Add intervals for summary requests.

utils/date.go

@@ -0,0 +1,42 @@
+package utils
+
+import "time"
+
+func StartOfDay() time.Time {
+	ref := time.Now()
+	return time.Date(ref.Year(), ref.Month(), ref.Day(), 0, 0, 0, 0, ref.Location())
+}
+
+func StartOfWeek() time.Time {
+	ref := time.Now()
+	return firstDayOfISOWeek(ref.Year(), ref.Day(), ref.Location())
+}
+
+func StartOfMonth() time.Time {
+	ref := time.Now()
+	return time.Date(ref.Year(), ref.Month(), 0, 0, 0, 0, 0, ref.Location())
+}
+
+func StartOfYear() time.Time {
+	ref := time.Now()
+	return time.Date(ref.Year(), 0, 0, 0, 0, 0, 0, ref.Location())
+}
+
+// https://stackoverflow.com/a/18632496
+func firstDayOfISOWeek(year int, week int, timezone *time.Location) time.Time {
+	date := time.Date(year, 0, 0, 0, 0, 0, 0, timezone)
+	isoYear, isoWeek := date.ISOWeek()
+	for date.Weekday() != time.Monday { // iterate back to Monday
+		date = date.AddDate(0, 0, -1)
+		isoYear, isoWeek = date.ISOWeek()
+	}
+	for isoYear < year { // iterate forward to the first day of the first week
+		date = date.AddDate(0, 0, 1)
+		isoYear, isoWeek = date.ISOWeek()
+	}
+	for isoWeek < week { // iterate forward to the first day of the given week
+		date = date.AddDate(0, 0, 1)
+		isoYear, isoWeek = date.ISOWeek()
+	}
+	return date
+}