Natural language

util/time.go

@@ -0,0 +1,95 @@
+package util
+
+import (
+	"errors"
+	"github.com/olebedev/when"
+	"regexp"
+	"strconv"
+	"strings"
+	"time"
+)
+
+var (
+	errUnparsableTime = errors.New("unable to parse time")
+	durationStrRegex  = regexp.MustCompile(`(?i)^(\d+)\s*(d|days?|h|hours?|m|mins?|minutes?|s|secs?|seconds?)$`)
+)
+
+func ParseFutureTime(s string, now time.Time) (time.Time, error) {
+	s = strings.TrimSpace(s)
+	t, err := parseUnixTime(s, now)
+	if err == nil {
+		return t, nil
+	}
+	t, err = parseFromDuration(s, now)
+	if err == nil {
+		return t, nil
+	}
+	t, err = parseNaturalTime(s, now)
+	if err == nil {
+		return t, nil
+	}
+	return time.Time{}, errUnparsableTime
+}
+
+func parseFromDuration(s string, now time.Time) (time.Time, error) {
+	d, err := parseDuration(s)
+	if err == nil {
+		return now.Add(d), nil
+	}
+	return time.Time{}, errUnparsableTime
+}
+
+func parseDuration(s string) (time.Duration, error) {
+	d, err := time.ParseDuration(s)
+	if err == nil {
+		return d, nil
+	}
+	matches := durationStrRegex.FindStringSubmatch(s)
+	if matches != nil {
+		number, err := strconv.Atoi(matches[1])
+		if err != nil {
+			return 0, errUnparsableTime
+		}
+		switch unit := matches[2][0:1]; unit {
+		case "d":
+			return time.Duration(number) * 24 * time.Hour, nil
+		case "h":
+			return time.Duration(number) * time.Hour, nil
+		case "m":
+			return time.Duration(number) * time.Minute, nil
+		case "s":
+			return time.Duration(number) * time.Second, nil
+		default:
+			return 0, errUnparsableTime
+		}
+	}
+	return 0, errUnparsableTime
+}
+
+func parseUnixTime(s string, now time.Time) (time.Time, error) {
+	t, err := strconv.Atoi(s)
+	if err != nil {
+		return time.Time{}, err
+	} else if int64(t) < now.Unix() {
+		return time.Time{}, errUnparsableTime
+	}
+	return time.Unix(int64(t), 0), nil
+}
+
+func parseNaturalTime(s string, now time.Time) (time.Time, error) {
+	r, err := when.EN.Parse(s, now) // returns "nil, nil" if no matches!
+	if err != nil || r == nil {
+		return time.Time{}, errUnparsableTime
+	} else if r.Time.After(now) {
+		return r.Time, nil
+	}
+	// Hack: If the time is parsable, but not in the future,
+	// simply append "tomorrow, " to it.
+	r, err = when.EN.Parse("tomorrow, "+s, now) // returns "nil, nil" if no matches!
+	if err != nil || r == nil {
+		return time.Time{}, errUnparsableTime
+	} else if r.Time.After(now) {
+		return r.Time, nil
+	}
+	return time.Time{}, errUnparsableTime
+}