如何计算当前第一周的NSDate？

// 获取当前日期的年份和月份
let currentDate = Date()
let calendar = Calendar.current
let year = calendar.component(.year, from: currentDate)
let month = calendar.component(.month, from: currentDate)

// 创建NSCalendar对象
let gregorian = NSCalendar(calendarIdentifier: .gregorian)

// 获取当前月份的第一天的NSDate
var components = DateComponents()
components.year = year
components.month = month
components.day = 1
let firstDayOfMonth = gregorian?.date(from: components)

// 获取当前月份的第一周的第一天的NSDate
let firstWeekday = gregorian?.component(.weekday, from: firstDayOfMonth!)
let daysToAdd = (8 - firstWeekday!) % 7
components.day = daysToAdd
let firstDayOfFirstWeek = gregorian?.date(byAdding: components, to: firstDayOfMonth!)

// 输出结果
let dateFormatter = DateFormatter()
dateFormatter.dateFormat = "yyyy-MM-dd"
let firstDayOfFirstWeekString = dateFormatter.string(from: firstDayOfFirstWeek!)
print("当前第一周的NSDate为：\(firstDayOfFirstWeekString)")