package monitoring

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

	"github.com/gorilla/mux"
	"github.com/prometheus/client_golang/prometheus"
	"github.com/prometheus/client_golang/prometheus/promauto"

	"payouts/internal/service/monitoring/config"
)

const (
	METRICS_NAMESPACE = "payouts"
)

// Metrics represents the metrics service
type Metrics interface {
	GetMiddleware() func(next http.Handler) http.Handler
}

// metrics represents the metrics service implementation
type metrics struct {
	httpDuration prometheus.ObserverVec
}

// NewMetrics instantiates metrics service
func NewMetrics(config config.Metrics) (Metrics, error) {
	var httpDuration prometheus.ObserverVec
	if config.Http.HistogramEnabled {
		httpDuration = CreateHttpHistogram(config.Http.Buckets)
	} else {
		httpDuration = CreateHttpSummary(config.Http.Buckets)

	}
	return &metrics{
		httpDuration: httpDuration,
	}, nil
}

// GetMiddleware returns the middleware to be used in mux router
func (m *metrics) GetMiddleware() func(next http.Handler) http.Handler {
	return GetMiddleware(m.httpDuration)
}

func CreateHttpSummary(buckets []float64) *prometheus.SummaryVec {
	return promauto.NewSummaryVec(prometheus.SummaryOpts{
		Name: "http_server_requests_seconds",
		Help: "Duration of HTTP requests.",
	}, []string{"uri", "method", "code"})
}

func CreateHttpHistogram(buckets []float64) *prometheus.HistogramVec {
	return promauto.NewHistogramVec(prometheus.HistogramOpts{
		Name:    "http_server_requests_seconds",
		Help:    "Duration of HTTP requests.",
		Buckets: buckets,
	}, []string{"uri", "method", "code"})

}

func GetMiddleware(histogramVec prometheus.ObserverVec) func(next http.Handler) http.Handler {
	return func(next http.Handler) http.Handler {
		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			route := mux.CurrentRoute(r)
			path, _ := route.GetPathTemplate()
			wd := &writerDelegate{
				ResponseWriter: w,
				statusCode:     http.StatusOK,
			}

			start := time.Now()
			defer func() {
				duration := time.Since(start).Seconds()
				code := strconv.Itoa(wd.statusCode)
				histogramVec.WithLabelValues(path, r.Method, code).Observe(duration)
			}()

			next.ServeHTTP(wd, r)
		})
	}
}

type writerDelegate struct {
	http.ResponseWriter
	statusCode int
}

// override the WriteHeader method
func (w *writerDelegate) WriteHeader(statusCode int) {
	w.statusCode = statusCode
	w.ResponseWriter.WriteHeader(statusCode)
}