Global Nerdy

In this article, we’ll expand on material covered in the three previous articles in this series on working with dates and times in Swift 5:

• The basic structs, which let us create dates and times, and work with their components. They are:
  • Date, which represents a single point in time,
  • DateComponents, which represents the units that make up a date, such as year, month, day, hour, and minute, and which can be used to represent either a single point in time or a duration of time, and
  • Calendar, which provides a context for Dates, and allows us to convert between Dates and DateComponents.
• The DateFormatter class, which converts Dates into formatted Strings, and formatted Strings into Dates.
• Date arithmetic, which make it possible to add time intervals to Dates, find the difference in time between two Dates, and compare Dates.

A more readable way to work with Dates and DateComponents

Suppose we want to find out what the date and time will be 2 months, 3 days, 4 hours, 5 minutes, and 6 seconds from now will be.

If you recall what we covered in the last installment in this series, you’d probably use code like this:

var timeInterval = DateComponents(
  month: 2,
  day: 3,
  hour: 4,
  minute: 5,
  second: 6
)
let futureDate = Calendar.current.date(byAdding: timeInterval, to: Date())!
print("2 months, 3 days, 4 hours, 5 minutes, and 6 seconds from now is \(futureDate.description(with: Locale(identifier: "en_US"))).")

In the code above, we did the following:

• We created an instance of a DateComponents struct.
• We set its properties so that it would represent a time interval of 2 months, 3 days, 4 hours, 5 minutes, and 6 seconds.
• We then used Calendar‘s date(byAdding:to:) method to add the time interval to a Date.

This code wouldn’t look out of place in a lot of other programming languages, but we can do better in Swift. What if I told you that by defining a few helper functions, you can turn the code above into the code below?

let coolerFutureDate = Date() + 2.months + 3.days + 4.hours + 5.minutes + 6.seconds
let coolerPastDate   = Date() - 2.months - 3.days - 4.hours - 5.minutes - 6.seconds

Or this code?

let coolerFutureDate = (2.months + 3.days + 4.hours + 5.minutes + 6.seconds).fromNow
let coolerPastDate   = (2.months + 3.days + 4.hours + 5.minutes + 6.seconds).ago

I’d much rather write the code above. This article will cover the code necessary to make this kind of syntactic magic possible.

Overloading + and - so that we can add and subtract DateComponents

First, let’s write some code that allows us to add and subtract DateComponents. Start a new playground and enter the following code into it:

func +(_ lhs: DateComponents, _ rhs: DateComponents) -> DateComponents {
  return combineComponents(lhs, rhs)
}

func -(_ lhs: DateComponents, _ rhs: DateComponents) -> DateComponents {
  return combineComponents(lhs, rhs, multiplier: -1)
}

func combineComponents(_ lhs: DateComponents,
                       _ rhs: DateComponents,
                       multiplier: Int = 1)
  -> DateComponents {
    var result = DateComponents()
    result.nanosecond = (lhs.nanosecond ?? 0) + (rhs.nanosecond ?? 0) * multiplier
    result.second     = (lhs.second     ?? 0) + (rhs.second     ?? 0) * multiplier
    result.minute     = (lhs.minute     ?? 0) + (rhs.minute     ?? 0) * multiplier
    result.hour       = (lhs.hour       ?? 0) + (rhs.hour       ?? 0) * multiplier
    result.day        = (lhs.day        ?? 0) + (rhs.day        ?? 0) * multiplier
    result.weekOfYear = (lhs.weekOfYear ?? 0) + (rhs.weekOfYear ?? 0) * multiplier
    result.month      = (lhs.month      ?? 0) + (rhs.month      ?? 0) * multiplier
    result.year       = (lhs.year       ?? 0) + (rhs.year       ?? 0) * multiplier
    return result
}

In the code above, we’ve overloaded the + and - operators so that we can add and subtract DateComponents. I derived these functions from Axel Schlueter’s SwiftDateTimeExtensions library. He wrote them when Swift was still in beta; I updated them so that they compile with the current version and added a couple of tweaks of my own.

The addition and subtraction operations are so similar and so tedious, which is a sign that there’s an opportunity to DRY up the code. I factored out the duplicate code from both the + and - overloads and put it into its own method, combineComponents, which does the actual DateComponents addition and subtraction.

You may have noticed a lot of ?? operators in the code for combineComponents. ?? is referred to as the nil coalescing operator, and it’s a clever bit of syntactic shorthand. For the expression below:

let finalValue = someOptionalValue ?? fallbackValue

• If someOptionalValue is not nil, finalValue is set to someOptionalValue‘s value.
• If someOptionalValue is nil, finalValue is set to fallbackValue‘s value.

Let’s confirm that our new operator overloads work. Add the following to the playground and run it:

// Let's define a couple of durations of time
// ------------------------------------------

var oneDayFiveHoursTenMinutes = DateComponents(
  day: 1,
  hour: 5,
  minute: 10
)
var threeDaysTenHoursThirtyMinutes = DateComponents(
  day: 3,
  hour: 10,
  minute: 30
)


// Now let's add and subtract them
// -------------------------------

let additionResult = oneDayFiveHoursTenMinutes + threeDaysTenHoursThirtyMinutes
print("1 day, 5 hours, and 10 minutes + 3 days, 10 hours, and 30 minutes equals:")
print("\(additionResult.day!) days, \(additionResult.hour!) hours, and \(additionResult.minute!) minutes.")

let subtractionResult = threeDaysTenHoursThirtyMinutes - oneDayFiveHoursTenMinutes
print("1 day, 5 hours, and 10 minutes - 3 days, 10 hours, and 30 minutes equals:")
print("\(subtractionResult.day!) days, \(subtractionResult.hour!) hours, and \(subtractionResult.minute!) minutes.")

You should see the following output:

1 day, 5 hours, and 10 minutes + 3 days, 10 hours, and 30 minutes equals:
4 days, 15 hours, and 40 minutes.
1 day, 5 hours, and 10 minutes – 3 days, 10 hours, and 30 minutes equals:
2 days, 5 hours, and 20 minutes.

Overloading - so that we can negate DateComponents

Now that we can add and subtract DateComponents, let’s overload the unary minus so that we can negate DateComponents:

prefix func -(components: DateComponents) -> DateComponents {
  var result = DateComponents()
  if components.nanosecond != nil { result.nanosecond = -components.nanosecond! }
  if components.second     != nil { result.second     = -components.second! }
  if components.minute     != nil { result.minute     = -components.minute! }
  if components.hour       != nil { result.hour       = -components.hour! }
  if components.day        != nil { result.day        = -components.day! }
  if components.weekOfYear != nil { result.weekOfYear = -components.weekOfYear! }
  if components.month      != nil { result.month      = -components.month! }
  if components.year       != nil { result.year       = -components.year! }
  return result
}

With this overload defined, we can now use the unary minus to negate DateComponents. Add the following to the playground and run it:

let negativeTime = -oneDayFiveHoursTenMinutes
print("Negating 1 day, 5 hours, and 10 minutes turns it into:")
print("\(negativeTime.day!) days, \(negativeTime.hour!) hours, and \(negativeTime.minute!) minutes.")

You should see the following output:

Negating 1 day, 5 hours, and 10 minutes turns it into:
-1 days, -5 hours, and -10 minutes.

