How to parse an ISO-8601 duration in Objective C?

Question

I\'m looking for an easy way to parse a string that contains an ISO-8601 duration in Objective C. The result should be something usable like a NSTimeI

Answer 1

Now in Swift! (Yes it's a little long, but it handles all cases and singular/plural).

Handles Years, Months, Weeks, Days, Hours, Minutes, and Seconds!

func convertFromISO8601Duration(isoValue: AnyObject) -> String? {

    var displayedString: String?
    var hasHitTimeSection = false
    var isSingular = false

    if let isoString = isoValue as? String {

        displayedString = String()

        for val in isoString {


            if val == "P" {
                // Do nothing when parsing the 'P'
                continue

            }else if val == "T" {
                // Indicate that we are now dealing with the 'time section' of the ISO8601 duration, then carry on.
                hasHitTimeSection = true
                continue
            }

            var tempString = String()

            if val >= "0" && val <= "9" {

                // We need to know whether or not the value is singular ('1') or not ('11', '23').
                if let safeDisplayedString = displayedString as String!
                    where count(displayedString!) > 0 && val == "1" {

                    let lastIndex = count(safeDisplayedString) - 1

                    let lastChar = safeDisplayedString[advance(safeDisplayedString.startIndex, lastIndex)]

                        //test if the current last char in the displayed string is a space (" "). If it is then we will say it's singular until proven otherwise.
                    if lastChar == " " {
                        isSingular = true
                    } else {
                        isSingular = false
                    }
                }
                else if val == "1" {
                    // if we are just dealing with a '1' then we will say it's singular until proven otherwise.
                    isSingular = true
                }
                else {
                    // ...otherwise it's a plural duration.
                    isSingular = false
                }

                tempString += "\(val)"

                displayedString! += tempString

            } else {

                // handle the duration type text. Make sure to use Months & Minutes correctly.
                switch val {

                case "Y", "y":

                    if isSingular {
                        tempString += " Year "
                    } else {
                        tempString += " Years "
                    }

                    break

                case "M", "m":

                    if hasHitTimeSection {

                        if isSingular {
                            tempString += " Minute "
                        } else {
                            tempString += " Minutes "
                        }
                    }
                    else {

                        if isSingular {
                            tempString += " Month "
                        } else {
                            tempString += " Months "
                        }
                    }

                    break

                case "W", "w":

                    if isSingular {
                        tempString += " Week "
                    } else {
                        tempString += " Weeks "
                    }

                    break

                case "D", "d":

                    if isSingular {
                        tempString += " Day "
                    } else {
                        tempString += " Days "
                    }

                    break

                case "H", "h":

                    if isSingular {
                        tempString += " Hour "
                    } else {
                        tempString += " Hours "
                    }

                    break

                case "S", "s":

                    if isSingular {
                        tempString += " Second "
                    } else {
                        tempString += " Seconds "
                    }

                    break

                default:
                    break

                }

                // reset our singular flag, since we're starting a new duration.
                isSingular = false

                displayedString! += tempString

            }

        }

    }

    return displayedString
}