Fitbit Export Weight Data to CSV

main.go

// Converts the data created by Fitbit export from the output JSON 
// to comma-separated values. 
// go run main.go > weight.csv
package main

import (
	"encoding/json"
	"fmt"
	"io/ioutil"
	"os"
)

type Measurement struct {
	Weight float32
	Date   string
	Time   string
}

func main() {

	path := "./data/"

	file, err := os.Open(path + ".")
	if err != nil {
		fmt.Fprintf(os.Stderr, "error: could not open data")
		os.Exit(1)
	}

	var measurements []Measurement

	stat, err := file.Stat()
	if stat.IsDir() {
		filenames, err := file.Readdirnames(0)
		if err != nil {
			fmt.Fprintf(os.Stderr, "error: could not read filenames")
			os.Exit(1)
		}

		for _, f := range filenames {
			ms, err := processFile(path + f)
			if err == nil { // no errors
				measurements = append(measurements, ms...)
			}
		}
	}

	printCSV(measurements)
}

func processFile(filename string) ([]Measurement, error) {
	f, err := os.Open(filename)
	if err != nil {
		return nil, fmt.Errorf(fmt.Sprintf("error: could not read %s", filename))
	}
	defer f.Close()

	bytes, _ := ioutil.ReadAll((f))

	var measurements []Measurement

	json.Unmarshal(bytes, &measurements)

	return measurements, nil
}

func printCSV(measurements []Measurement) {

	fmt.Println("date, time, weight (kg)")

	for _, m := range measurements {
		fmt.Printf("%s, %s, %f\n", m.Date, m.Time, conv(m.Weight))
	}
}

func conv(lbs float32) float32 {
	return lbs * 0.4535924
}