package metrics

import (
	_ "embed"
	"net/http"

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

// Metrics holds all Prometheus metrics for the relay.
type Metrics struct {
	// Request metrics
	requestsTotal       *prometheus.CounterVec
	requestDuration     *prometheus.HistogramVec
	requestSizeBytes    *prometheus.HistogramVec
	responseSizeBytes   *prometheus.HistogramVec

	// Connection metrics
	activeConnections   prometheus.Gauge
	activeSubscriptions prometheus.Gauge
	connectionsTotal    prometheus.Counter

	// Auth metrics
	authAttemptsTotal   *prometheus.CounterVec
	rateLimitHitsTotal  *prometheus.CounterVec

	// Storage metrics
	eventsTotal         prometheus.Gauge
	dbSizeBytes         prometheus.Gauge
	eventDeletionsTotal prometheus.Counter

	// Config
	config *Config
}

// Config configures the metrics.
type Config struct {
	// Namespace is the Prometheus namespace (e.g., "muxstr")
	Namespace string

	// Subsystem is the Prometheus subsystem (e.g., "relay")
	Subsystem string

	// Buckets for latency histogram (in seconds)
	LatencyBuckets []float64

	// Buckets for size histograms (in bytes)
	SizeBuckets []float64
}

// DefaultConfig returns default metrics configuration.
func DefaultConfig() *Config {
	return &Config{
		Namespace: "muxstr",
		Subsystem: "relay",
		LatencyBuckets: []float64{
			0.001, 0.005, 0.01, 0.05, 0.1, 0.5, 1.0, 5.0, 10.0,
		},
		SizeBuckets: []float64{
			100, 1000, 10000, 100000, 1000000, 10000000,
		},
	}
}

// New creates a new Metrics instance and registers all metrics.
func New(config *Config) *Metrics {
	if config == nil {
		config = DefaultConfig()
	}

	m := &Metrics{
		config: config,
	}

	// Request metrics
	m.requestsTotal = promauto.NewCounterVec(
		prometheus.CounterOpts{
			Namespace: config.Namespace,
			Subsystem: config.Subsystem,
			Name:      "requests_total",
			Help:      "Total number of requests by method and status",
		},
		[]string{"method", "status"},
	)

	m.requestDuration = promauto.NewHistogramVec(
		prometheus.HistogramOpts{
			Namespace: config.Namespace,
			Subsystem: config.Subsystem,
			Name:      "request_duration_seconds",
			Help:      "Request latency distribution in seconds",
			Buckets:   config.LatencyBuckets,
		},
		[]string{"method"},
	)

	m.requestSizeBytes = promauto.NewHistogramVec(
		prometheus.HistogramOpts{
			Namespace: config.Namespace,
			Subsystem: config.Subsystem,
			Name:      "request_size_bytes",
			Help:      "Request size distribution in bytes",
			Buckets:   config.SizeBuckets,
		},
		[]string{"method"},
	)

	m.responseSizeBytes = promauto.NewHistogramVec(
		prometheus.HistogramOpts{
			Namespace: config.Namespace,
			Subsystem: config.Subsystem,
			Name:      "response_size_bytes",
			Help:      "Response size distribution in bytes",
			Buckets:   config.SizeBuckets,
		},
		[]string{"method"},
	)

	// Connection metrics
	m.activeConnections = promauto.NewGauge(
		prometheus.GaugeOpts{
			Namespace: config.Namespace,
			Subsystem: config.Subsystem,
			Name:      "active_connections",
			Help:      "Current number of active gRPC connections",
		},
	)

	m.activeSubscriptions = promauto.NewGauge(
		prometheus.GaugeOpts{
			Namespace: config.Namespace,
			Subsystem: config.Subsystem,
			Name:      "active_subscriptions",
			Help:      "Current number of active subscriptions",
		},
	)

	m.connectionsTotal = promauto.NewCounter(
		prometheus.CounterOpts{
			Namespace: config.Namespace,
			Subsystem: config.Subsystem,
			Name:      "connections_total",
			Help:      "Total number of connections since startup",
		},
	)

	// Auth metrics
	m.authAttemptsTotal = promauto.NewCounterVec(
		prometheus.CounterOpts{
			Namespace: config.Namespace,
			Subsystem: config.Subsystem,
			Name:      "auth_attempts_total",
			Help:      "Total authentication attempts by result",
		},
		[]string{"result"},
	)

	m.rateLimitHitsTotal = promauto.NewCounterVec(
		prometheus.CounterOpts{
			Namespace: config.Namespace,
			Subsystem: config.Subsystem,
			Name:      "rate_limit_hits_total",
			Help:      "Total rate limit rejections",
		},
		[]string{"authenticated"},
	)

