package remotewrite

import (
	"flag"
	"fmt"
	"net/http"
	"net/url"
	"path/filepath"
	"strconv"
	"sync"
	"sync/atomic"
	"time"

	"github.com/VictoriaMetrics/VictoriaMetrics/lib/httpserver"

	"github.com/VictoriaMetrics/VictoriaMetrics/lib/auth"
	"github.com/VictoriaMetrics/VictoriaMetrics/lib/bloomfilter"
	"github.com/VictoriaMetrics/VictoriaMetrics/lib/bytesutil"
	"github.com/VictoriaMetrics/VictoriaMetrics/lib/cgroup"
	"github.com/VictoriaMetrics/VictoriaMetrics/lib/fasttime"
	"github.com/VictoriaMetrics/VictoriaMetrics/lib/flagutil"
	"github.com/VictoriaMetrics/VictoriaMetrics/lib/fs"
	"github.com/VictoriaMetrics/VictoriaMetrics/lib/logger"
	"github.com/VictoriaMetrics/VictoriaMetrics/lib/memory"
	"github.com/VictoriaMetrics/VictoriaMetrics/lib/persistentqueue"
	"github.com/VictoriaMetrics/VictoriaMetrics/lib/procutil"
	"github.com/VictoriaMetrics/VictoriaMetrics/lib/prompbmarshal"
	"github.com/VictoriaMetrics/VictoriaMetrics/lib/promrelabel"
	"github.com/VictoriaMetrics/VictoriaMetrics/lib/promutils"
	"github.com/VictoriaMetrics/VictoriaMetrics/lib/ratelimiter"
	"github.com/VictoriaMetrics/VictoriaMetrics/lib/streamaggr"
	"github.com/VictoriaMetrics/VictoriaMetrics/lib/tenantmetrics"
	"github.com/VictoriaMetrics/metrics"
	"github.com/cespare/xxhash/v2"
)

var (
	remoteWriteURLs = flagutil.NewArrayString("remoteWrite.url", "Remote storage URL to write data to. It must support either VictoriaMetrics remote write protocol "+
		"or Prometheus remote_write protocol. Example url: http://<victoriametrics-host>:8428/api/v1/write . "+
		"Pass multiple -remoteWrite.url options in order to replicate the collected data to multiple remote storage systems. "+
		"The data can be sharded among the configured remote storage systems if -remoteWrite.shardByURL flag is set")
	remoteWriteMultitenantURLs = flagutil.NewArrayString("remoteWrite.multitenantURL", "Base path for multitenant remote storage URL to write data to. "+
		"See https://docs.victoriametrics.com/vmagent/#multitenancy for details. Example url: http://<vminsert>:8480 . "+
		"Pass multiple -remoteWrite.multitenantURL flags in order to replicate data to multiple remote storage systems. "+
		"This flag is deprecated in favor of -enableMultitenantHandlers . See https://docs.victoriametrics.com/vmagent/#multitenancy")
	enableMultitenantHandlers = flag.Bool("enableMultitenantHandlers", false, "Whether to process incoming data via multitenant insert handlers according to "+
		"https://docs.victoriametrics.com/cluster-victoriametrics/#url-format . By default incoming data is processed via single-node insert handlers "+
		"according to https://docs.victoriametrics.com/#how-to-import-time-series-data ."+
		"See https://docs.victoriametrics.com/vmagent/#multitenancy for details")
	shardByURL = flag.Bool("remoteWrite.shardByURL", false, "Whether to shard outgoing series across all the remote storage systems enumerated via -remoteWrite.url . "+
		"By default the data is replicated across all the -remoteWrite.url . See https://docs.victoriametrics.com/vmagent/#sharding-among-remote-storages")
	shardByURLLabels = flagutil.NewArrayString("remoteWrite.shardByURL.labels", "Optional list of labels, which must be used for sharding outgoing samples "+
		"among remote storage systems if -remoteWrite.shardByURL command-line flag is set. By default all the labels are used for sharding in order to gain "+
		"even distribution of series over the specified -remoteWrite.url systems. See also -remoteWrite.shardByURL.ignoreLabels")
	shardByURLIgnoreLabels = flagutil.NewArrayString("remoteWrite.shardByURL.ignoreLabels", "Optional list of labels, which must be ignored when sharding outgoing samples "+
		"among remote storage systems if -remoteWrite.shardByURL command-line flag is set. By default all the labels are used for sharding in order to gain "+
		"even distribution of series over the specified -remoteWrite.url systems. See also -remoteWrite.shardByURL.labels")
	tmpDataPath = flag.String("remoteWrite.tmpDataPath", "vmagent-remotewrite-data", "Path to directory for storing pending data, which isn't sent to the configured -remoteWrite.url . "+
		"See also -remoteWrite.maxDiskUsagePerURL and -remoteWrite.disableOnDiskQueue")
	keepDanglingQueues = flag.Bool("remoteWrite.keepDanglingQueues", false, "Keep persistent queues contents at -remoteWrite.tmpDataPath in case there are no matching -remoteWrite.url. "+
		"Useful when -remoteWrite.url is changed temporarily and persistent queue files will be needed later on.")
	queues = flag.Int("remoteWrite.queues", cgroup.AvailableCPUs()*2, "The number of concurrent queues to each -remoteWrite.url. Set more queues if default number of queues "+
		"isn't enough for sending high volume of collected data to remote storage. "+
		"Default value depends on the number of available CPU cores. It should work fine in most cases since it minimizes resource usage")
	showRemoteWriteURL = flag.Bool("remoteWrite.showURL", false, "Whether to show -remoteWrite.url in the exported metrics. "+
		"It is hidden by default, since it can contain sensitive info such as auth key")
	maxPendingBytesPerURL = flagutil.NewArrayBytes("remoteWrite.maxDiskUsagePerURL", 0, "The maximum file-based buffer size in bytes at -remoteWrite.tmpDataPath "+
		"for each -remoteWrite.url. When buffer size reaches the configured maximum, then old data is dropped when adding new data to the buffer. "+
		"Buffered data is stored in ~500MB chunks. It is recommended to set the value for this flag to a multiple of the block size 500MB. "+
		"Disk usage is unlimited if the value is set to 0")
	significantFigures = flagutil.NewArrayInt("remoteWrite.significantFigures", 0, "The number of significant figures to leave in metric values before writing them "+
		"to remote storage. See https://en.wikipedia.org/wiki/Significant_figures . Zero value saves all the significant figures. "+
		"This option may be used for improving data compression for the stored metrics. See also -remoteWrite.roundDigits")
	roundDigits = flagutil.NewArrayInt("remoteWrite.roundDigits", 100, "Round metric values to this number of decimal digits after the point before "+
		"writing them to remote storage. "+
		"Examples: -remoteWrite.roundDigits=2 would round 1.236 to 1.24, while -remoteWrite.roundDigits=-1 would round 126.78 to 130. "+
		"By default, digits rounding is disabled. Set it to 100 for disabling it for a particular remote storage. "+
		"This option may be used for improving data compression for the stored metrics")
	sortLabels = flag.Bool("sortLabels", false, `Whether to sort labels for incoming samples before writing them to all the configured remote storage systems. `+
		`This may be needed for reducing memory usage at remote storage when the order of labels in incoming samples is random. `+
		`For example, if m{k1="v1",k2="v2"} may be sent as m{k2="v2",k1="v1"}`+
		`Enabled sorting for labels can slow down ingestion performance a bit`)
	maxHourlySeries = flag.Int("remoteWrite.maxHourlySeries", 0, "The maximum number of unique series vmagent can send to remote storage systems during the last hour. "+
		"Excess series are logged and dropped. This can be useful for limiting series cardinality. See https://docs.victoriametrics.com/vmagent/#cardinality-limiter")
	maxDailySeries = flag.Int("remoteWrite.maxDailySeries", 0, "The maximum number of unique series vmagent can send to remote storage systems during the last 24 hours. "+
		"Excess series are logged and dropped. This can be useful for limiting series churn rate. See https://docs.victoriametrics.com/vmagent/#cardinality-limiter")
	maxIngestionRate = flag.Int("maxIngestionRate", 0, "The maximum number of samples vmagent can receive per second. Data ingestion is paused when the limit is exceeded. "+
		"By default there are no limits on samples ingestion rate. See also -remoteWrite.rateLimit")

