package main

import (
	"context"
	"log"
	"math/rand"
	"net/http"
	"os"
	"os/signal"
	"syscall"
	"time"

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

var counter = prometheus.NewCounterVec(
	prometheus.CounterOpts{
		Name: "random_counter_total",
		Help: "A counter that increments randomly from 1 to 30 seconds",
	},
	[]string{},
)

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

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

	ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt, syscall.SIGTERM)
	defer stop()

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

	<-ctx.Done()
	log.Println("Shutdown the server")
	// Give one more second for gracefully shutdown
	ctx, cancel := context.WithTimeout(context.Background(), time.Second)
	defer cancel()
	server.Shutdown(ctx)
}

func startCounting(ctx context.Context) {
	for {
		select {
		case <-ctx.Done():
			return
		default:
			counter.WithLabelValues().Add(1)
			sleepDuration := time.Duration(rand.Intn(29) + 1)
			time.Sleep(sleepDuration * time.Second)
		}
	}
}