package main

import (
	"flag"
	"sync"
	"time"

	"github.com/VictoriaMetrics/VictoriaMetrics/app/vmstorage"
	"github.com/VictoriaMetrics/VictoriaMetrics/lib/appmetrics"
	"github.com/VictoriaMetrics/VictoriaMetrics/lib/bytesutil"
	"github.com/VictoriaMetrics/VictoriaMetrics/lib/decimal"
	"github.com/VictoriaMetrics/VictoriaMetrics/lib/logger"
	"github.com/VictoriaMetrics/VictoriaMetrics/lib/prompbmarshal"
	"github.com/VictoriaMetrics/VictoriaMetrics/lib/protoparser/prometheus"
	"github.com/VictoriaMetrics/VictoriaMetrics/lib/storage"
)

var (
	selfScrapeInterval = flag.Duration("selfScrapeInterval", 0, "Interval for self-scraping own metrics at /metrics page")
	selfScrapeInstance = flag.String("selfScrapeInstance", "self", "Value for 'instance' label, which is added to self-scraped metrics")
	selfScrapeJob      = flag.String("selfScrapeJob", "victoria-metrics", "Value for 'job' label, which is added to self-scraped metrics")
)

var selfScraperStopCh chan struct{}
var selfScraperWG sync.WaitGroup

func startSelfScraper() {
	selfScraperStopCh = make(chan struct{})
	selfScraperWG.Add(1)
	go func() {
		defer selfScraperWG.Done()
		selfScraper(*selfScrapeInterval)
	}()
}

func stopSelfScraper() {
	close(selfScraperStopCh)
	selfScraperWG.Wait()
}

func selfScraper(scrapeInterval time.Duration) {
	if scrapeInterval <= 0 {
		// Self-scrape is disabled.
		return
	}
	logger.Infof("started self-scraping `/metrics` page with interval %.3f seconds", scrapeInterval.Seconds())

	var bb bytesutil.ByteBuffer
	var rows prometheus.Rows
	var mrs []storage.MetricRow
	var labels []prompbmarshal.Label
	t := time.NewTicker(scrapeInterval)
	f := func(currentTime time.Time, sendStaleMarkers bool) {
		currentTimestamp := currentTime.UnixNano() / 1e6
		bb.Reset()
		appmetrics.WritePrometheusMetrics(&bb)
		s := bytesutil.ToUnsafeString(bb.B)
		rows.Reset()
		rows.Unmarshal(s)
		mrs = mrs[:0]
		for i := range rows.Rows {
			r := &rows.Rows[i]
			labels = labels[:0]
			labels = addLabel(labels, "", r.Metric)
			labels = addLabel(labels, "job", *selfScrapeJob)
			labels = addLabel(labels, "instance", *selfScrapeInstance)
			for j := range r.Tags {
				t := &r.Tags[j]
				labels = addLabel(labels, t.Key, t.Value)
			}
			if len(mrs) < cap(mrs) {
				mrs = mrs[:len(mrs)+1]
			} else {
				mrs = append(mrs, storage.MetricRow{})
			}
			mr := &mrs[len(mrs)-1]
			mr.MetricNameRaw = storage.MarshalMetricNameRaw(mr.MetricNameRaw[:0], labels)
			mr.Timestamp = currentTimestamp
			if sendStaleMarkers {
				mr.Value = decimal.StaleNaN
			} else {
				mr.Value = r.Value
			}
		}
		if err := vmstorage.AddRows(mrs); err != nil {
			logger.Errorf("cannot store self-scraped metrics: %s", err)
		}
	}
	for {
		select {
		case <-selfScraperStopCh:
			f(time.Now(), true)
			t.Stop()
			logger.Infof("stopped self-scraping `/metrics` page")
			return
		case currentTime := <-t.C:
			f(currentTime, false)
		}
	}
}

func addLabel(dst []prompbmarshal.Label, key, value string) []prompbmarshal.Label {
	if len(dst) < cap(dst) {
		dst = dst[:len(dst)+1]
	} else {
		dst = append(dst, prompbmarshal.Label{})
	}
	lb := &dst[len(dst)-1]
	lb.Name = key
	lb.Value = value
	return dst
}