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package cal
import (
"fmt"
"strconv"
"strings"
"time"
)
// parseDuration parses an RFC 5545 duration: [+-]P[nW][nD][T[nH][nM][nS]].
// A leading '-' means before the reference time, so "-PT15M" is -15m.
func parseDuration(s string) (time.Duration, error) {
orig := s
neg := false
switch {
case strings.HasPrefix(s, "-"):
neg, s = true, s[1:]
case strings.HasPrefix(s, "+"):
s = s[1:]
}
if !strings.HasPrefix(s, "P") {
return 0, fmt.Errorf("not a duration: %q", orig)
}
s = s[1:]
var d time.Duration
inTime := false
num := ""
for _, r := range s {
switch {
case r >= '0' && r <= '9':
num += string(r)
continue
case r == 'T':
inTime = true
continue
}
if num == "" {
return 0, fmt.Errorf("unit %q with no count in %q", r, orig)
}
n, err := strconv.Atoi(num)
if err != nil {
return 0, fmt.Errorf("bad count in %q", orig)
}
num = ""
var unit time.Duration
switch r {
case 'W':
unit = 7 * 24 * time.Hour
case 'D':
unit = 24 * time.Hour
case 'H':
if !inTime {
return 0, fmt.Errorf("H outside time part in %q", orig)
}
unit = time.Hour
case 'M':
if !inTime {
return 0, fmt.Errorf("M outside time part in %q", orig)
}
unit = time.Minute
case 'S':
if !inTime {
return 0, fmt.Errorf("S outside time part in %q", orig)
}
unit = time.Second
default:
return 0, fmt.Errorf("unknown unit %q in %q", r, orig)
}
d += time.Duration(n) * unit
}
if num != "" {
return 0, fmt.Errorf("trailing count in %q", orig)
}
if neg {
d = -d
}
return d, nil
}
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