package main

import (
	"log"
	"net/http"
	"os"
	"os/signal"
	"sync/atomic"
	"syscall"
	"time"

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

var (
	counter = prometheus.NewCounterVec(
		prometheus.CounterOpts{
			Name: "custom_counter_total",
			Help: "A counter that increments every 30 seconds",
		},
		[]string{},
	)
	counterValue uint64
)

func main() {
	// Register Prometheus metrics
	prometheus.MustRegister(counter)

	// Start background counter incrementer
	go incrementCounterEvery30s()

	// Set up HTTP server
	http.Handle("/metrics", promhttp.Handler())
	server := &http.Server{Addr: ":8080"}

	// Handle graceful shutdown
	stop := make(chan os.Signal, 1)
	signal.Notify(stop, os.Interrupt, syscall.SIGTERM)

	go func() {
		log.Println("Starting server on :8080")
		if err := server.ListenAndServe(); err != nil && err != http.ErrServerClosed {
			log.Fatalf("Server error: %v", err)
		}
	}()

	<-stop
	log.Println("\nShutting down server...")
}

func incrementCounterEvery30s() {
	ticker := time.NewTicker(30 * time.Second)
	defer ticker.Stop()

	for range ticker.C {
		newVal := atomic.AddUint64(&counterValue, 1)
		counter.WithLabelValues().Add(1)
		log.Printf("Counter incremented to %d", newVal)
	}
}