package metrics

import (
	"fmt"
	"net/http"
	"sync"
	"time"

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

var (
	// Default metrics
	requestDuration = prometheus.NewHistogramVec(
		prometheus.HistogramOpts{
			Name:    "http_request_duration_seconds",
			Help:    "Duration of HTTP requests in seconds",
			Buckets: prometheus.DefBuckets,
		},
		[]string{"method", "path", "status"},
	)

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

	otpGenerationTotal = prometheus.NewCounterVec(
		prometheus.CounterOpts{
			Name: "otp_generation_total",
			Help: "Total number of OTP generations",
		},
		[]string{"user_id", "otp_id"},
	)

	otpVerificationTotal = prometheus.NewCounterVec(
		prometheus.CounterOpts{
			Name: "otp_verification_total",
			Help: "Total number of OTP verifications",
		},
		[]string{"user_id", "otp_id", "success"},
	)

	activeUsers = prometheus.NewGauge(
		prometheus.GaugeOpts{
			Name: "active_users",
			Help: "Number of active users",
		},
	)

	cacheHits = prometheus.NewCounterVec(
		prometheus.CounterOpts{
			Name: "cache_hits_total",
			Help: "Total number of cache hits",
		},
		[]string{"cache"},
	)

	cacheMisses = prometheus.NewCounterVec(
		prometheus.CounterOpts{
			Name: "cache_misses_total",
			Help: "Total number of cache misses",
		},
		[]string{"cache"},
	)
)

func init() {
	// Register metrics with prometheus
	prometheus.MustRegister(
		requestDuration,
		requestTotal,
		otpGenerationTotal,
		otpVerificationTotal,
		activeUsers,
		cacheHits,
		cacheMisses,
	)
}

// MetricsService provides metrics functionality
type MetricsService struct {
	activeUsersMutex sync.RWMutex
	activeUserIDs    map[string]bool
}

// NewMetricsService creates a new MetricsService
func NewMetricsService() *MetricsService {
	return &MetricsService{
		activeUserIDs: make(map[string]bool),
	}
}

// Handler returns an HTTP handler for metrics
func (s *MetricsService) Handler() http.Handler {
	return promhttp.Handler()
}

// RecordRequest records metrics for an HTTP request
func (s *MetricsService) RecordRequest(method, path string, status int, duration time.Duration) {
	labels := prometheus.Labels{
		"method": method,
		"path":   path,
		"status": fmt.Sprintf("%d", status),
	}

	requestDuration.With(labels).Observe(duration.Seconds())
	requestTotal.With(labels).Inc()
}

// RecordOTPGeneration records metrics for OTP generation
func (s *MetricsService) RecordOTPGeneration(userID, otpID string) {
	otpGenerationTotal.With(prometheus.Labels{
		"user_id": userID,
		"otp_id":  otpID,
	}).Inc()
}

// RecordOTPVerification records metrics for OTP verification
func (s *MetricsService) RecordOTPVerification(userID, otpID string, success bool) {
	otpVerificationTotal.With(prometheus.Labels{
		"user_id": userID,
		"otp_id":  otpID,
		"success": fmt.Sprintf("%t", success),
	}).Inc()
}

// RecordUserActivity records user activity
func (s *MetricsService) RecordUserActivity(userID string) {
	s.activeUsersMutex.Lock()
	defer s.activeUsersMutex.Unlock()

	if !s.activeUserIDs[userID] {
		s.activeUserIDs[userID] = true
		activeUsers.Inc()
	}
}

// RecordUserInactivity records user inactivity
func (s *MetricsService) RecordUserInactivity(userID string) {
	s.activeUsersMutex.Lock()
	defer s.activeUsersMutex.Unlock()

	if s.activeUserIDs[userID] {
		delete(s.activeUserIDs, userID)
		activeUsers.Dec()
	}
}

// RecordCacheHit records a cache hit
func (s *MetricsService) RecordCacheHit(cache string) {
	cacheHits.With(prometheus.Labels{
		"cache": cache,
	}).Inc()
}

// RecordCacheMiss records a cache miss
func (s *MetricsService) RecordCacheMiss(cache string) {
	cacheMisses.With(prometheus.Labels{
		"cache": cache,
	}).Inc()
}

// Middleware creates a middleware that records request metrics
func (s *MetricsService) Middleware(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		start := time.Now()

		// Create response writer that captures status code
		rw := &responseWriter{ResponseWriter: w, status: http.StatusOK}

		// Call next handler
		next.ServeHTTP(rw, r)

		// Record metrics
		s.RecordRequest(r.Method, r.URL.Path, rw.status, time.Since(start))
	})
}

// responseWriter wraps http.ResponseWriter to capture status code
type responseWriter struct {
	http.ResponseWriter
	status int
}

func (rw *responseWriter) WriteHeader(code int) {
	rw.status = code
	rw.ResponseWriter.WriteHeader(code)
}