Overloading + and - so that we can add Dates and DateComponents and subtract DateComponents from Dates

With the unary minus defined, we can now define the following operations:

• Date + DateComponents, which makes it easier to do date arithmetic.
• DateComponents + Date, which should be possible because addition is commutative (which is just a fancy way of saying that a + b and b + a should give you the same result).
• Date - DateComponents, which once again makes it easier to do date arithmetic.

// Date + DateComponents
func +(_ lhs: Date, _ rhs: DateComponents) -> Date
{
  return Calendar.current.date(byAdding: rhs, to: lhs)!
}

// DateComponents + Dates
func +(_ lhs: DateComponents, _ rhs: Date) -> Date
{
  return rhs + lhs
}

// Date - DateComponents
func -(_ lhs: Date, _ rhs: DateComponents) -> Date
{
  return lhs + (-rhs)
}

Note that we didn’t define an overload for calculating Date - DateComponents — such an operation doesn’t make any sense.

With these overloads defined, a lot of Date/DateComponents arithmetic in Swift becomes much easier to enter and read. Add the following to the playground and run it:

// What time will it be 1 day, 5 hours, and 10 minutes from now?
// -------------------------------------------------------------

// Here's the standard way of finding out:
let futureDate0 = Calendar.current.date(
  byAdding: oneDayFiveHoursTenMinutes,
  to: Date()
)

// With our overloads and function definitions, we can now do it this way:
let futureDate1 = Date() + oneDayFiveHoursTenMinutes
print("Date() + oneDayFiveHoursTenMinutes = \(futureDate1.description(with: Locale(identifier: "en_US")))")

// This will work as well:
let futureDate2 = oneDayFiveHoursTenMinutes + Date()
print("oneDayFiveHoursTenMinutes + Date() = \(futureDate2.description(with: Locale(identifier: "en_US")))")


// What time was it 3 days, 10 hours, and 30 minutes ago?
// ------------------------------------------------------

// Doing it the standard way takes some work
var minus3Days5Hours30minutes = threeDaysTenHoursThirtyMinutes
minus3Days5Hours30minutes.day = -threeDaysTenHoursThirtyMinutes.day!
minus3Days5Hours30minutes.hour = -threeDaysTenHoursThirtyMinutes.hour!
minus3Days5Hours30minutes.minute = -threeDaysTenHoursThirtyMinutes.minute!
let pastDate0 = Calendar.current.date(byAdding: minus3Days5Hours30minutes, to: Date())

// With our overloads and function definitions, it's so much easier:
let pastDate1 = Date() - threeDaysTenHoursThirtyMinutes
print("Date() - threeDaysTenHoursThirtyMinutes = \(pastDate1.description(with: Locale(identifier: "en_US")))")

On my computer, the output looked like this:

Date() + oneDayFiveHoursTenMinutes = Friday, May 29, 2020 at 3:20:54 PM Eastern Daylight Time
oneDayFiveHoursTenMinutes + Date() = Friday, May 29, 2020 at 3:20:54 PM Eastern Daylight Time
Date() – threeDaysTenHoursThirtyMinutes = Sunday, May 24, 2020 at 11:40:54 PM Eastern Daylight Time

Extending Date so that creating dates and debugging are simpler

Creating Dates in Swift is a roundabout process. Usually, you end up creating them in one of two ways:

• Instantiating a DateComponents struct and then using it to create a Date using Calendar‘s date(from:) method, or
• Creating a String representation of the Date and then using it to create a Date using DateFormatter‘s date(from:) method.

Let’s simplify things by extending the Date struct with a couple of convenient init method overloads. Let’s also make it easier to print out the value of a Date for debugging.

Add the following to the playground:

extension Date {

  init(year: Int,
       month: Int,
       day: Int,
       hour: Int = 0,
       minute: Int = 0,
       second: Int = 0,
       timeZone: TimeZone = TimeZone(abbreviation: "UTC")!) {
    var components = DateComponents()
    components.year = year
    components.month = month
    components.day = day
    components.hour = hour
    components.minute = minute
    components.second = second
    components.timeZone = timeZone
    self = Calendar.current.date(from: components)!
  }

  init(dateString: String) {
    let formatter = DateFormatter()
    formatter.dateFormat = "yyyy-MM-dd HH:mm:ss zz"
    self = formatter.date(from: dateString)!
  }

  var desc: String {
    get {
      let PREFERRED_LOCALE = "en_US" // Use whatever locale you prefer!
      return self.description(with: Locale(identifier: PREFERRED_LOCALE))
    }
  }

}

With these methods, initializing Dates is a lot more simple. Add the following to the playground and run it:

// The Stevenote where the original iPhone was announced took place
// on January 9, 2007 at 10:00 a.m. PST
let iPhoneStevenoteDate = Date(year: 2007,
                               month: 1,
                               day: 9,
                               hour: 10,
                               minute: 0,
                               second: 0,
                               timeZone: TimeZone(abbreviation: "PST")!)
print("iPhoneStevenoteDate: \(iPhoneStevenoteDate.desc)")

// The original iPhone went on sale on June 27, 2007
let iPhoneReleaseDate = Date(year: 2007, month: 6, day: 27) // June 27, 2007, 00:00:00 UTC
print("iPhoneReleaseDate: \(iPhoneReleaseDate.desc)")

// The Stevenote where the original iPad was announced took place
// on January 27, 2010 at 10:00 a.m. PST
let iPadStevenoteDate = Date(dateString: "2010-01-27 10:00:00 PST")
print("iPadStevenoteDate: \(iPadStevenoteDate.desc)")

On my computer, the output looked like this:

iPhoneStevenoteDate: Tuesday, January 9, 2007 at 1:00:00 PM Eastern Standard Time
iPhoneReleaseDate: Tuesday, June 26, 2007 at 8:00:00 PM Eastern Daylight Time
iPadStevenoteDate: Wednesday, January 27, 2010 at 1:00:00 PM Eastern Standard Time

Overloading - so that we can use it to find the difference between two Dates

When we’re trying to determine the time between two given Dates, what we’re doing is finding the difference between them. Wouldn’t it be nice if we could use the - operator to find the difference between Dates, just as we can use it to find the difference between numbers?

Let’s code an overload to do just that. Add the following to the playground:

func -(_ lhs: Date, _ rhs: Date) -> DateComponents
{
  return Calendar.current.dateComponents(
    [.year, .month, .weekOfYear, .day, .hour, .minute, .second, .nanosecond],
    from: rhs,
    to: lhs)
}

Let’s test it in action. Add the following to the playground and run it:

let timeFromAnnouncementToRelease = iPhoneReleaseDate - iPhoneStevenoteDate
timeFromAnnouncementToRelease.year    // 0
timeFromAnnouncementToRelease.month   // 5
timeFromAnnouncementToRelease.day     // 17
timeFromAnnouncementToRelease.hour    // 7
timeFromAnnouncementToRelease.minute  // 0

// How long ago was the first moon landing, which took place
// on July 20, 1969, 20:18 UTC?
Date() - Date(dateString: "1969-07-20 20:18:00 UTC")
// At the time of writing, this value was a Date with the following properties:
// - year: 47 
// - month: 1 
// - day: 9 
// - hour: 22 
// - minute: 14

On my computer, the output looked like this:

The first iPhone users had to wait this long:
0 years, 5 months, 2 weeks, 3 days, 7 hours, and 0 minutes.
It’s been this long since the first moon landing:
50 years, 10 months, 1 weeks, 0 days, 18 hours, and 22 minutes.