	// Storage metrics
	m.eventsTotal = promauto.NewGauge(
		prometheus.GaugeOpts{
			Namespace: config.Namespace,
			Subsystem: config.Subsystem,
			Name:      "events_total",
			Help:      "Total events stored in database",
		},
	)

	m.dbSizeBytes = promauto.NewGauge(
		prometheus.GaugeOpts{
			Namespace: config.Namespace,
			Subsystem: config.Subsystem,
			Name:      "db_size_bytes",
			Help:      "Database file size in bytes",
		},
	)

	m.eventDeletionsTotal = promauto.NewCounter(
		prometheus.CounterOpts{
			Namespace: config.Namespace,
			Subsystem: config.Subsystem,
			Name:      "event_deletions_total",
			Help:      "Total events deleted (NIP-09)",
		},
	)

	return m
}

// RecordRequest records a completed request with its status and duration.
func (m *Metrics) RecordRequest(method, status string, durationSeconds float64) {
	m.requestsTotal.WithLabelValues(method, status).Inc()
	m.requestDuration.WithLabelValues(method).Observe(durationSeconds)
}

// RecordRequestSize records the size of a request.
func (m *Metrics) RecordRequestSize(method string, sizeBytes int) {
	m.requestSizeBytes.WithLabelValues(method).Observe(float64(sizeBytes))
}

// RecordResponseSize records the size of a response.
func (m *Metrics) RecordResponseSize(method string, sizeBytes int) {
	m.responseSizeBytes.WithLabelValues(method).Observe(float64(sizeBytes))
}

// IncrementConnections increments the active connections gauge.
func (m *Metrics) IncrementConnections() {
	m.activeConnections.Inc()
	m.connectionsTotal.Inc()
}

// DecrementConnections decrements the active connections gauge.
func (m *Metrics) DecrementConnections() {
	m.activeConnections.Dec()
}

// SetActiveConnections sets the active connections gauge to a specific value.
func (m *Metrics) SetActiveConnections(count int) {
	m.activeConnections.Set(float64(count))
}

// IncrementSubscriptions increments the active subscriptions gauge.
func (m *Metrics) IncrementSubscriptions() {
	m.activeSubscriptions.Inc()
}

// DecrementSubscriptions decrements the active subscriptions gauge.
func (m *Metrics) DecrementSubscriptions() {
	m.activeSubscriptions.Dec()
}

// SetActiveSubscriptions sets the active subscriptions gauge to a specific value.
func (m *Metrics) SetActiveSubscriptions(count int) {
	m.activeSubscriptions.Set(float64(count))
}

// RecordAuthAttempt records an authentication attempt.
func (m *Metrics) RecordAuthAttempt(success bool) {
	result := "failure"
	if success {
		result = "success"
	}
	m.authAttemptsTotal.WithLabelValues(result).Inc()
}

// RecordRateLimitHit records a rate limit rejection.
func (m *Metrics) RecordRateLimitHit(authenticated bool) {
	auth := "false"
	if authenticated {
		auth = "true"
	}
	m.rateLimitHitsTotal.WithLabelValues(auth).Inc()
}

// UpdateStorageStats updates storage-related metrics.
func (m *Metrics) UpdateStorageStats(eventCount int64, dbSizeBytes int64) {
	m.eventsTotal.Set(float64(eventCount))
	m.dbSizeBytes.Set(float64(dbSizeBytes))
}

// RecordEventDeletion records an event deletion.
func (m *Metrics) RecordEventDeletion() {
	m.eventDeletionsTotal.Inc()
}

// RequestStatus represents the status of a request for metrics.
type RequestStatus string

const (
	StatusOK              RequestStatus = "ok"
	StatusError           RequestStatus = "error"
	StatusUnauthenticated RequestStatus = "unauthenticated"
	StatusRateLimited     RequestStatus = "rate_limited"
	StatusInvalidRequest  RequestStatus = "invalid_request"
)

//go:embed dashboard.html
var dashboardHTML []byte

func (m *Metrics) Serve(addr, path string) error {
	mux := http.NewServeMux()
	mux.Handle(path, promhttp.Handler())
	mux.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
		w.Header().Set("Content-Type", "text/html; charset=utf-8")
		w.Write(dashboardHTML)
	})
	return http.ListenAndServe(addr, mux)
}