	streamAggrConfig = flagutil.NewArrayString("remoteWrite.streamAggr.config", "Optional path to file with stream aggregation config. "+
		"See https://docs.victoriametrics.com/stream-aggregation/ . "+
		"See also -remoteWrite.streamAggr.keepInput, -remoteWrite.streamAggr.dropInput and -remoteWrite.streamAggr.dedupInterval")
	streamAggrKeepInput = flagutil.NewArrayBool("remoteWrite.streamAggr.keepInput", "Whether to keep all the input samples after the aggregation "+
		"with -remoteWrite.streamAggr.config. By default, only aggregates samples are dropped, while the remaining samples "+
		"are written to the corresponding -remoteWrite.url . See also -remoteWrite.streamAggr.dropInput and https://docs.victoriametrics.com/stream-aggregation/")
	streamAggrDropInput = flagutil.NewArrayBool("remoteWrite.streamAggr.dropInput", "Whether to drop all the input samples after the aggregation "+
		"with -remoteWrite.streamAggr.config. By default, only aggregates samples are dropped, while the remaining samples "+
		"are written to the corresponding -remoteWrite.url . See also -remoteWrite.streamAggr.keepInput and https://docs.victoriametrics.com/stream-aggregation/")
	streamAggrDedupInterval = flagutil.NewArrayDuration("remoteWrite.streamAggr.dedupInterval", 0, "Input samples are de-duplicated with this interval before optional aggregation "+
		"with -remoteWrite.streamAggr.config . See also -dedup.minScrapeInterval and https://docs.victoriametrics.com/stream-aggregation/#deduplication")
	streamAggrIgnoreOldSamples = flagutil.NewArrayBool("remoteWrite.streamAggr.ignoreOldSamples", "Whether to ignore input samples with old timestamps outside the current aggregation interval "+
		"for the corresponding -remoteWrite.streamAggr.config . See https://docs.victoriametrics.com/stream-aggregation/#ignoring-old-samples")
	streamAggrDropInputLabels = flagutil.NewArrayString("streamAggr.dropInputLabels", "An optional list of labels to drop from samples "+
		"before stream de-duplication and aggregation . See https://docs.victoriametrics.com/stream-aggregation/#dropping-unneeded-labels")

	disableOnDiskQueue = flag.Bool("remoteWrite.disableOnDiskQueue", false, "Whether to disable storing pending data to -remoteWrite.tmpDataPath "+
		"when the configured remote storage systems cannot keep up with the data ingestion rate. See https://docs.victoriametrics.com/vmagent/#disabling-on-disk-persistence ."+
		"See also -remoteWrite.dropSamplesOnOverload")
	dropSamplesOnOverload = flag.Bool("remoteWrite.dropSamplesOnOverload", false, "Whether to drop samples when -remoteWrite.disableOnDiskQueue is set and if the samples "+
		"cannot be pushed into the configured remote storage systems in a timely manner. See https://docs.victoriametrics.com/vmagent/#disabling-on-disk-persistence")
)

var (
	// rwctxsDefault contains statically populated entries when -remoteWrite.url is specified.
	rwctxsDefault []*remoteWriteCtx

	// rwctxsMap contains dynamically populated entries when -remoteWrite.multitenantURL is specified.
	rwctxsMap     = make(map[tenantmetrics.TenantID][]*remoteWriteCtx)
	rwctxsMapLock sync.Mutex

	// Data without tenant id is written to defaultAuthToken if -remoteWrite.multitenantURL is specified.
	defaultAuthToken = &auth.Token{}

	// ErrQueueFullHTTPRetry must be returned when TryPush() returns false.
	ErrQueueFullHTTPRetry = &httpserver.ErrorWithStatusCode{
		Err: fmt.Errorf("remote storage systems cannot keep up with the data ingestion rate; retry the request later " +
			"or remove -remoteWrite.disableOnDiskQueue from vmagent command-line flags, so it could save pending data to -remoteWrite.tmpDataPath; " +
			"see https://docs.victoriametrics.com/vmagent/#disabling-on-disk-persistence"),
		StatusCode: http.StatusTooManyRequests,
	}
)

// MultitenancyEnabled returns true if -enableMultitenantHandlers or -remoteWrite.multitenantURL is specified.
func MultitenancyEnabled() bool {
	return *enableMultitenantHandlers || len(*remoteWriteMultitenantURLs) > 0
}