Extending Int to add some syntactic magic to date components

We’ve already got some syntactic niceties, but the real Swift magic happens when we add this code to the mix. Add the following to the playground:

extension Int {

  var second: DateComponents {
    var components = DateComponents()
    components.second = self;
    return components
  }
  
  var seconds: DateComponents {
    return self.second
  }
  
  var minute: DateComponents {
    var components = DateComponents()
    components.minute = self;
    return components
  }
  
  var minutes: DateComponents {
    return self.minute
  }
  
  var hour: DateComponents {
    var components = DateComponents()
    components.hour = self;
    return components
  }
  
  var hours: DateComponents {
    return self.hour
  }
  
  var day: DateComponents {
    var components = DateComponents()
    components.day = self;
    return components
  }
  
  var days: DateComponents {
    return self.day
  }
  
  var week: DateComponents {
    var components = DateComponents()
    components.weekOfYear = self;
    return components
  }
  
  var weeks: DateComponents {
    return self.week
  }
  
  var month: DateComponents {
    var components = DateComponents()
    components.month = self;
    return components
  }
  
  var months: DateComponents {
    return self.month
  }
  
  var year: DateComponents {
    var components = DateComponents()
    components.year = self;
    return components
  }
  
  var years: DateComponents {
    return self.year
  }
  
}

This additions to Int allow us to convert Ints to DateComponents in an easy-to-read way, and with our overloads to add and subtract DateComponents to and from each other, and to add Dates to DateComponents, we can now perform all sorts of syntactic magic like this (add the following to the playground and run it):

// A quick test of some future dates
print("One hour from now is: \((Date() + 1.hour).desc)")
print("One day from now is: \((Date() + 1.day).desc)")
print("One week from now is: \((Date() + 1.week).desc)")
print("One month from now is: \((Date() + 1.month).desc)")
print("One year from now is: \((Date() + 1.year).desc)")

// What was the date 10 years, 9 months, 8 days, 7 hours, and 6 minutes ago?
let aLittleWhileBack = Date() - 10.years - 9.months - 8.days - 7.hours - 6.minutes
print("10 years, 9 months, 8 days, 7 hours, and 6 minutes ago, it was: \(aLittleWhileBack.desc)")

On my computer, the output looked like this:

One hour from now is: Thursday, May 28, 2020 at 11:57:49 AM Eastern Daylight Time
One day from now is: Friday, May 29, 2020 at 10:57:49 AM Eastern Daylight Time
One week from now is: Thursday, June 4, 2020 at 10:57:49 AM Eastern Daylight Time
One month from now is: Sunday, June 28, 2020 at 10:57:49 AM Eastern Daylight Time
One year from now is: Friday, May 28, 2021 at 10:57:49 AM Eastern Daylight Time
10 years, 9 months, 8 days, 7 hours, and 6 minutes ago, it was: Thursday, August 20, 2009 at 3:51:49 AM Eastern Daylight Time

Extending DateComponents to add even more syntactic magic: fromNow and ago

And finally, a couple of additions to the DateComponents struct to make Date/DateComponent calculations even more concise and readable. Add these to the playground:

extension DateComponents {
  
  var fromNow: Date {
    return Calendar.current.date(byAdding: self,
                                 to: Date())!
  }
  
  var ago: Date {
    return Calendar.current.date(byAdding: -self,
                                 to: Date())!
  }
  
}

Let’s try them out! Add these to the playground and run them:

// We’re now in Serious Syntax Magic Land!
// ---------------------------------------

print("2.weeks.fromNow: \(2.weeks.fromNow.desc)")
print("3.months.fromNow: \(3.months.fromNow.desc)")

let futureDate3 = (2.months + 3.days + 4.hours + 5.minutes + 6.seconds).fromNow
print("futureDate3: \(futureDate3.desc)")

let pastDate2 = (2.months + 3.days + 4.hours + 5.minutes + 6.seconds).ago
print("pastDate2: \(pastDate2.desc)")

On my computer, the output looked like this:

2.weeks.fromNow: Thursday, June 11, 2020 at 11:03:36 AM Eastern Daylight Time
3.months.fromNow: Friday, August 28, 2020 at 11:03:36 AM Eastern Daylight Time
futureDate3: Friday, July 31, 2020 at 3:08:42 PM Eastern Daylight Time
pastDate2: Wednesday, March 25, 2020 at 6:58:30 AM Eastern Daylight Time

Wrapping it all up

Here’s the playground containing all the code we just worked with:

import UIKit

var timeInterval = DateComponents(
  month: 2,
  day: 3,
  hour: 4,
  minute: 5,
  second: 6
)
let futureDate = Calendar.current.date(byAdding: timeInterval, to: Date())!
print("2 months, 3 days, 4 hours, 5 minutes, and 6 seconds from now is \(futureDate.description(with: Locale(identifier: "en_US"))).")


// Overloading + and - so that we can add and subtract DateComponents
// ==================================================================

func +(_ lhs: DateComponents, _ rhs: DateComponents) -> DateComponents {
  return combineComponents(lhs, rhs)
}

func -(_ lhs: DateComponents, _ rhs: DateComponents) -> DateComponents {
  return combineComponents(lhs, rhs, multiplier: -1)
}

func combineComponents(_ lhs: DateComponents,
                       _ rhs: DateComponents,
                       multiplier: Int = 1)
  -> DateComponents {
    var result = DateComponents()
    result.nanosecond = (lhs.nanosecond ?? 0) + (rhs.nanosecond ?? 0) * multiplier
    result.second     = (lhs.second     ?? 0) + (rhs.second     ?? 0) * multiplier
    result.minute     = (lhs.minute     ?? 0) + (rhs.minute     ?? 0) * multiplier
    result.hour       = (lhs.hour       ?? 0) + (rhs.hour       ?? 0) * multiplier
    result.day        = (lhs.day        ?? 0) + (rhs.day        ?? 0) * multiplier
    result.weekOfYear = (lhs.weekOfYear ?? 0) + (rhs.weekOfYear ?? 0) * multiplier
    result.month      = (lhs.month      ?? 0) + (rhs.month      ?? 0) * multiplier
    result.year       = (lhs.year       ?? 0) + (rhs.year       ?? 0) * multiplier
    return result
}


// Let's define a couple of durations of time
// ------------------------------------------

var oneDayFiveHoursTenMinutes = DateComponents(
  day: 1,
  hour: 5,
  minute: 10
)
var threeDaysTenHoursThirtyMinutes = DateComponents(
  day: 3,
  hour: 10,
  minute: 30
)


// Now let's add and subtract them
// -------------------------------

let additionResult = oneDayFiveHoursTenMinutes + threeDaysTenHoursThirtyMinutes
print("1 day, 5 hours, and 10 minutes + 3 days, 10 hours, and 30 minutes equals:")
print("\(additionResult.day!) days, \(additionResult.hour!) hours, and \(additionResult.minute!) minutes.")

let subtractionResult = threeDaysTenHoursThirtyMinutes - oneDayFiveHoursTenMinutes
print("1 day, 5 hours, and 10 minutes - 3 days, 10 hours, and 30 minutes equals:")
print("\(subtractionResult.day!) days, \(subtractionResult.hour!) hours, and \(subtractionResult.minute!) minutes.")


