Count Days between Dates Swift (Considering what may be tomorrow.)

Question

I have this code:

extension Date {
    /// From today to self
    /// - Returns: number of days.
    func getDaysUntil() -> Int? {        
        return Calendar.current.dateComponents([.day], from: Date(), to: self).day
    }
}

I need everything to be considered in terms of EST. So regardless of which time zone we are in, everything should be regarded as EST.

I am having a problem when comparing today with tomorrow.

So take the following case:

Date() // (now): : June 15. self (compare to): : June 16.

Regardless the time of day today, I want to say that it's 1 day until the comparison date (self).

So, if it's 11:59pm and the comparison date (self) is 12:01am, I want the result to be 1 day. If it's 12:01am and the comparison date (self) is 11:59pm, I still want the comparison result to be 1.

As it is, no matter what I do, when we get to those extreme edges, the date calculation is off by 1, one way or the other.

Also, this isn't just a today vs. tomorrow issue. The correct count should be the result (considering the today/tomorrow conundrum) for any date.

Is there some fancy trick, or does anyone have any suggestion how we could accomplish this? Thanks!

Answer 1

If you need a default "don't care" time calendrical calculation what you need is to use noon time. Check WWDC session 227 Solutions to Common Date and Time Challenges . Check the "Midnight" part and what is said about why people should NOT use midnight.

extension Calendar {
    static let iso8601 = Calendar(identifier: .iso8601)
}

---

extension Date {
    /// From today's noon to self's noon
    /// - Returns: number of days.
    var daysFromToday: Int {
        Calendar.iso8601.dateComponents([.day], from: Date().noon, to: noon).day!
    }
    /// Noon time
    /// - Returns: same date at noon
    var noon: Date {
        Calendar.iso8601.date(bySettingHour: 12, minute: 0, second: 0, of: self)!
    }
}

---

Usage:

let yesterday = DateComponents(calendar: .iso8601, year: 2022, month: 5, day: 2, hour: 23, minute: 59, second: 59).date!

yesterday.daysFromToday  // -1