clientWrapper) netMapSnapshot(ctx context.Context, _ prmNetMapSnapshot) (netmap.NetMap, error) {
	cl, err := c.getClient()
	if err != nil {
		return netmap.NetMap{}, err
	}

	start := time.Now()
	res, err := cl.NetMapSnapshot(ctx, sdkClient.PrmNetMapSnapshot{})
	c.incRequests(time.Since(start), methodNetMapSnapshot)
	var st apistatus.Status
	if res != nil {
		st = res.Status()
	}
	if err = c.handleError(ctx, st, err); err != nil {
		return netmap.NetMap{}, fmt.Errorf("network map snapshot on client: %w", err)
	}

	return res.NetMap(), nil
}

// objectPatch patches object in FrostFS.
func (c *clientWrapper) objectPatch(ctx context.Context, prm PrmObjectPatch) (ResPatchObject, error) {
	cl, err := c.getClient()
	if err != nil {
		return ResPatchObject{}, err
	}

	start := time.Now()
	pObj, err := cl.ObjectPatchInit(ctx, sdkClient.PrmObjectPatch{
		Address:        prm.addr,
		Session:        prm.stoken,
		Key:            prm.key,
		BearerToken:    prm.btoken,
		MaxChunkLength: prm.maxPayloadPatchChunkLength,
	})
	if err = c.handleError(ctx, nil, err); err != nil {
		return ResPatchObject{}, fmt.Errorf("init patching on API client: %w", err)
	}
	c.incRequests(time.Since(start), methodObjectPatch)

	start = time.Now()
	attrPatchSuccess := pObj.PatchAttributes(ctx, prm.newAttrs, prm.replaceAttrs)
	c.incRequests(time.Since(start), methodObjectPatch)

	if attrPatchSuccess {
		start = time.Now()
		_ = pObj.PatchPayload(ctx, prm.rng, prm.payload)
		c.incRequests(time.Since(start), methodObjectPatch)
	}

	res, err := pObj.Close(ctx)
	var st apistatus.Status
	if res != nil {
		st = res.Status()
	}
	if err = c.handleError(ctx, st, err); err != nil {
		return ResPatchObject{}, fmt.Errorf("client failure: %w", err)
	}

	return ResPatchObject{ObjectID: res.ObjectID()}, nil
}

// objectPut writes object to FrostFS.
func (c *clientWrapper) objectPut(ctx context.Context, prm PrmObjectPut) (ResPutObject, error) {
	if prm.bufferMaxSize == 0 {
		prm.bufferMaxSize = defaultBufferMaxSizeForPut
	}

	if prm.clientCut {
		return c.objectPutClientCut(ctx, prm)
	}

	return c.objectPutServerCut(ctx, prm)
}

func (c *clientWrapper) objectPutServerCut(ctx context.Context, prm PrmObjectPut) (ResPutObject, error) {
	cl, err := c.getClient()
	if err != nil {
		return ResPutObject{}, err
	}

	cliPrm := sdkClient.PrmObjectPutInit{
		CopiesNumber: prm.copiesNumber,
		Session:      prm.stoken,
		Key:          prm.key,
		BearerToken:  prm.btoken,
	}

	start := time.Now()
	wObj, err := cl.ObjectPutInit(ctx, cliPrm)
	c.incRequests(time.Since(start), methodObjectPut)
	if err = c.handleError(ctx, nil, err); err != nil {
		return ResPutObject{}, fmt.Errorf("init writing on API client: %w", err)
	}

	if wObj.WriteHeader(ctx, prm.hdr) {
		sz := prm.hdr.PayloadSize()

		if data := prm.hdr.Payload(); len(data) > 0 {
			if prm.payload != nil {
				prm.payload = io.MultiReader(bytes.NewReader(data), prm.payload)
			} else {
				prm.payload = bytes.NewReader(data)
				sz = uint64(len(data))
			}
		}

		if prm.payload != nil {
			if sz == 0 || sz > prm.bufferMaxSize {
				sz = prm.bufferMaxSize
			}

			buf := make([]byte, sz)

			var n int

			for {
				n, err = prm.payload.Read(buf)
				if n > 0 {
					start = time.Now()
					successWrite := wObj.WritePayloadChunk(ctx, buf[:n])
					c.incRequests(time.Since(start), methodObjectPut)
					if !successWrite {
						break
					}

					continue
				}

				if errors.Is(err, io.EOF) {
					break
				}

				return ResPutObject{}, fmt.Errorf("read payload: %w", c.handleError(ctx, nil, err))
			}
		}
	}