// Overloading - so that we can negate DateComponents
// --------------------------------------------------

// We'll need to overload unary - so we can negate components
prefix func -(components: DateComponents) -> DateComponents {
  var result = DateComponents()
  if components.nanosecond != nil { result.nanosecond = -components.nanosecond! }
  if components.second     != nil { result.second     = -components.second! }
  if components.minute     != nil { result.minute     = -components.minute! }
  if components.hour       != nil { result.hour       = -components.hour! }
  if components.day        != nil { result.day        = -components.day! }
  if components.weekOfYear != nil { result.weekOfYear = -components.weekOfYear! }
  if components.month      != nil { result.month      = -components.month! }
  if components.year       != nil { result.year       = -components.year! }
  return result
}


let negativeTime = -oneDayFiveHoursTenMinutes
print("Negating 1 day, 5 hours, and 10 minutes turns it into:")
print("\(negativeTime.day!) days, \(negativeTime.hour!) hours, and \(negativeTime.minute!) minutes.")


// Overloading + and - so that we can add Dates and DateComponents
// and subtract DateComponents from Dates

// Date + DateComponents
func +(_ lhs: Date, _ rhs: DateComponents) -> Date
{
  return Calendar.current.date(byAdding: rhs, to: lhs)!
}

// DateComponents + Dates
func +(_ lhs: DateComponents, _ rhs: Date) -> Date
{
  return rhs + lhs
}

// Date - DateComponents
func -(_ lhs: Date, _ rhs: DateComponents) -> Date
{
  return lhs + (-rhs)
}


// What time will it be 1 day, 5 hours, and 10 minutes from now?
// -------------------------------------------------------------

// Here's the standard way of finding out:
let futureDate0 = Calendar.current.date(
  byAdding: oneDayFiveHoursTenMinutes,
  to: Date()
)

// With our overloads and function definitions, we can now do it this way:
let futureDate1 = Date() + oneDayFiveHoursTenMinutes
print("Date() + oneDayFiveHoursTenMinutes = \(futureDate1.description(with: Locale(identifier: "en_US")))")

// This will work as well:
let futureDate2 = oneDayFiveHoursTenMinutes + Date()
print("oneDayFiveHoursTenMinutes + Date() = \(futureDate2.description(with: Locale(identifier: "en_US")))")


// What time was it 3 days, 10 hours, and 30 minutes ago?
// ------------------------------------------------------

// Doing it the standard way takes some work
var minus3Days5Hours30minutes = threeDaysTenHoursThirtyMinutes
minus3Days5Hours30minutes.day = -threeDaysTenHoursThirtyMinutes.day!
minus3Days5Hours30minutes.hour = -threeDaysTenHoursThirtyMinutes.hour!
minus3Days5Hours30minutes.minute = -threeDaysTenHoursThirtyMinutes.minute!
let pastDate0 = Calendar.current.date(byAdding: minus3Days5Hours30minutes, to: Date())

// With our overloads and function definitions, it's so much easier:
let pastDate1 = Date() - threeDaysTenHoursThirtyMinutes
print("Date() - threeDaysTenHoursThirtyMinutes = \(pastDate1.description(with: Locale(identifier: "en_US")))")


// Extending Date so that creating dates and debugging are simpler
// ===============================================================

extension Date {

  init(year: Int,
       month: Int,
       day: Int,
       hour: Int = 0,
       minute: Int = 0,
       second: Int = 0,
       timeZone: TimeZone = TimeZone(abbreviation: "UTC")!) {
    var components = DateComponents()
    components.year = year
    components.month = month
    components.day = day
    components.hour = hour
    components.minute = minute
    components.second = second
    components.timeZone = timeZone
    self = Calendar.current.date(from: components)!
  }

  init(dateString: String) {
    let formatter = DateFormatter()
    formatter.dateFormat = "yyyy-MM-dd HH:mm:ss zz"
    self = formatter.date(from: dateString)!
  }

  var desc: String {
    get {
      let PREFERRED_LOCALE = "en_US" // Use whatever locale you prefer!
      return self.description(with: Locale(identifier: PREFERRED_LOCALE))
    }
  }

}


// The Stevenote where the original iPhone was announced took place
// on January 9, 2007 at 10:00 a.m. PST
let iPhoneStevenoteDate = Date(year: 2007,
                               month: 1,
                               day: 9,
                               hour: 10,
                               minute: 0,
                               second: 0,
                               timeZone: TimeZone(abbreviation: "PST")!)
print("iPhoneStevenoteDate: \(iPhoneStevenoteDate.desc)")

// The original iPhone went on sale on June 27, 2007
let iPhoneReleaseDate = Date(year: 2007, month: 6, day: 27) // June 27, 2007, 00:00:00 UTC
print("iPhoneReleaseDate: \(iPhoneReleaseDate.desc)")

// The Stevenote where the original iPad was announced took place
// on January 27, 2010 at 10:00 a.m. PST
let iPadStevenoteDate = Date(dateString: "2010-01-27 10:00:00 PST")
print("iPadStevenoteDate: \(iPadStevenoteDate.desc)")


// Overloading - so that we can use it to find the difference
// between two Dates
// ==========================================================

func -(_ lhs: Date, _ rhs: Date) -> DateComponents
{
  return Calendar.current.dateComponents(
    [.year, .month, .weekOfYear, .day, .hour, .minute, .second, .nanosecond],
    from: rhs,
    to: lhs)
}

// How long was it between the announcement of the original iPhone
// and its release in the stores?
let iPhoneWait = iPhoneReleaseDate - iPhoneStevenoteDate
print("The first iPhone users had to wait this long: ")
print("\(iPhoneWait.year!) years, " +
  "\(iPhoneWait.month!) months, " +
  "\(iPhoneWait.weekOfYear!) weeks, " +
  "\(iPhoneWait.day!) days, " +
  "\(iPhoneWait.hour!) hours, and " +
  "\(iPhoneWait.minute!) minutes.")

// How long ago was the first moon landing, which took place
// on July 20, 1969, 20:18 UTC?
let timeSinceMoonLanding = Date() - Date(dateString: "1969-07-20 20:18:00 UTC")
print("It’s been this long since the first moon landing: ")
print("\(timeSinceMoonLanding.year!) years, " +
  "\(timeSinceMoonLanding.month!) months, " +
  "\(timeSinceMoonLanding.weekOfYear!) weeks, " +
  "\(timeSinceMoonLanding.day!) days, " +
  "\(timeSinceMoonLanding.hour!) hours, and " +
  "\(timeSinceMoonLanding.minute!) minutes.")


