friendly.go

// Package friendly maps user-friendly strings to time.Duration
package friendly

import (
	"fmt"
	"regexp"
	"strconv"
	"strings"
	"time"
)

var durationUnitsRe = regexp.MustCompile(`([+-]?[0-9.]+)\s*((?:m[io]|[ywhsd])[a-z]*)`)

// ToDuration converts a string to a time.Duration
func ToDuration(s string) (time.Duration, error) {
	var ret int64
	parts := durationUnitsRe.FindAllStringSubmatch(strings.ToLower(s), -1)
	for _, part := range parts {
		num, err := strconv.ParseFloat(part[1], 64)
		if err != nil {
			return 0, fmt.Errorf("Invalid 8601 duration '%s': %s", s, err.Error())
		}
		unit := part[2]
		switch unit[:1] {
		case "m":
			if strings.HasPrefix("minutes", unit) {
				ret = ret + int64(num*(60.0*1000000000.0))
			} else if strings.HasPrefix("months", unit) {
				ret = ret + int64(num*(30.0*24.0*60.0*60.0*1000000000.0))
			} else {
				return 0, fmt.Errorf("Invalid 8601 duration '%s'", s)
			}
		case "y":
			if strings.HasPrefix("years", unit) {
				ret = ret + int64(num*(365.0*24.0*60.0*60.0*1000000000.0))
			} else {
				return 0, fmt.Errorf("Invalid 8601 duration '%s'", s)
			}
		case "w":
			if strings.HasPrefix("weeks", unit) {
				ret = ret + int64(num*(7.0*24.0*60.0*60.0*1000000000.0))
			} else {
				return 0, fmt.Errorf("Invalid 8601 duration '%s'", s)
			}
		case "h":
			if strings.HasPrefix("hours", unit) {
				ret = ret + int64(num*(60.0*60.0*1000000000.0))
			} else {
				return 0, fmt.Errorf("Invalid 8601 duration '%s'", s)
			}
		case "s":
			if strings.HasPrefix("seconds", unit) {
				ret = ret + int64(num*(1000000000.0))
			} else {
				return 0, fmt.Errorf("Invalid 8601 duration '%s'", s)
			}
		case "d":
			if strings.HasPrefix("days", unit) {
				ret = ret + int64(num*(24.0*60.0*60.0*1000000000.0))
			} else {
				return 0, fmt.Errorf("Invalid 8601 duration '%s'", s)
			}
		default:
			return 0, fmt.Errorf("Invalid 8601 duration '%s'", s)
		}
	}
	return time.Duration(ret), nil
}