res_levis_backend/internal/pkg/bridge/mqtt.go

package bridge

import (
	"fmt"
	"log/slog"

	"github.com/AFASystems/presence/internal/pkg/config"
	mqtt "github.com/eclipse/paho.mqtt.golang"
	"github.com/google/uuid"
)

const defaultMQTTPort = 1883
const subscribeTopic = "publish_out/#"
const disconnectQuiesceMs = 250

// MQTTClient wraps paho MQTT client and options.
type MQTTClient struct {
	Client mqtt.Client
}

// NewMQTTClient creates and connects an MQTT client. Returns error instead of panic on connect failure.
func NewMQTTClient(cfg *config.Config, publishHandler func(mqtt.Message)) (*MQTTClient, error) {
	opts := mqtt.NewClientOptions()
	opts.AddBroker(fmt.Sprintf("tcp://%s:%d", cfg.MQTTHost, defaultMQTTPort))
	opts.SetClientID(fmt.Sprintf("bridge-%s", uuid.New().String()))
	opts.SetAutoReconnect(true)
	opts.SetConnectRetry(true)
	opts.SetConnectRetryInterval(config.SMALL_TICKER_INTERVAL)
	opts.SetMaxReconnectInterval(config.LARGE_TICKER_INTERVAL)
	opts.SetCleanSession(false)
	opts.SetDefaultPublishHandler(func(c mqtt.Client, m mqtt.Message) {
		publishHandler(m)
	})
	opts.OnConnect = func(client mqtt.Client) {
		slog.Info("MQTT connected")
	}
	opts.OnConnectionLost = func(client mqtt.Client, err error) {
		slog.Error("MQTT connection lost", "err", err)
	}

	client := mqtt.NewClient(opts)
	token := client.Connect()
	token.Wait()
	if err := token.Error(); err != nil {
		return nil, fmt.Errorf("mqtt connect: %w", err)
	}
	return &MQTTClient{Client: client}, nil
}

// Subscribe subscribes to the default bridge topic.
func (m *MQTTClient) Subscribe() {
	token := m.Client.Subscribe(subscribeTopic, 1, nil)
	token.Wait()
	slog.Info("MQTT subscribed", "topic", subscribeTopic)
}

// Disconnect disconnects the client with quiesce.
func (m *MQTTClient) Disconnect() {
	m.Client.Disconnect(disconnectQuiesceMs)
	slog.Info("MQTT disconnected")
}