Viewer metrics api (#208)

* Add support for ending the inbound stream. Closes #191

* Add a simple success response to API requests

* Add viewers over time API

* Move controllers to admin directory

metrics/viewers.go

@@ -0,0 +1,31 @@
+package metrics
+
+import (
+	"time"
+
+	"github.com/gabek/owncast/core"
+)
+
+// How often we poll for updates
+const viewerMetricsPollingInterval = 5 * time.Minute
+
+func startViewerCollectionMetrics() {
+	collectViewerCount()
+
+	for range time.Tick(viewerMetricsPollingInterval) {
+		collectViewerCount()
+	}
+}
+
+func collectViewerCount() {
+	if len(Metrics.Viewers) > maxCollectionValues {
+		Metrics.Viewers = Metrics.Viewers[1:]
+	}
+
+	count := core.GetStatus().ViewerCount
+	value := timestampedValue{
+		Value: count,
+		Time:  time.Now(),
+	}
+	Metrics.Viewers = append(Metrics.Viewers, value)
+}