fix: store new metrics in buffer before resetting

Borg repo information can take a long time to gather.
Before resetting the old metrics we store the new ones in a buffer
and update everything at the end.

buffer.go

@@ -0,0 +1,14 @@
+package main
+
+type MetricsBuffer struct {
+	RepoName          string
+	ArchiveCount      float64
+	LastArchiveTime   float64
+	LastModified      float64
+	TotalChunks       float64
+	TotalCsize        float64
+	TotalSize         float64
+	TotalUniqueChunks float64
+	UniqueCsize       float64
+	UniqueSize        float64
+}

main.go

@@ -57,13 +57,12 @@ func main() {
 
 func RecordMetrics(m Metrics) {
 	for {
-		m.Reset()
-
 		entries, err := os.ReadDir(*backupDir)
 		if err != nil {
 			log.Fatalln(err)
 		}
 
+		buffer := []MetricsBuffer{}
 		for _, entry := range entries {
 			if !entry.IsDir() || strings.HasPrefix(entry.Name(), ".") {
 				log.Printf(">> Ignoring %v\n", entry.Name())
@@ -86,17 +85,21 @@ func RecordMetrics(m Metrics) {
 			stats := info.Cache.Stats
 
 			log.Printf("> Got info for: %v\n", path)
-			m.ArchiveCount.With(prometheus.Labels{"repo_name": entry.Name()}).Set(float64(len(list.Archives)))
+			buffer = append(buffer, MetricsBuffer{
-			m.LastArchiveTime.With(prometheus.Labels{"repo_name": entry.Name()}).Set(list.LastArchiveUnix())
+				RepoName:          entry.Name(),
-			m.LastModified.With(prometheus.Labels{"repo_name": entry.Name()}).Set(info.LastmodUnix())
+				ArchiveCount:      float64(len(list.Archives)),
-			m.TotalChunks.With(prometheus.Labels{"repo_name": entry.Name()}).Set(stats.Total_chunks)
+				LastArchiveTime:   list.LastArchiveUnix(),
-			m.TotalCsize.With(prometheus.Labels{"repo_name": entry.Name()}).Set(stats.Total_csize)
+				LastModified:      info.LastmodUnix(),
-			m.TotalSize.With(prometheus.Labels{"repo_name": entry.Name()}).Set(stats.Total_size)
+				TotalChunks:       stats.Total_chunks,
-			m.TotalUniqueChunks.With(prometheus.Labels{"repo_name": entry.Name()}).Set(stats.Total_unique_chunks)
+				TotalCsize:        stats.Total_csize,
-			m.UniqueCsize.With(prometheus.Labels{"repo_name": entry.Name()}).Set(stats.Unique_csize)
+				TotalSize:         stats.Total_size,
-			m.UniqueSize.With(prometheus.Labels{"repo_name": entry.Name()}).Set(stats.Unique_size)
+				TotalUniqueChunks: stats.Total_unique_chunks,
+				UniqueCsize:       stats.Unique_csize,
+				UniqueSize:        stats.Unique_size,
+			})
 		}
 
+		m.Update(buffer)
 		log.Printf("> Waiting %v\n", INTERVAL)
 		time.Sleep(INTERVAL)
 	}

metrics.go

@@ -56,3 +56,21 @@ func (m *Metrics) Reset() {
 	m.UniqueCsize.Reset()
 	m.UniqueSize.Reset()
 }
+
+// Update these metrics with the given buffer.
+//
+// Resets the metrics beforehand. Expected to be called on every loop iteration.
+func (m *Metrics) Update(buffer []MetricsBuffer) {
+	m.Reset()
+	for _, buf := range buffer {
+		m.ArchiveCount.With(prometheus.Labels{"repo_name": buf.RepoName}).Set(buf.ArchiveCount)
+		m.LastArchiveTime.With(prometheus.Labels{"repo_name": buf.RepoName}).Set(buf.LastArchiveTime)
+		m.LastModified.With(prometheus.Labels{"repo_name": buf.RepoName}).Set(buf.LastModified)
+		m.TotalChunks.With(prometheus.Labels{"repo_name": buf.RepoName}).Set(buf.TotalChunks)
+		m.TotalCsize.With(prometheus.Labels{"repo_name": buf.RepoName}).Set(buf.TotalCsize)
+		m.TotalSize.With(prometheus.Labels{"repo_name": buf.RepoName}).Set(buf.TotalSize)
+		m.TotalUniqueChunks.With(prometheus.Labels{"repo_name": buf.RepoName}).Set(buf.TotalUniqueChunks)
+		m.UniqueCsize.With(prometheus.Labels{"repo_name": buf.RepoName}).Set(buf.UniqueCsize)
+		m.UniqueSize.With(prometheus.Labels{"repo_name": buf.RepoName}).Set(buf.UniqueSize)
+	}
+}