package remotewrite

import (
	"flag"
	"sync"
	"time"

	"github.com/VictoriaMetrics/VictoriaMetrics/lib/bytesutil"
	"github.com/VictoriaMetrics/VictoriaMetrics/lib/logger"
	"github.com/VictoriaMetrics/VictoriaMetrics/lib/persistentqueue"
	"github.com/VictoriaMetrics/VictoriaMetrics/lib/prompbmarshal"
	"github.com/VictoriaMetrics/metrics"
	"github.com/golang/snappy"
)

var flushInterval = flag.Duration("remoteWrite.flushInterval", time.Second, "Interval for flushing the data to remote storage. "+
	"Higher value reduces network bandwidth usage at the cost of delayed push of scraped data to remote storage")

// the maximum number of rows to send per each block.
const maxRowsPerBlock = 10000

type pendingSeries struct {
	mu sync.Mutex
	wr writeRequest

	stopCh            chan struct{}
	periodicFlusherWG sync.WaitGroup
}

func newPendingSeries(pushBlock func(block []byte)) *pendingSeries {
	var ps pendingSeries
	ps.wr.pushBlock = pushBlock
	ps.stopCh = make(chan struct{})
	ps.periodicFlusherWG.Add(1)
	go func() {
		defer ps.periodicFlusherWG.Done()
		ps.periodicFlusher()
	}()
	return &ps
}

func (ps *pendingSeries) MustStop() {
	close(ps.stopCh)
	ps.periodicFlusherWG.Wait()
}

func (ps *pendingSeries) Push(tss []prompbmarshal.TimeSeries) {
	ps.mu.Lock()
	ps.wr.push(tss)
	ps.mu.Unlock()
}

func (ps *pendingSeries) periodicFlusher() {
	ticker := time.NewTicker(*flushInterval)
	defer ticker.Stop()
	mustStop := false
	for !mustStop {
		select {
		case <-ps.stopCh:
			mustStop = true
		case <-ticker.C:
			if time.Since(ps.wr.lastFlushTime) < *flushInterval/2 {
				continue
			}
		}
		ps.mu.Lock()
		ps.wr.flush()
		ps.mu.Unlock()
	}
}

type writeRequest struct {
	wr            prompbmarshal.WriteRequest
	pushBlock     func(block []byte)
	lastFlushTime time.Time

	tss []prompbmarshal.TimeSeries

	labels  []prompbmarshal.Label
	samples []prompbmarshal.Sample
	buf     []byte
}

func (wr *writeRequest) reset() {
	wr.wr.Timeseries = nil

	for i := range wr.tss {
		ts := &wr.tss[i]
		ts.Labels = nil
		ts.Samples = nil
	}
	wr.tss = wr.tss[:0]

	for i := range wr.labels {
		label := &wr.labels[i]
		label.Name = ""
		label.Value = ""
	}
	wr.labels = wr.labels[:0]

	wr.samples = wr.samples[:0]
	wr.buf = wr.buf[:0]
}

func (wr *writeRequest) flush() {
	wr.wr.Timeseries = wr.tss
	wr.lastFlushTime = time.Now()
	pushWriteRequest(&wr.wr, wr.pushBlock)
	wr.reset()
}

func (wr *writeRequest) push(src []prompbmarshal.TimeSeries) {
	tssDst := wr.tss
	for i := range src {
		tssDst = append(tssDst, prompbmarshal.TimeSeries{})
		dst := &tssDst[len(tssDst)-1]
		wr.copyTimeSeries(dst, &src[i])
		if len(wr.tss) >= maxRowsPerBlock {
			wr.flush()
			tssDst = wr.tss
		}
	}
	wr.tss = tssDst
}

func (wr *writeRequest) copyTimeSeries(dst, src *prompbmarshal.TimeSeries) {
	labelsDst := wr.labels
	labelsLen := len(wr.labels)
	samplesDst := wr.samples
	buf := wr.buf
	for i := range src.Labels {
		labelsDst = append(labelsDst, prompbmarshal.Label{})
		dstLabel := &labelsDst[len(labelsDst)-1]
		srcLabel := &src.Labels[i]

		buf = append(buf, srcLabel.Name...)
		dstLabel.Name = bytesutil.ToUnsafeString(buf[len(buf)-len(srcLabel.Name):])
		buf = append(buf, srcLabel.Value...)
		dstLabel.Value = bytesutil.ToUnsafeString(buf[len(buf)-len(srcLabel.Value):])
	}
	dst.Labels = labelsDst[labelsLen:]

	samplesDst = append(samplesDst, prompbmarshal.Sample{})
	dstSample := &samplesDst[len(samplesDst)-1]
	if len(src.Samples) != 1 {
		logger.Panicf("BUG: unexpected number of samples in time series; got %d; want 1", len(src.Samples))
	}
	*dstSample = src.Samples[0]
	dst.Samples = samplesDst[len(samplesDst)-1:]

	wr.samples = samplesDst
	wr.labels = labelsDst
	wr.buf = buf
}

func pushWriteRequest(wr *prompbmarshal.WriteRequest, pushBlock func(block []byte)) {
	if len(wr.Timeseries) == 0 {
		// Nothing to push
		return
	}
	bb := writeRequestBufPool.Get()
	bb.B = prompbmarshal.MarshalWriteRequest(bb.B[:0], wr)
	zb := snappyBufPool.Get()
	zb.B = snappy.Encode(zb.B[:cap(zb.B)], bb.B)
	writeRequestBufPool.Put(bb)
	if len(zb.B) <= persistentqueue.MaxBlockSize {
		pushBlock(zb.B)
		blockSizeRows.Update(float64(len(wr.Timeseries)))
		blockSizeBytes.Update(float64(len(zb.B)))
		snappyBufPool.Put(zb)
		return
	}
	snappyBufPool.Put(zb)

	// Too big block. Recursively split it into smaller parts.
	timeseries := wr.Timeseries
	n := len(timeseries) / 2
	wr.Timeseries = timeseries[:n]
	pushWriteRequest(wr, pushBlock)
	wr.Timeseries = timeseries[n:]
	pushWriteRequest(wr, pushBlock)
	wr.Timeseries = timeseries
}

var (
	blockSizeBytes = metrics.NewHistogram(`vmagent_remotewrite_block_size_bytes`)
	blockSizeRows  = metrics.NewHistogram(`vmagent_remotewrite_block_size_rows`)
)

var writeRequestBufPool bytesutil.ByteBufferPool
var snappyBufPool bytesutil.ByteBufferPool