import Control.Monad.Trans.Maybe
import Control.Monad.IO.Class
import Data.Char (isNumber, isPunctuation)
import Control.Monad.Error

askPassword :: MaybeT IO ()
askPassword = do
  liftIO $ putStrLn "Enter your new password:"
  value <- msum $ repeat getValidPassword
  liftIO $ putStrLn "Storing in database..."

getValidPassword :: MaybeT IO String
getValidPassword = do
  s <- liftIO getLine
  guard (isValid s)
  return s

isValid :: String -> Bool
isValid s = length s >= 8
            && any isNumber s
            && any isPunctuation s


data PwdError = PwdError String

type PwdErrorMonad = ErrorT PwdError IO

instance Error PwdError where
    noMsg      = PwdError ""
    strMsg msg = PwdError msg

askPassword' :: PwdErrorMonad ()
askPassword' = do
    liftIO $ putStrLn "Enter your new password:"
    value <- msum $ repeat $ getValidPassword'
    liftIO $ putStrLn "Storing in database..."
handleErr (PwdError err) = do
    liftIO $ putStrLn err
    throwError $ PwdError err

getValidPassword' :: PwdErrorMonad String
getValidPassword' = action `catchError` handleErr
  where
    action = do
        s <- liftIO getLine
        if length s < 8 then
            throwError $ PwdError "Incorrect input: password is too short!"
        else
            if not (any isNumber s) then
                throwError $ PwdError "Incorrect input: password must contain some digits!"
            else
                if not (any isPunctuation s) then
                    throwError $ PwdError "Incorrect input: password must contain some punctuations!"
                else
                    return s