internal: initial metrics aggregator

Signed-off-by: NotAShelf <raf@notashelf.dev>
Change-Id: I9cdd6e2b33bb65182568db9db4460bc46a6a6964

internal/aggregate/metrics.go

@@ -0,0 +1,101 @@
+package aggregate
+
+import (
+	"github.com/prometheus/client_golang/prometheus"
+	"notashelf.dev/watchdog/internal/config"
+)
+
+// Records analytics events as Prometheus metrics
+type MetricsAggregator struct {
+	registry     *PathRegistry
+	cfg          config.Config
+	pageviews    *prometheus.CounterVec
+	customEvents *prometheus.CounterVec
+	pathOverflow prometheus.Counter
+}
+
+// Creates a new metrics aggregator with dynamic labels based on config
+func NewMetricsAggregator(registry *PathRegistry, cfg config.Config) *MetricsAggregator {
+	// Build label names based on what's enabled in config
+	labels := []string{"path"} // path is always included
+
+	if cfg.Site.Collect.Country {
+		labels = append(labels, "country")
+	}
+
+	if cfg.Site.Collect.Device {
+		labels = append(labels, "device")
+	}
+
+	if cfg.Site.Collect.Referrer != "off" {
+		labels = append(labels, "referrer")
+	}
+
+	pageviews := prometheus.NewCounterVec(
+		prometheus.CounterOpts{
+			Name: "web_pageviews_total",
+			Help: "Total number of pageviews",
+		},
+		labels,
+	)
+
+	customEvents := prometheus.NewCounterVec(
+		prometheus.CounterOpts{
+			Name: "web_custom_events_total",
+			Help: "Total number of custom events",
+		},
+		[]string{"event"},
+	)
+
+	pathOverflow := prometheus.NewCounter(
+		prometheus.CounterOpts{
+			Name: "web_path_overflow_total",
+			Help: "Paths rejected due to cardinality limit",
+		},
+	)
+
+	return &MetricsAggregator{
+		registry:     registry,
+		cfg:          cfg,
+		pageviews:    pageviews,
+		customEvents: customEvents,
+		pathOverflow: pathOverflow,
+	}
+}
+
+// Records a pageview with the configured dimensions
+func (m *MetricsAggregator) RecordPageview(path, country, device, referrer string) {
+	// Build label values in the same order as label names
+	labels := prometheus.Labels{"path": path}
+
+	if m.cfg.Site.Collect.Country {
+		labels["country"] = country
+	}
+
+	if m.cfg.Site.Collect.Device {
+		labels["device"] = device
+	}
+
+	if m.cfg.Site.Collect.Referrer != "off" {
+		labels["referrer"] = referrer
+	}
+
+	m.pageviews.With(labels).Inc()
+}
+
+// Records a custom event
+func (m *MetricsAggregator) RecordCustomEvent(eventName string) {
+	m.customEvents.With(prometheus.Labels{"event": eventName}).Inc()
+}
+
+// Records a path that was rejected due to cardinality limits
+func (m *MetricsAggregator) RecordPathOverflow() {
+	m.pathOverflow.Inc()
+}
+
+// Registers all metrics with the provided Prometheus registry
+func (m *MetricsAggregator) MustRegister(reg prometheus.Registerer) {
+	reg.MustRegister(m.pageviews)
+	reg.MustRegister(m.customEvents)
+	reg.MustRegister(m.pathOverflow)
+}

