operation with hours using swift, sum and difference - swift

Question

On my project I need to work with hours and min.
I can't find to much info online.
here my issue:
let time1 = "22:00"
let time2 = "20:00"
Question 1:
how do I subtract the time1 - time2 ?
I'm expecting result = 02:00 h
i start writing some code, converting this time to date..
let formatter = DateFormatter()
formatter.dateFormat = "HH:mm"
var time1d = formatter.date(from: time1)!
let time2d = formatter.date(from: time2)!
but now how do I subtract this two hours?
Question 2:
let time1 = "22:00"
let time2 = "20:00"
How do i sum time1 + time2 ? for example should give me result 42:00 hours
thanks for the help

Answer 1

This is not a Date. If you are only gonna work with hours and minutes and the input will always be a string properly formatted you should struct your data.
Create a Time structure
struct Time {
let hour: Int
let minute: Int
}
And a custom initializer. This assumes your string is always properly formatted 00:00:
extension Time {
init?(string: String) {
guard string.count == 5,
Array(string)[2] == ":",
let hour = Int(string.prefix(2)),
let minute = Int(string.suffix(2)),
0...59 ~= minute else {
return nil
}
self.hour = hour
self.minute = minute
}
}
For displaying your Time struct property you can conform it to CustomStringConvertible and provide a custom description
extension Time: CustomStringConvertible {
var description: String {
String(format: "%02d:%02d", hour, minute)
}
}
Regarding adding and subtracting you can make your Time struct conform to AdditiveArithmetic and implement the required operators:
extension Time: AdditiveArithmetic {
static func - (lhs: Time, rhs: Time) -> Time {
let minutes = lhs.minute - rhs.minute + lhs.hour * 60 - rhs.hour * 60
return .init(hour: minutes/60, minute: minutes%60)
}
static func + (lhs: Time, rhs: Time) -> Time {
let minutes = lhs.minute + rhs.minute + lhs.hour * 60 + rhs.hour * 60
return .init(hour: minutes/60, minute: minutes%60)
}
static var zero: Time { .init(hour: 0, minute: 0) }
}
Playground testing:
let time1 = Time(string: "22:00")!
let time2 = Time(string: "20:00")!
let time3 = time1-time2
print(time3)
let time4 = time1+time2
print(time4)
Those will print
02:00
42:00

Answer 2

First we create the calculateDifference function which uses dateComponents function provided by Swift.
let time1 = "22:00"
let time2 = "20:00"
func formattedTime(_ time: String) -> Date? {
let formatter = DateFormatter()
formatter.locale = Locale(identifier: "en_US_POSIX")
formatter.dateFormat = "HH:mm"
return formatter.date(from: time)
}
func calculateDifference(_ from: String, _ to: String) -> (hour: Int, minutes: Int) {
guard let fromTime = formattedTime(from),
let toTime = formattedTime(to) else {
return (0,0)
}
let calendar = Calendar.current
let components = calendar.dateComponents([.hour, .minute], from: fromTime, to: toTime)
return (components.hour ?? 0, components.minute ?? 0)
}
Then we create the calculateSum which uses the calculateDifference internally to get the hours by supplying the default hour as 00:00
func calculateSum(_ time1: String, _ time2: String) -> (hour: Int, minutes: Int) {
let defaultTime = "00:00"
let calculatedTime1 = calculateDifference(defaultTime, time1)
let calcaultedTime2 = calculateDifference(defaultTime, time2)
return(calculatedTime1.hour + calcaultedTime2.hour,
calculatedTime1.minutes + calcaultedTime2.minutes)
}
Now if we run the below, we get the required results. Of course, some formatting will be required.
let difference = calculateDifference(time2, time1)
print("\(difference.hour):\(difference.minutes)")
let sum = calculateSum(time1, time2)
print("\(sum.hour):\(sum.minutes)")