feat: docs api design

pkg/tools/times.go

@@ -0,0 +1,21 @@
+package tools
+
+import "time"
+
+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)
+		_, isoWeek = date.ISOWeek()
+	}
+	return date
+}