package middleware

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

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

var (
	httpRequestsTotal = promauto.NewCounterVec(
		prometheus.CounterOpts{
			Name: "streamapp_http_requests_total",
			Help: "Total number of HTTP requests.",
		},
		[]string{"method", "path", "status"},
	)

	httpRequestDuration = promauto.NewHistogramVec(
		prometheus.HistogramOpts{
			Name:    "streamapp_http_request_duration_seconds",
			Help:    "Duration of HTTP requests in seconds.",
			Buckets: prometheus.DefBuckets,
		},
		[]string{"method", "path"},
	)
)

// Metrics is an HTTP middleware that records request count and duration.
func Metrics(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		start := time.Now()

		// Wrap response writer to capture status code.
		wrapped := &statusWriter{ResponseWriter: w, status: 200}

		next.ServeHTTP(wrapped, r)

		duration := time.Since(start).Seconds()
		path := sanitizePath(r.URL.Path)

		httpRequestsTotal.WithLabelValues(r.Method, path, strconv.Itoa(wrapped.status)).Inc()
		httpRequestDuration.WithLabelValues(r.Method, path).Observe(duration)
	})
}

type statusWriter struct {
	http.ResponseWriter
	status  int
	written bool
}

func (w *statusWriter) WriteHeader(status int) {
	if !w.written {
		w.status = status
		w.written = true
	}
	w.ResponseWriter.WriteHeader(status)
}

// Hijack implements http.Hijacker, required for WebSocket upgrades.
func (w *statusWriter) Hijack() (net.Conn, *bufio.ReadWriter, error) {
	if hj, ok := w.ResponseWriter.(http.Hijacker); ok {
		return hj.Hijack()
	}
	return nil, nil, fmt.Errorf("underlying ResponseWriter does not implement http.Hijacker")
}

var (
	uuidRegex    = regexp.MustCompile(`[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}`)
	numericRegex = regexp.MustCompile(`/\d+(/|$)`)
)

// sanitizePath normalizes URL paths to avoid high-cardinality labels.
// Replaces dynamic segments (UUIDs, numeric IDs) with placeholders.
func sanitizePath(path string) string {
	path = uuidRegex.ReplaceAllString(path, "{id}")
	path = numericRegex.ReplaceAllStringFunc(path, func(m string) string {
		if m[len(m)-1] == '/' {
			return "/{id}/"
		}
		return "/{id}"
	})
	return path
}