private func firstDayOfWeek(date:Date) -> Date {
        let cal = Calendar.current
        let firstWeekDay = cal.firstWeekday
        let thisWeekDay = cal.components(.weekday, from: date).weekday!
        var diff = thisWeekDay
        if thisWeekDay < firstWeekDay {
            diff += cal.weekdaySymbols.count
        }
        diff -= firstWeekDay
        diff = -1 * diff
        let firstDay = cal.date(byAdding: .day, value: diff, to: date, options: Calendar.Options.matchStrictly)!
        return firstDay
    }