pkg/time: add FormatString and Split

Down the line, FormatString should replace Format
with new semantics. It is added now as FormatString
to aid in the transition.

Closes #1508

Change-Id: I1d80aab593a7e8b18dd500d73aef12fb9e5bfa4b
Signed-off-by: Marcel van Lohuizen <mpvl@golang.org>

pkg/time/testdata/gen.txtar

@@ -19,6 +19,9 @@ parse: {
 	t2: time.Parse(_layout, _layout)
 }
 
+split: {
+	t1: time.Split("2017-07-14T02:40:00.000123456Z")
+}
 -- out/time --
 Errors:
 t2: invalid value "no time" (does not satisfy time.Time): error in call to time.Time: invalid time "no time":
@@ -32,4 +35,15 @@ parse: {
 	t1: "2021-07-01T17:54:00Z"
 	t2: "2006-01-02T22:04:05Z"
 }
+split: {
+	t1: {
+		year:       2017
+		month:      7
+		day:        14
+		hour:       2
+		minute:     40
+		second:     0
+		nanosecond: 123456
+	}
+}
 

pkg/time/time.go

@@ -139,13 +139,24 @@ func timeFormat(value, layout string) (bool, error) {
 	return true, nil
 }
 
-// Format defines a type string that must adhere to a certain layout.
+// FormatString defines a type string that must adhere to a certain layout.
 //
 // See Parse for a description on layout strings.
 func Format(value, layout string) (bool, error) {
 	return timeFormat(value, layout)
 }
 
+// FormatString returns a textual representation of the time value formatted
+// according to the layout defined by the argument. See Parse for more
+// information on the layout string.
+func FormatString(layout, value string) (string, error) {
+	t, err := time.Parse(time.RFC3339Nano, value)
+	if err != nil {
+		return "", err
+	}
+	return t.Format(layout), nil
+}
+
 // Parse parses a formatted string and returns the time value it represents.
 // The layout defines the format by showing how the reference time,
 // defined to be
@@ -195,3 +206,35 @@ func Unix(sec int64, nsec int64) string {
 	t := time.Unix(sec, nsec)
 	return t.UTC().Format(time.RFC3339Nano)
 }
+
+// Parts holds individual parts of a parsed time stamp.
+type Parts struct {
+	Year   int `json:"year"`
+	Month  int `json:"month"`
+	Day    int `json:"day"`
+	Hour   int `json:"hour"`
+	Minute int `json:"minute"`
+
+	// Second is equal to div(Nanosecond, 1_000_000_000)
+	Second     int `json:"second"`
+	Nanosecond int `json:"nanosecond"`
+}
+
+// Split parses a time string into its individual parts.
+func Split(t string) (*Parts, error) {
+	st, err := time.Parse(time.RFC3339Nano, t)
+	if err != nil {
+		return nil, err
+	}
+	year, month, day := st.Date()
+	return &Parts{
+		Year:   year,
+		Month:  int(month),
+		Day:    day,
+		Hour:   st.Hour(),
+		Minute: st.Minute(),
+
+		Second:     st.Second(),
+		Nanosecond: st.Nanosecond(),
+	}, nil
+}