// Package metrics provides Prometheus metrics for upaas.
//
//nolint:revive // "metrics" matches the domain; runtime/metrics is rarely imported directly
package metrics

import (
	"github.com/prometheus/client_golang/prometheus"
	"github.com/prometheus/client_golang/prometheus/promauto"
	"go.uber.org/fx"
)

// Params contains dependencies for Metrics.
type Params struct {
	fx.In
}

// Metrics holds all Prometheus metrics for the application.
type Metrics struct {
	// Deployment metrics.
	DeploymentsTotal    *prometheus.CounterVec
	DeploymentDuration  *prometheus.HistogramVec
	DeploymentsInFlight *prometheus.GaugeVec

	// Container health metrics.
	ContainerHealthy *prometheus.GaugeVec

	// Webhook metrics.
	WebhookEventsTotal *prometheus.CounterVec

	// HTTP request metrics.
	HTTPRequestsTotal     *prometheus.CounterVec
	HTTPRequestDuration   *prometheus.HistogramVec
	HTTPResponseSizeBytes *prometheus.HistogramVec

	// Audit log metrics.
	AuditEventsTotal *prometheus.CounterVec
}

// New creates a new Metrics instance with all Prometheus metrics registered
// in the default Prometheus registry.
func New(_ fx.Lifecycle, _ Params) (*Metrics, error) {
	return newMetrics(promauto.With(prometheus.DefaultRegisterer)), nil
}

// NewForTest creates a Metrics instance with a custom registry for test isolation.
func NewForTest(reg prometheus.Registerer) *Metrics {
	return newMetrics(promauto.With(reg))
}

// newMetrics creates a Metrics instance using the given factory.
func newMetrics(factory promauto.Factory) *Metrics {
	return &Metrics{
		DeploymentsTotal:      newDeploymentsTotal(factory),
		DeploymentDuration:    newDeploymentDuration(factory),
		DeploymentsInFlight:   newDeploymentsInFlight(factory),
		ContainerHealthy:      newContainerHealthy(factory),
		WebhookEventsTotal:    newWebhookEventsTotal(factory),
		HTTPRequestsTotal:     newHTTPRequestsTotal(factory),
		HTTPRequestDuration:   newHTTPRequestDuration(factory),
		HTTPResponseSizeBytes: newHTTPResponseSizeBytes(factory),
		AuditEventsTotal:      newAuditEventsTotal(factory),
	}
}

func newDeploymentsTotal(f promauto.Factory) *prometheus.CounterVec {
	return f.NewCounterVec(prometheus.CounterOpts{
		Namespace: "upaas",
		Subsystem: "deployments",
		Name:      "total",
		Help:      "Total number of deployments by app and status.",
	}, []string{"app", "status"})
}

func newDeploymentDuration(f promauto.Factory) *prometheus.HistogramVec {
	return f.NewHistogramVec(prometheus.HistogramOpts{
		Namespace: "upaas",
		Subsystem: "deployments",
		Name:      "duration_seconds",
		Help:      "Duration of deployments in seconds by app and status.",
		Buckets:   []float64{10, 30, 60, 120, 300, 600, 1800},
	}, []string{"app", "status"})
}

func newDeploymentsInFlight(f promauto.Factory) *prometheus.GaugeVec {
	return f.NewGaugeVec(prometheus.GaugeOpts{
		Namespace: "upaas",
		Subsystem: "deployments",
		Name:      "in_flight",
		Help:      "Number of deployments currently in progress by app.",
	}, []string{"app"})
}

func newContainerHealthy(f promauto.Factory) *prometheus.GaugeVec {
	return f.NewGaugeVec(prometheus.GaugeOpts{
		Namespace: "upaas",
		Subsystem: "container",
		Name:      "healthy",
		Help:      "Whether the app container is healthy (1) or unhealthy (0).",
	}, []string{"app"})
}

func newWebhookEventsTotal(f promauto.Factory) *prometheus.CounterVec {
	return f.NewCounterVec(prometheus.CounterOpts{
		Namespace: "upaas",
		Subsystem: "webhook",
		Name:      "events_total",
		Help:      "Total number of webhook events by app, event type, and matched status.",
	}, []string{"app", "event_type", "matched"})
}

func newHTTPRequestsTotal(f promauto.Factory) *prometheus.CounterVec {
	return f.NewCounterVec(prometheus.CounterOpts{
		Namespace: "upaas",
		Subsystem: "http",
		Name:      "requests_total",
		Help:      "Total number of HTTP requests by method and status code.",
	}, []string{"method", "status_code"})
}

func newHTTPRequestDuration(f promauto.Factory) *prometheus.HistogramVec {
	return f.NewHistogramVec(prometheus.HistogramOpts{
		Namespace: "upaas",
		Subsystem: "http",
		Name:      "request_duration_seconds",
		Help:      "Duration of HTTP requests in seconds by method.",
		Buckets:   prometheus.DefBuckets,
	}, []string{"method"})
}

//nolint:mnd // bucket boundaries are domain-specific constants
func newHTTPResponseSizeBytes(f promauto.Factory) *prometheus.HistogramVec {
	return f.NewHistogramVec(prometheus.HistogramOpts{
		Namespace: "upaas",
		Subsystem: "http",
		Name:      "response_size_bytes",
		Help:      "Size of HTTP responses in bytes by method.",
		Buckets:   prometheus.ExponentialBuckets(100, 10, 7),
	}, []string{"method"})
}

func newAuditEventsTotal(f promauto.Factory) *prometheus.CounterVec {
	return f.NewCounterVec(prometheus.CounterOpts{
		Namespace: "upaas",
		Subsystem: "audit",
		Name:      "events_total",
		Help:      "Total number of audit log events by action.",
	}, []string{"action"})
}