Date+ISO8601.swift

//
//  Date+ISO8601.swift
//  Created by Christopher Fuller for Southern California Public Radio
//  Original version at https://github.com/SCPR/swift-experiments/blob/master/source/NSDateExtension.swift
//  Updated by Christopher Fuller for Swift 3 compatibility
//
//  Copyright (c) 2016 Southern California Public Radio
//
//  Permission is hereby granted, free of charge, to any person obtaining a copy
//  of this software and associated documentation files (the "Software"), to deal
//  in the Software without restriction, including without limitation the rights
//  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
//  copies of the Software, and to permit persons to whom the Software is
//  furnished to do so, subject to the following conditions:
//
//  The above copyright notice and this permission notice shall be included in all
//  copies or substantial portions of the Software.
//
//  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
//  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
//  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
//  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
//  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
//  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
//  SOFTWARE.
//

extension Date {

    private static let stringFromDateFormatter = Date.dateFormatter(
        timeZone: TimeZone(secondsFromGMT: 0)
    )

    private static let dateFromStringFormatter = Date.dateFormatter(
        timeZone: TimeZone.autoupdatingCurrent
    )

    private static func dateFormatter(timeZone: TimeZone?) -> DateFormatter {
        let dateFormatter = DateFormatter()
        dateFormatter.timeZone = timeZone
        dateFormatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ss.SSSZZZZZ"
        dateFormatter.locale = Locale(identifier: "en_US_POSIX")
        return dateFormatter
    }

    var ISO8601String: String {
        return Date.stringFromDateFormatter.string(from: self)
    }

    init?(ISO8601String string: String) {
        guard let date = Date.dateFromStringFormatter.date(from: string) else {
            return nil
        }
        self.init(timeInterval: 0, since: date)
    }

}

Example Usage

Convert String to Date

Supports ISO8601 formats including, but not limited to, these examples:

let _ = Date(ISO8601String: "2016-10-25T01:00:00.000Z")      // => Optional(2016-10-25 01:00:00 +0000)
let _ = Date(ISO8601String: "2016-10-25T01:00:00.000-00:00") // => Optional(2016-10-25 01:00:00 +0000)

Supports time zones:

let _ = Date(ISO8601String: "2016-10-25T01:00:00.000-07:00") // => Optional(2016-10-25 08:00:00 +0000)

Convert Date to String

Outputs GMT format:

let date = Date(timeIntervalSince1970: 1477382400)
let _ = date.ISO8601String // => "2016-10-25T08:00:00.000Z"