package sensor

import (
	"crypto/rand"
	"log/slog"
	"time"

	mqtt "github.com/eclipse/paho.mqtt.golang"
)

// MQTTConfig selects the broker, sensor topic, and optional broker credentials.
type MQTTConfig struct {
	Broker   string
	Topic    string
	Username string
	Password string
}

// StartMQTT connects in the background, retrying initial failures and reconnecting
// after outages. Every connection subscribes again because sessions are clean.
// The caller must Disconnect the returned client during shutdown.
func StartMQTT(config MQTTConfig, sampler *Sampler, logger *slog.Logger) mqtt.Client {
	options := mqtt.NewClientOptions().
		AddBroker(config.Broker).
		SetClientID("laundry-" + rand.Text()[:12]).
		SetUsername(config.Username).
		SetPassword(config.Password).
		SetAutoReconnect(true).
		SetConnectRetry(true).
		SetConnectRetryInterval(5 * time.Second).
		SetConnectTimeout(5 * time.Second)
	options.SetOnConnectHandler(func(client mqtt.Client) {
		token := client.Subscribe(config.Topic, 0, func(_ mqtt.Client, message mqtt.Message) {
			if err := sampler.Receive(message.Payload()); err != nil {
				logger.Warn("Ignoring invalid sensor payload", "error", err)
			}
		})
		if !token.WaitTimeout(10 * time.Second) {
			logger.Error("MQTT subscription timed out")
		} else if err := token.Error(); err != nil {
			logger.Error("MQTT subscription failed", "error", err)
		} else {
			logger.Info("MQTT sensor subscription ready", "topic", config.Topic)
		}
	})
	options.SetConnectionLostHandler(func(_ mqtt.Client, err error) {
		logger.Warn("MQTT connection lost; reconnecting", "error", err)
	})
	client := mqtt.NewClient(options)
	client.Connect()
	return client
}