rdev/internal/metrics/metrics.go

// Package metrics provides Prometheus metrics for the rdev API.
package metrics

import (
	"net/http"
	"regexp"
	"strconv"
	"time"

	"github.com/prometheus/client_golang/prometheus"
	"github.com/prometheus/client_golang/prometheus/promauto"
	"github.com/prometheus/client_golang/prometheus/promhttp"
)

var (
	// Commands
	commandsTotal = promauto.NewCounterVec(prometheus.CounterOpts{
		Name: "rdev_commands_total",
		Help: "Total number of commands executed",
	}, []string{"project", "type", "status"})

	commandDuration = promauto.NewHistogramVec(prometheus.HistogramOpts{
		Name:    "rdev_command_duration_seconds",
		Help:    "Duration of command execution in seconds",
		Buckets: prometheus.ExponentialBuckets(0.1, 2, 15), // 0.1s to ~27min
	}, []string{"project", "type"})

	// Streams
	activeStreams = promauto.NewGaugeVec(prometheus.GaugeOpts{
		Name: "rdev_active_streams",
		Help: "Number of active SSE streams",
	}, []string{"project"})

	streamReconnects = promauto.NewCounterVec(prometheus.CounterOpts{
		Name: "rdev_stream_reconnects_total",
		Help: "Total number of SSE stream reconnections",
	}, []string{"project"})

	// Authentication
	authFailures = promauto.NewCounterVec(prometheus.CounterOpts{
		Name: "rdev_auth_failures_total",
		Help: "Total number of authentication failures",
	}, []string{"reason"})

	// API Requests
	requestDuration = promauto.NewHistogramVec(prometheus.HistogramOpts{
		Name:    "rdev_api_request_duration_seconds",
		Help:    "Duration of API requests in seconds",
		Buckets: prometheus.DefBuckets,
	}, []string{"method", "path", "status"})

	requestsTotal = promauto.NewCounterVec(prometheus.CounterOpts{
		Name: "rdev_api_requests_total",
		Help: "Total number of API requests",
	}, []string{"method", "path", "status"})
)

// RecordCommand records a command execution.
func RecordCommand(project, cmdType, status string, durationMs int64) {
	commandsTotal.WithLabelValues(project, cmdType, status).Inc()
	commandDuration.WithLabelValues(project, cmdType).Observe(float64(durationMs) / 1000.0)
}

// IncActiveStreams increments the active stream count for a project.
func IncActiveStreams(project string) {
	activeStreams.WithLabelValues(project).Inc()
}

// DecActiveStreams decrements the active stream count for a project.
func DecActiveStreams(project string) {
	activeStreams.WithLabelValues(project).Dec()
}

// RecordStreamReconnect records a stream reconnection.
func RecordStreamReconnect(project string) {
	streamReconnects.WithLabelValues(project).Inc()
}

// RecordAuthFailure records an authentication failure.
func RecordAuthFailure(reason string) {
	authFailures.WithLabelValues(reason).Inc()
}

// Handler returns the Prometheus HTTP handler.
func Handler() http.Handler {
	return promhttp.Handler()
}

// Middleware returns an HTTP middleware that records request metrics.
func Middleware(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		start := time.Now()

		// Wrap the response writer to capture status code
		rw := &responseWriter{ResponseWriter: w, statusCode: http.StatusOK}

		next.ServeHTTP(rw, r)

		duration := time.Since(start).Seconds()
		status := strconv.Itoa(rw.statusCode)
		path := normalizePath(r.URL.Path)

		requestDuration.WithLabelValues(r.Method, path, status).Observe(duration)
		requestsTotal.WithLabelValues(r.Method, path, status).Inc()
	})
}

// responseWriter wraps http.ResponseWriter to capture status code.
type responseWriter struct {
	http.ResponseWriter
	statusCode int
}

func (rw *responseWriter) WriteHeader(code int) {
	rw.statusCode = code
	rw.ResponseWriter.WriteHeader(code)
}

// pathNormalizers contains patterns to normalize variable path segments.
// Order matters - more specific patterns first.
var pathNormalizers = []struct {
	pattern *regexp.Regexp
	replace string
}{
	// /keys/uuid -> /keys/{id}
	{regexp.MustCompile(`^/keys/[^/]+$`), "/keys/{id}"},
	// /projects/{id}/claude-config/{type}/{name} -> /projects/{id}/claude-config/{type}/{name}
	{regexp.MustCompile(`^/projects/[^/]+/claude-config/(commands|skills|agents)/[^/]+$`), "/projects/{id}/claude-config/$1/{name}"},
	// /projects/{id}/... (any sub-path) - must be last as it's most general
	{regexp.MustCompile(`^/projects/[^/]+(/.*)?$`), "/projects/{id}$1"},
}

// normalizePath normalizes the URL path for consistent metric labels.
// Replaces variable path segments with placeholders to prevent cardinality explosion.
func normalizePath(path string) string {
	for _, n := range pathNormalizers {
		if n.pattern.MatchString(path) {
			return n.pattern.ReplaceAllString(path, n.replace)
		}
	}
	return path
}