	res, err := wObj.Close(ctx)
	var st apistatus.Status
	if res != nil {
		st = res.Status()
	}
	if err = c.handleError(ctx, st, err); err != nil { // here err already carries both status and client errors
		return ResPutObject{}, fmt.Errorf("client failure: %w", err)
	}

	return ResPutObject{
		ObjectID: res.StoredObjectID(),
		Epoch:    res.StoredEpoch(),
	}, nil
}

func (c *clientWrapper) objectPutClientCut(ctx context.Context, prm PrmObjectPut) (ResPutObject, error) {
	putInitPrm := PrmObjectPutClientCutInit{
		PrmObjectPut: prm,
	}

	start := time.Now()
	wObj, err := c.objectPutInitTransformer(putInitPrm)
	c.incRequests(time.Since(start), methodObjectPut)
	if err = c.handleError(ctx, nil, err); err != nil {
		return ResPutObject{}, fmt.Errorf("init writing on API client: %w", err)
	}

	if wObj.WriteHeader(ctx, prm.hdr) {
		sz := prm.hdr.PayloadSize()

		if data := prm.hdr.Payload(); len(data) > 0 {
			if prm.payload != nil {
				prm.payload = io.MultiReader(bytes.NewReader(data), prm.payload)
			} else {
				prm.payload = bytes.NewReader(data)
				sz = uint64(len(data))
			}
		}

		if prm.payload != nil {
			if sz == 0 || sz > prm.bufferMaxSize {
				sz = prm.bufferMaxSize
			}

			buf := make([]byte, sz)

			var n int

			for {
				n, err = prm.payload.Read(buf)
				if n > 0 {
					start = time.Now()
					successWrite := wObj.WritePayloadChunk(ctx, buf[:n])
					c.incRequests(time.Since(start), methodObjectPut)
					if !successWrite {
						break
					}

					continue
				}

				if errors.Is(err, io.EOF) {
					break
				}

				return ResPutObject{}, fmt.Errorf("read payload: %w", c.handleError(ctx, nil, err))
			}
		}
	}

	res, err := wObj.Close(ctx)
	var st apistatus.Status
	if res != nil {
		st = res.Status
	}
	if err = c.handleError(ctx, st, err); err != nil { // here err already carries both status and client errors
		return ResPutObject{}, fmt.Errorf("client failure: %w", err)
	}

	return ResPutObject{
		ObjectID: res.OID,
		Epoch:    res.Epoch,
	}, nil
}

// objectDelete invokes sdkClient.ObjectDelete parse response status to error.
func (c *clientWrapper) objectDelete(ctx context.Context, prm PrmObjectDelete) error {
	cl, err := c.getClient()
	if err != nil {
		return err
	}

	cnr := prm.addr.Container()
	obj := prm.addr.Object()

	cliPrm := sdkClient.PrmObjectDelete{
		BearerToken: prm.btoken,
		Session:     prm.stoken,
		ContainerID: &cnr,
		ObjectID:    &obj,
		Key:         prm.key,
	}

	start := time.Now()
	res, err := cl.ObjectDelete(ctx, cliPrm)
	c.incRequests(time.Since(start), methodObjectDelete)
	var st apistatus.Status
	if res != nil {
		st = res.Status()
	}
	if err = c.handleError(ctx, st, err); err != nil {
		return fmt.Errorf("delete object on client: %w", err)
	}
	return nil
}

// objectGet returns reader for object.
func (c *clientWrapper) objectGet(ctx context.Context, prm PrmObjectGet) (ResGetObject, error) {
	cl, err := c.getClient()
	if err != nil {
		return ResGetObject{}, err
	}

	prmCnr := prm.addr.Container()
	prmObj := prm.addr.Object()

	cliPrm := sdkClient.PrmObjectGet{
		BearerToken: prm.btoken,
		Session:     prm.stoken,
		ContainerID: &prmCnr,
		ObjectID:    &prmObj,
		Key:         prm.key,
	}

	var res ResGetObject

	rObj, err := cl.ObjectGetInit(ctx, cliPrm)
	if err = c.handleError(ctx, nil, err); err != nil {
		return ResGetObject{}, fmt.Errorf("init object reading on client: %w", err)
	}

	start := time.Now()
	successReadHeader := rObj.ReadHeader(&res.Header)
	c.incRequests(time.Since(start), methodObjectGet)
	if !successReadHeader {
		rObjRes, err := rObj.Close()
		var st apistatus.Status
		if rObjRes != nil {
			st = rObjRes.Status()
		}
		err = c.handleError(ctx, st, err)
		return res, fmt.Errorf("read header: %w", err)
	}