internal/aggregate/metrics_test.go

@@ -0,0 +1,192 @@
+package aggregate
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/testutil"
+	"notashelf.dev/watchdog/internal/config"
+)
+
+func TestMetricsAggregator_RecordPageview(t *testing.T) {
+	registry := NewPathRegistry(100)
+	cfg := config.Config{
+		Site: config.SiteConfig{
+			Collect: config.CollectConfig{
+				Pageviews: true,
+				Country:   true,
+				Device:    true,
+				Referrer:  "domain",
+			},
+		},
+	}
+
+	agg := NewMetricsAggregator(registry, cfg)
+
+	// Record pageview with all dimensions
+	agg.RecordPageview("/home", "US", "desktop", "google.com")
+
+	// Verify metric was recorded
+	expected := `
+# HELP web_pageviews_total Total number of pageviews
+# TYPE web_pageviews_total counter
+web_pageviews_total{country="US",device="desktop",path="/home",referrer="google.com"} 1
+`
+	if err := testutil.CollectAndCompare(agg.pageviews, strings.NewReader(expected)); err != nil {
+		t.Errorf("unexpected metric value: %v", err)
+	}
+}
+
+func TestMetricsAggregator_RecordPageview_MinimalDimensions(t *testing.T) {
+	registry := NewPathRegistry(100)
+	cfg := config.Config{
+		Site: config.SiteConfig{
+			Collect: config.CollectConfig{
+				Pageviews: true,
+				Country:   false,
+				Device:    false,
+				Referrer:  "off",
+			},
+		},
+	}
+
+	agg := NewMetricsAggregator(registry, cfg)
+
+	// Record pageview with only path
+	agg.RecordPageview("/home", "", "", "")
+
+	// Verify metric was recorded
+	expected := `
+# HELP web_pageviews_total Total number of pageviews
+# TYPE web_pageviews_total counter
+web_pageviews_total{path="/home"} 1
+`
+	if err := testutil.CollectAndCompare(agg.pageviews, strings.NewReader(expected)); err != nil {
+		t.Errorf("unexpected metric value: %v", err)
+	}
+}
+
+func TestMetricsAggregator_PathOverflow(t *testing.T) {
+	// Create registry with limit of 2
+	registry := NewPathRegistry(2)
+	cfg := config.Config{
+		Site: config.SiteConfig{
+			Collect: config.CollectConfig{
+				Pageviews: true,
+			},
+		},
+	}
+
+	agg := NewMetricsAggregator(registry, cfg)
+
+	// Add two paths successfully
+	registry.Add("/path1")
+	registry.Add("/path2")
+
+	// Try to add third path - should be rejected
+	if registry.Add("/path3") {
+		t.Error("expected path to be rejected")
+	}
+
+	// Record overflow
+	agg.RecordPathOverflow()
+
+	// Verify overflow metric
+	expected := `
+# HELP web_path_overflow_total Paths rejected due to cardinality limit
+# TYPE web_path_overflow_total counter
+web_path_overflow_total 1
+`
+	if err := testutil.CollectAndCompare(agg.pathOverflow, strings.NewReader(expected)); err != nil {
+		t.Errorf("unexpected metric value: %v", err)
+	}
+}
+
+func TestMetricsAggregator_RecordCustomEvent(t *testing.T) {
+	registry := NewPathRegistry(100)
+	cfg := config.Config{
+		Site: config.SiteConfig{
+			Collect: config.CollectConfig{
+				Pageviews: true,
+			},
+			CustomEvents: []string{"signup", "purchase"},
+		},
+	}
+
+	agg := NewMetricsAggregator(registry, cfg)
+
+	// Record custom event
+	agg.RecordCustomEvent("signup")
+
+	// Verify metric was recorded
+	expected := `
+# HELP web_custom_events_total Total number of custom events
+# TYPE web_custom_events_total counter
+web_custom_events_total{event="signup"} 1
+`
+	if err := testutil.CollectAndCompare(agg.customEvents, strings.NewReader(expected)); err != nil {
+		t.Errorf("unexpected metric value: %v", err)
+	}
+}
+
+func TestMetricsAggregator_RecordCustomEvent_MultipleEvents(t *testing.T) {
+	registry := NewPathRegistry(100)
+	cfg := config.Config{
+		Site: config.SiteConfig{
+			Collect: config.CollectConfig{
+				Pageviews: true,
+			},
+			CustomEvents: []string{"signup", "purchase"},
+		},
+	}
+
+	agg := NewMetricsAggregator(registry, cfg)
+
+	// Record multiple events
+	agg.RecordCustomEvent("signup")
+	agg.RecordCustomEvent("signup")
+	agg.RecordCustomEvent("purchase")
+
+	// Verify metrics
+	if err := testutil.CollectAndCompare(agg.customEvents, strings.NewReader(`
+# HELP web_custom_events_total Total number of custom events
+# TYPE web_custom_events_total counter
+web_custom_events_total{event="purchase"} 1
+web_custom_events_total{event="signup"} 2
+`)); err != nil {
+		t.Errorf("unexpected metric value: %v", err)
+	}
+}
+
+func TestMetricsAggregator_MustRegister(t *testing.T) {
+	registry := NewPathRegistry(100)
+	cfg := config.Config{
+		Site: config.SiteConfig{
+			Collect: config.CollectConfig{
+				Pageviews: true,
+			},
+		},
+	}
+
+	promRegistry := prometheus.NewRegistry()
+	agg := NewMetricsAggregator(registry, cfg)
+
+	// Register metrics
+	agg.MustRegister(promRegistry)
+
+	// Record some metrics to ensure they show up
+	agg.RecordPageview("/test", "", "", "")
+	agg.RecordPathOverflow()
+
+	// Verify metrics can be gathered
+	metrics, err := promRegistry.Gather()
+	if err != nil {
+		t.Fatalf("failed to gather metrics: %v", err)
+	}
+
+	// Should have at least pageviews and path overflow metrics
+	if len(metrics) < 2 {
+		t.Errorf("expected at least 2 metric families, got %d", len(metrics))
+	}
+}