package metrics

import (
	"net/http"

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

// Registry 持有 NixMsg 指标与独立注册表（避免污染默认全局注册表）。
type Registry struct {
	reg *prometheus.Registry

	Connections           *prometheus.GaugeVec
	EndpointsTotal        prometheus.Gauge
	DeliveriesPending     prometheus.Gauge
	MessagesScheduled     prometheus.Gauge
	DispatchToPushSeconds prometheus.Observer
	AckSeconds            prometheus.Observer
	WriteQueueLength      prometheus.Gauge
	WriteCommitSeconds    prometheus.Observer
	PasswordHashQueue     prometheus.Gauge
	ErrorsTotal           *prometheus.CounterVec
}

// New 按 DEVELOPMENT 4.3 注册指标。
func New() *Registry {
	reg := prometheus.NewRegistry()
	r := &Registry{reg: reg}

	r.Connections = prometheus.NewGaugeVec(prometheus.GaugeOpts{
		Name: "nixmsg_connections",
		Help: "Current online connections by transport (ws or tcp).",
	}, []string{"transport"})

	r.EndpointsTotal = prometheus.NewGauge(prometheus.GaugeOpts{
		Name: "nixmsg_endpoints",
		Help: "Total number of endpoints.",
	})

	r.DeliveriesPending = prometheus.NewGauge(prometheus.GaugeOpts{
		Name: "nixmsg_deliveries_pending",
		Help: "Number of pending deliveries.",
	})

	r.MessagesScheduled = prometheus.NewGauge(prometheus.GaugeOpts{
		Name: "nixmsg_messages_scheduled",
		Help: "Number of scheduled messages not yet dispatched.",
	})

	dispatchHist := prometheus.NewHistogram(prometheus.HistogramOpts{
		Name:    "nixmsg_dispatch_to_push_duration_seconds",
		Help:    "Latency from message due time to push.",
		Buckets: prometheus.DefBuckets,
	})
	r.DispatchToPushSeconds = dispatchHist

	ackHist := prometheus.NewHistogram(prometheus.HistogramOpts{
		Name:    "nixmsg_ack_duration_seconds",
		Help:    "Latency from push to ack.",
		Buckets: prometheus.DefBuckets,
	})
	r.AckSeconds = ackHist

	r.WriteQueueLength = prometheus.NewGauge(prometheus.GaugeOpts{
		Name: "nixmsg_write_queue_length",
		Help: "Number of write operations waiting or in the current batch.",
	})

	commitHist := prometheus.NewHistogram(prometheus.HistogramOpts{
		Name:    "nixmsg_write_batch_commit_duration_seconds",
		Help:    "Duration of each merged write-queue commit.",
		Buckets: prometheus.DefBuckets,
	})
	r.WriteCommitSeconds = commitHist

	r.PasswordHashQueue = prometheus.NewGauge(prometheus.GaugeOpts{
		Name: "nixmsg_password_hash_queue_length",
		Help: "Number of password hash jobs waiting for a pool slot.",
	})

	r.ErrorsTotal = prometheus.NewCounterVec(prometheus.CounterOpts{
		Name: "nixmsg_errors_total",
		Help: "Count of application error codes.",
	}, []string{"code"})

	reg.MustRegister(
		r.Connections,
		r.EndpointsTotal,
		r.DeliveriesPending,
		r.MessagesScheduled,
		dispatchHist,
		ackHist,
		r.WriteQueueLength,
		commitHist,
		r.PasswordHashQueue,
		r.ErrorsTotal,
	)

	// 初始化 transport 标签，便于空载抓取也能看到序列。
	r.Connections.WithLabelValues("ws").Set(0)
	r.Connections.WithLabelValues("tcp").Set(0)

	return r
}

// Handler 返回 Prometheus 文本格式的 /metrics 处理函数（访问规则由 A 线加）。
func (r *Registry) Handler() http.Handler {
	return promhttp.HandlerFor(r.reg, promhttp.HandlerOpts{})
}

// Gatherer 暴露底层 Gatherer（测试用）。
func (r *Registry) Gatherer() prometheus.Gatherer {
	return r.reg
}