package dnstt

import "github.com/prometheus/client_golang/prometheus"

const namespace = "dnstt"

// Exporter exposes aggregate DNSTT traffic metrics from a Collector.
type Exporter struct {
	collector *Collector

	activeClients *prometheus.Desc
	peakClients   *prometheus.Desc
	queries       *prometheus.Desc
	bytesIn       *prometheus.Desc
	bytesOut      *prometheus.Desc
	sessions      *prometheus.Desc
}

// NewExporter creates a Prometheus collector for DNSTT metrics.
func NewExporter(collector *Collector) *Exporter {
	labels := append([]string{"domain"}, collector.GeoLabelNames()...)
	return &Exporter{
		collector: collector,
		activeClients: prometheus.NewDesc(
			prometheus.BuildFQName(namespace, "", "active_clients"),
			"Number of DNSTT client sessions observed within the active timeout window.",
			labels,
			nil,
		),
		peakClients: prometheus.NewDesc(
			prometheus.BuildFQName(namespace, "", "peak_clients"),
			"Maximum concurrent active DNSTT client sessions observed.",
			labels,
			nil,
		),
		queries: prometheus.NewDesc(
			prometheus.BuildFQName(namespace, "", "queries_total"),
			"Total DNSTT DNS queries observed.",
			labels,
			nil,
		),
		bytesIn: prometheus.NewDesc(
			prometheus.BuildFQName(namespace, "", "bytes_in_total"),
			"Total bytes observed in DNSTT DNS queries.",
			labels,
			nil,
		),
		bytesOut: prometheus.NewDesc(
			prometheus.BuildFQName(namespace, "", "bytes_out_total"),
			"Total bytes observed in DNSTT DNS responses.",
			labels,
			nil,
		),
		sessions: prometheus.NewDesc(
			prometheus.BuildFQName(namespace, "", "sessions_total"),
			"Total unique DNSTT client sessions observed.",
			labels,
			nil,
		),
	}
}

// Describe sends metric descriptors to Prometheus.
func (e *Exporter) Describe(ch chan<- *prometheus.Desc) {
	ch <- e.activeClients
	ch <- e.peakClients
	ch <- e.queries
	ch <- e.bytesIn
	ch <- e.bytesOut
	ch <- e.sessions
}

// Collect sends current metric values to Prometheus.
func (e *Exporter) Collect(ch chan<- prometheus.Metric) {
	for _, tunnel := range e.collector.Snapshot().Tunnels {
		for _, series := range tunnel.Series {
			labels := e.labelValues(series)
			ch <- prometheus.MustNewConstMetric(e.activeClients, prometheus.GaugeValue, float64(series.ActiveClients), labels...)
			ch <- prometheus.MustNewConstMetric(e.peakClients, prometheus.GaugeValue, float64(series.PeakClients), labels...)
			ch <- prometheus.MustNewConstMetric(e.queries, prometheus.CounterValue, float64(series.TotalQueries), labels...)
			ch <- prometheus.MustNewConstMetric(e.bytesIn, prometheus.CounterValue, float64(series.BytesIn), labels...)
			ch <- prometheus.MustNewConstMetric(e.bytesOut, prometheus.CounterValue, float64(series.BytesOut), labels...)
			ch <- prometheus.MustNewConstMetric(e.sessions, prometheus.CounterValue, float64(series.TotalSessions), labels...)
		}
	}
}

func (e *Exporter) labelValues(series SeriesSnapshot) []string {
	values := []string{series.Domain}
	for _, label := range e.collector.GeoLabelNames() {
		switch label {
		case "country":
			values = append(values, series.Country)
		case "asn":
			values = append(values, series.ASN)
		}
	}
	return values
}