sauna/sauna.go

package sauna

import (
	"encoding/json"
	"log"
	"math/rand"
	"net/http"
	"strconv"
	"sync"
	"time"

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

type temperature struct {
	Value float64   `json:"value"`
	Unit  string    `json:"unit"`
	Time  time.Time `json:"time"`
	Valid bool      `json:"valid"`
}

var (
	logger            log.Logger = *log.Default()
	sauna_mutex       sync.Mutex
	sauna_temperature = temperature{
		Value: 0.0,
		Unit:  "°C",
	}
)

var messagePubHandler mqtt.MessageHandler = func(client mqtt.Client, msg mqtt.Message) {
	logger.Printf("Received message: %s from topic: %s\n", msg.Payload(), msg.Topic())
}

var saunaHandler mqtt.MessageHandler = func(client mqtt.Client, msg mqtt.Message) {
	logger.Printf("Received message: %s from topic: %s\n", msg.Payload(), msg.Topic())
	sauna_mutex.Lock()
	err := json.Unmarshal(msg.Payload(), &sauna_temperature)
	sauna_temperature.Time = time.Now()
	if err != nil {
		sauna_temperature.Valid = false
		sauna_mutex.Unlock()
		logger.Print(err)
		return
	}
	sauna_temperature.Valid = true
	sauna_mutex.Unlock()
}

var connectHandler mqtt.OnConnectHandler = func(client mqtt.Client) {
	logger.Println("Connected")
	subscribe(client)
}

var connectLostHandler mqtt.ConnectionLostHandler = func(client mqtt.Client, err error) {
	logger.Printf("Connect lost: %v", err)
}

func init() {
	logger.SetPrefix("apiservice/sauna: ")
}

func http_endpoint_sauna(w http.ResponseWriter, r *http.Request) {
	w.Header().Set("Content-type", "application/json; charset=utf-8;")
	if r.Method == http.MethodGet {
		sauna_mutex.Lock()
		data, err := json.Marshal(sauna_temperature)
		sauna_mutex.Unlock()
		if err != nil {
			w.WriteHeader(http.StatusInternalServerError)
			w.Write(json.RawMessage(`{"error": "cannot marshal object to json"}`))
		} else {
			w.WriteHeader(http.StatusOK)
			w.Write(data)
		}
	} else {
		w.WriteHeader(http.StatusMethodNotAllowed)
	}
}

func connect() mqtt.Client {
	// MQTT connection
	opts := mqtt.NewClientOptions()
	opts.AddBroker("tcp://nuc:1883")
	opts.SetClientID("apiservice/sauna/" + strconv.Itoa(rand.Int()))
	opts.SetDefaultPublishHandler(messagePubHandler)
	opts.OnConnect = connectHandler
	opts.OnConnectionLost = connectLostHandler
	client := mqtt.NewClient(opts)
	if token := client.Connect(); token.Wait() && token.Error() != nil {
		logger.Panic(token.Error())
	}
	return client
}

func subscribe(client mqtt.Client) {
	// MQTT subscribtion
	topic := "sauna/temperature"
	token := client.Subscribe(topic, 1, saunaHandler)
	token.Wait()
	logger.Printf("Subscribed to topic %s", topic)
}

func Start() {
	client := connect()
	subscribe(client)

	http.HandleFunc("/api/sauna", http_endpoint_sauna)
}