package main

import (
	"flag"
	"sync"
	"time"

	"github.com/VictoriaMetrics/VictoriaMetrics/app/vmstorage"
	"github.com/VictoriaMetrics/VictoriaMetrics/lib/bytesutil"
	"github.com/VictoriaMetrics/VictoriaMetrics/lib/httpserver"
	"github.com/VictoriaMetrics/VictoriaMetrics/lib/logger"
	"github.com/VictoriaMetrics/VictoriaMetrics/lib/prompb"
	"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")

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 []prompb.Label
	t := time.NewTicker(scrapeInterval)
	var currentTimestamp int64
	for {
		select {
		case <-selfScraperStopCh:
			t.Stop()
			logger.Infof("stopped self-scraping `/metrics` page")
			return
		case currentTime := <-t.C:
			currentTimestamp = currentTime.UnixNano() / 1e6
		}
		bb.Reset()
		httpserver.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", "victoria-metrics")
			labels = addLabel(labels, "instance", "self")
			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
			mr.Value = r.Value
		}
		logger.Infof("writing %d rows at timestamp %d", len(mrs), currentTimestamp)
		vmstorage.AddRows(mrs)
	}
}

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