Swift - check if a timestamp is yesterday, today, tomorrow, or X days ago

I'm trying to work out how to decide if a given timestamp occurs today, or +1 / -1 days. Essentially, I'd like to do something like this (Pseudocode)

IF days_from_today(timestamp) == -1 RETURN 'Yesterday'
ELSE IF days_from_today(timestamp) == 0 RETURN 'Today'
ELSE IF days_from_today(timestamp) == 1 RETURN 'Tomorrow'
ELSE IF days_from_today(timestamp) < 1 RETURN days_from_today(timestamp) + ' days ago'
ELSE RETURN 'In ' + days_from_today(timestamp) + ' ago'

Crucially though, it needs to be in Swift and I'm struggling with the NSDate / NSCalendar objects. I started with working out the time difference like this:

let calendar = NSCalendar.currentCalendar()
let date = NSDate(timeIntervalSince1970: Double(timestamp))
let timeDifference = calendar.components([.Second,.Minute,.Day,.Hour],
    fromDate: date, toDate: NSDate(), options: NSCalendarOptions())

However comparing in this way isn't easy, because the .Day is different depending on the time of day and the timestamp. In PHP I'd just use mktime to create a new date, based on the start of the day (i.e. mktime(0,0,0)), but I'm not sure of the easiest way to do that in Swift.

Does anybody have a good idea on how to approach this? Perhaps an extension to NSDate or something similar would be best?

Swift 3/4/5:

Calendar.current.isDateInToday(yourDate)
Calendar.current.isDateInYesterday(yourDate)
Calendar.current.isDateInTomorrow(yourDate)

Additionally:

Calendar.current.isDateInWeekend(yourDate)

Note that for some countries weekend may be different than Saturday-Sunday, it depends on the calendar.

You can also use autoupdatingCurrent instead of current calendar, which will track user updates. You use it the same way:

Calendar.autoupdatingCurrent.isDateInToday(yourDate)

Calendar is a type alias for the NSCalendar.

Calendar has methods for all three cases

func isDateInYesterday(_ date: Date) -> Bool
func isDateInToday(_ date: Date) -> Bool
func isDateInTomorrow(_ date: Date) -> Bool

To calculate the days earlier than yesterday use

func dateComponents(_ components: Set<Calendar.Component>, 
                      from start: Date, 
                          to end: Date) -> DateComponents

pass [.day] to components and get the day property from the result.

---

This is a function which considers also is in for earlier and later dates by stripping the time part (Swift 3+).

func dayDifference(from interval : TimeInterval) -> String
{
    let calendar = Calendar.current
    let date = Date(timeIntervalSince1970: interval)
    if calendar.isDateInYesterday(date) { return "Yesterday" }
    else if calendar.isDateInToday(date) { return "Today" }
    else if calendar.isDateInTomorrow(date) { return "Tomorrow" }
    else {
        let startOfNow = calendar.startOfDay(for: Date())
        let startOfTimeStamp = calendar.startOfDay(for: date)
        let components = calendar.dateComponents([.day], from: startOfNow, to: startOfTimeStamp)
        let day = components.day!
        if day < 1 { return "\(-day) days ago" }
        else { return "In \(day) days" }
    }
}

Alternatively you could use DateFormatter for Yesterday, Today and Tomorrow to get localized strings for free

func dayDifference(from interval : TimeInterval) -> String
{
    let calendar = Calendar.current
    let date = Date(timeIntervalSince1970: interval)
    let startOfNow = calendar.startOfDay(for: Date())
    let startOfTimeStamp = calendar.startOfDay(for: date)
    let components = calendar.dateComponents([.day], from: startOfNow, to: startOfTimeStamp)
    let day = components.day!
    if abs(day) < 2 {
        let formatter = DateFormatter()
        formatter.dateStyle = .short
        formatter.timeStyle = .none
        formatter.doesRelativeDateFormatting = true
        return formatter.string(from: date)
    } else if day > 1 {
        return "In \(day) days"
    } else {
        return "\(-day) days ago"
    }
}

Update:

In macOS 10.15 / iOS 13 RelativeDateTimeFormatter was introduced to return (localized) strings relative to a specific date.

Swift 4 update:

let calendar = Calendar.current
let date = Date()
        
calendar.isDateInYesterday(date)
calendar.isDateInToday(date)
calendar.isDateInTomorrow(date)

NSCalender has new methods that you can use directly.

NSCalendar.currentCalendar().isDateInTomorrow(NSDate())//Replace NSDate() with your date
NSCalendar.currentCalendar().isDateInYesterday()
NSCalendar.currentCalendar().isDateInTomorrow()

Hope this helps

On Swift 5 and iOS 13 use the RelativeDateTimeFormatter,

let formatter = RelativeDateTimeFormatter()
formatter.dateTimeStyle = .named 

formatter.localizedString(from: DateComponents(day: -1)) // "yesterday"
formatter.localizedString(from: DateComponents(day: 1)) // "Tomorrow"
formatter.localizedString(from: DateComponents(hour: 2)) // "in 2 hours"
formatter.localizedString(from: DateComponents(minute: 45)) // "in 45 minutes"

1)According to your example you want to receive labels "Yesterday", "Today" and etc. iOS can do this by default:

https://developer.apple.com/documentation/foundation/nsdateformatter/1415848-doesrelativedateformatting?language=objc

2)If you want to compute your custom label when iOS don't add these labels by itself then alternatively you can use 2 DateFormatter objects with both doesRelativeDateFormatting == true and doesRelativeDateFormatting == false and compare if their result date strings are the same or different