// Extending Int to add some syntactic magic to date components
// ============================================================

extension Int {

  var second: DateComponents {
    var components = DateComponents()
    components.second = self;
    return components
  }

  var seconds: DateComponents {
    return self.second
  }

  var minute: DateComponents {
    var components = DateComponents()
    components.minute = self;
    return components
  }

  var minutes: DateComponents {
    return self.minute
  }

  var hour: DateComponents {
    var components = DateComponents()
    components.hour = self;
    return components
  }

  var hours: DateComponents {
    return self.hour
  }

  var day: DateComponents {
    var components = DateComponents()
    components.day = self;
    return components
  }

  var days: DateComponents {
    return self.day
  }

  var week: DateComponents {
    var components = DateComponents()
    components.weekOfYear = self;
    return components
  }

  var weeks: DateComponents {
    return self.week
  }

  var month: DateComponents {
    var components = DateComponents()
    components.month = self;
    return components
  }

  var months: DateComponents {
    return self.month
  }

  var year: DateComponents {
    var components = DateComponents()
    components.year = self;
    return components
  }

  var years: DateComponents {
    return self.year
  }

}


// A quick test of some future dates
print("One hour from now is: \((Date() + 1.hour).desc)")
print("One day from now is: \((Date() + 1.day).desc)")
print("One week from now is: \((Date() + 1.week).desc)")
print("One month from now is: \((Date() + 1.month).desc)")
print("One year from now is: \((Date() + 1.year).desc)")

// What was the date 10 years, 9 months, 8 days, 7 hours, and 6 minutes ago?
let aLittleWhileBack = Date() - 10.years - 9.months - 8.days - 7.hours - 6.minutes
print("10 years, 9 months, 8 days, 7 hours, and 6 minutes ago, it was: \(aLittleWhileBack.desc)")


// Extending DateComponents to add even more syntactic magic: fromNow and ago
// ==========================================================================

extension DateComponents {

  var fromNow: Date {
    return Calendar.current.date(byAdding: self,
                                 to: Date())!
  }

  var ago: Date {
    return Calendar.current.date(byAdding: -self,
                                 to: Date())!
  }

}

// We’re now in Serious Syntax Magic Land!
// ---------------------------------------

print("2.weeks.fromNow: \(2.weeks.fromNow.desc)")
print("3.months.fromNow: \(3.months.fromNow.desc)")

let futureDate3 = (2.months + 3.days + 4.hours + 5.minutes + 6.seconds).fromNow
print("futureDate3: \(futureDate3.desc)")

let pastDate2 = (2.months + 3.days + 4.hours + 5.minutes + 6.seconds).ago
print("pastDate2: \(pastDate2.desc)")

You can download the playground here (4KB, zipped Xcode playground file).

The How to work with dates and times in Swift 5 series

Here are the articles in this series:

• Part 1: Creating and deconstructing dates with the Date, Calendar, and DateComponents structs
• Part 2: Formatting and parsing dates and times with DateFormatter
• Part 3: Date arithmetic
• Part 4: Adding Swift syntactic magic

What we’ve covered so far, and what we’ll cover in this installment

So far, in this series on programming with dates and times in Swift 5, we’ve looked at:

• The basic structs, which let us create dates and times, and work with their components. They are:
  • Date, which represents a single point in time,
  • DateComponents, which represents the units that make up a date, such as year, month, day, hour, and minute, and which can be used to represent either a single point in time or a duration of time, and
  • Calendar, which provides a context for Dates, and allows us to convert between Dates and DateComponents.
• The DateFormatter class, which converts Dates into formatted Strings, and formatted Strings into Dates.

With this knowledge under our belts, let’s get to this article’s topic: doing date calculations.

Creating a couple of Dates to work with

Let’s create a couple of Dates to work with:

• The date and time of the Stevenote where the iPhone was introduced: January 9, 2007, 10:00 a.m. Pacific time (UTC-8), and
• The date and time of the Stevenote where the iPad was introduced: January 27, 2010, 10:00 a.m. Pacific time (UTC-8).

Start with a fresh playground, and paste or enter the following code into it:

// The user's calendar incorporates the user's locale and
// time zone settings, which means it's the one you'll use
// most often.
let userCalendar = Calendar.current

// Let's create a Date for the start of the Stevenote
// where the iPhone was introduced (January 9, 2007, 10:00:00 Pacific time)
// using DateComponents.
let iPhoneStevenoteDateComponents = DateComponents(
  timeZone: TimeZone(abbreviation: "PST"),
  year: 2007,
  month: 1,
  day: 9,
  hour: 10
)
let iPhoneStevenoteDate = userCalendar.date(from: iPhoneStevenoteDateComponents)!

// Let's create a Date for the start of the Stevenote
// where the iPad was introduced (January 27, 2010, 10:00:00 Pacific time)
// using DateFormatter.
var dateMakerFormatter = DateFormatter()
dateMakerFormatter.calendar = userCalendar
dateMakerFormatter.dateFormat = "MMM d, yyyy, hh:mm a zz"
let iPadStevenoteDate = dateMakerFormatter.date(from: "Jan 27, 2010, 10:00 AM PST")!

In the code above, we’ve created our dates in two different ways:

• We created iPhoneStevenoteDate by setting up a DateComponents struct and then using the user’s Calendar to convert those DateComponents into a Date.
• We created iPadStevenoteDate by converting its String representation into a Date using a DateFormatter.

Date comparisons, part 1

Now that we have two Dates, let’s compare them. In Swift 5, we can use familiar comparison operators — <, <=, ==, !=, >, >== — to tell which Date came first, or if they represent the exact (and I do mean exact) same point in time.

Add the following code to the playground and run it:

print("Did the iPhone Stevenote come BEFORE the iPad Stevenote? " +
      "\(iPhoneStevenoteDate < iPadStevenoteDate)")

print("Did the iPhone Stevenote come AFTER the iPad Stevenote? " +
      "\(iPhoneStevenoteDate > iPadStevenoteDate)")

print("Did the iPad Stevenote come BEFORE the iPhone Stevenote? " +
      "\(iPadStevenoteDate < iPhoneStevenoteDate)")

print("Does the iPad Stevenote come AFTER the iPhone Stevenote? " +
      "\(iPadStevenoteDate > iPhoneStevenoteDate)")

print("Do the iPhone Stevenote and the iPad Stevenote fall on the EXACT SAME date and time? " +
      "\(iPhoneStevenoteDate == iPadStevenoteDate)")

print("Do the iPhone Stevenote and the iPad Stevenote fall on different dates and times? " +
      "\(iPhoneStevenoteDate != iPadStevenoteDate)")

The output should be:

Did the iPhone Stevenote come BEFORE the iPad Stevenote? true
Did the iPhone Stevenote come AFTER the iPad Stevenote? false
Did the iPad Stevenote come BEFORE the iPhone Stevenote? false
Does the iPad Stevenote come AFTER the iPhone Stevenote? true
Do the iPhone Stevenote and the iPad Stevenote fall on the EXACT SAME date and time? false
Do the iPhone Stevenote and the iPad Stevenote fall on different dates and times? true

Note that these are comparisons of Dates, which measure time down to the nearest nanosecond. If you compare two Dates named date1 and date2, where date2 represents a point in time one nanosecond after date1, they will not be equal; date2 will be greater than date1.

A little later on in this article, we’ll look at more “human” ways of comparing Dates.

How far apart are the iPhone and iPad Stevenotes, part 1: In seconds, using Date’s timeIntervalSince() method

Date‘s timeIntervalSince method can give us the difference between two dates and times — in seconds.