// Contains the current relabelConfigs.
var allRelabelConfigs atomic.Pointer[relabelConfigs]

// maxQueues limits the maximum value for `-remoteWrite.queues`. There is no sense in setting too high value,
// since it may lead to high memory usage due to big number of buffers.
var maxQueues = cgroup.AvailableCPUs() * 16

const persistentQueueDirname = "persistent-queue"

// InitSecretFlags must be called after flag.Parse and before any logging.
func InitSecretFlags() {
	if !*showRemoteWriteURL {
		// remoteWrite.url can contain authentication codes, so hide it at `/metrics` output.
		flagutil.RegisterSecretFlag("remoteWrite.url")
	}
}

var (
	shardByURLLabelsMap       map[string]struct{}
	shardByURLIgnoreLabelsMap map[string]struct{}
)

// Init initializes remotewrite.
//
// It must be called after flag.Parse().
//
// Stop must be called for graceful shutdown.
func Init() {
	if len(*remoteWriteURLs) == 0 && len(*remoteWriteMultitenantURLs) == 0 {
		logger.Fatalf("at least one `-remoteWrite.url` or `-remoteWrite.multitenantURL` command-line flag must be set")
	}
	if len(*remoteWriteURLs) > 0 && len(*remoteWriteMultitenantURLs) > 0 {
		logger.Fatalf("cannot set both `-remoteWrite.url` and `-remoteWrite.multitenantURL` command-line flags")
	}
	if *maxHourlySeries > 0 {
		hourlySeriesLimiter = bloomfilter.NewLimiter(*maxHourlySeries, time.Hour)
		_ = metrics.NewGauge(`vmagent_hourly_series_limit_max_series`, func() float64 {
			return float64(hourlySeriesLimiter.MaxItems())
		})
		_ = metrics.NewGauge(`vmagent_hourly_series_limit_current_series`, func() float64 {
			return float64(hourlySeriesLimiter.CurrentItems())
		})
	}
	if *maxDailySeries > 0 {
		dailySeriesLimiter = bloomfilter.NewLimiter(*maxDailySeries, 24*time.Hour)
		_ = metrics.NewGauge(`vmagent_daily_series_limit_max_series`, func() float64 {
			return float64(dailySeriesLimiter.MaxItems())
		})
		_ = metrics.NewGauge(`vmagent_daily_series_limit_current_series`, func() float64 {
			return float64(dailySeriesLimiter.CurrentItems())
		})
	}

	if *queues > maxQueues {
		*queues = maxQueues
	}
	if *queues <= 0 {
		*queues = 1
	}

	if len(*shardByURLLabels) > 0 && len(*shardByURLIgnoreLabels) > 0 {
		logger.Fatalf("-remoteWrite.shardByURL.labels and -remoteWrite.shardByURL.ignoreLabels cannot be set simultaneously; " +
			"see https://docs.victoriametrics.com/vmagent/#sharding-among-remote-storages")
	}
	shardByURLLabelsMap = newMapFromStrings(*shardByURLLabels)
	shardByURLIgnoreLabelsMap = newMapFromStrings(*shardByURLIgnoreLabels)

	initLabelsGlobal()

	// Register SIGHUP handler for config reload before loadRelabelConfigs.
	// This guarantees that the config will be re-read if the signal arrives just after loadRelabelConfig.
	// See https://github.com/VictoriaMetrics/VictoriaMetrics/issues/1240
	sighupCh := procutil.NewSighupChan()

	rcs, err := loadRelabelConfigs()
	if err != nil {
		logger.Fatalf("cannot load relabel configs: %s", err)
	}
	allRelabelConfigs.Store(rcs)
	relabelConfigSuccess.Set(1)
	relabelConfigTimestamp.Set(fasttime.UnixTimestamp())

	if len(*remoteWriteURLs) > 0 {
		rwctxsDefault = newRemoteWriteCtxs(nil, *remoteWriteURLs)
	}
	dropDanglingQueues()

	// Start config reloader.
	configReloaderWG.Add(1)
	go func() {
		defer configReloaderWG.Done()
		for {
			select {
			case <-sighupCh:
			case <-configReloaderStopCh:
				return
			}
			reloadRelabelConfigs()
			reloadStreamAggrConfigs()
		}
	}()
}

func dropDanglingQueues() {
	if *keepDanglingQueues {
		return
	}
	if len(*remoteWriteMultitenantURLs) > 0 {
		// Do not drop dangling queues for *remoteWriteMultitenantURLs, since it is impossible to determine
		// unused queues for multitenant urls - they are created on demand when new sample for the given
		// tenant is pushed to remote storage.
		return
	}
	// Remove dangling persistent queues, if any.
	// This is required for the case when the number of queues has been changed or URL have been changed.
	// See https://github.com/VictoriaMetrics/VictoriaMetrics/issues/4014
	//
	existingQueues := make(map[string]struct{}, len(rwctxsDefault))
	for _, rwctx := range rwctxsDefault {
		existingQueues[rwctx.fq.Dirname()] = struct{}{}
	}

	queuesDir := filepath.Join(*tmpDataPath, persistentQueueDirname)
	files := fs.MustReadDir(queuesDir)
	removed := 0
	for _, f := range files {
		dirname := f.Name()
		if _, ok := existingQueues[dirname]; !ok {
			logger.Infof("removing dangling queue %q", dirname)
			fullPath := filepath.Join(queuesDir, dirname)
			fs.MustRemoveAll(fullPath)
			removed++
		}
	}
	if removed > 0 {
		logger.Infof("removed %d dangling queues from %q, active queues: %d", removed, *tmpDataPath, len(rwctxsDefault))
	}
}

func reloadRelabelConfigs() {
	relabelConfigReloads.Inc()
	logger.Infof("reloading relabel configs pointed by -remoteWrite.relabelConfig and -remoteWrite.urlRelabelConfig")
	rcs, err := loadRelabelConfigs()
	if err != nil {
		relabelConfigReloadErrors.Inc()
		relabelConfigSuccess.Set(0)
		logger.Errorf("cannot reload relabel configs; preserving the previous configs; error: %s", err)
		return
	}
	allRelabelConfigs.Store(rcs)
	relabelConfigSuccess.Set(1)
	relabelConfigTimestamp.Set(fasttime.UnixTimestamp())
	logger.Infof("successfully reloaded relabel configs")
}

