package main

import (
	"context"
	"fmt"
	"sync/atomic"
	"time"

	"go.mongodb.org/mongo-driver/event"
	"go.mongodb.org/mongo-driver/mongo"
	"go.mongodb.org/mongo-driver/mongo/options"
)

func main() {
	var heartbeatsStartedCounter atomic.Int64

	now := time.Now()

	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
	defer cancel()
	client, err := mongo.Connect(ctx, options.Client().ApplyURI("mongodb://localhost:27017").SetServerMonitor(&event.ServerMonitor{
		ServerHeartbeatStarted: func(_ *event.ServerHeartbeatStartedEvent) {
			heartbeatsStartedCounter.Add(1)
		},
	}))

	if err != nil {
		panic(err)
	}

	defer client.Disconnect(ctx)

	ticker := time.Tick(1 * time.Second)
	for {
		fmt.Printf("[%05d] total heartbeats until now: %d\n", int(time.Since(now).Seconds()), heartbeatsStartedCounter.Load())
		<-ticker
	}
}

$ go run .
[00000] total heartbeats until now: 0
[00001] total heartbeats until now: 2
[00002] total heartbeats until now: 2
[00003] total heartbeats until now: 2
[00004] total heartbeats until now: 2
[00005] total heartbeats until now: 2
[00006] total heartbeats until now: 2
[00007] total heartbeats until now: 2
[00008] total heartbeats until now: 2
[00009] total heartbeats until now: 2
[00010] total heartbeats until now: 2
[00011] total heartbeats until now: 3
[00012] total heartbeats until now: 3
[00013] total heartbeats until now: 3
[00014] total heartbeats until now: 3
[00015] total heartbeats until now: 3
[00016] total heartbeats until now: 3
[00017] total heartbeats until now: 3
[00018] total heartbeats until now: 3
[00019] total heartbeats until now: 3
[00020] total heartbeats until now: 3
[00021] total heartbeats until now: 4
[00022] total heartbeats until now: 4
[00023] total heartbeats until now: 4
[00024] total heartbeats until now: 4

$ K_SERVICE=test go run .
[00000] total heartbeats until now: 0
[00001] total heartbeats until now: 20
[00002] total heartbeats until now: 49
[00003] total heartbeats until now: 63
[00004] total heartbeats until now: 81
[00005] total heartbeats until now: 94
[00006] total heartbeats until now: 107
[00007] total heartbeats until now: 117
[00008] total heartbeats until now: 128
[00009] total heartbeats until now: 138
[00010] total heartbeats until now: 148
[00011] total heartbeats until now: 157
[00012] total heartbeats until now: 173
[00013] total heartbeats until now: 190
[00014] total heartbeats until now: 210
[00015] total heartbeats until now: 230
[00016] total heartbeats until now: 253
[00017] total heartbeats until now: 274
[00018] total heartbeats until now: 298
[00019] total heartbeats until now: 319
[00020] total heartbeats until now: 343
[00021] total heartbeats until now: 365
[00022] total heartbeats until now: 387
[00023] total heartbeats until now: 400
[00024] total heartbeats until now: 416