Add the following code to the playground and run it:

print("Number of seconds between the iPhone Stevenote and the iPad Stevenote: " +
      "\(iPhoneStevenoteDate.timeIntervalSince(iPadStevenoteDate))")

print("Number of seconds between the iPad Stevenote and the iPhone Stevenote: " +
      "\(iPadStevenoteDate.timeIntervalSince(iPhoneStevenoteDate))")

The output should be:

Number of seconds between the iPhone Stevenote and the iPad Stevenote: -96249600.0
Number of seconds between the iPad Stevenote and the iPhone Stevenote: 96249600.0

The results tell us that there were 96,248,600 seconds between the iPhone Stevenote and the iPad Stevenote.

While there are cases when you’ll want to know how many seconds there are between two given points in time, there are also many cases where you’ll want to find the differences between two points in time using other units, such as days, weeks, months, and years, not to mention hours and minutes. Date‘s timeIntervalSince method isn’t going to work for these cases.

How far apart are the iPhone and iPad Stevenotes, part 2: In days, using Calendar’s dateComponents(_:from:to:) method

Most of the time, when you are calculating how far apart two given Dates are, you’ll be using this method of the Calendar struct:

dateComponents(components, from: startDate, to: endDate)

Here’s a run-down of its parameters:

Let’s use dateComponents(_:from:to:) to find out how many days there were between the iPhone Stevenote and the iPad Stevenote.

Add the following code to the playground and run it:

let daysBetweenStevenotes = userCalendar.dateComponents([.day],
                                                        from: iPhoneStevenoteDate,
                                                        to: iPadStevenoteDate)
print("There were \(daysBetweenStevenotes.day!) days between the iPhone Stevenote of 2007 and the iPad Stevenote of 2010.")

The output should be:

There were 1114 days between the iPhone Stevenote of 2007 and the iPad Stevenote of 2010.

In the code above, we passed dateComponents(_:from:to:) three values:

• An array containing the Calendar.Component value .day, which specifies that we want the result expressed as the difference between iPadStevenoteDate and iPhoneStevenoteDate in terms of days.
• The two dates in question, iPhoneStevenoteDate and iPadStevenoteDate.

As the result tells us, there were 1,114 days between the iPhone Stevenote and the iPad Stevenote.

How far apart are the iPhone and iPad Stevenotes, part 3: In weeks

By changing the contents of the array of Calendar.Component values that we provide in the first argument of Calendar’s dateComponents(_:from:to:) method, we can get the result expressed in different time units.

Add the following code to the playground and run it:

let weeksBetweenStevenotes = userCalendar.dateComponents([.weekOfYear],
                                                         from: iPhoneStevenoteDate,
                                                         to: iPadStevenoteDate)
print("There were \(weeksBetweenStevenotes.weekOfYear!) weeks between the iPhone Stevenote of 2007 and the iPad Stevenote of 2010.")

The output should be:

There were 159 weeks between the iPhone Stevenote of 2007 and the iPad Stevenote of 2010.

In the code above, we passed dateComponents(_:from:to:) three values:

• An array containing the Calendar.Component value .weekOfYear, which specifies that we want the result expressed as the difference between iPadStevenoteDate and iPhoneStevenoteDate in terms of the numbered weeks of the year on which both dates fall. For example, if event1 took place on week 2 of a year and event2 took place on week 5, the difference between the two in .weekOfYear terms would be 3.
• The two dates in question, iPhoneStevenoteDate and iPadStevenoteDate.

The result indicates that 159 weeks passed between the iPhone Stevenote and the iPad Stevenote.

If you do the math, 159 times 7 days is 1,113 days, but our previous calculation said that the iPhone Stevenote and the iPad Stevenote were 1,114 days apart. That’s because the two events are 159 whole weeks apart, plus an extra day.

How far apart are the iPhone and iPad Stevenotes, part 4: In years, months, and days

We can also put multiple values of Calendar.Component into the array that we provide as the first argument of Calendar’s dateComponents(_:from:to:) method.

Add the following code to the playground and run it:

let yearsMonthsDaysHoursMinutesBetweenStevenotes = userCalendar.dateComponents(
  [.year, .month, .day, .hour, .minute],
  from: iPhoneStevenoteDate,
  to: iPadStevenoteDate
)
let years = yearsMonthsDaysHoursMinutesBetweenStevenotes.year!
let months = yearsMonthsDaysHoursMinutesBetweenStevenotes.month!
let days = yearsMonthsDaysHoursMinutesBetweenStevenotes.day!
let hours = yearsMonthsDaysHoursMinutesBetweenStevenotes.hour!
let minutes = yearsMonthsDaysHoursMinutesBetweenStevenotes.minute!
print("There were \(years) years, \(months) months, \(days) days, \(hours) hours, and \(minutes) minutes between the the iPhone Stevenote of 2007 and the iPad Stevenote of 2010.")

In the code above, we passed dateComponents(_:from:to:) three values:

• An array containing the Calendar.Component values .year, .month, .day, .hour, .minute, which specifies that we want the result expressed as the difference between iPadStevenoteDate and iPhoneStevenoteDate in terms of years, months, days, hours, and minutes. The method uses the largest applicable component before using smaller ones — for example, it will give results like 1 month and 5 days rather than 35 days.
• The two dates in question, iPhoneStevenoteDate and iPadStevenoteDate.

The results show that the iPhone Stevenote and the iPad Stevenote were 3 years and 18 days apart.

Date addition, part 1: What’s the last day of a 90-day warranty that starts today?

Now that we know how to answer the question “What’s the difference in time between two Dates?”, let’s try answering a different question: “If we add a time interval to a Date, what’s the resulting Date?”

To answer this question, we’ll use this method of Calendar:

date(byAdding: timeInterval, value: numberOfTimeUnits to: startDate)

Here’s a run-down of its parameters:

Let’s start with a simple bit of code that tells us the last day of a 90-day warranty whose term starts right now:

// What's the last day of a 90-day warranty that starts today?
let lastDay = userCalendar.date(byAdding: .day, value: 90, to: Date())!
print("90 days from now is: \(lastDay.description(with: Locale(identifier: "en_US")))")

The result is a Date representing a point in time 90 days from the present. On my computer, the output looked like this:

90 days from now is: Optional(“Tuesday, August 25, 2020 at 10:30:46 PM Eastern Daylight Time”)

Date addition, part 2: What was the date 5 weeks ago?

Just as we can convert addition to subtraction by adding a negative value, we can also do Date subtraction by providing date(byAdding:value:to:) with negative values. Here’s an example of code that returns a date that is an interval of time prior to the date in question:

// What was the date 5 weeks ago?
let fiveWeeksAgo = userCalendar.date(byAdding: .weekOfYear, value: -5, to: Date())!
print("5 weeks ago was: \(fiveWeeksAgo.description(with: Locale(identifier: "en_US")))")

The result is a Date representing a point in time 5 weeks in the past. On my computer, the output looked like this:

5 weeks ago was: Wednesday, April 22, 2020 at 11:12:40 PM Eastern Daylight Time

Date addition, part 3: What time will it be 4 hours and 30 minutes from now, and 4 hours and 30 minutes ago?

