Added TimeSpan.Format and MarshalText methods, compatible with RFC5545.

.gitignore

@@ -4,6 +4,7 @@
 *.so
 
 # Folders
+.idea/
 _obj/
 _test/
 vendor/

timespan/daterange_test.go

@@ -304,6 +304,7 @@ func TestDurationInZoneWithDaylightSaving(t *testing.T) {
 }
 
 func isEq(t *testing.T, a, b interface{}, msg ...interface{}) {
+	t.Helper()
 	if a != b {
 		sa := make([]string, len(msg))
 		for i, m := range msg {

timespan/timespan.go

@@ -8,6 +8,7 @@ import (
 	"fmt"
 	"github.com/rickb777/date"
 	"time"
+	"github.com/rickb777/date/period"
 )
 
 // TimestampFormat is a simple format for date & time, "2006-01-02 15:04:05".
@@ -144,3 +145,25 @@ func (ts TimeSpan) Merge(other TimeSpan) TimeSpan {
 		return NewTimeSpan(ts.mark, other.End())
 	}
 }
+
+// RFC5545DateTimeLayout is the format string used by iCalendar (RFC5545). Note
+// that "Z" is to be appended when the time is UTC.
+const RFC5545DateTimeLayout = "20060102T150405"
+
+func (ts TimeSpan) Format() string {
+	format := RFC5545DateTimeLayout
+	if ts.mark.Location().String() == "UTC" {
+		format = RFC5545DateTimeLayout + "Z"
+	}
+	s := ts.Start()
+	e := ts.End()
+	p := period.Between(s, e)
+	return fmt.Sprintf("%s/%s", s.Format(format), p)
+}
+
+// MarshalText formats the timespan as a string. This implements
+// then encoding.TextMarshaler interface.
+func (ts TimeSpan) MarshalText() (text []byte, err error) {
+	s := ts.Format()
+	return []byte(s), nil
+}

timespan/timespan_test.go

@@ -96,6 +96,29 @@ func TestTSString(t *testing.T) {
 	isEq(t, s, "24h0m0s from 2015-03-27 00:00:00 to 2015-03-28 00:00:00")
 }
 
+func TestTSFormat(t *testing.T) {
+	// use Berlin, which is UTC-1
+	berlin, _ := time.LoadLocation("Europe/Berlin")
+	t0 := time.Date(2015, 3, 27, 10, 13, 14, 0, time.UTC)
+
+	cases := []struct{
+		start time.Time
+		duration time.Duration
+		exp string
+	}{
+		{t0, time.Hour, "20150327T101314Z/PT1H"},
+		{t0.In(berlin), time.Minute, "20150327T111314/PT1M"},
+	}
+
+	for _, c := range cases {
+		ts := TimeSpan{c.start, c.duration}
+		b, err := ts.MarshalText()
+		isEq(t, ts.Format(), c.exp)
+		isEq(t, err, nil)
+		isEq(t, string(b), c.exp)
+	}
+}
+
 func TestTSContains(t *testing.T) {
 	ts := NewTimeSpan(t0327, t0329)
 	isEq(t, ts.Contains(t0327.Add(minusOneNano)), false)