Check out example codes for "swift credit card validate". It will help you in understanding the concepts better.

Code Example 1

enum CardType: String {
    case Unknown, Amex, Visa, MasterCard, Diners, Discover, JCB, Elo, Hipercard, UnionPay

    static let allCards = [Amex, Visa, MasterCard, Diners, Discover, JCB, Elo, Hipercard, UnionPay]

    var regex : String {
        switch self {
        case .Amex:
           return "^3[47][0-9]{5,}$"
        case .Visa:
           return "^4[0-9]{6,}([0-9]{3})?$"
        case .MasterCard:
           return "^(5[1-5][0-9]{4}|677189)[0-9]{5,}$"
        case .Diners:
           return "^3(?:0[0-5]|[68][0-9])[0-9]{4,}$"
        case .Discover:
           return "^6(?:011|5[0-9]{2})[0-9]{3,}$"
        case .JCB:
           return "^(?:2131|1800|35[0-9]{3})[0-9]{3,}$"
        case .UnionPay:
           return "^(62|88)[0-9]{5,}$"
        case .Hipercard:
           return "^(606282|3841)[0-9]{5,}$"
        case .Elo:
           return "^((((636368)|(438935)|(504175)|(451416)|(636297))[0-9]{0,10})|((5067)|(4576)|(4011))[0-9]{0,12})$"
        default:
           return ""
        }
    }
}
extension UITextField{ 

  func validateCreditCardFormat()-> (type: CardType, valid: Bool) {
          // Get only numbers from the input string
          var input = self.text!
          let numberOnly = input.stringByReplacingOccurrencesOfString("[^0-9]", withString: "", options: .RegularExpressionSearch)

      var type: CardType = .Unknown
      var formatted = ""
      var valid = false

      // detect card type
      for card in CardType.allCards {
          if (matchesRegex(card.regex, text: numberOnly)) {
              type = card
              break
          }
      }

      // check validity
      valid = luhnCheck(numberOnly)

      // format
      var formatted4 = ""
      for character in numberOnly.characters {
          if formatted4.characters.count == 4 {
              formatted += formatted4 + " "
              formatted4 = ""
          }
          formatted4.append(character)
      }

      formatted += formatted4 // the rest

      // return the tuple
      return (type, valid)
  }

  func matchesRegex(regex: String!, text: String!) -> Bool {
      do {
          let regex = try NSRegularExpression(pattern: regex, options: [.CaseInsensitive])
          let nsString = text as NSString
          let match = regex.firstMatchInString(text, options: [], range: NSMakeRange(0, nsString.length))
          return (match != nil)
      } catch {
          return false
      }
  }

  func luhnCheck(number: String) -> Bool {
      var sum = 0
      let digitStrings = number.characters.reverse().map { String($0) }

      for tuple in digitStrings.enumerate() {
          guard let digit = Int(tuple.element) else { return false }
          let odd = tuple.index % 2 == 1

          switch (odd, digit) {
          case (true, 9):
              sum += 9
          case (true, 0...8):
              sum += (digit * 2) % 9
          default:
              sum += digit
          }
      }

      return sum % 10 == 0
  }
}

Learn ReactJs, React Native from akashmittal.com