var (
	relabelConfigReloads      = metrics.NewCounter(`vmagent_relabel_config_reloads_total`)
	relabelConfigReloadErrors = metrics.NewCounter(`vmagent_relabel_config_reloads_errors_total`)
	relabelConfigSuccess      = metrics.NewGauge(`vmagent_relabel_config_last_reload_successful`, nil)
	relabelConfigTimestamp    = metrics.NewCounter(`vmagent_relabel_config_last_reload_success_timestamp_seconds`)
)

func reloadStreamAggrConfigs() {
	if len(*remoteWriteMultitenantURLs) > 0 {
		rwctxsMapLock.Lock()
		for _, rwctxs := range rwctxsMap {
			reinitStreamAggr(rwctxs)
		}
		rwctxsMapLock.Unlock()
	} else {
		reinitStreamAggr(rwctxsDefault)
	}
}

func reinitStreamAggr(rwctxs []*remoteWriteCtx) {
	for _, rwctx := range rwctxs {
		rwctx.reinitStreamAggr()
	}
}

func newRemoteWriteCtxs(at *auth.Token, urls []string) []*remoteWriteCtx {
	if len(urls) == 0 {
		logger.Panicf("BUG: urls must be non-empty")
	}

	maxInmemoryBlocks := memory.Allowed() / len(urls) / *maxRowsPerBlock / 100
	if maxInmemoryBlocks / *queues > 100 {
		// There is no much sense in keeping higher number of blocks in memory,
		// since this means that the producer outperforms consumer and the queue
		// will continue growing. It is better storing the queue to file.
		maxInmemoryBlocks = 100 * *queues
	}
	if maxInmemoryBlocks < 2 {
		maxInmemoryBlocks = 2
	}
	rwctxs := make([]*remoteWriteCtx, len(urls))
	for i, remoteWriteURLRaw := range urls {
		remoteWriteURL, err := url.Parse(remoteWriteURLRaw)
		if err != nil {
			logger.Fatalf("invalid -remoteWrite.url=%q: %s", remoteWriteURL, err)
		}
		sanitizedURL := fmt.Sprintf("%d:secret-url", i+1)
		if at != nil {
			// Construct full remote_write url for the given tenant according to https://docs.victoriametrics.com/cluster-victoriametrics/#url-format
			remoteWriteURL.Path = fmt.Sprintf("%s/insert/%d:%d/prometheus/api/v1/write", remoteWriteURL.Path, at.AccountID, at.ProjectID)
			sanitizedURL = fmt.Sprintf("%s:%d:%d", sanitizedURL, at.AccountID, at.ProjectID)
		}
		if *showRemoteWriteURL {
			sanitizedURL = fmt.Sprintf("%d:%s", i+1, remoteWriteURL)
		}
		rwctxs[i] = newRemoteWriteCtx(i, remoteWriteURL, maxInmemoryBlocks, sanitizedURL)
	}
	return rwctxs
}

var configReloaderStopCh = make(chan struct{})
var configReloaderWG sync.WaitGroup

// StartIngestionRateLimiter starts ingestion rate limiter.
//
// Ingestion rate limiter must be started before Init() call.
//
// StopIngestionRateLimiter must be called before Stop() call in order to unblock all the callers
// to ingestion rate limiter. Otherwise deadlock may occur at Stop() call.
func StartIngestionRateLimiter() {
	if *maxIngestionRate <= 0 {
		return
	}
	ingestionRateLimitReached := metrics.NewCounter(`vmagent_max_ingestion_rate_limit_reached_total`)
	ingestionRateLimiterStopCh = make(chan struct{})
	ingestionRateLimiter = ratelimiter.New(int64(*maxIngestionRate), ingestionRateLimitReached, ingestionRateLimiterStopCh)
}

// StopIngestionRateLimiter stops ingestion rate limiter.
func StopIngestionRateLimiter() {
	if ingestionRateLimiterStopCh == nil {
		return
	}
	close(ingestionRateLimiterStopCh)
	ingestionRateLimiterStopCh = nil
}

var (
	ingestionRateLimiter       *ratelimiter.RateLimiter
	ingestionRateLimiterStopCh chan struct{}
)

// Stop stops remotewrite.
//
// It is expected that nobody calls TryPush during and after the call to this func.
func Stop() {
	close(configReloaderStopCh)
	configReloaderWG.Wait()

	for _, rwctx := range rwctxsDefault {
		rwctx.MustStop()
	}
	rwctxsDefault = nil

	// There is no need in locking rwctxsMapLock here, since nobody should call TryPush during the Stop call.
	for _, rwctxs := range rwctxsMap {
		for _, rwctx := range rwctxs {
			rwctx.MustStop()
		}
	}
	rwctxsMap = nil

	if sl := hourlySeriesLimiter; sl != nil {
		sl.MustStop()
	}
	if sl := dailySeriesLimiter; sl != nil {
		sl.MustStop()
	}
}

// PushDropSamplesOnFailure pushes wr to the configured remote storage systems set via -remoteWrite.url and -remoteWrite.multitenantURL
//
// If at is nil, then the data is pushed to the configured -remoteWrite.url.
// If at isn't nil, the data is pushed to the configured -remoteWrite.multitenantURL.
//
// PushDropSamplesOnFailure can modify wr contents.
func PushDropSamplesOnFailure(at *auth.Token, wr *prompbmarshal.WriteRequest) {
	_ = tryPush(at, wr, true)
}

