// Package metrics exposes Prometheus metrics for the logarchiver service. The
// logging stack ships no metrics convention today, so this is the first
// /metrics endpoint there; it is opt-in via config.
package metrics

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

// Metrics holds the collectors.
type Metrics struct {
	objectsStored   *prometheus.CounterVec
	eventsArchived  *prometheus.CounterVec
	rawBytes        *prometheus.CounterVec
	storedBytes     *prometheus.CounterVec
	storeFailures   *prometheus.CounterVec
	indexFailures   *prometheus.CounterVec
	messagesFetched prometheus.Counter
	acksSent        prometheus.Counter
	batchesFlushed  *prometheus.CounterVec
	pendingEvents   prometheus.Gauge
}

// New registers the collectors on reg (use prometheus.DefaultRegisterer for the
// default /metrics handler).
func New(reg prometheus.Registerer) *Metrics {
	f := promauto.With(reg)
	return &Metrics{
		objectsStored: f.NewCounterVec(prometheus.CounterOpts{
			Name: "logarchiver_objects_stored_total",
			Help: "Objects successfully sealed, uploaded and indexed.",
		}, []string{"subject"}),
		eventsArchived: f.NewCounterVec(prometheus.CounterOpts{
			Name: "logarchiver_events_archived_total",
			Help: "Log events archived.",
		}, []string{"subject"}),
		rawBytes: f.NewCounterVec(prometheus.CounterOpts{
			Name: "logarchiver_raw_bytes_total",
			Help: "Raw NDJSON bytes archived (pre-compression).",
		}, []string{"subject"}),
		storedBytes: f.NewCounterVec(prometheus.CounterOpts{
			Name: "logarchiver_stored_bytes_total",
			Help: "Stored object bytes written to S3 (post-compression/encryption).",
		}, []string{"subject"}),
		storeFailures: f.NewCounterVec(prometheus.CounterOpts{
			Name: "logarchiver_store_failures_total",
			Help: "Failed store attempts (seal/upload); batch not acked.",
		}, []string{"subject"}),
		indexFailures: f.NewCounterVec(prometheus.CounterOpts{
			Name: "logarchiver_index_failures_total",
			Help: "Failed index writes after a successful S3 upload; batch not acked.",
		}, []string{"subject"}),
		messagesFetched: f.NewCounter(prometheus.CounterOpts{
			Name: "logarchiver_messages_fetched_total",
			Help: "JetStream messages fetched.",
		}),
		acksSent: f.NewCounter(prometheus.CounterOpts{
			Name: "logarchiver_acks_total",
			Help: "JetStream acknowledgements sent (after successful persist).",
		}),
		batchesFlushed: f.NewCounterVec(prometheus.CounterOpts{
			Name: "logarchiver_batches_flushed_total",
			Help: "Batches flushed, labelled by trigger (full|age|shutdown).",
		}, []string{"trigger"}),
		pendingEvents: f.NewGauge(prometheus.GaugeOpts{
			Name: "logarchiver_pending_events",
			Help: "Events currently buffered in open batches (unacked).",
		}),
	}
}

// ObjectStored records a successful persist.
func (m *Metrics) ObjectStored(subject string, events int, rawBytes, storedBytes int64) {
	m.objectsStored.WithLabelValues(subject).Inc()
	m.eventsArchived.WithLabelValues(subject).Add(float64(events))
	m.rawBytes.WithLabelValues(subject).Add(float64(rawBytes))
	m.storedBytes.WithLabelValues(subject).Add(float64(storedBytes))
}

// StoreFailed records a seal/upload failure.
func (m *Metrics) StoreFailed(subject string) { m.storeFailures.WithLabelValues(subject).Inc() }

// IndexFailed records an index-write failure.
func (m *Metrics) IndexFailed(subject string) { m.indexFailures.WithLabelValues(subject).Inc() }

// MessagesFetched records fetched messages.
func (m *Metrics) MessagesFetched(n int) { m.messagesFetched.Add(float64(n)) }

// Acked records sent acknowledgements.
func (m *Metrics) Acked(n int) { m.acksSent.Add(float64(n)) }

// BatchFlushed records a flush by trigger.
func (m *Metrics) BatchFlushed(trigger string) { m.batchesFlushed.WithLabelValues(trigger).Inc() }

// SetPending sets the pending-events gauge.
func (m *Metrics) SetPending(n int) { m.pendingEvents.Set(float64(n)) }