UITextField Phone Number Format

Extensions+UITextField.swift

import UIKit

extension UITextField {
  
  func handlePhoneNumberField(withReplacingString string: String, in range: NSRange) {
    let textFieldString = text! as NSString
    var newString = textFieldString.replacingCharacters(in: range, with: string)
    let validationSet = CharacterSet.decimalDigits.inverted
    
    let numberArray = newString.components(separatedBy: validationSet)
    newString = numberArray.joined()
    
    if newString.count > 11 {
      return
    }
    
    if newString.count > 0 {
      if newString.first == "7" {
        newString.insert("+", at: newString.startIndex)
      } else if newString.first != "8" {
        newString.insert("7", at: newString.startIndex)
        newString.insert("+", at: newString.startIndex)
      } else {
        newString.remove(at: newString.startIndex)
        newString.insert("7", at: newString.startIndex)
        newString.insert("+", at: newString.startIndex)
      }
    }
    
    if newString.count > 2 {
      let newIndex = newString.index(newString.startIndex, offsetBy: 2)
      let newIndexPlus = newString.index(newString.startIndex, offsetBy: 3)
      newString.insert(" ", at: newIndex)
      newString.insert("(", at: newIndexPlus)
    }
    
    if newString.count > 7 {
      let newIndex = newString.index(newString.startIndex, offsetBy: 7)
      let newIndexPlus = newString.index(newString.startIndex, offsetBy: 8)
      newString.insert(")", at: newIndex)
      newString.insert(" ", at: newIndexPlus)
    }
    
    if newString.count > 12 {
      let newIndex = newString.index(newString.startIndex, offsetBy: 12)
      newString.insert("-", at: newIndex)
    }
    
    if newString.count > 15 {
      let newIndex = newString.index(newString.startIndex, offsetBy: 15)
      newString.insert("-", at: newIndex)
    }
    
    text = newString
  }
  
}