The date(byAdding:value:to:) method works when you just want to add one kind of time unit — a minute, hour, day, week, month, or year — to a Date. If you want to add multiple kinds of time units to a Date, such as 4 hours and 30 minutes, you need to use this Calendar method instead:

date(byAdding: timeIntervalComponents, to: startDate)

Here’s a run-down of its parameters:

Here’s the code that answers the question “What time will it be 4 hours and 30 minutes from now?”

// What time will it be 4 hours and 30 minutes from now?
// First, we need to define a DateComponents struct representing
// a time interval of 4 hours and 30 minutes
var fourHoursThirtyMinutes = DateComponents()
fourHoursThirtyMinutes.hour = 4
fourHoursThirtyMinutes.minute = 30

// Now add the interval to the Date
let fourHoursThirtyMinutesFromNow = userCalendar.date(
  byAdding: fourHoursThirtyMinutes,
  to: Date()
)!
print("4 hours and 30 minutes from now will be: \(fourHoursThirtyMinutesFromNow.description(with: Locale(identifier: "en_US")))")

// What time was it 4 hours and 30 minutes ago?
var minusFourHoursThirtyMinutes = DateComponents()
minusFourHoursThirtyMinutes.hour = -4
minusFourHoursThirtyMinutes.minute = -30
let fourHoursThirtyMinutesAgo = userCalendar.date(
  byAdding: fourHoursThirtyMinutes,
  to: Date()
)!
print("4 hours and 30 minutes ago was: \(fourHoursThirtyMinutesAgo.description(with: Locale(identifier: "en_US")))")

// Let's define some Dates relative to the SwiftUI announcement
// (June 3, 2019, 12:08 p.m. PDT)
let swiftUIAnnouncementDateComponents = DateComponents(
  timeZone: TimeZone(abbreviation: "PDT"),
  year: 2019,
  month: 6,
  day: 3,
  hour: 12,
  minute: 8
)
let swiftUIAnnouncement = userCalendar.date(from: swiftUIAnnouncementDateComponents)!

let swiftUIAnnouncementPlusOneSecond = userCalendar.date(
  byAdding: .second,
  value: 1,
  to: swiftUIAnnouncement
)!
let swiftUIAnnouncementPlusFiveMinutes = userCalendar.date(
  byAdding: .minute,
  value: 5,
  to: swiftUIAnnouncement
)!
let swiftUIAnnouncementPlusThreeHours = userCalendar.date(
  byAdding: .hour,
  value: 3,
  to: swiftUIAnnouncement
)!

// This returns false, because when measuring time at the granularity of a SECOND,
// swiftUIAnnouncement happens BEFORE swiftUIAnnouncementPlusOneSecond.
let test1 = userCalendar.compare(swiftUIAnnouncement,
                                 to: swiftUIAnnouncementPlusOneSecond,
                                 toGranularity: .second)
  == .orderedSame
print("test1: \(test1)")

// This returns true, because when measuring time at the granularity of a SECOND,
// swiftUIAnnouncement happens BEFORE swiftUIAnnouncementPlusOneSecond.
let test2 = userCalendar.compare(swiftUIAnnouncement,
                                 to: swiftUIAnnouncementPlusOneSecond,
                                 toGranularity: .second)
  == .orderedAscending
print("test2: \(test2)")

// This returns true, because when measuring time at the granularity of a MINUTE,
// swiftUIAnnouncement happens AT THE SAME TIME AS swiftUIAnnouncementPlusOneSecond.
let test3 = userCalendar.compare(swiftUIAnnouncement,
                                 to: swiftUIAnnouncementPlusOneSecond,
                                 toGranularity: .minute)
  == .orderedSame
print("test3: \(test3)")

// This returns true, because when measuring time at the granularity of an HOUR,
// swiftUIAnnouncement happens AT THE SAME TIME AS swiftUIAnnouncementPlusFiveMinutes.
let test4 = userCalendar.compare(swiftUIAnnouncement,
                                 to: swiftUIAnnouncementPlusFiveMinutes,
                                 toGranularity: .hour)
  == .orderedSame
print("test4: \(test4)")

// This returns true, because when measuring time at the granularity of a MINUTE,
// swiftUIAnnouncementPlusFiveMinutes happens AFTER swiftUIAnnouncement.
let test5 = userCalendar.compare(swiftUIAnnouncementPlusFiveMinutes,
                                 to: swiftUIAnnouncement,
                                 toGranularity: .minute)
  == .orderedDescending
print("test5: \(test5)")

// This returns true, because when measuring time at the granularity of a DAY,
// swiftUIAnnouncement happens AT THE SAME TIME AS swiftUIAnnouncementPlusThreeHours.
let test6 = userCalendar.compare(swiftUIAnnouncement,
                                 to: swiftUIAnnouncementPlusThreeHours,
                                 toGranularity: .day)
  == .orderedSame
print("test6: \(test6)")

import UIKit


// Creating a couple of Dates to work with
// =======================================

// The user's calendar incorporates the user's locale and
// time zone settings, which means it's the one you'll use
// most often.
let userCalendar = Calendar.current

// Let's create a Date for the start of the Stevenote
// where the iPhone was introduced (January 9, 2007, 10:00:00 Pacific time)
// using DateComponents.
let iPhoneStevenoteDateComponents = DateComponents(
  timeZone: TimeZone(abbreviation: "PST"),
  year: 2007,
  month: 1,
  day: 9,
  hour: 10
)
let iPhoneStevenoteDate = userCalendar.date(from: iPhoneStevenoteDateComponents)!


// Date comparisons, part 1
// ========================

// Let's create a Date for the start of the Stevenote
// where the iPad was introduced (January 27, 2010, 10:00:00 Pacific time)
// using DateFormatter.
var dateMakerFormatter = DateFormatter()
dateMakerFormatter.calendar = userCalendar
dateMakerFormatter.dateFormat = "MMM d, yyyy, hh:mm a zz"
let iPadStevenoteDate = dateMakerFormatter.date(from: "Jan 27, 2010, 10:00 AM PST")!


print("Did the iPhone Stevenote come BEFORE the iPad Stevenote? " +
      "\(iPhoneStevenoteDate < iPadStevenoteDate)")

print("Did the iPhone Stevenote come AFTER the iPad Stevenote? " +
      "\(iPhoneStevenoteDate > iPadStevenoteDate)")

print("Did the iPad Stevenote come BEFORE the iPhone Stevenote? " +
      "\(iPadStevenoteDate < iPhoneStevenoteDate)")

print("Does the iPad Stevenote come AFTER the iPhone Stevenote? " +
      "\(iPadStevenoteDate > iPhoneStevenoteDate)")

print("Do the iPhone Stevenote and the iPad Stevenote fall on the EXACT SAME date and time? " +
      "\(iPhoneStevenoteDate == iPadStevenoteDate)")

print("Do the iPhone Stevenote and the iPad Stevenote fall on different dates and times? " +
      "\(iPhoneStevenoteDate != iPadStevenoteDate)")


// How far apart are the iPhone and iPad Stevenotes, part 1: In seconds,
// using Date’s timeIntervalSince() method
// =====================================================================

print("Number of seconds between the iPhone Stevenote and the iPad Stevenote: " +
      "\(iPhoneStevenoteDate.timeIntervalSince(iPadStevenoteDate))")

print("Number of seconds between the iPad Stevenote and the iPhone Stevenote: " +
      "\(iPadStevenoteDate.timeIntervalSince(iPhoneStevenoteDate))")


// How far apart are the iPhone and iPad Stevenotes, part 2:
// In days, using Calendar’s dateComponents(_:from:to:) method
// ===========================================================

let daysBetweenStevenotes = userCalendar.dateComponents([.day],
                                                        from: iPhoneStevenoteDate,
                                                        to: iPadStevenoteDate)
print("There were \(daysBetweenStevenotes.day!) days between the iPhone Stevenote of 2007 and the iPad Stevenote of 2010.")


