Main.hs

module Main where

import Data.Char ( isLower, isUpper )
import Control.Monad.Trans.Maybe
import Control.Monad.Trans.Reader
import Control.Monad.Trans.Class

type Env = (Maybe String, Maybe String, Maybe String)

main :: IO ()
main = do
    maybeCreds <- runMaybeT $ do 
        usr <- runReaderT readUserName (Nothing, Nothing, Nothing)
        email <- readEmail
        pass <- readPassword
        return (usr, email, pass)
    case maybeCreds of 
        Nothing -> print "Could not log in."
        Just (u, e, p) -> print $ "Logging in: "++u++e++p

readUserName :: MaybeT (ReaderT Env IO) String
readUserName = MaybeT $ do 
    (maybeOldUser, _, _ ) <- ask
    case maybeOldUser of
        Just str -> return $ Just str
        Nothing -> do
            lift $ putStrLn "Please enter your username: "
            input <- lift getLine
            if length input > 5
                then return $ Just input
                else return Nothing

readEmail :: MaybeT IO String
readEmail = MaybeT $ do
    putStrLn "Please enter your email: "
    str <- getLine
    if '@' `elem` str && '.' `elem` str
        then return $ Just str
        else return Nothing

readPassword :: MaybeT IO String
readPassword = MaybeT $ do
    putStrLn "Please enter your password: "
    str <- getLine
    if length str < 8 || not (any isUpper str) || not (any isLower str)
        then return Nothing
        else return $ Just str