	res.Payload = &objectReadCloser{
		reader: rObj,
		elapsedTimeCallback: func(elapsed time.Duration) {
			c.incRequests(elapsed, methodObjectGet)
		},
	}

	return res, nil
}

// objectHead invokes sdkClient.ObjectHead parse response status to error and return result as is.
func (c *clientWrapper) objectHead(ctx context.Context, prm PrmObjectHead) (object.Object, error) {
	cl, err := c.getClient()
	if err != nil {
		return object.Object{}, err
	}

	prmCnr := prm.addr.Container()
	prmObj := prm.addr.Object()

	cliPrm := sdkClient.PrmObjectHead{
		BearerToken: prm.btoken,
		Session:     prm.stoken,
		Raw:         prm.raw,
		ContainerID: &prmCnr,
		ObjectID:    &prmObj,
		Key:         prm.key,
	}

	var obj object.Object

	start := time.Now()
	res, err := cl.ObjectHead(ctx, cliPrm)
	c.incRequests(time.Since(start), methodObjectHead)
	var st apistatus.Status
	if res != nil {
		st = res.Status()
	}
	if err = c.handleError(ctx, st, err); err != nil {
		return obj, fmt.Errorf("read object header via client: %w", err)
	}
	if !res.ReadHeader(&obj) {
		return obj, errors.New("missing object header in response")
	}

	return obj, nil
}

// objectRange returns object range reader.
func (c *clientWrapper) objectRange(ctx context.Context, prm PrmObjectRange) (ResObjectRange, error) {
	cl, err := c.getClient()
	if err != nil {
		return ResObjectRange{}, err
	}

	prmCnr := prm.addr.Container()
	prmObj := prm.addr.Object()

	cliPrm := sdkClient.PrmObjectRange{
		BearerToken: prm.btoken,
		Session:     prm.stoken,
		ContainerID: &prmCnr,
		ObjectID:    &prmObj,
		Offset:      prm.off,
		Length:      prm.ln,
		Key:         prm.key,
	}

	start := time.Now()
	res, err := cl.ObjectRangeInit(ctx, cliPrm)
	c.incRequests(time.Since(start), methodObjectRange)
	if err = c.handleError(ctx, nil, err); err != nil {
		return ResObjectRange{}, fmt.Errorf("init payload range reading on client: %w", err)
	}

	return ResObjectRange{
		payload: res,
		elapsedTimeCallback: func(elapsed time.Duration) {
			c.incRequests(elapsed, methodObjectRange)
		},
	}, nil
}

// objectSearch invokes sdkClient.ObjectSearchInit parse response status to error and return result as is.
func (c *clientWrapper) objectSearch(ctx context.Context, prm PrmObjectSearch) (ResObjectSearch, error) {
	cl, err := c.getClient()
	if err != nil {
		return ResObjectSearch{}, err
	}

	cliPrm := sdkClient.PrmObjectSearch{
		ContainerID: &prm.cnrID,
		Filters:     prm.filters,
		Session:     prm.stoken,
		BearerToken: prm.btoken,
		Key:         prm.key,
	}

	res, err := cl.ObjectSearchInit(ctx, cliPrm)
	if err = c.handleError(ctx, nil, err); err != nil {
		return ResObjectSearch{}, fmt.Errorf("init object searching on client: %w", err)
	}

	return ResObjectSearch{r: res, handleError: c.handleError}, nil
}

// sessionCreate invokes sdkClient.SessionCreate parse response status to error and return result as is.
func (c *clientWrapper) sessionCreate(ctx context.Context, prm prmCreateSession) (resCreateSession, error) {
	cl, err := c.getClient()
	if err != nil {
		return resCreateSession{}, err
	}

	cliPrm := sdkClient.PrmSessionCreate{
		Expiration: prm.exp,
		Key:        &prm.key,
	}

	start := time.Now()
	res, err := cl.SessionCreate(ctx, cliPrm)
	c.incRequests(time.Since(start), methodSessionCreate)
	var st apistatus.Status
	if res != nil {
		st = res.Status()
	}
	if err = c.handleError(ctx, st, err); err != nil {
		return resCreateSession{}, fmt.Errorf("session creation on client: %w", err)
	}

	return resCreateSession{
		id:         res.ID(),
		sessionKey: res.PublicKey(),
	}, nil
}

func (c *clientStatusMonitor) isHealthy() bool {
	return c.healthy.Load() == statusHealthy
}

