various: add internal health and runtime metrics

Signed-off-by: NotAShelf <raf@notashelf.dev>
Change-Id: Iae1dcf8495a00159d588c6e2344312f36a6a6964

internal/health/metrics.go

@@ -0,0 +1,56 @@
+package health
+
+import (
+	"time"
+
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/collectors"
+)
+
+// Holds health and runtime metrics for the watchdog process
+type Collector struct {
+	buildInfo prometheus.Gauge
+	startTime prometheus.Gauge
+}
+
+// Creates a health metrics collector with build metadata
+func NewCollector(version, commit, buildDate string) *Collector {
+	buildInfo := prometheus.NewGauge(prometheus.GaugeOpts{
+		Name: "watchdog_build_info",
+		Help: "Build metadata for the running watchdog instance",
+		ConstLabels: prometheus.Labels{
+			"version":    version,
+			"commit":     commit,
+			"build_date": buildDate,
+		},
+	})
+	buildInfo.Set(1)
+
+	startTime := prometheus.NewGauge(prometheus.GaugeOpts{
+		Name: "watchdog_start_time_seconds",
+		Help: "Unix timestamp of when the watchdog process started",
+	})
+	startTime.Set(float64(time.Now().Unix()))
+
+	return &Collector{
+		buildInfo: buildInfo,
+		startTime: startTime,
+	}
+}
+
+// Registers all health metrics plus Go runtime collectors
+func (c *Collector) Register(reg prometheus.Registerer) error {
+	if err := reg.Register(c.buildInfo); err != nil {
+		return err
+	}
+	if err := reg.Register(c.startTime); err != nil {
+		return err
+	}
+	if err := reg.Register(collectors.NewGoCollector()); err != nil {
+		return err
+	}
+	if err := reg.Register(collectors.NewProcessCollector(collectors.ProcessCollectorOpts{})); err != nil {
+		return err
+	}
+	return nil
+}

internal/health/metrics_test.go

@@ -0,0 +1,103 @@
+package health
+
+import (
+	"testing"
+
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+func TestNewCollector_RegistersMetrics(t *testing.T) {
+	reg := prometheus.NewRegistry()
+	c := NewCollector("v0.1.0", "abc1234", "2026-03-02")
+
+	if err := c.Register(reg); err != nil {
+		t.Fatalf("Register failed: %v", err)
+	}
+
+	metrics, err := reg.Gather()
+	if err != nil {
+		t.Fatalf("Gather failed: %v", err)
+	}
+
+	// Should have at least build_info and uptime
+	names := make(map[string]bool)
+	for _, m := range metrics {
+		names[m.GetName()] = true
+	}
+
+	if !names["watchdog_build_info"] {
+		t.Error("expected watchdog_build_info metric")
+	}
+	if !names["watchdog_start_time_seconds"] {
+		t.Error("expected watchdog_start_time_seconds metric")
+	}
+}
+
+func TestNewCollector_BuildInfoLabels(t *testing.T) {
+	reg := prometheus.NewRegistry()
+	c := NewCollector("v1.2.3", "deadbeef", "2026-03-02")
+
+	if err := c.Register(reg); err != nil {
+		t.Fatalf("Register failed: %v", err)
+	}
+
+	metrics, err := reg.Gather()
+	if err != nil {
+		t.Fatalf("Gather failed: %v", err)
+	}
+
+	for _, m := range metrics {
+		if m.GetName() != "watchdog_build_info" {
+			continue
+		}
+
+		labels := make(map[string]string)
+		for _, l := range m.GetMetric()[0].GetLabel() {
+			labels[l.GetName()] = l.GetValue()
+		}
+
+		if labels["version"] != "v1.2.3" {
+			t.Errorf("expected version label %q, got %q", "v1.2.3", labels["version"])
+		}
+		if labels["commit"] != "deadbeef" {
+			t.Errorf("expected commit label %q, got %q", "deadbeef", labels["commit"])
+		}
+		if labels["build_date"] != "2026-03-02" {
+			t.Errorf(
+				"expected build_date label %q, got %q",
+				"2026-03-02",
+				labels["build_date"],
+			)
+		}
+		return
+	}
+
+	t.Error("watchdog_build_info metric not found in gathered metrics")
+}
+
+func TestNewCollector_StartTimeIsPositive(t *testing.T) {
+	reg := prometheus.NewRegistry()
+	c := NewCollector("v0.1.0", "abc1234", "2026-03-02")
+
+	if err := c.Register(reg); err != nil {
+		t.Fatalf("Register failed: %v", err)
+	}
+
+	metrics, err := reg.Gather()
+	if err != nil {
+		t.Fatalf("Gather failed: %v", err)
+	}
+
+	for _, m := range metrics {
+		if m.GetName() != "watchdog_start_time_seconds" {
+			continue
+		}
+		val := m.GetMetric()[0].GetGauge().GetValue()
+		if val <= 0 {
+			t.Errorf("expected positive start time, got %v", val)
+		}
+		return
+	}
+
+	t.Error("watchdog_start_time_seconds metric not found")
+}