gtime: add FormatInterval (#880)

* gtime: added FormatInterval

* improved comment

backend/gtime/gtime.go

@@ -85,3 +85,35 @@ func parse(inp string) (time.Duration, string, error) {
 
 	return time.Duration(num), string(result[2]), nil
 }
+
+// FormatInterval converts a duration into the units that Grafana uses
+func FormatInterval(inter time.Duration) string {
+	year := time.Hour * 24 * 365
+	day := time.Hour * 24
+
+	if inter >= year {
+		return fmt.Sprintf("%dy", inter/year)
+	}
+
+	if inter >= day {
+		return fmt.Sprintf("%dd", inter/day)
+	}
+
+	if inter >= time.Hour {
+		return fmt.Sprintf("%dh", inter/time.Hour)
+	}
+
+	if inter >= time.Minute {
+		return fmt.Sprintf("%dm", inter/time.Minute)
+	}
+
+	if inter >= time.Second {
+		return fmt.Sprintf("%ds", inter/time.Second)
+	}
+
+	if inter >= time.Millisecond {
+		return fmt.Sprintf("%dms", inter/time.Millisecond)
+	}
+
+	return "1ms"
+}

backend/gtime/gtime_test.go

@@ -100,3 +100,23 @@ func calculateDays5y() int {
 
 	return daysInYear
 }
+
+func TestFormatInterval(t *testing.T) {
+	testCases := []struct {
+		name     string
+		duration time.Duration
+		expected string
+	}{
+		{"61s", time.Second * 61, "1m"},
+		{"30ms", time.Millisecond * 30, "30ms"},
+		{"23h", time.Hour * 23, "23h"},
+		{"24h", time.Hour * 24, "1d"},
+		{"367d", time.Hour * 24 * 367, "1y"},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			require.Equal(t, tc.expected, FormatInterval(tc.duration))
+		})
+	}
+}