How to have a date variable update year in counter - swift

Question

I am working on a function to print the time until Christmas. I have accomplished this however the function will only calculate the difference between the current date and Christmas of the current year. How can I update my function to calculate the difference between the current date and Christmas of every year ?
I have tried replacing the year value in my endTime constant to a variable, however this produces an error.
import UIKit
let formatter = DateFormatter()
let userCalendar = Calendar.current
let requestedComponent: Set<Calendar.Component> = [
.month,
.day,
.hour,
.minute,
.second
]
formatter.dateFormat = "MM/dd/yy hh:mm:ss a"
let startTime = Date()
let endTime = formatter.date(from: "12/25/19 12:00:00 a")
let timeDiff = userCalendar.dateComponents(requestedComponent, from: startTime, to: endTime!)
print(timeDiff)
I am at a loss for any simple solution to the problem as I am new to swift and xcode.

Answer 1

Only a couple of lines are wrong:
let whatYear = 2021 // *
let formatter = DateFormatter()
let userCalendar = Calendar(identifier: .gregorian) // *
let requestedComponent: Set<Calendar.Component> = [
.month,
.day,
.hour,
.minute,
.second
]
formatter.dateFormat = "MM/dd/yy hh:mm:ss a"
let startTime = Date()
let endTime = userCalendar.date(from: DateComponents(year:whatYear, month:12, day:25)) // *
let timeDiff = userCalendar.dateComponents(requestedComponent, from: startTime, to: endTime!)
print(timeDiff)
// month: 26 day: 9 hour: 14 minute: 14 second: 46 isLeapMonth: false

Answer 2

let now: Date = Date()
var calendar: Calendar = Calendar(identifier: .gregorian)
let nyTimeZone: TimeZone = TimeZone(identifier: "America/New_York")!
let newYearsComponents: DateComponents = DateComponents(calendar: calendar, timeZone: nil, era: nil,
year: nil, month: 1, day: 1,
hour: 0, minute: 0, second: 0, nanosecond: 0,
weekday: nil, weekdayOrdinal: nil, quarter: nil, weekOfMonth: nil, weekOfYear: nil, yearForWeekOfYear: nil)
let newYears: Date = calendar.nextDate(after: now, matching: newYearsComponents, matchingPolicy: .nextTime, repeatedTimePolicy: .first, direction: .forward)!
let units: Set<Calendar.Component> = Set(arrayLiteral: .month, .day, .hour, .minute, .second)
let timeLeftUntilNewYears: DateComponents = calendar.dateComponents(units, from: now, to: newYears)
source: https://engineering.shopspring.com/manipulating-dates-and-time-zones-in-ios-development-2f0e0d0e93be

Answer 3

You can retrieve the year of the current year and use it combined with month 12 and day 25 to create a date on the current year. You may need to add one year to it in case we are in the last week of the year.
extension Calendar {
static let gregorian = Calendar(identifier: .gregorian)
}
extension Date {
static var nextChristmas: Date {
DateComponents(calendar: .gregorian,
year: Date().year + (Date().month == 12 && Date().day > 25 ? 1 : 0),
month: 12,
day: 25).date!
}
static var timeLeftTillChristmas: DateComponents { Calendar.gregorian.dateComponents([.day, .hour, .minute, .second], from: Date(), to: Date.nextChristmas) }
var year: Int { Calendar.gregorian.component(.year, from: self) }
var month: Int { Calendar.gregorian.component(.month, from: self) }
var day: Int { Calendar.gregorian.component(.day, from: self) }
}
Date.nextChristmas.description(with: .current) // Wednesday, December 25, 2019 at 12:00:00 AM Brasilia Standard Time
Date.timeLeftTillChristmas // day: 70 hour: 7 minute: 19 second: 34