Start Of Day / End Of Day — Swift 5.7

extension Date {
    var startOfDay: Date {
        return Calendar.current.startOfDay(for: self)
    }

    var endOfDay: Date {
        var components = DateComponents()
        components.day = 1
        components.second = -1
        return Calendar.current.date(byAdding: components, to: startOfDay)!
    }
    
    var startOfWeek: Date {
        Calendar.current.dateComponents([.calendar, .yearForWeekOfYear, .weekOfYear], from: self).date!
    }
    
    var endOfWeek: Date {
        var components = DateComponents()
        components.weekOfYear = 1
        components.second = -1
        return Calendar.current.date(byAdding: components, to: startOfWeek)!
    }
    
    var startOfMonth: Date {
        let components = Calendar.current.dateComponents([.year, .month], from: startOfDay)
        return Calendar.current.date(from: components)!
    }

    var endOfMonth: Date {
        var components = DateComponents()
        components.month = 1
        components.second = -1
        return Calendar.current.date(byAdding: components, to: startOfMonth)!
    }
}


// End of day = Start of tomorrow minus 1 second
// End of week = Start of next week minus 1 second
// End of month = Start of next month minus 1 second