checkPhoneNumber

gistfile1.txt

    func checkPhoneNumber(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {

        let validationSet = NSCharacterSet.decimalDigits.inverted
        let components = string.components(separatedBy: validationSet)

        guard components.count == 1 else { return false }

        guard var newString = (textField.text as NSString?)?.replacingCharacters(in: range, with: string) else { return false }

        let validComponents = newString.components(separatedBy: validationSet)
        newString = validComponents.joined(separator: "")

        let localNumberMaxLength = 7
        let areaCodeMaxLength = 3
        let countryCodeMaxLength = 3

        if newString.count > (localNumberMaxLength + areaCodeMaxLength + countryCodeMaxLength) {
            return false
        }

        var resultString = ""
        let localNumberLength = min(newString.count, localNumberMaxLength)

        if localNumberLength > 0 {
            let offset = newString.count - localNumberLength
            let number = String(describing: newString.suffix(from: String.Index.init(encodedOffset: offset)))
            resultString.append(number)

            if resultString.count > 5 {
                resultString.insert("-", at: String.Index.init(encodedOffset: 5)) // XXXXX-XX
            }

            if resultString.count > 3 {
                resultString.insert("-", at: String.Index.init(encodedOffset: 3)) // XXX-XX-XX
            }
        }

        if newString.count > localNumberLength {
            let areaCodeLength = min((newString.count - localNumberMaxLength), areaCodeMaxLength)
            let start = newString.index(newString.startIndex, offsetBy: (newString.count - localNumberMaxLength - areaCodeLength))
            let end = newString.index(newString.startIndex, offsetBy: (newString.count - localNumberMaxLength))
            let area = "(\(newString[start..<end])) "

            resultString = "\(area)\(resultString)"
        }

        if newString.count > localNumberLength + areaCodeMaxLength {

            let countryCodeLength = min((newString.count - localNumberMaxLength - areaCodeMaxLength), countryCodeMaxLength)
            let countryCode = "+\(newString[newString.index(newString.startIndex, offsetBy: 0)..<newString.index(newString.startIndex, offsetBy: countryCodeLength)]) "
            resultString = "\(countryCode)\(resultString)"
        }

        textField.text = resultString

        return false
    }