Some conversation-starting progress.

Still tons of work to do, but it's probably far enough along to get some feedback.

pkg/custom-provider/types.go

@@ -0,0 +1,50 @@
+package provider
+
+import (
+	"context"
+	"fmt"
+	"time"
+
+	prom "github.com/directxman12/k8s-prometheus-adapter/pkg/client"
+	"github.com/golang/glog"
+	pmodel "github.com/prometheus/common/model"
+	utilruntime "k8s.io/apimachinery/pkg/util/runtime"
+	"k8s.io/apimachinery/pkg/util/wait"
+)
+
+type cachingMetricsLister struct {
+	SeriesRegistry
+
+	promClient     prom.Client
+	updateInterval time.Duration
+}
+
+func (l *cachingMetricsLister) Run() {
+	l.RunUntil(wait.NeverStop)
+}
+
+func (l *cachingMetricsLister) RunUntil(stopChan <-chan struct{}) {
+	go wait.Until(func() {
+		if err := l.updateMetrics(); err != nil {
+			utilruntime.HandleError(err)
+		}
+	}, l.updateInterval, stopChan)
+}
+
+func (l *cachingMetricsLister) updateMetrics() error {
+	startTime := pmodel.Now().Add(-1 * l.updateInterval)
+
+	sels := l.Selectors()
+
+	// TODO: use an actual context here
+	series, err := l.promClient.Series(context.Background(), pmodel.Interval{startTime, 0}, sels...)
+	if err != nil {
+		return fmt.Errorf("unable to update list of all available metrics: %v", err)
+	}
+
+	glog.V(10).Infof("Set available metric list from Prometheus to: %v", series)
+
+	l.SetSeries(series)
+
+	return nil
+}