swift 日期的基本操作

//
//  ZFDateTool.swift
//  MyStudyDemo
//
//  Created by FranZhou on 16/6/12.
//  Copyright © 2016年 kimree. All rights reserved.
//

import UIKit

public class ZFDateTool: NSObject {

    // dateformat  default = "yyyy-MM-dd"
    public static var formatString: String! = "yyyy-MM-dd"{
        willSet{
            self.dateFormatter.dateFormat = newValue
        }
    }

    private static let dateFormatter: NSDateFormatter = {
        let dateFormat = NSDateFormatter()
        dateFormat.dateFormat = ZFDateTool.formatString
        return dateFormat
    }()

    // MARK: - 获得字符串时间
    public class func dateFromString(dateString: String, formatString:String = ZFDateTool.formatString) -> NSDate?{
        var dateFormat = ZFDateTool.dateFormatter
        if formatString != ZFDateTool.formatString{
            dateFormat = dateFormat.copy() as! NSDateFormatter
            dateFormat.dateFormat = formatString
        }

        return dateFormat.dateFromString(dateString)
    }

    // MARK: - 获取时间字符串
    public class func stringFromDate(date: NSDate = NSDate(), formatString:String = ZFDateTool.formatString) -> String{
        var dateFormat = ZFDateTool.dateFormatter
        if formatString != ZFDateTool.formatString{
            dateFormat = dateFormatter.copy() as! NSDateFormatter
            dateFormat.dateFormat = formatString
        }

        return dateFormat.stringFromDate(date)
    }

    // MARK: - timestamp  基于秒
    public class func timestamp(date: NSDate = NSDate()) -> Double{
        let timestamp = date.timeIntervalSince1970
        return timestamp
    }

    public class func dateFromTimestamp(timestamp: Double) -> NSDate{
        let date = NSDate(timeIntervalSince1970: timestamp)
        return date
    }

    // MARK: - 获取 年 月 日 星期
    private static let calendar: NSCalendar = {
        let calendar = NSCalendar.currentCalendar()

        // 设定每周的第一天从星期几开始，比如:
        // 如需设定从星期日开始，则firstWeekday传入1
        // 如需设定从星期一开始，则firstWeekday传入2
        // 该设置只影响 NSCalendar  不会影响到 NSDateComponents 的处理方式
        calendar.firstWeekday = 2

        return calendar
    }()

    public class func yearWithDate(date: NSDate = NSDate()) -> Int{
        let components = calendar.components(NSCalendarUnit.Year, fromDate: date)
        return components.year
    }

    public class func monthWithDate(date: NSDate = NSDate()) -> Int{
        let month = calendar.ordinalityOfUnit(NSCalendarUnit.Month, inUnit: NSCalendarUnit.Year, forDate: date)
        return month
    }

    public class func dayWithDate(date: NSDate = NSDate()) -> Int{
        let day = calendar.ordinalityOfUnit(NSCalendarUnit.Day, inUnit: NSCalendarUnit.Month, forDate: date)
        return day
    }

    public class func weekdayWithDate(date: NSDate = NSDate()) -> Int{
        // calendar.components(NSCalendarUnit.Weekday, fromDate: date) 该方法获取的weekday永远都是 1 星期天  2 星期一 ....  这种顺序
        // 如果想获得 firstWeekday 进行处理后的正确星期时间， 用下述方法
        let weekday = calendar.ordinalityOfUnit(NSCalendarUnit.Weekday, inUnit: NSCalendarUnit.WeekOfYear, forDate: date)
        return weekday
    }

}