package obsx

import (
	"net/http"

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

// MetricsConfig configures the metrics factory.
type MetricsConfig struct {
	Namespace string
	Subsystem string
}

// Metrics is a factory for creating Prometheus metrics with consistent naming.
type Metrics struct {
	cfg      MetricsConfig
	registry *prometheus.Registry
}

// NewMetrics creates a new Metrics factory.
func NewMetrics(cfg MetricsConfig) *Metrics {
	reg := prometheus.NewRegistry()
	reg.MustRegister(prometheus.NewProcessCollector(prometheus.ProcessCollectorOpts{}))
	reg.MustRegister(prometheus.NewGoCollector())
	return &Metrics{cfg: cfg, registry: reg}
}

// Counter creates and registers a new CounterVec.
func (m *Metrics) Counter(name, help string, labels ...string) *prometheus.CounterVec {
	c := prometheus.NewCounterVec(prometheus.CounterOpts{
		Namespace: m.cfg.Namespace,
		Subsystem: m.cfg.Subsystem,
		Name:      name,
		Help:      help,
	}, labels)
	m.registry.MustRegister(c)
	return c
}

// Histogram creates and registers a new HistogramVec.
func (m *Metrics) Histogram(name, help string, buckets []float64, labels ...string) *prometheus.HistogramVec {
	if buckets == nil {
		buckets = prometheus.DefBuckets
	}
	h := prometheus.NewHistogramVec(prometheus.HistogramOpts{
		Namespace: m.cfg.Namespace,
		Subsystem: m.cfg.Subsystem,
		Name:      name,
		Help:      help,
		Buckets:   buckets,
	}, labels)
	m.registry.MustRegister(h)
	return h
}

// Gauge creates and registers a new GaugeVec.
func (m *Metrics) Gauge(name, help string, labels ...string) *prometheus.GaugeVec {
	g := prometheus.NewGaugeVec(prometheus.GaugeOpts{
		Namespace: m.cfg.Namespace,
		Subsystem: m.cfg.Subsystem,
		Name:      name,
		Help:      help,
	}, labels)
	m.registry.MustRegister(g)
	return g
}

// Handler returns an http.Handler for the /metrics endpoint.
func (m *Metrics) Handler() http.Handler {
	return promhttp.HandlerFor(m.registry, promhttp.HandlerOpts{})
}

// Registry returns the underlying Prometheus registry.
func (m *Metrics) Registry() *prometheus.Registry {
	return m.registry
}