// TryPush tries sending wr to the configured remote storage systems set via -remoteWrite.url and -remoteWrite.multitenantURL
//
// If at is nil, then the data is pushed to the configured -remoteWrite.url.
// If at isn't nil, the data is pushed to the configured -remoteWrite.multitenantURL.
//
// TryPush can modify wr contents, so the caller must re-initialize wr before calling TryPush() after unsuccessful attempt.
// TryPush may send partial data from wr on unsuccessful attempt, so repeated call for the same wr may send the data multiple times.
//
// The caller must return ErrQueueFullHTTPRetry to the client, which sends wr, if TryPush returns false.
func TryPush(at *auth.Token, wr *prompbmarshal.WriteRequest) bool {
	return tryPush(at, wr, *dropSamplesOnOverload)
}

func tryPush(at *auth.Token, wr *prompbmarshal.WriteRequest, dropSamplesOnFailure bool) bool {
	tss := wr.Timeseries

	if at == nil && MultitenancyEnabled() {
		// Write data to default tenant if at isn't set when multitenancy is enabled.
		at = defaultAuthToken
	}

	var tenantRctx *relabelCtx
	var rwctxs []*remoteWriteCtx
	if at == nil {
		rwctxs = rwctxsDefault
	} else if len(*remoteWriteMultitenantURLs) == 0 {
		// Convert at to (vm_account_id, vm_project_id) labels.
		tenantRctx = getRelabelCtx()
		defer putRelabelCtx(tenantRctx)
		rwctxs = rwctxsDefault
	} else {
		rwctxsMapLock.Lock()
		tenantID := tenantmetrics.TenantID{
			AccountID: at.AccountID,
			ProjectID: at.ProjectID,
		}
		rwctxs = rwctxsMap[tenantID]
		if rwctxs == nil {
			rwctxs = newRemoteWriteCtxs(at, *remoteWriteMultitenantURLs)
			rwctxsMap[tenantID] = rwctxs
		}
		rwctxsMapLock.Unlock()
	}

	rowsCount := getRowsCount(tss)

	if *disableOnDiskQueue {
		// Quick check whether writes to configured remote storage systems are blocked.
		// This allows saving CPU time spent on relabeling and block compression
		// if some of remote storage systems cannot keep up with the data ingestion rate.
		for _, rwctx := range rwctxs {
			if rwctx.fq.IsWriteBlocked() {
				pushFailures.Inc()
				if dropSamplesOnFailure {
					// Just drop samples
					samplesDropped.Add(rowsCount)
					return true
				}
				return false
			}
		}
	}

	var rctx *relabelCtx
	rcs := allRelabelConfigs.Load()
	pcsGlobal := rcs.global
	if pcsGlobal.Len() > 0 {
		rctx = getRelabelCtx()
		defer putRelabelCtx(rctx)
	}
	globalRowsPushedBeforeRelabel.Add(rowsCount)
	maxSamplesPerBlock := *maxRowsPerBlock
	// Allow up to 10x of labels per each block on average.
	maxLabelsPerBlock := 10 * maxSamplesPerBlock

	for len(tss) > 0 {
		// Process big tss in smaller blocks in order to reduce the maximum memory usage
		samplesCount := 0
		labelsCount := 0
		i := 0
		for i < len(tss) {
			samplesCount += len(tss[i].Samples)
			labelsCount += len(tss[i].Samples) * len(tss[i].Labels)
			i++
			if samplesCount >= maxSamplesPerBlock || labelsCount >= maxLabelsPerBlock {
				break
			}
		}

		ingestionRateLimiter.Register(samplesCount)

		tssBlock := tss
		if i < len(tss) {
			tssBlock = tss[:i]
			tss = tss[i:]
		} else {
			tss = nil
		}
		if tenantRctx != nil {
			tenantRctx.tenantToLabels(tssBlock, at.AccountID, at.ProjectID)
		}
		if rctx != nil {
			rowsCountBeforeRelabel := getRowsCount(tssBlock)
			tssBlock = rctx.applyRelabeling(tssBlock, pcsGlobal)
			rowsCountAfterRelabel := getRowsCount(tssBlock)
			rowsDroppedByGlobalRelabel.Add(rowsCountBeforeRelabel - rowsCountAfterRelabel)
		}
		sortLabelsIfNeeded(tssBlock)
		tssBlock = limitSeriesCardinality(tssBlock)
		if !tryPushBlockToRemoteStorages(rwctxs, tssBlock) {
			if !*disableOnDiskQueue {
				logger.Panicf("BUG: tryPushBlockToRemoteStorages must return true if -remoteWrite.disableOnDiskQueue isn't set")
			}
			pushFailures.Inc()
			if dropSamplesOnFailure {
				samplesDropped.Add(rowsCount)
				return true
			}
			return false
		}
	}
	return true
}

var (
	samplesDropped = metrics.NewCounter(`vmagent_remotewrite_samples_dropped_total`)
	pushFailures   = metrics.NewCounter(`vmagent_remotewrite_push_failures_total`)
)

func tryPushBlockToRemoteStorages(rwctxs []*remoteWriteCtx, tssBlock []prompbmarshal.TimeSeries) bool {
	if len(tssBlock) == 0 {
		// Nothing to push
		return true
	}

	if len(rwctxs) == 1 {
		// Fast path - just push data to the configured single remote storage
		return rwctxs[0].TryPush(tssBlock)
	}

	// We need to push tssBlock to multiple remote storages.
	// This is either sharding or replication depending on -remoteWrite.shardByURL command-line flag value.
	if *shardByURL {
		// Shard the data among rwctxs
		tssByURL := make([][]prompbmarshal.TimeSeries, len(rwctxs))
		tmpLabels := promutils.GetLabels()
		for _, ts := range tssBlock {
			hashLabels := ts.Labels
			if len(shardByURLLabelsMap) > 0 {
				hashLabels = tmpLabels.Labels[:0]
				for _, label := range ts.Labels {
					if _, ok := shardByURLLabelsMap[label.Name]; ok {
						hashLabels = append(hashLabels, label)
					}
				}
				tmpLabels.Labels = hashLabels
			} else if len(shardByURLIgnoreLabelsMap) > 0 {
				hashLabels = tmpLabels.Labels[:0]
				for _, label := range ts.Labels {
					if _, ok := shardByURLIgnoreLabelsMap[label.Name]; !ok {
						hashLabels = append(hashLabels, label)
					}
				}
				tmpLabels.Labels = hashLabels
			}
			h := getLabelsHash(hashLabels)
			idx := h % uint64(len(tssByURL))
			tssByURL[idx] = append(tssByURL[idx], ts)
		}
		promutils.PutLabels(tmpLabels)

		// Push sharded data to remote storages in parallel in order to reduce
		// the time needed for sending the data to multiple remote storage systems.
		var wg sync.WaitGroup
		var anyPushFailed atomic.Bool
		for i, rwctx := range rwctxs {
			tssShard := tssByURL[i]
			if len(tssShard) == 0 {
				continue
			}
			wg.Add(1)
			go func(rwctx *remoteWriteCtx, tss []prompbmarshal.TimeSeries) {
				defer wg.Done()
				if !rwctx.TryPush(tss) {
					anyPushFailed.Store(true)
				}
			}(rwctx, tssShard)
		}
		wg.Wait()
		return !anyPushFailed.Load()
	}

