package promscrape

import (
	"crypto/tls"
	"crypto/x509"
	"math/rand"
	"time"

	"github.com/VictoriaMetrics/VictoriaMetrics/lib/bytesutil"
	"github.com/VictoriaMetrics/VictoriaMetrics/lib/logger"
	"github.com/VictoriaMetrics/VictoriaMetrics/lib/prompbmarshal"
	"github.com/VictoriaMetrics/VictoriaMetrics/lib/promrelabel"
	parser "github.com/VictoriaMetrics/VictoriaMetrics/lib/protoparser/prometheus"
	"github.com/VictoriaMetrics/metrics"
)

// ScrapeWork represents a unit of work for scraping Prometheus metrics.
type ScrapeWork struct {
	// Full URL (including query args) for the scrape.
	ScrapeURL string

	// Interval for scraping the ScrapeURL.
	ScrapeInterval time.Duration

	// Timeout for scraping the ScrapeURL.
	ScrapeTimeout time.Duration

	// How to deal with conflicting labels.
	// See https://prometheus.io/docs/prometheus/latest/configuration/configuration/#scrape_config
	HonorLabels bool

	// How to deal with scraped timestamps.
	// See https://prometheus.io/docs/prometheus/latest/configuration/configuration/#scrape_config
	HonorTimestamps bool

	// Labels to add to the scraped metrics.
	//
	// The list contains at least the following labels according to https://prometheus.io/docs/prometheus/latest/configuration/configuration/#relabel_config
	//
	//     * job
	//     * __address__
	//     * __scheme__
	//     * __metrics_path__
	//     * __param_<name>
	//     * __meta_*
	//     * user-defined labels set via `relabel_configs` section in `scrape_config`
	//
	// See also https://prometheus.io/docs/concepts/jobs_instances/
	Labels []prompbmarshal.Label

	// Optional `Authorization` header.
	//
	// It may contain `Basic ....` or `Bearer ....` string.
	Authorization string

	// Optional TLS config
	TLSRootCA             *x509.CertPool
	TLSCertificate        *tls.Certificate
	TLSServerName         string
	TLSInsecureSkipVerify bool

	// Optional `metric_relabel_configs`.
	MetricRelabelConfigs []promrelabel.ParsedRelabelConfig

	// The maximum number of metrics to scrape after relabeling.
	ScrapeLimit int
}

type scrapeWork struct {
	// Config for the scrape.
	Config ScrapeWork

	// ReadData is called for reading the data.
	ReadData func(dst []byte) ([]byte, error)

	// PushData is called for pushing collected data.
	PushData func(wr *prompbmarshal.WriteRequest)

	bodyBuf []byte
	rows    parser.Rows
	tmpRow  parser.Row

	writeRequest prompbmarshal.WriteRequest
	labels       []prompbmarshal.Label
	samples      []prompbmarshal.Sample
}

func (sw *scrapeWork) run(stopCh <-chan struct{}) {
	// Randomize start time for the first scrape in order to spread load
	// when scraping many targets.
	randSleep := time.Duration(float64(sw.Config.ScrapeInterval) * rand.Float64())
	timer := time.NewTimer(randSleep)
	var ticker *time.Ticker
	select {
	case <-stopCh:
		timer.Stop()
		return
	case t := <-timer.C:
		ticker = time.NewTicker(sw.Config.ScrapeInterval)
		timestamp := t.UnixNano() / 1e6
		sw.scrapeAndLogError(timestamp)
	}
	defer ticker.Stop()
	for {
		startTime := time.Now()
		select {
		case <-stopCh:
			return
		case t := <-ticker.C:
			// Adjust t if it is from the past (i.e. stale tick)
			// This can be the case if the previous scrape took longer than the scrape interval.
			if t.Sub(startTime) < 0 {
				t = startTime
			}
			timestamp := t.UnixNano() / 1e6
			sw.scrapeAndLogError(timestamp)
		}
	}
}

func (sw *scrapeWork) logError(s string) {
	logger.ErrorfSkipframes(1, "error when scraping %q: %s", sw.Config.ScrapeURL, s)
}

func (sw *scrapeWork) scrapeAndLogError(timestamp int64) {
	if err := sw.scrapeInternal(timestamp); err != nil {
		logger.Errorf("error when scraping %q: %s", sw.Config.ScrapeURL, err)
	}
}

var (
	scrapeDuration              = metrics.NewHistogram("vm_promscrape_scrape_duration_seconds")
	scrapeResponseSize          = metrics.NewHistogram("vm_promscrape_scrape_response_size_bytes")
	scrapedSamples              = metrics.NewHistogram("vm_promscrape_scraped_samples")
	scrapesSkippedByScrapeLimit = metrics.NewCounter("vm_promscrape_scrapes_skipped_by_scrape_limit_total")
	scrapesFailed               = metrics.NewCounter("vm_promscrape_scrapes_failed_total")
	pushDataDuration            = metrics.NewHistogram("vm_promscrape_push_data_duration_seconds")
)

