add lite summary statistics

exporter.go

@@ -7,36 +7,93 @@ import (
 	"flag"
 	"fmt"
 	"log"
+	"math"
 	"net/http"
 	"os/exec"
+	"sync"
 	"time"
 
 	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promauto"
 	"github.com/prometheus/client_golang/prometheus/promhttp"
 )
 
 var (
-	addr = flag.String("listen-address", ":9454", "The address to listen on for HTTP requests.")
+	addr         = flag.String("listen-address", ":9454", "The address to listen on for HTTP requests.")
+	pollInterval = flag.Duration("poll-interval", 1*time.Second, "Time between executions of `lifepo4wered-cli get`")
 
-	lifepo4weredVars = prometheus.NewGaugeVec(
+	lifepo4weredVars = promauto.NewGaugeVec(
 		prometheus.GaugeOpts{
 			Name: "lifepo4wered",
 			Help: "Variables gathered from the lifepo4wered-cli tool",
 		},
 		[]string{"var"},
 	)
+
+	lifepo4weredSummaries = map[string]*liteSummary{
+		"VIN":  newLiteSummary("voltage_in", "Voltage in (mV)"),
+		"VOUT": newLiteSummary("voltage_out", "Voltage out (mV)"),
+		"VBAT": newLiteSummary("voltage_bat", "Battery voltage (mV)"),
+		"IOUT": newLiteSummary("current_out", "Current out (mA)"),
+	}
+	lifepo4weredPOut = newLiteSummary("power_out", "Power out (mW)")
 )
 
-func init() {
-	prometheus.MustRegister(lifepo4weredVars)
+type liteSummary struct {
+	mu    sync.Mutex
+	min   float64
+	max   float64
+	sum   float64
+	count int
+
+	desc *prometheus.Desc
 }
 
-func getVars() {
+func newLiteSummary(varName, help string) *liteSummary {
+	s := &liteSummary{
+		min:  math.Inf(1),
+		max:  math.Inf(-1),
+		desc: prometheus.NewDesc("lifepo4wered_"+varName, help, []string{"stat"}, nil),
+	}
+	prometheus.MustRegister(s)
+	return s
+}
+
+func (s *liteSummary) Describe(ch chan<- *prometheus.Desc) { ch <- s.desc }
+
+func (s *liteSummary) Collect(ch chan<- prometheus.Metric) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	ch <- prometheus.MustNewConstMetric(s.desc, prometheus.GaugeValue, s.min, "min")
+	ch <- prometheus.MustNewConstMetric(s.desc, prometheus.GaugeValue, s.max, "max")
+	mean := s.sum
+	if s.count > 0 {
+		mean /= float64(s.count)
+	}
+	ch <- prometheus.MustNewConstMetric(s.desc, prometheus.GaugeValue, mean, "mean")
+	s.min = math.Inf(1)
+	s.max = math.Inf(-1)
+	s.sum, s.count = 0, 0
+}
+
+func (s *liteSummary) Observe(x float64) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	s.min = min(s.min, x)
+	s.max = max(s.max, x)
+	s.sum += x
+	s.count++
+}
+
+func pollVars() {
 	cmd := exec.Command("lifepo4wered-cli", "get")
 	out, err := cmd.Output()
 	if err != nil {
 		log.Fatalf("Couldn't execute command: %v", err)
 	}
+	pout := 1
+	labels := prometheus.Labels{"var": ""}
+
 	s := bufio.NewScanner(bytes.NewReader(out))
 	for s.Scan() {
 		// token space equals space number
@@ -45,20 +102,33 @@ func getVars() {
 		if _, err := fmt.Sscanf(s.Text(), "%s = %d", &name, &num); err != nil {
 			log.Fatalf("Couldn't scan line: %v", err)
 		}
-		lifepo4weredVars.With(prometheus.Labels{"var": name}).Set(float64(num))
+		labels["var"] = name
+		lifepo4weredVars.With(labels).Set(float64(num))
+
+		v, ok := lifepo4weredSummaries[name]
+		if !ok {
+			continue
+		}
+		v.Observe(float64(num))
+		switch name {
+		case "VOUT", "IOUT":
+			pout *= num
+		}
 	}
 	if err := s.Err(); err != nil {
 		log.Fatalf("Couldn't scan output: %v", err)
 	}
+
+	lifepo4weredPOut.Observe(float64(pout) / 1e3) // mV * mA = µW; 1000µW = 1mW.
 }
 
 func main() {
 	flag.Parse()
 
-	getVars()
+	pollVars()
 	go func() {
-		for range time.Tick(15 * time.Second) {
-			getVars()
+		for range time.Tick(*pollInterval) {
+			pollVars()
 		}
 	}()