Using Date in Swift, using ISO8601DateFormatter() and DateFormatter()

Date.swift

// Date extension
extension Date {
  static func getStringFromDate(date: Date) -> String {
    let dateFormatter = DateFormatter()
    dateFormatter.dateFormat = "EEEE, MMM d, yyyy"
    let dateString = dateFormatter.string(from: date)
    return dateString
  }
  static func getDateFromString(dateString: String) -> Date? {
    let formatter = ISO8601DateFormatter()
    formatter.formatOptions = [.withInternetDateTime,
                               .withDashSeparatorInDate,
                               .withFullDate,
                               .withFractionalSeconds,
                               .withColonSeparatorInTimeZone]
    guard let date = formatter.date(from: dateString) else {
      return nil
    }
    return date
  }
  // get an ISO timestamp
  static func getISOTimestamp() -> String {
    let isoDateFormatter = ISO8601DateFormatter()
    let timestamp = isoDateFormatter.string(from: Date())
    return timestamp
  }
}

extension String {
  // create a formatted date from ISO
  // e.g "MMM d, yyyy hh:mm a"
  // e.g usage addedAt.formattedDate("MMM d, yyyy")
  public func formatISODateString(dateFormat: String) -> String {
    var formatDate = self
    let isoDateFormatter = ISO8601DateFormatter()
    if let date = isoDateFormatter.date(from: self) {
      let dateFormatter = DateFormatter()
      dateFormatter.dateFormat = dateFormat
      formatDate = dateFormatter.string(from: date)
    }
    return formatDate
  }
  
  // e.g usage createdAt.date()
  public func date() -> Date {
    var date = Date()
    let isoDateFormatter = ISO8601DateFormatter()
    if let isoDate = isoDateFormatter.date(from: self) {
      date = isoDate
    }
    return date
  }
}

// testing Date extension
let date = Date.getDateFromString(dateString: "2018-11-02T06:02:45+00:00")
print(date?.description ?? "invalid date")
if let date = date {
  let dateString = Date.getStringFromDate(date: date)
  print(dateString)
}

// Date resources
// https://developer.apple.com/documentation/foundation/iso8601dateformatter/1643324-formatoptions
// http://nsdateformatter.com/
// https://developer.apple.com/documentation/foundation/iso8601dateformatter
// https://developer.apple.com/documentation/foundation/dateformatter
// https://www.unixtimestamp.com/index.php



// making a Date from a String using DateFormatter()
let dateString = "2016-12-01"
let dateFormatter = DateFormatter()
dateFormatter.dateFormat = "yyyy-MM-dd"
let date = dateFormatter.date(from: dateString)
print(date ?? "not a date")
dateFormatter.dateFormat = "EEEE, MMMM d, yyyy"
let formatString = dateFormatter.string(from: date!)
print(formatString)



// making a date from a TimeInterval
let timeInterval: TimeInterval = 1544378400000 // TimeInterval
let dateFormatter = DateFormatter()
let date = Date(timeIntervalSinceNow: timeInterval/1000000) // milli to seconds
// using DateFormatter()
dateFormatter.dateFormat = "MMMM, dd, yyyy h:mm a"
let dateString = dateFormatter.string(from: date)
print(dateString) // December, 27, 2018 8:08 AM



// using ISO8601DateFormatter() to make a timestamp for the current date
let isoDateFormatter = ISO8601DateFormatter()
isoDateFormatter.formatOptions = [.withInternetDateTime,
                                  .withDashSeparatorInDate,
                                  .withFullDate,
                                  .withFractionalSeconds,
                                  .withColonSeparatorInTimeZone]
isoDateFormatter.timeZone = TimeZone.current
let timestamp = isoDateFormatter.string(from: Date())
print(timestamp) // 2018-12-09T11:08:48-05:00



// convert ISO timestamp string to formatted date
let timestampString = "2018-12-09T11:08:48-05:00"
if let date = isoDateFormatter.date(from: timestampString) {
  let dateFormatter = DateFormatter()
  dateFormatter.dateFormat = "MMMM, dd, yyyy h:mm a"
  let dateFormattedString = dateFormatter.string(from: date)
  print(dateFormattedString) // December, 09, 2018 11:08 AM
} else {
  print("not a valid date")
}

// if ISO8601 comes in this format "2014-12-10T15:18:20.704000Z" be sure to using .withFractionalSeconds as a 
// format option