func (sw *scrapeWork) scrapeInternal(timestamp int64) error {
	var err error
	sw.bodyBuf, err = sw.ReadData(sw.bodyBuf[:0])
	endTimestamp := time.Now().UnixNano() / 1e6
	duration := float64(endTimestamp-timestamp) / 1e3
	scrapeDuration.Update(duration)
	scrapeResponseSize.Update(float64(len(sw.bodyBuf)))
	up := 1
	if err != nil {
		up = 0
		scrapesFailed.Inc()
	} else {
		bodyString := bytesutil.ToUnsafeString(sw.bodyBuf)
		sw.rows.UnmarshalWithErrLogger(bodyString, sw.logError)
	}
	srcRows := sw.rows.Rows
	samplesScraped := len(srcRows)
	scrapedSamples.Update(float64(samplesScraped))
	for i := range srcRows {
		sw.addRowToTimeseries(&srcRows[i], timestamp)
	}
	sw.rows.Reset()
	if sw.Config.ScrapeLimit > 0 && len(sw.writeRequest.Timeseries) > sw.Config.ScrapeLimit {
		prompbmarshal.ResetWriteRequest(&sw.writeRequest)
		up = 0
		scrapesSkippedByScrapeLimit.Inc()
	}
	samplesPostRelabeling := len(sw.writeRequest.Timeseries)
	sw.addAutoTimeseries("up", float64(up), timestamp)
	sw.addAutoTimeseries("scrape_duration_seconds", duration, timestamp)
	sw.addAutoTimeseries("scrape_samples_scraped", float64(samplesScraped), timestamp)
	sw.addAutoTimeseries("scrape_samples_post_metric_relabeling", float64(samplesPostRelabeling), timestamp)
	startTime := time.Now()
	sw.PushData(&sw.writeRequest)
	pushDataDuration.UpdateDuration(startTime)
	prompbmarshal.ResetWriteRequest(&sw.writeRequest)
	sw.labels = sw.labels[:0]
	sw.samples = sw.samples[:0]
	tsmGlobal.Update(&sw.Config, up == 1, timestamp, int64(duration*1000), err)
	return err
}

// addAutoTimeseries adds automatically generated time series with the given name, value and timestamp.
//
// See https://prometheus.io/docs/concepts/jobs_instances/#automatically-generated-labels-and-time-series
func (sw *scrapeWork) addAutoTimeseries(name string, value float64, timestamp int64) {
	sw.tmpRow.Metric = name
	sw.tmpRow.Tags = nil
	sw.tmpRow.Value = value
	sw.tmpRow.Timestamp = timestamp
	sw.addRowToTimeseries(&sw.tmpRow, timestamp)
}

func (sw *scrapeWork) addRowToTimeseries(r *parser.Row, timestamp int64) {
	labelsLen := len(sw.labels)
	sw.labels = appendLabels(sw.labels, r.Metric, r.Tags, sw.Config.Labels, sw.Config.HonorLabels)
	sw.labels = promrelabel.ApplyRelabelConfigs(sw.labels, labelsLen, sw.Config.MetricRelabelConfigs, true)
	if len(sw.labels) == labelsLen {
		// Skip row without labels.
		return
	}
	labels := sw.labels[labelsLen:]
	sw.samples = append(sw.samples, prompbmarshal.Sample{})
	sample := &sw.samples[len(sw.samples)-1]
	sample.Value = r.Value
	sample.Timestamp = r.Timestamp
	if !sw.Config.HonorTimestamps || sample.Timestamp == 0 {
		sample.Timestamp = timestamp
	}
	wr := &sw.writeRequest
	wr.Timeseries = append(wr.Timeseries, prompbmarshal.TimeSeries{})
	ts := &wr.Timeseries[len(wr.Timeseries)-1]
	ts.Labels = labels
	ts.Samples = sw.samples[len(sw.samples)-1:]
}

func appendLabels(dst []prompbmarshal.Label, metric string, src []parser.Tag, extraLabels []prompbmarshal.Label, honorLabels bool) []prompbmarshal.Label {
	dstLen := len(dst)
	dst = append(dst, prompbmarshal.Label{
		Name:  "__name__",
		Value: metric,
	})
	for i := range src {
		tag := &src[i]
		dst = append(dst, prompbmarshal.Label{
			Name:  tag.Key,
			Value: tag.Value,
		})
	}
	dst = append(dst, extraLabels...)
	labels := dst[dstLen:]
	if len(labels) <= 1 {
		// Fast path - only a single label.
		return dst
	}

	// de-duplicate labels
	dstLabels := labels[:0]
	for i := range labels {
		label := &labels[i]
		prevLabel := promrelabel.GetLabelByName(dstLabels, label.Name)
		if prevLabel == nil {
			dstLabels = append(dstLabels, *label)
			continue
		}
		if honorLabels {
			// Skip the extra label with the same name.
			continue
		}
		// Rename the prevLabel to "exported_" + label.Name.
		// See https://prometheus.io/docs/prometheus/latest/configuration/configuration/#scrape_config
		exportedName := "exported_" + label.Name
		if promrelabel.GetLabelByName(dstLabels, exportedName) != nil {
			// Override duplicate with the current label.
			*prevLabel = *label
			continue
		}
		prevLabel.Name = exportedName
		dstLabels = append(dstLabels, *label)
	}
	return dst[:dstLen+len(dstLabels)]
}