// How far apart are the iPhone and iPad Stevenotes, part 3: In weeks
// ==================================================================

let weeksBetweenStevenotes = userCalendar.dateComponents([.weekOfYear],
                                                         from: iPhoneStevenoteDate,
                                                         to: iPadStevenoteDate)
print("There were \(weeksBetweenStevenotes.weekOfYear!) weeks between the iPhone Stevenote of 2007 and the iPad Stevenote of 2010.")


// How far apart are the iPhone and iPad Stevenotes, part 4:
// In years, months, and days
// =========================================================

let yearsMonthsDaysHoursMinutesBetweenStevenotes = userCalendar.dateComponents(
  [.year, .month, .day, .hour, .minute],
  from: iPhoneStevenoteDate,
  to: iPadStevenoteDate
)
let years = yearsMonthsDaysHoursMinutesBetweenStevenotes.year!
let months = yearsMonthsDaysHoursMinutesBetweenStevenotes.month!
let days = yearsMonthsDaysHoursMinutesBetweenStevenotes.day!
let hours = yearsMonthsDaysHoursMinutesBetweenStevenotes.hour!
let minutes = yearsMonthsDaysHoursMinutesBetweenStevenotes.minute!
print("There were \(years) years, \(months) months, \(days) days, \(hours) hours, and \(minutes) minutes between the the iPhone Stevenote of 2007 and the iPad Stevenote of 2010.")


// Date addition, part 1:
// What’s the last day of a 90-day warranty that starts today?
// ===========================================================

let lastDay = userCalendar.date(byAdding: .day, value: 90, to: Date())!
print("90 days from now is: \(lastDay.description(with: Locale(identifier: "en_US")))")


// Date addition, part 2: What was the date 5 weeks ago?
// =====================================================
let fiveWeeksAgo = userCalendar.date(byAdding: .weekOfYear, value: -5, to: Date())!
print("5 weeks ago was: \(fiveWeeksAgo.description(with: Locale(identifier: "en_US")))")


// Date addition, part 3:
// What time will it be 4 hours and 30 minutes from now, and
// 4 hours and 30 minutes ago?
// =========================================================

// What time will it be 4 hours and 30 minutes from now?
// First, we need to define a DateComponents struct representing
// a time interval of 4 hours and 30 minutes
var fourHoursThirtyMinutes = DateComponents()
fourHoursThirtyMinutes.hour = 4
fourHoursThirtyMinutes.minute = 30

// Now add the interval to the Date
let fourHoursThirtyMinutesFromNow = userCalendar.date(
  byAdding: fourHoursThirtyMinutes,
  to: Date()
)!
print("4 hours and 30 minutes from now will be: \(fourHoursThirtyMinutesFromNow.description(with: Locale(identifier: "en_US")))")

// What time was it 4 hours and 30 minutes ago?
var minusFourHoursThirtyMinutes = DateComponents()
minusFourHoursThirtyMinutes.hour = -4
minusFourHoursThirtyMinutes.minute = -30
let fourHoursThirtyMinutesAgo = userCalendar.date(
  byAdding: fourHoursThirtyMinutes,
  to: Date()
)!
print("4 hours and 30 minutes ago was: \(fourHoursThirtyMinutesAgo.description(with: Locale(identifier: "en_US")))")


// Date comparisons, part 2: Making Date comparisons a little more “human”
// =======================================================================

// Let's define some Dates relative to the SwiftUI announcement
// (June 3, 2019, 12:08 p.m. PDT)
let swiftUIAnnouncementDateComponents = DateComponents(
  timeZone: TimeZone(abbreviation: "PDT"),
  year: 2019,
  month: 6,
  day: 3,
  hour: 12,
  minute: 8
)
let swiftUIAnnouncement = userCalendar.date(from: swiftUIAnnouncementDateComponents)!

let swiftUIAnnouncementPlusOneSecond = userCalendar.date(
  byAdding: .second,
  value: 1,
  to: swiftUIAnnouncement
)!
let swiftUIAnnouncementPlusFiveMinutes = userCalendar.date(
  byAdding: .minute,
  value: 5,
  to: swiftUIAnnouncement
)!
let swiftUIAnnouncementPlusThreeHours = userCalendar.date(
  byAdding: .hour,
  value: 3,
  to: swiftUIAnnouncement
)!

// This returns false, because when measuring time at the granularity of a SECOND,
// swiftUIAnnouncement happens BEFORE swiftUIAnnouncementPlusOneSecond.
let test1 = userCalendar.compare(swiftUIAnnouncement,
                                 to: swiftUIAnnouncementPlusOneSecond,
                                 toGranularity: .second)
  == .orderedSame
print("test1: \(test1)")

// This returns true, because when measuring time at the granularity of a SECOND,
// swiftUIAnnouncement happens BEFORE swiftUIAnnouncementPlusOneSecond.
let test2 = userCalendar.compare(swiftUIAnnouncement,
                                 to: swiftUIAnnouncementPlusOneSecond,
                                 toGranularity: .second)
  == .orderedAscending
print("test2: \(test2)")

// This returns true, because when measuring time at the granularity of a MINUTE,
// swiftUIAnnouncement happens AT THE SAME TIME AS swiftUIAnnouncementPlusOneSecond.
let test3 = userCalendar.compare(swiftUIAnnouncement,
                                 to: swiftUIAnnouncementPlusOneSecond,
                                 toGranularity: .minute)
  == .orderedSame
print("test3: \(test3)")

// This returns true, because when measuring time at the granularity of an HOUR,
// swiftUIAnnouncement happens AT THE SAME TIME AS swiftUIAnnouncementPlusFiveMinutes.
let test4 = userCalendar.compare(swiftUIAnnouncement,
                                 to: swiftUIAnnouncementPlusFiveMinutes,
                                 toGranularity: .hour)
  == .orderedSame
print("test4: \(test4)")

// This returns true, because when measuring time at the granularity of a MINUTE,
// swiftUIAnnouncementPlusFiveMinutes happens AFTER swiftUIAnnouncement.
let test5 = userCalendar.compare(swiftUIAnnouncementPlusFiveMinutes,
                                 to: swiftUIAnnouncement,
                                 toGranularity: .minute)
  == .orderedDescending
print("test5: \(test5)")

// This returns true, because when measuring time at the granularity of a DAY,
// swiftUIAnnouncement happens AT THE SAME TIME AS swiftUIAnnouncementPlusThreeHours.
let test6 = userCalendar.compare(swiftUIAnnouncement,
                                 to: swiftUIAnnouncementPlusThreeHours,
                                 toGranularity: .day)
  == .orderedSame
print("test6: \(test6)")