// Package metrics defines and registers the Prometheus collectors
// exported on /metrics.
package metrics

import (
	"net/http"

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

// Metrics bundles all collectors. Each field is the public handle the
// rest of the service uses to record observations.
type Metrics struct {
	BuildInfo      *prometheus.GaugeVec
	HTTPRequests   *prometheus.CounterVec
	UpdateJobs     *prometheus.CounterVec
	UpdateDuration *prometheus.HistogramVec
	QueueDepth     prometheus.Gauge
	LastUpdateTime *prometheus.GaugeVec
	DockerPingUp   prometheus.Gauge
}

// New constructs Metrics and registers them with the given registry.
// Use prometheus.NewRegistry() in tests so collectors don't leak between
// runs; production code uses prometheus.DefaultRegisterer.
func New(reg prometheus.Registerer) *Metrics {
	m := &Metrics{
		BuildInfo: prometheus.NewGaugeVec(prometheus.GaugeOpts{
			Name: "package_updater_build_info",
			Help: "Always 1. Labels carry version/commit for dashboards.",
		}, []string{"version", "commit"}),
		HTTPRequests: prometheus.NewCounterVec(prometheus.CounterOpts{
			Name: "package_updater_http_requests_total",
			Help: "HTTP requests handled, labelled by endpoint and status.",
		}, []string{"endpoint", "status_code"}),
		UpdateJobs: prometheus.NewCounterVec(prometheus.CounterOpts{
			Name: "package_updater_update_jobs_total",
			Help: "Update jobs executed, labelled by project/service/status.",
		}, []string{"project", "service", "status"}),
		UpdateDuration: prometheus.NewHistogramVec(prometheus.HistogramOpts{
			Name:    "package_updater_update_duration_seconds",
			Help:    "Time taken to pull + up a single service.",
			Buckets: []float64{0.5, 1, 2, 5, 10, 30, 60, 120, 300},
		}, []string{"project", "service"}),
		QueueDepth: prometheus.NewGauge(prometheus.GaugeOpts{
			Name: "package_updater_queue_depth",
			Help: "Current number of submissions waiting in the queue.",
		}),
		LastUpdateTime: prometheus.NewGaugeVec(prometheus.GaugeOpts{
			Name: "package_updater_last_update_timestamp",
			Help: "Unix timestamp of the most recent successful update per service.",
		}, []string{"project", "service"}),
		DockerPingUp: prometheus.NewGauge(prometheus.GaugeOpts{
			Name: "package_updater_docker_ping_up",
			Help: "1 if the Docker socket responded to ping, 0 otherwise.",
		}),
	}
	reg.MustRegister(
		m.BuildInfo, m.HTTPRequests, m.UpdateJobs, m.UpdateDuration,
		m.QueueDepth, m.LastUpdateTime, m.DockerPingUp,
	)
	return m
}

// Handler returns the /metrics HTTP handler bound to the given registry.
func Handler(gatherer prometheus.Gatherer) http.Handler {
	return promhttp.HandlerFor(gatherer, promhttp.HandlerOpts{})
}