Create all dates in specific month and year as in `gregorian` calendar

NSDate+Utility.swift

import UIKit

extension NSDate{
    
    /**
    Create all dates in specific month and year as in `gregorian` calendar
    
    **Usage Example**
    
    `NSDate.datesInMonthCalendar(month: 8, year: 2015)`
    
    `26	27	28	29	30	31	1`
    
    `2	3	4	5	6	7	8`
    
    `9	10	11	12	13	14	15`
    
    `16	17	18	19	20	21	22`
    
    `23	24	25	26	27	28	29`
    
    `30	31	1	2	3	4	5`
    
    :param: Month,Year
    :returns: [NSDate], contains 6 weeks, the size equals 6 * 7 = 42
    */
    class func datesInCalendar( #month: Int, year: Int )  -> [NSDate]{
        
        var datesInMonthCalendar = [NSDate]()
        
        let cal = NSCalendar(identifier: "gregorian")!
        
        let components = NSDateComponents()
        
        components.year = year
        components.month = month
        components.day = 1
        
        for i in 0..<6{
            
            var aDateInThatWeek = cal.dateFromComponents(components)!
            
            var startOfTheWeek: NSDate?
            var interval: NSTimeInterval = 0.0
            
            cal.rangeOfUnit( .CalendarUnitWeekOfMonth, startDate: &startOfTheWeek, interval: &interval, forDate: aDateInThatWeek)
            var endOfWeek = startOfTheWeek!.dateByAddingTimeInterval(interval-1)
            
            let dmyOptions = NSCalendarUnit.CalendarUnitDay | NSCalendarUnit.CalendarUnitMonth | NSCalendarUnit.CalendarUnitYear
            let startDayComponents = cal.components( dmyOptions, fromDate: startOfTheWeek!)
            let endDayComponents = cal.components( dmyOptions, fromDate: endOfWeek)
            
            var currentComponent = startDayComponents
            
            var xDate = cal.dateFromComponents(startDayComponents)!
            var endDate = cal.dateFromComponents(endDayComponents)!
            
            // iterate from start day of a week til the end of week.
            while(xDate.compare(endDate) == .OrderedAscending || xDate.compare(endDate) == .OrderedSame){
                
                let resultDay = cal.component( .CalendarUnitDay, fromDate: xDate)
                let resultMonth = cal.component(.CalendarUnitMonth, fromDate: xDate)
                
                datesInMonthCalendar += [xDate]
                
                currentComponent.day += 1
                xDate = cal.dateFromComponents(currentComponent)!
            }
            
            components.day = currentComponent.day
            components.month = currentComponent.month
            components.year = currentComponent.year
            
        }
        
        return datesInMonthCalendar
    }

}