Example of Swift date manager which can convert dates to strings and vice versa, with auto detection of date formats

DateManager.swift

//
//  DateManager.swift
//
//  Created by Rutger Bresjer on 30/12/2016.
//  Copyright © 2016 Woost. All rights reserved.
//

import Foundation

class DateManager {
  static let shared = DateManager()
  private init() {}
  
  private let defaultDateFormat = "EEEE dd MMMM yyyy"
  
  private lazy var dateFormatter: DateFormatter = {
    let _dateFormatter = DateFormatter()
    _dateFormatter.locale = Bundle.main.preferredLocalizations.first.flatMap(Locale.init) ?? Locale.current
    
    return _dateFormatter
  }()
  
  func string(from date: Date, format: String? = nil) -> String {
    dateFormatter.dateFormat = format ?? defaultDateFormat
    return dateFormatter.string(from: date)
  }
  
  func date(from string: String, format: String? = nil) -> Date? {
    guard let dateFormat = format ?? dateFormat(for: string) else { return nil }
    
    dateFormatter.dateFormat = dateFormat
    return dateFormatter.date(from: string)
  }
  
  private func dateFormat(for string: String) -> String? {
    let dateFormats = [
      (dateFormat: "yyyyMMdd",
       regex: "^(19|20)\\d\\d(0[1-9]|1[012])(0[1-9]|[12][0-9]|3[01])$"),
      (dateFormat: "yyyy-MM-dd",
       regex: "^(19|20)\\d\\d-(0[1-9]|1[012])-(0[1-9]|[12][0-9]|3[01])$"),
      (dateFormat: "yyyy-MM-dd HH:mm:ss",
       regex: "^(19|20)\\d\\d-(0[1-9]|1[012])-(0[1-9]|[12][0-9]|3[01]) ([01][0-9]|2[0-3]):([0-5][0-9]):([0-5][0-9])$"),
      (dateFormat: "yyyyMMddHHmmss",
       regex: "^(19|20)\\d\\d(0[1-9]|1[012])(0[1-9]|[12][0-9]|3[01])([01][0-9]|2[0-3])([0-5][0-9])([0-5][0-9])$")
    ]
    
    return dateFormats
      .filter { string.range(of: $0.regex, options: .regularExpression) != nil }
      .first
      .map { $0.dateFormat }
  }
  
}

extension Date {
  var formattedString: String {
    return DateManager.shared.string(from: self)
  }
  
  var monthYearString: String {
    return DateManager.shared.string(from: self, format: "MMMM yyyy")
  }
}

extension String {
  var date: Date? {
    return DateManager.shared.date(from: self)
  }
}

Example.swift

// Easily get a date from a string
let date = "20161230".date

// Or with time
let datetime = "2016-12-30 13:30:00".date

// And get a string from a date
let dateString = date?.formattedString

// Or just the month and the year
let monthYearString = date?.monthYearString