	// Replicate data among rwctxs.
	// Push block to remote storages in parallel in order to reduce
	// the time needed for sending the data to multiple remote storage systems.
	var wg sync.WaitGroup
	wg.Add(len(rwctxs))
	var anyPushFailed atomic.Bool
	for _, rwctx := range rwctxs {
		go func(rwctx *remoteWriteCtx) {
			defer wg.Done()
			if !rwctx.TryPush(tssBlock) {
				anyPushFailed.Store(true)
			}
		}(rwctx)
	}
	wg.Wait()
	return !anyPushFailed.Load()
}

// sortLabelsIfNeeded sorts labels if -sortLabels command-line flag is set.
func sortLabelsIfNeeded(tss []prompbmarshal.TimeSeries) {
	if !*sortLabels {
		return
	}
	for i := range tss {
		promrelabel.SortLabels(tss[i].Labels)
	}
}

func limitSeriesCardinality(tss []prompbmarshal.TimeSeries) []prompbmarshal.TimeSeries {
	if hourlySeriesLimiter == nil && dailySeriesLimiter == nil {
		return tss
	}
	dst := make([]prompbmarshal.TimeSeries, 0, len(tss))
	for i := range tss {
		labels := tss[i].Labels
		h := getLabelsHash(labels)
		if hourlySeriesLimiter != nil && !hourlySeriesLimiter.Add(h) {
			hourlySeriesLimitRowsDropped.Add(len(tss[i].Samples))
			logSkippedSeries(labels, "-remoteWrite.maxHourlySeries", hourlySeriesLimiter.MaxItems())
			continue
		}
		if dailySeriesLimiter != nil && !dailySeriesLimiter.Add(h) {
			dailySeriesLimitRowsDropped.Add(len(tss[i].Samples))
			logSkippedSeries(labels, "-remoteWrite.maxDailySeries", dailySeriesLimiter.MaxItems())
			continue
		}
		dst = append(dst, tss[i])
	}
	return dst
}

var (
	hourlySeriesLimiter *bloomfilter.Limiter
	dailySeriesLimiter  *bloomfilter.Limiter

	hourlySeriesLimitRowsDropped = metrics.NewCounter(`vmagent_hourly_series_limit_rows_dropped_total`)
	dailySeriesLimitRowsDropped  = metrics.NewCounter(`vmagent_daily_series_limit_rows_dropped_total`)
)

func getLabelsHash(labels []prompbmarshal.Label) uint64 {
	bb := labelsHashBufPool.Get()
	b := bb.B[:0]
	for _, label := range labels {
		b = append(b, label.Name...)
		b = append(b, label.Value...)
	}
	h := xxhash.Sum64(b)
	bb.B = b
	labelsHashBufPool.Put(bb)
	return h
}

var labelsHashBufPool bytesutil.ByteBufferPool

func logSkippedSeries(labels []prompbmarshal.Label, flagName string, flagValue int) {
	select {
	case <-logSkippedSeriesTicker.C:
		// Do not use logger.WithThrottler() here, since this will increase CPU usage
		// because every call to logSkippedSeries will result to a call to labelsToString.
		logger.Warnf("skip series %s because %s=%d reached", labelsToString(labels), flagName, flagValue)
	default:
	}
}

var logSkippedSeriesTicker = time.NewTicker(5 * time.Second)

func labelsToString(labels []prompbmarshal.Label) string {
	var b []byte
	b = append(b, '{')
	for i, label := range labels {
		b = append(b, label.Name...)
		b = append(b, '=')
		b = strconv.AppendQuote(b, label.Value)
		if i+1 < len(labels) {
			b = append(b, ',')
		}
	}
	b = append(b, '}')
	return string(b)
}

var (
	globalRowsPushedBeforeRelabel = metrics.NewCounter("vmagent_remotewrite_global_rows_pushed_before_relabel_total")
	rowsDroppedByGlobalRelabel    = metrics.NewCounter("vmagent_remotewrite_global_relabel_metrics_dropped_total")
)

type remoteWriteCtx struct {
	idx int
	fq  *persistentqueue.FastQueue
	c   *client

	sas          atomic.Pointer[streamaggr.Aggregators]
	deduplicator *streamaggr.Deduplicator

	streamAggrKeepInput bool
	streamAggrDropInput bool

	pss        []*pendingSeries
	pssNextIdx atomic.Uint64

	rowsPushedAfterRelabel *metrics.Counter
	rowsDroppedByRelabel   *metrics.Counter
}

func newRemoteWriteCtx(argIdx int, remoteWriteURL *url.URL, maxInmemoryBlocks int, sanitizedURL string) *remoteWriteCtx {
	// strip query params, otherwise changing params resets pq
	pqURL := *remoteWriteURL
	pqURL.RawQuery = ""
	pqURL.Fragment = ""
	h := xxhash.Sum64([]byte(pqURL.String()))
	queuePath := filepath.Join(*tmpDataPath, persistentQueueDirname, fmt.Sprintf("%d_%016X", argIdx+1, h))
	maxPendingBytes := maxPendingBytesPerURL.GetOptionalArg(argIdx)
	if maxPendingBytes != 0 && maxPendingBytes < persistentqueue.DefaultChunkFileSize {
		// See https://github.com/VictoriaMetrics/VictoriaMetrics/issues/4195
		logger.Warnf("rounding the -remoteWrite.maxDiskUsagePerURL=%d to the minimum supported value: %d", maxPendingBytes, persistentqueue.DefaultChunkFileSize)
		maxPendingBytes = persistentqueue.DefaultChunkFileSize
	}
	fq := persistentqueue.MustOpenFastQueue(queuePath, sanitizedURL, maxInmemoryBlocks, maxPendingBytes, *disableOnDiskQueue)
	_ = metrics.GetOrCreateGauge(fmt.Sprintf(`vmagent_remotewrite_pending_data_bytes{path=%q, url=%q}`, queuePath, sanitizedURL), func() float64 {
		return float64(fq.GetPendingBytes())
	})
	_ = metrics.GetOrCreateGauge(fmt.Sprintf(`vmagent_remotewrite_pending_inmemory_blocks{path=%q, url=%q}`, queuePath, sanitizedURL), func() float64 {
		return float64(fq.GetInmemoryQueueLen())
	})
	_ = metrics.GetOrCreateGauge(fmt.Sprintf(`vmagent_remotewrite_queue_blocked{path=%q, url=%q}`, queuePath, sanitizedURL), func() float64 {
		if fq.IsWriteBlocked() {
			return 1
		}
		return 0
	})

	var c *client
	switch remoteWriteURL.Scheme {
	case "http", "https":
		c = newHTTPClient(argIdx, remoteWriteURL.String(), sanitizedURL, fq, *queues)
	default:
		logger.Fatalf("unsupported scheme: %s for remoteWriteURL: %s, want `http`, `https`", remoteWriteURL.Scheme, sanitizedURL)
	}
	c.init(argIdx, *queues, sanitizedURL)

