swift Date拓展 用于写日历

public extension Date {
    
    var day: Int {
        return Calendar.current.component(Calendar.Component.day, from: self)
    }
    
    var month: Int {
        return Calendar.current.component(Calendar.Component.month, from: self)
    }
    
    var year: Int {
        return Calendar.current.component(Calendar.Component.year, from: self)
    }
    
    /// 是否在未来
    var isInFuture: Bool {
        return self > Date()
    }
    
    /// 是否在过去
    var isInPast: Bool {
        return self < Date()
    }
    
    /// 是否在本天
    var isInToday: Bool {
        return self.day == Date().day && self.month == Date().month && self.year == Date().year
    }
    
    /// 是否在本月
    var isInMonth: Bool {
        return self.month == Date().month && self.year == Date().year
    }
    
    //获得当前月份第一天星期几
    var weekdayForFirstday: Int {
        var calendar = Calendar.current
        calendar.firstWeekday = 1
        var comp = calendar.dateComponents([.year, .month, .day], from: self)
        comp.day = 1
        let firstDayInMonth = calendar.date(from: comp)!
        let weekday = calendar.ordinality(of: Calendar.Component.weekday, in: Calendar.Component.weekOfMonth, for: firstDayInMonth)
        return weekday! - 1
    }
    
    // 获得一个月总天数
    var daysInMonth: Int {
        return Calendar.current.range(of: Calendar.Component.day, in: Calendar.Component.month, for: self)!.count
    }
    

    /// 获取其他月的数据
    ///
    /// - Parameter poor: 与当前的date相差几个月 (-1---上月,  1---下月)
    /// - Returns: 目标date
    func getOtherMonthDate(_ poor: Int) -> Date {
        var dateComponents = DateComponents()
        dateComponents.month = poor
        return Calendar.current.date(byAdding: dateComponents, to: self)!
    }
    
}