package httpapi

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 (
	httpRequests = promauto.NewCounterVec(prometheus.CounterOpts{
		Namespace: "voice_platform", Subsystem: "http", Name: "requests_total",
		Help: "Total HTTP requests by service, method, route and status.",
	}, []string{"service", "method", "route", "status"})
	httpDuration = promauto.NewHistogramVec(prometheus.HistogramOpts{
		Namespace: "voice_platform", Subsystem: "http", Name: "request_duration_seconds",
		Help:    "HTTP request duration by service, method and route.",
		Buckets: []float64{0.005, 0.01, 0.025, 0.05, 0.1, 0.25, 0.5, 1, 2.5, 5},
	}, []string{"service", "method", "route"})
	httpInflight = promauto.NewGaugeVec(prometheus.GaugeOpts{
		Namespace: "voice_platform", Subsystem: "http", Name: "inflight_requests",
		Help: "Current in-flight HTTP requests by service.",
	}, []string{"service"})
)

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

func metricsMiddleware(serviceName string, next http.Handler) http.Handler {
	return http.HandlerFunc(func(writer http.ResponseWriter, request *http.Request) {
		startedAt := time.Now()
		httpInflight.WithLabelValues(serviceName).Inc()
		defer httpInflight.WithLabelValues(serviceName).Dec()
		recorder := &statusRecorder{ResponseWriter: writer, status: http.StatusOK}
		defer func() {
			route := request.Pattern
			if route == "" {
				route = "unmatched"
			}
			httpRequests.WithLabelValues(serviceName, request.Method, route, strconv.Itoa(recorder.status)).Inc()
			httpDuration.WithLabelValues(serviceName, request.Method, route).Observe(time.Since(startedAt).Seconds())
		}()
		next.ServeHTTP(recorder, request)
	})
}

type statusRecorder struct {
	http.ResponseWriter
	status int
	bytes  int
}

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

func (r *statusRecorder) Write(body []byte) (int, error) {
	written, err := r.ResponseWriter.Write(body)
	r.bytes += written
	return written, err
}

func (r *statusRecorder) Unwrap() http.ResponseWriter { return r.ResponseWriter }