Calculate time difference from Int in Swift - swift

Question

I need to calculate the difference between two Int and format it to show hours, minutes. I can the function below to partially apart from the initial int difference.
Example: If i have a start Int of 0811 and then an end Int of 0912 the difference is 101. If I then take 12 from the result I should have 91. When I use the result to convert to time it returns 1 hour and 31 mins - which is correct. However I need to somehow convert it further up the chain and then take it off to format the time correctly. This should mean the 101 should be 1 hour 1 minute.
func calculateTimeDifference(start: Int, end: Int, longVersion: Bool) -> String {
let count = end - start
let total = minutesToHoursMinutes(minutes: count)
var formatted = ""
if total.hours != 0 {
formatted += "\(total.hours)"
let amount = total.hours > 1 ? " hours " : " hour "
formatted += amount
}
if total.leftMinutes != 0 {
formatted += "\(total.leftMinutes)"
let amount = total.leftMinutes > 1 ? " minutes " : " minute "
formatted += amount
}
return String(describing: formatted)
}
func minutesToHoursMinutes(minutes : Int) -> (hours : Int, leftMinutes : Int) {
return (minutes / 60, (minutes % 60))
}

Answer 1

You shouldn't calculate the difference between two times expressed in Ints by subtracting them. Use the proper Date API.
Here, I converted the Ints to strings first and then parsed them using a date formatter. After that timeIntervalSince can tell you the difference in seconds. You just need some modulus and division to get the hours and minutes from that:
func calculateTimeDifference(start: Int, end: Int) -> String {
let formatter = DateFormatter()
formatter.dateFormat = "HHmm"
var startString = "\(start)"
if startString.characters.count < 4 {
for _ in 0..<(4 - startString.characters.count) {
startString = "0" + startString
}
}
var endString = "\(end)"
if endString.characters.count < 4 {
for _ in 0..<(4 - endString.characters.count) {
endString = "0" + endString
}
}
let startDate = formatter.date(from: startString)!
let endDate = formatter.date(from: endString)!
let difference = endDate.timeIntervalSince(startDate)
return "\(Int(difference) / 3600)Hr \(Int(difference) % 3600 / 60)Min"
}

Answer 2

Inherintly you are approaching this from a strange angle and causing yourself issues.
Instead of Int, which is inappropriate for storing a time, use TimeInterval which can hold a full date information, e.g.:
let second:TimeInterval = 1.0
let minute:TimeInterval = 60.0
let hour:TimeInterval = 60.0 * minute
let day:TimeInterval = 24 * hour
Then when you want to determine the time difference between two times it's very basic arithmetic.

Answer 3

SWIFT 4
In Swift 4 characters is deprecated, so Sweepers solution in Swift 4 is
func calculateTimeDifference(start: Int, end: Int) -> String {
let formatter = DateFormatter()
formatter.dateFormat = "HHmm"
var startString = "\(start)"
if startString.count < 4 {
for _ in 0..<(4 - startString.count) {
startString = "0" + startString
}
}
var endString = "\(end)"
if endString.count < 4 {
for _ in 0..<(4 - endString.count) {
endString = "0" + endString
}
}
let startDate = formatter.date(from: startString)!
let endDate = formatter.date(from: endString)!
let difference = endDate.timeIntervalSince(startDate)
return "\(Int(difference) / 3600)Hr \(Int(difference) % 3600 / 60)Min"
}