feat: create a way to expire metrics

main.go

@@ -149,6 +149,8 @@ func fetchMetrics(ctx context.Context, accounts []cfaccounts.Account, zones []cf
 	}
 
 	wg.Wait()
+
+	registeredMetrics.Report(trackedMetrics)
 }
 
 func runExporter() {

metrics.go

@@ -0,0 +1,111 @@
+package main
+
+import (
+	"strings"
+	"sync"
+	"time"
+
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+const joinChar = "|"
+const maxAge = 1 * time.Hour
+
+type reportableMetrics []*metricTracker
+
+var registeredMetrics = reportableMetrics{}
+
+func (rm reportableMetrics) Report(gauge prometheus.Gauge) {
+	total := 0
+	for _, m := range rm {
+		total += len(m.expirations)
+	}
+	gauge.Set(float64(total))
+}
+
+func register(m *metricTracker) {
+	registeredMetrics = append(registeredMetrics, m)
+}
+
+type metricTracker struct {
+	sync.Mutex
+	expirations map[string]time.Time
+}
+
+func newMetricTracker() *metricTracker {
+	mt := &metricTracker{expirations: map[string]time.Time{}}
+	register(mt)
+	return mt
+}
+
+func (m *metricTracker) touch(labels []string) {
+	m.Lock()
+	defer m.Unlock()
+	m.expirations[strings.Join(labels, joinChar)] = time.Now().Add(maxAge)
+}
+
+func (m *metricTracker) collect(del func(...string) bool) {
+	m.Lock()
+	defer m.Unlock()
+	now := time.Now()
+	for k, v := range m.expirations {
+		if v.Before(now) {
+			delete(m.expirations, k)
+			if del(strings.Split(k, joinChar)...) {
+				expiredMetrics.Inc()
+			}
+		}
+	}
+}
+
+type trackedGauge struct {
+	tracker *metricTracker
+	gauge   *prometheus.GaugeVec
+}
+
+func NewTrackedGauge(gauge *prometheus.GaugeVec) *trackedGauge {
+	return &trackedGauge{
+		tracker: newMetricTracker(),
+		gauge:   gauge,
+	}
+}
+
+func (tg *trackedGauge) Describe(ch chan<- *prometheus.Desc) {
+	tg.gauge.Describe(ch)
+}
+
+func (tg *trackedGauge) Collect(ch chan<- prometheus.Metric) {
+	tg.tracker.collect(tg.gauge.DeleteLabelValues)
+	tg.gauge.Collect(ch)
+}
+
+func (tg *trackedGauge) Set(val float64, labels ...string) {
+	tg.gauge.WithLabelValues(labels...).Set(val)
+	tg.tracker.touch(labels)
+}
+
+type trackedCounter struct {
+	tracker *metricTracker
+	counter *prometheus.CounterVec
+}
+
+func NewTrackedCounter(counter *prometheus.CounterVec) *trackedCounter {
+	return &trackedCounter{
+		tracker: newMetricTracker(),
+		counter: counter,
+	}
+}
+
+func (tc *trackedCounter) Describe(ch chan<- *prometheus.Desc) {
+	tc.counter.Describe(ch)
+}
+
+func (tc *trackedCounter) Collect(ch chan<- prometheus.Metric) {
+	tc.tracker.collect(tc.counter.DeleteLabelValues)
+	tc.counter.Collect(ch)
+}
+
+func (tc *trackedCounter) Add(val float64, labels ...string) {
+	tc.counter.WithLabelValues(labels...).Add(val)
+	tc.tracker.touch(labels)
+}