package temperature

import (
	"context"
	"errors"
	"io/ioutil"
	"strconv"
	"strings"
	"sync"
	"time"

	"git.joco.dk/sng/fermentord/internal/metrics"
	"github.com/rs/zerolog/log"
)

type TemperatureReading struct {
	Sensor string
	Time   time.Time
	Value  int64
}

var (
	ErrReadSensor = errors.New("Failed to read sensor temperature")

	C chan *TemperatureReading

	sensors []string
	mutex   *sync.Mutex
	ticker  *time.Ticker
)

func Initialize(readingInterval time.Duration) {
	C = make(chan *TemperatureReading)
	sensors = make([]string, 0)
	mutex = &sync.Mutex{}
	ticker = time.NewTicker(readingInterval)
}

func SetSensors(newSensors []string) {
	mutex.Lock()
	sensors = newSensors
	mutex.Unlock()
}

func Serve(ctx context.Context, wg *sync.WaitGroup) {
	wg.Add(1)
	defer wg.Done()

	for {
		select {
		case <-ticker.C:
			readSensors()

		case <-ctx.Done():
			ticker.Stop()
			return
		}
	}
}

func readSensors() {
	mutex.Lock()
	defer mutex.Unlock()

	for _, sensor := range sensors {
		start := time.Now()
		t, err := read(sensor)
		dur := time.Since(start).Seconds()

		if err != nil {
			log.Error().
				Err(err).
				Str("sensor", sensor).
				Msg("Error reading temperature sensor.")
		}

		metrics.TemperatureSensorReadingDegreesCelcius.
			WithLabelValues("sensor", sensor).
			Set(float64(t))

		metrics.TemperatureSensorReadingDurationSeconds.
			WithLabelValues("sensor", sensor).
			Observe(dur)

		C <- &TemperatureReading{
			Time:   time.Now(),
			Sensor: sensor,
			Value:  t,
		}
	}
}

// read returns the temperature of the specified sensor in millidegrees celcius.
func read(sensor string) (int64, error) {
	path := "/sys/bus/w1/devices/" + sensor + "/w1_slave"

	data, err := ioutil.ReadFile(path)
	if err != nil {
		return 0.0, err
	}

	raw := string(data)

	if !strings.Contains(raw, " YES") {
		return 0.0, ErrReadSensor
	}

	i := strings.LastIndex(raw, "t=")
	if i == -1 {
		return 0.0, ErrReadSensor
	}

	c, err := strconv.ParseInt(raw[i+2:len(raw)-1], 10, 64)
	if err != nil {
		return 0.0, err
	}

	return c, nil
}