	// Initialize pss
	sf := significantFigures.GetOptionalArg(argIdx)
	rd := roundDigits.GetOptionalArg(argIdx)
	pssLen := *queues
	if n := cgroup.AvailableCPUs(); pssLen > n {
		// There is no sense in running more than availableCPUs concurrent pendingSeries,
		// since every pendingSeries can saturate up to a single CPU.
		pssLen = n
	}
	pss := make([]*pendingSeries, pssLen)
	for i := range pss {
		pss[i] = newPendingSeries(fq, c.useVMProto, sf, rd)
	}

	rwctx := &remoteWriteCtx{
		idx: argIdx,
		fq:  fq,
		c:   c,
		pss: pss,

		rowsPushedAfterRelabel: metrics.GetOrCreateCounter(fmt.Sprintf(`vmagent_remotewrite_rows_pushed_after_relabel_total{path=%q, url=%q}`, queuePath, sanitizedURL)),
		rowsDroppedByRelabel:   metrics.GetOrCreateCounter(fmt.Sprintf(`vmagent_remotewrite_relabel_metrics_dropped_total{path=%q, url=%q}`, queuePath, sanitizedURL)),
	}

	// Initialize sas
	sasFile := streamAggrConfig.GetOptionalArg(argIdx)
	dedupInterval := streamAggrDedupInterval.GetOptionalArg(argIdx)
	ignoreOldSamples := streamAggrIgnoreOldSamples.GetOptionalArg(argIdx)
	if sasFile != "" {
		opts := &streamaggr.Options{
			DedupInterval:    dedupInterval,
			DropInputLabels:  *streamAggrDropInputLabels,
			IgnoreOldSamples: ignoreOldSamples,
		}
		sas, err := streamaggr.LoadFromFile(sasFile, rwctx.pushInternalTrackDropped, opts)
		if err != nil {
			logger.Fatalf("cannot initialize stream aggregators from -remoteWrite.streamAggr.config=%q: %s", sasFile, err)
		}
		rwctx.sas.Store(sas)
		rwctx.streamAggrKeepInput = streamAggrKeepInput.GetOptionalArg(argIdx)
		rwctx.streamAggrDropInput = streamAggrDropInput.GetOptionalArg(argIdx)
		metrics.GetOrCreateCounter(fmt.Sprintf(`vmagent_streamaggr_config_reload_successful{path=%q}`, sasFile)).Set(1)
		metrics.GetOrCreateCounter(fmt.Sprintf(`vmagent_streamaggr_config_reload_success_timestamp_seconds{path=%q}`, sasFile)).Set(fasttime.UnixTimestamp())
	} else if dedupInterval > 0 {
		rwctx.deduplicator = streamaggr.NewDeduplicator(rwctx.pushInternalTrackDropped, dedupInterval, *streamAggrDropInputLabels)
	}

	return rwctx
}

func (rwctx *remoteWriteCtx) MustStop() {
	// sas and deduplicator must be stopped before rwctx is closed
	// because sas can write pending series to rwctx.pss if there are any
	sas := rwctx.sas.Swap(nil)
	sas.MustStop()

	if rwctx.deduplicator != nil {
		rwctx.deduplicator.MustStop()
		rwctx.deduplicator = nil
	}

	for _, ps := range rwctx.pss {
		ps.MustStop()
	}
	rwctx.idx = 0
	rwctx.pss = nil
	rwctx.fq.UnblockAllReaders()
	rwctx.c.MustStop()
	rwctx.c = nil

	rwctx.fq.MustClose()
	rwctx.fq = nil

	rwctx.rowsPushedAfterRelabel = nil
	rwctx.rowsDroppedByRelabel = nil
}

func (rwctx *remoteWriteCtx) TryPush(tss []prompbmarshal.TimeSeries) bool {
	// Apply relabeling
	var rctx *relabelCtx
	var v *[]prompbmarshal.TimeSeries
	rcs := allRelabelConfigs.Load()
	pcs := rcs.perURL[rwctx.idx]
	if pcs.Len() > 0 {
		rctx = getRelabelCtx()
		// Make a copy of tss before applying relabeling in order to prevent
		// from affecting time series for other remoteWrite.url configs.
		// See https://github.com/VictoriaMetrics/VictoriaMetrics/issues/467
		// and https://github.com/VictoriaMetrics/VictoriaMetrics/issues/599
		v = tssPool.Get().(*[]prompbmarshal.TimeSeries)
		tss = append(*v, tss...)
		rowsCountBeforeRelabel := getRowsCount(tss)
		tss = rctx.applyRelabeling(tss, pcs)
		rowsCountAfterRelabel := getRowsCount(tss)
		rwctx.rowsDroppedByRelabel.Add(rowsCountBeforeRelabel - rowsCountAfterRelabel)
	}
	rowsCount := getRowsCount(tss)
	rwctx.rowsPushedAfterRelabel.Add(rowsCount)

	// Apply stream aggregation or deduplication if they are configured
	sas := rwctx.sas.Load()
	if sas != nil {
		matchIdxs := matchIdxsPool.Get()
		matchIdxs.B = sas.Push(tss, matchIdxs.B)
		if !rwctx.streamAggrKeepInput {
			if rctx == nil {
				rctx = getRelabelCtx()
				// Make a copy of tss before dropping aggregated series
				v = tssPool.Get().(*[]prompbmarshal.TimeSeries)
				tss = append(*v, tss...)
			}
			tss = dropAggregatedSeries(tss, matchIdxs.B, rwctx.streamAggrDropInput)
		}
		matchIdxsPool.Put(matchIdxs)
	} else if rwctx.deduplicator != nil {
		rwctx.deduplicator.Push(tss)
		clear(tss)
		tss = tss[:0]
	}

