// Prometheus metrics: counter, histogram, gauge, and /metrics endpoint.
package main

import (
	"fmt"
	"log"
	"math/rand/v2"
	"net/http"
	"time"

	"git.codelab.vc/pkg/obsx"
)

func main() {
	metrics := obsx.NewMetrics(obsx.MetricsConfig{
		Namespace: "myapp",
		Subsystem: "api",
	})

	requests := metrics.Counter("requests_total", "Total HTTP requests", "method", "status")
	duration := metrics.Histogram("request_duration_seconds", "Request latency", nil, "method")
	inflight := metrics.Gauge("inflight_requests", "Current in-flight requests")

	mux := http.NewServeMux()

	mux.HandleFunc("GET /hello", func(w http.ResponseWriter, r *http.Request) {
		inflight.WithLabelValues().Inc()
		defer inflight.WithLabelValues().Dec()

		start := time.Now()

		// Simulate work.
		time.Sleep(time.Duration(rand.IntN(100)) * time.Millisecond)

		w.WriteHeader(http.StatusOK)
		fmt.Fprintln(w, "hello, world")

		requests.WithLabelValues("GET", "200").Inc()
		duration.WithLabelValues("GET").Observe(time.Since(start).Seconds())
	})

	mux.Handle("GET /metrics", metrics.Handler())

	log.Println("listening on :8080 (try GET /hello, GET /metrics)")
	log.Fatal(http.ListenAndServe(":8080", mux))
}