1 files changed, 79 insertions, 0 deletions
diff --git a/pim/lib/cal/duration.go b/pim/lib/cal/duration.go
new file mode 100644
index 0000000..4217ab7
--- /dev/null
+++ b/pim/lib/cal/duration.go
@@ -0,0 +1,79 @@
+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
+}