log_temperature/json.go

package temperature

import (
	"bufio"
	"encoding/json"
	"errors"
	"fmt"
	"strings"
)

// JSONParser reads the json output
type jsonParser struct {
	scanner *bufio.Scanner
}

// NewJSONParser returns a parser for reading json temperature strings
func NewJSONParser(reader *bufio.Reader) Parser {
	return &jsonParser{scanner: bufio.NewScanner(reader)}
}

// {"time" : "2018-04-13 23:04:50", "model" : "Acurite 606TX Sensor", "id" : -5, "battery" : "OK", "temperature_C" : 21.800}
type jsonPacket struct {
	Time          string
	Model         string
	ID            int
	Battery       string
	Temperature_C float64
}

// Measure returns the temperature. Null if it can't
func (jp jsonParser) Measure() (*Measurement, error) {
	if !jp.scanner.Scan() {
		return nil, errors.New("EOF")
	}
	if err := jp.scanner.Err(); err != nil {
		return nil, err
	}
	text := jp.scanner.Text()
	firstIndex := strings.Index(text, "{")
	if firstIndex != -1 {
		text = text[firstIndex:]
	}

	buffer := []byte(text)
	if json.Valid(buffer) {
		var jsonPacket jsonPacket

		err := json.Unmarshal(buffer, &jsonPacket)
		if err != nil {
			fmt.Println(err.Error())
			return nil, err
		}
		if len(jsonPacket.Model) > 0 {
			batteryState := BATT_BAD
			if strings.Compare(jsonPacket.Battery, "OK") == 0 {
				batteryState = BATT_GOOD
			}
			fmt.Printf("Model: %s, ID:%d, Temperature:%f, Battery good: %t\n", jsonPacket.Model, jsonPacket.ID, jsonPacket.Temperature_C, batteryState)

			return &Measurement{ID: jsonPacket.ID, Temperature: jsonPacket.Temperature_C, BatteryState: batteryState}, nil
		}
	}
	return nil, nil
}