elm/exercises/phone-number/PhoneNumber.example

module PhoneNumber (..) where

import String


nums =
  [ '1', '2', '3', '4', '5', '6', '7', '8', '9', '0' ]


getNumber : String -> Maybe String
getNumber text =
  getValidNum (String.filter isDigit text)


isDigit : Char -> Bool
isDigit char =
  List.any (\n -> n == char) nums


getValidNum : String -> Maybe String
getValidNum num =
  if String.length num == 10 then
    Just num
  else if (String.length num == 11) && (String.left 1 num == "1") then
    Just (String.dropLeft 1 num)
  else
    Nothing


prettyPrint : String -> Maybe String
prettyPrint input =
  Maybe.map formatNumber (getNumber input)


formatNumber : String -> String
formatNumber input =
  String.concat
    [ "("
    , (String.slice 0 3 input)
    , ") "
    , (String.slice 3 6 input)
    , "-"
    , (String.slice 6 10 input)
    ]