package metrics

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

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

var (
	requestsTotal = promauto.NewCounterVec(
		prometheus.CounterOpts{
			Name: "http_requests_total",
			Help: "Total number of HTTP requests",
		},
		[]string{"method", "path", "status"},
	)
	requestDuration = promauto.NewHistogramVec(
		prometheus.HistogramOpts{
			Name:    "http_request_duration_seconds",
			Help:    "Duration of HTTP requests",
			Buckets: prometheus.DefBuckets,
		},
		[]string{"method", "path"},
	)
	requestsInFlight = promauto.NewGauge(prometheus.GaugeOpts{
		Name: "http_requests_in_flight",
		Help: "Number of HTTP requests currently in flight",
	})
)

func Handler() http.Handler {
	return promhttp.Handler()
}

type recorder struct {
	http.ResponseWriter
	status int
}

func (r *recorder) WriteHeader(code int) {
	r.status = code
	r.ResponseWriter.WriteHeader(code)
}

func Middleware(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		requestsInFlight.Inc()
		defer requestsInFlight.Dec()

		start := time.Now()
		rec := &recorder{ResponseWriter: w, status: http.StatusOK}
		next.ServeHTTP(rec, r)

		status := strconv.Itoa(rec.status)
		requestsTotal.WithLabelValues(r.Method, r.URL.Path, status).Inc()
		requestDuration.WithLabelValues(r.Method, r.URL.Path).Observe(time.Since(start).Seconds())
	})
}