func (c *clientStatusMonitor) setHealthy() {
	c.healthy.Store(statusHealthy)
}

func (c *clientStatusMonitor) setUnhealthy() {
	c.healthy.Store(statusUnhealthyOnRequest)
}

func (c *clientStatusMonitor) address() string {
	return c.addr
}

func (c *clientStatusMonitor) incErrorRate() {
	c.mu.Lock()
	c.currentErrorCount++
	c.overallErrorCount++

	thresholdReached := c.currentErrorCount >= c.errorThreshold
	if thresholdReached {
		c.setUnhealthy()
		c.currentErrorCount = 0
	}
	c.mu.Unlock()

	if thresholdReached {
		c.log(zapcore.WarnLevel, "error threshold reached",
			zap.String("address", c.addr), zap.Uint32("threshold", c.errorThreshold))
	}
}

func (c *clientStatusMonitor) incErrorRateToUnhealthy(err error) {
	c.mu.Lock()
	c.currentErrorCount = 0
	c.overallErrorCount++
	c.setUnhealthy()
	c.mu.Unlock()

	c.log(zapcore.WarnLevel, "explicitly mark node unhealthy", zap.String("address", c.addr), zap.Error(err))
}

func (c *clientStatusMonitor) log(level zapcore.Level, msg string, fields ...zap.Field) {
	if c.logger == nil {
		return
	}

	c.logger.Log(level, msg, fields...)
}

func (c *clientStatusMonitor) currentErrorRate() uint32 {
	c.mu.RLock()
	defer c.mu.RUnlock()
	return c.currentErrorCount
}

func (c *clientStatusMonitor) overallErrorRate() uint64 {
	c.mu.RLock()
	defer c.mu.RUnlock()
	return c.overallErrorCount
}

func (c *clientStatusMonitor) methodsStatus() []StatusSnapshot {
	result := make([]StatusSnapshot, len(c.methods))
	for i, val := range c.methods {
		result[i] = val.Snapshot()
	}

	return result
}

func (c *clientWrapper) incRequests(elapsed time.Duration, method MethodIndex) {
	methodStat := c.methods[method]
	methodStat.IncRequests(elapsed)
	if c.prm.poolRequestInfoCallback != nil {
		c.prm.poolRequestInfoCallback(RequestInfo{
			Address: c.prm.address,
			Method:  method,
			Elapsed: elapsed,
		})
	}
}

func (c *clientWrapper) close() error {
	if !c.isDialed() {
		return nil
	}
	if cl := c.getClientRaw(); cl != nil {
		return cl.Close()
	}
	return nil
}

func (c *clientWrapper) scheduleGracefulClose() {
	cl := c.getClientRaw()
	if cl == nil {
		return
	}

	time.AfterFunc(c.prm.gracefulCloseOnSwitchTimeout, func() {
		if err := cl.Close(); err != nil {
			c.log(zap.DebugLevel, "close unhealthy client during rebalance", zap.String("address", c.address()), zap.Error(err))
		}
	})
}

func (c *clientStatusMonitor) handleError(ctx context.Context, st apistatus.Status, err error) error {
	if stErr := apistatus.ErrFromStatus(st); stErr != nil {
		switch stErr.(type) {
		case *apistatus.ServerInternal,
			*apistatus.WrongMagicNumber,
			*apistatus.SignatureVerification:
			c.incErrorRate()
		case *apistatus.NodeUnderMaintenance:
			c.incErrorRateToUnhealthy(stErr)
		}

		if err == nil {
			err = stErr
		}

		return err
	}

	if err != nil {
		if needCountError(ctx, err) {
			if sdkClient.IsErrNodeUnderMaintenance(err) {
				c.incErrorRateToUnhealthy(err)
			} else {
				c.incErrorRate()
			}
		}

		return err
	}

	return nil
}

func needCountError(ctx context.Context, err error) bool {
	// non-status logic error that could be returned
	// from the SDK client; should not be considered
	// as a connection error
	var siErr *object.SplitInfoError
	if errors.As(err, &siErr) {
		return false
	}
	var eiErr *object.ECInfoError
	if errors.As(err, &eiErr) {
		return false
	}

	if ctx != nil && errors.Is(ctx.Err(), context.Canceled) {
		return false
	}

	return true
}

// clientBuilder is a type alias of client constructors which open connection
// to the given endpoint.
type clientBuilder = func(endpoint string) client

// RequestInfo groups info about pool request.
type RequestInfo struct {
	Address string
	Method  MethodIndex
	Elapsed time.Duration
}