package metrics

import (
	"os"
	"regexp"
	"strings"
	"testing"

	"github.com/prometheus/client_golang/prometheus"
)

// TestGrafanaDashboardOnlyUsesMetricsThatExist keeps deploy/grafana/fancy-dns.json
// from drifting away from the collectors: a renamed metric would otherwise
// leave a panel empty and nothing would say why.
func TestGrafanaDashboardOnlyUsesMetricsThatExist(t *testing.T) {
	initCollectors()
	descs := make(chan *prometheus.Desc, 256)
	go func() { Registry.Describe(descs); close(descs) }()
	known := map[string]bool{}
	nameRe := regexp.MustCompile(`fqName: "([a-z0-9_]+)"`)
	for d := range descs {
		if m := nameRe.FindStringSubmatch(d.String()); m != nil {
			known[m[1]] = true
		}
	}
	if !known["fancydns_queries_total"] {
		t.Fatalf("collector names were not read; got %v", known)
	}

	raw, err := os.ReadFile("../../deploy/grafana/fancy-dns.json")
	if err != nil {
		t.Fatal(err)
	}
	used := regexp.MustCompile(`fancydns_[a-z0-9_]+`).FindAllString(string(raw), -1)
	if len(used) == 0 {
		t.Fatal("the dashboard references no fancydns metrics")
	}
	for _, name := range used {
		base := name
		for _, suffix := range []string{"_bucket", "_count", "_sum"} {
			base = strings.TrimSuffix(base, suffix)
		}
		if !known[base] {
			t.Errorf("the dashboard queries %s, which the resolver does not export", name)
		}
	}
}