metrics

var (
	// AddrTag annotates the host:port the metrics HTTP server listens on,
	// supplied to fx as the named value "metricsAddr".
	AddrTag = fx.ResultTags(`name:"metricsAddr"`)

	// NamespaceTag annotates the Prometheus namespace prefixed onto every
	// collector, supplied to fx as the named value "metricsNamespace".
	NamespaceTag = fx.ResultTags(`name:"metricsNamespace"`)
)

var Module = fx.Options(
	fx.Provide(func(p MetricsParams) *Factory {
		return New(p.Namespace, promauto.With(p.Registerer))
	}),
	fx.Invoke(func(p MetricsParams) error {
		if p.Addr == "" {
			return errors.New("metrics addr not set")
		}

		mux := http.NewServeMux()
		mux.Handle("/metrics", promhttp.HandlerFor(p.Gatherer, promhttp.HandlerOpts{
			Registry: p.Registerer,
		}))

		svr := &http.Server{
			Addr:              p.Addr,
			Handler:           mux,
			ReadHeaderTimeout: 5 * time.Second,
			ReadTimeout:       10 * time.Second,
		}

		log := p.Logger.With(
			tag.Component("metrics"),
			tag.String("addr", p.Addr),
		)

		p.Lifecycle.Append(fx.Hook{
			OnStart: func(context.Context) error {
				go func() {
					defer func() { _ = svr.Close() }()

					log.Info("Starting metrics server")
					if err := svr.ListenAndServe(); err != nil && !errors.Is(err, http.ErrServerClosed) {
						log.Error("Failed to run metrics server", tag.Error(err))
						_ = p.Shutdowner.Shutdown(fx.ExitCode(1))
					}
				}()

				return nil
			},
			OnStop: func(ctx context.Context) error {
				log.Info("Shutting down metrics server")
				if err := svr.Shutdown(ctx); err != nil && !errors.Is(err, http.ErrServerClosed) {
					return err
				}

				return nil
			},
		})

		return nil
	}),
)