go-examples/converter/converter.go

package converter

import "errors"
import "fmt"
import "strconv"
import "strings"

const (
	markerMiles           = "mi"
	markerKm              = "km"
	markerFeet            = "ft"
	markerMeter           = "m"
	MilesToKm     float64 = 1.609344
	FeetsToMeters float64 = 3.28084
)

var (
	inUnit  string
	inVal   float64
	asMeter float64
	err     error
	convVal float64
)

func Convert(input, convTo string) (string, error) {
	switch {
	case strings.HasSuffix(input, markerKm):
		inUnit = markerKm
	case strings.HasSuffix(input, markerFeet):
		inUnit = markerFeet
	case strings.HasSuffix(input, markerMeter):
		inUnit = markerMeter
	case strings.HasSuffix(input, markerMiles):
		inUnit = markerMiles
	default:
		return "", errors.New("Invalid input: " + input)
	}
	inVal, err = strconv.ParseFloat(input[:len(input)-len(inUnit)], 64)
	if err != nil {
		return "", errors.New("Invalid input number (" + err.Error() + ")")
	}

	switch inUnit {
	case markerMiles:
		asMeter = inVal * MilesToKm * 1000
	case markerKm:
		asMeter = inVal * 1000
	case markerFeet:
		asMeter = inVal * FeetsToMeters
	case markerMeter:
		asMeter = inVal
	}

	switch convTo {
	case markerMiles:
		convVal = asMeter / (MilesToKm * 1000)
	case markerKm:
		convVal = asMeter / 1000
	case markerFeet:
		convVal = asMeter / FeetsToMeters
	case markerMeter:
		convVal = asMeter
	default:
		return "", errors.New("Invalid unit: " + convTo)
	}

	return fmt.Sprintf("%.2f%s", convVal, convTo), nil
}