	// Try pushing the data to remote storage
	ok := rwctx.tryPushInternal(tss)

	// Return back relabeling contexts to the pool
	if rctx != nil {
		*v = prompbmarshal.ResetTimeSeries(tss)
		tssPool.Put(v)
		putRelabelCtx(rctx)
	}

	return ok
}

var matchIdxsPool bytesutil.ByteBufferPool

func dropAggregatedSeries(src []prompbmarshal.TimeSeries, matchIdxs []byte, dropInput bool) []prompbmarshal.TimeSeries {
	dst := src[:0]
	if !dropInput {
		for i, match := range matchIdxs {
			if match == 1 {
				continue
			}
			dst = append(dst, src[i])
		}
	}
	tail := src[len(dst):]
	clear(tail)
	return dst
}

func (rwctx *remoteWriteCtx) pushInternalTrackDropped(tss []prompbmarshal.TimeSeries) {
	if rwctx.tryPushInternal(tss) {
		return
	}
	if !*disableOnDiskQueue {
		logger.Panicf("BUG: tryPushInternal must return true if -remoteWrite.disableOnDiskQueue isn't set")
	}
	pushFailures.Inc()
	if *dropSamplesOnOverload {
		rowsCount := getRowsCount(tss)
		samplesDropped.Add(rowsCount)
	}
}

func (rwctx *remoteWriteCtx) tryPushInternal(tss []prompbmarshal.TimeSeries) bool {
	var rctx *relabelCtx
	var v *[]prompbmarshal.TimeSeries
	if len(labelsGlobal) > 0 {
		// Make a copy of tss before adding extra labels in order to prevent
		// from affecting time series for other remoteWrite.url configs.
		rctx = getRelabelCtx()
		v = tssPool.Get().(*[]prompbmarshal.TimeSeries)
		tss = append(*v, tss...)
		rctx.appendExtraLabels(tss, labelsGlobal)
	}

	pss := rwctx.pss
	idx := rwctx.pssNextIdx.Add(1) % uint64(len(pss))

	ok := pss[idx].TryPush(tss)

	if rctx != nil {
		*v = prompbmarshal.ResetTimeSeries(tss)
		tssPool.Put(v)
		putRelabelCtx(rctx)
	}

	return ok
}

func (rwctx *remoteWriteCtx) reinitStreamAggr() {
	sasFile := streamAggrConfig.GetOptionalArg(rwctx.idx)
	if sasFile == "" {
		// There is no stream aggregation for rwctx
		return
	}

	logger.Infof("reloading stream aggregation configs pointed by -remoteWrite.streamAggr.config=%q", sasFile)
	metrics.GetOrCreateCounter(fmt.Sprintf(`vmagent_streamaggr_config_reloads_total{path=%q}`, sasFile)).Inc()
	opts := &streamaggr.Options{
		DedupInterval:    streamAggrDedupInterval.GetOptionalArg(rwctx.idx),
		DropInputLabels:  *streamAggrDropInputLabels,
		IgnoreOldSamples: streamAggrIgnoreOldSamples.GetOptionalArg(rwctx.idx),
	}
	sasNew, err := streamaggr.LoadFromFile(sasFile, rwctx.pushInternalTrackDropped, opts)
	if err != nil {
		metrics.GetOrCreateCounter(fmt.Sprintf(`vmagent_streamaggr_config_reloads_errors_total{path=%q}`, sasFile)).Inc()
		metrics.GetOrCreateCounter(fmt.Sprintf(`vmagent_streamaggr_config_reload_successful{path=%q}`, sasFile)).Set(0)
		logger.Errorf("cannot reload stream aggregation config from -remoteWrite.streamAggr.config=%q; continue using the previously loaded config; error: %s", sasFile, err)
		return
	}
	sas := rwctx.sas.Load()
	if !sasNew.Equal(sas) {
		sasOld := rwctx.sas.Swap(sasNew)
		sasOld.MustStop()
		logger.Infof("successfully reloaded stream aggregation configs at -remoteWrite.streamAggr.config=%q", sasFile)
	} else {
		sasNew.MustStop()
		logger.Infof("the config at -remoteWrite.streamAggr.config=%q wasn't changed", sasFile)
	}
	metrics.GetOrCreateCounter(fmt.Sprintf(`vmagent_streamaggr_config_reload_successful{path=%q}`, sasFile)).Set(1)
	metrics.GetOrCreateCounter(fmt.Sprintf(`vmagent_streamaggr_config_reload_success_timestamp_seconds{path=%q}`, sasFile)).Set(fasttime.UnixTimestamp())
}

var tssPool = &sync.Pool{
	New: func() interface{} {
		a := []prompbmarshal.TimeSeries{}
		return &a
	},
}

func getRowsCount(tss []prompbmarshal.TimeSeries) int {
	rowsCount := 0
	for _, ts := range tss {
		rowsCount += len(ts.Samples)
	}
	return rowsCount
}

// CheckStreamAggrConfigs checks configs pointed by -remoteWrite.streamAggr.config
func CheckStreamAggrConfigs() error {
	pushNoop := func(_ []prompbmarshal.TimeSeries) {}
	for idx, sasFile := range *streamAggrConfig {
		if sasFile == "" {
			continue
		}
		opts := &streamaggr.Options{
			DedupInterval:    streamAggrDedupInterval.GetOptionalArg(idx),
			DropInputLabels:  *streamAggrDropInputLabels,
			IgnoreOldSamples: streamAggrIgnoreOldSamples.GetOptionalArg(idx),
		}
		sas, err := streamaggr.LoadFromFile(sasFile, pushNoop, opts)
		if err != nil {
			return fmt.Errorf("cannot load -remoteWrite.streamAggr.config=%q: %w", sasFile, err)
		}
		sas.MustStop()
	}
	return nil
}

func newMapFromStrings(a []string) map[string]struct{} {
	m := make(map[string]struct{}, len(a))
	for _, s := range a {
		m[s] = struct{}{}
	}
	return m
}