package aether

import (
	"github.com/prometheus/client_golang/prometheus"
)

// PrometheusMetricsAdapter exposes BroadcasterMetrics as Prometheus metrics.
// It implements prometheus.Collector and can be registered with a Prometheus registry.
type PrometheusMetricsAdapter struct {
	metrics BroadcasterMetrics

	eventsPublishedDesc     *prometheus.Desc
	eventsReceivedDesc      *prometheus.Desc
	activeSubscriptionsDesc *prometheus.Desc
	publishErrorsDesc       *prometheus.Desc
	subscribeErrorsDesc     *prometheus.Desc
	droppedEventsDesc       *prometheus.Desc
}

// NewPrometheusMetricsAdapter creates a new PrometheusMetricsAdapter that wraps
// a BroadcasterMetrics implementation and exposes it as Prometheus metrics.
//
// The adapter implements prometheus.Collector and should be registered with
// a Prometheus registry:
//
//	eb := aether.NewEventBus()
//	adapter := aether.NewPrometheusMetricsAdapter(eb.Metrics())
//	prometheus.MustRegister(adapter)
func NewPrometheusMetricsAdapter(metrics BroadcasterMetrics) *PrometheusMetricsAdapter {
	return &PrometheusMetricsAdapter{
		metrics: metrics,
		eventsPublishedDesc: prometheus.NewDesc(
			"aether_events_published_total",
			"Total number of events published per namespace",
			[]string{"namespace"},
			nil,
		),
		eventsReceivedDesc: prometheus.NewDesc(
			"aether_events_received_total",
			"Total number of events received per namespace",
			[]string{"namespace"},
			nil,
		),
		activeSubscriptionsDesc: prometheus.NewDesc(
			"aether_active_subscriptions",
			"Number of active subscriptions per namespace",
			[]string{"namespace"},
			nil,
		),
		publishErrorsDesc: prometheus.NewDesc(
			"aether_publish_errors_total",
			"Total number of publish errors per namespace",
			[]string{"namespace"},
			nil,
		),
		subscribeErrorsDesc: prometheus.NewDesc(
			"aether_subscribe_errors_total",
			"Total number of subscribe errors per namespace",
			[]string{"namespace"},
			nil,
		),
		droppedEventsDesc: prometheus.NewDesc(
			"aether_dropped_events_total",
			"Total number of dropped events per namespace",
			[]string{"namespace"},
			nil,
		),
	}
}

// Describe implements prometheus.Collector.
func (a *PrometheusMetricsAdapter) Describe(ch chan<- *prometheus.Desc) {
	ch <- a.eventsPublishedDesc
	ch <- a.eventsReceivedDesc
	ch <- a.activeSubscriptionsDesc
	ch <- a.publishErrorsDesc
	ch <- a.subscribeErrorsDesc
	ch <- a.droppedEventsDesc
}

// Collect implements prometheus.Collector.
func (a *PrometheusMetricsAdapter) Collect(ch chan<- prometheus.Metric) {
	namespaces := a.metrics.Namespaces()

	for _, ns := range namespaces {
		ch <- prometheus.MustNewConstMetric(
			a.eventsPublishedDesc,
			prometheus.CounterValue,
			float64(a.metrics.EventsPublished(ns)),
			ns,
		)
		ch <- prometheus.MustNewConstMetric(
			a.eventsReceivedDesc,
			prometheus.CounterValue,
			float64(a.metrics.EventsReceived(ns)),
			ns,
		)
		ch <- prometheus.MustNewConstMetric(
			a.activeSubscriptionsDesc,
			prometheus.GaugeValue,
			float64(a.metrics.ActiveSubscriptions(ns)),
			ns,
		)
		ch <- prometheus.MustNewConstMetric(
			a.publishErrorsDesc,
			prometheus.CounterValue,
			float64(a.metrics.PublishErrors(ns)),
			ns,
		)
		ch <- prometheus.MustNewConstMetric(
			a.subscribeErrorsDesc,
			prometheus.CounterValue,
			float64(a.metrics.SubscribeErrors(ns)),
			ns,
		)
		ch <- prometheus.MustNewConstMetric(
			a.droppedEventsDesc,
			prometheus.CounterValue,
			float64(a.metrics.DroppedEvents(ns)),
			ns,
		)
	}
}