package gather

import (
	"context"
	"fmt"
	"io"
	"math"
	"mime"
	"net/http"
	"time"

	"github.com/influxdata/influxdb/v2"
	"github.com/matttproud/golang_protobuf_extensions/pbutil"
	dto "github.com/prometheus/client_model/go"
	"github.com/prometheus/common/expfmt"
)

// prometheusScraper handles parsing prometheus metrics.
// implements Scraper interfaces.
type prometheusScraper struct{}

// Gather parse metrics from a scraper target url.
func (p *prometheusScraper) Gather(ctx context.Context, target influxdb.ScraperTarget) (collected MetricsCollection, err error) {
	resp, err := http.Get(target.URL)
	if err != nil {
		return collected, err
	}
	defer resp.Body.Close()

	return p.parse(resp.Body, resp.Header, target)
}

func (p *prometheusScraper) parse(r io.Reader, header http.Header, target influxdb.ScraperTarget) (collected MetricsCollection, err error) {
	var parser expfmt.TextParser
	now := time.Now()

	mediatype, params, err := mime.ParseMediaType(header.Get("Content-Type"))
	if err != nil {
		return collected, err
	}
	// Prepare output
	metricFamilies := make(map[string]*dto.MetricFamily)
	if mediatype == "application/vnd.google.protobuf" &&
		params["encoding"] == "delimited" &&
		params["proto"] == "io.prometheus.client.MetricFamily" {
		for {
			mf := &dto.MetricFamily{}
			if _, err := pbutil.ReadDelimited(r, mf); err != nil {
				if err == io.EOF {
					break
				}
				return collected, fmt.Errorf("reading metric family protocol buffer failed: %s", err)
			}
			metricFamilies[mf.GetName()] = mf
		}
	} else {
		metricFamilies, err = parser.TextToMetricFamilies(r)
		if err != nil {
			return collected, fmt.Errorf("reading text format failed: %s", err)
		}
	}
	ms := make([]Metrics, 0)

	// read metrics
	for name, family := range metricFamilies {
		for _, m := range family.Metric {
			// reading tags
			tags := makeLabels(m)
			// reading fields
			var fields map[string]interface{}
			switch family.GetType() {
			case dto.MetricType_SUMMARY:
				// summary metric
				fields = makeQuantiles(m)
				fields["count"] = float64(m.GetSummary().GetSampleCount())
				fields["sum"] = float64(m.GetSummary().GetSampleSum())
			case dto.MetricType_HISTOGRAM:
				// histogram metric
				fields = makeBuckets(m)
				fields["count"] = float64(m.GetHistogram().GetSampleCount())
				fields["sum"] = float64(m.GetHistogram().GetSampleSum())
			default:
				// standard metric
				fields = getNameAndValue(m)
			}
			if len(fields) == 0 {
				continue
			}
			tm := now
			if m.TimestampMs != nil && *m.TimestampMs > 0 {
				tm = time.Unix(0, *m.TimestampMs*1000000)
			}
			me := Metrics{
				Timestamp: tm,
				Tags:      tags,
				Fields:    fields,
				Name:      name,
				Type:      MetricType(family.GetType()),
			}
			ms = append(ms, me)
		}

	}

	collected = MetricsCollection{
		MetricsSlice: ms,
		OrgID:        target.OrgID,
		BucketID:     target.BucketID,
	}

	return collected, nil
}

// Get labels from metric
func makeLabels(m *dto.Metric) map[string]string {
	result := map[string]string{}
	for _, lp := range m.Label {
		result[lp.GetName()] = lp.GetValue()
	}
	return result
}

// Get Buckets from histogram metric
func makeBuckets(m *dto.Metric) map[string]interface{} {
	fields := make(map[string]interface{})
	for _, b := range m.GetHistogram().Bucket {
		fields[fmt.Sprint(b.GetUpperBound())] = float64(b.GetCumulativeCount())
	}
	return fields
}

// Get name and value from metric
func getNameAndValue(m *dto.Metric) map[string]interface{} {
	fields := make(map[string]interface{})
	if m.Gauge != nil {
		if !math.IsNaN(m.GetGauge().GetValue()) {
			fields["gauge"] = float64(m.GetGauge().GetValue())
		}
	} else if m.Counter != nil {
		if !math.IsNaN(m.GetCounter().GetValue()) {
			fields["counter"] = float64(m.GetCounter().GetValue())
		}
	} else if m.Untyped != nil {
		if !math.IsNaN(m.GetUntyped().GetValue()) {
			fields["value"] = float64(m.GetUntyped().GetValue())
		}
	}
	return fields
}

// Get Quantiles from summary metric
func makeQuantiles(m *dto.Metric) map[string]interface{} {
	fields := make(map[string]interface{})
	for _, q := range m.GetSummary().Quantile {
		if !math.IsNaN(q.GetValue()) {
			fields[fmt.Sprint(q.GetQuantile())] = float64(q.GetValue())
		}
	}
	return fields
}
