Get first day of a week with Swift

FirstWeekDay

//: Playground - noun: a place where people can play

import UIKit

let today = NSDate.new()
let gregorian = NSCalendar.currentCalendar()

let weekdayComponetns = gregorian.components(NSCalendarUnit.Weekday, fromDate: today)

let compontentsToSubstract = NSDateComponents.new()
// Sunday -> -(weekdayComponetns.weekday - gregorian.firstWeekday)
// Monday -> -(weekdayComponetns.weekday - gregorian.firstWeekday - 1)
compontentsToSubstract.day = -(weekdayComponetns.weekday - gregorian.firstWeekday - 1)
var beginningOfWeek = gregorian.dateByAddingComponents(compontentsToSubstract, toDate: today, options: NSCalendarOptions(rawValue: 0))

let components = gregorian.components(([NSCalendarUnit.Year, NSCalendarUnit.Month, NSCalendarUnit.Day]), fromDate: beginningOfWeek!)
beginningOfWeek = gregorian.dateFromComponents(components)