module Exercise04 where

import Data.Bifunctor
import Data.Maybe

{-WETT-}
xmlLight :: String -> Bool
xmlLight xml = helper xml []

helper :: String -> [String] -> Bool
helper "" tags = null tags
helper (f : xml) tags
  | f == '<' = if not (null xml) && head xml == '/' then not (null tags) && isJust endTag && head tags == fst (fromJust endTag) && snd (fromJust endTag) `helper` tail tags else isJust openTag && snd (fromJust openTag) `helper` (fst (fromJust openTag) : tags)
--   | f == '<' && not (null xml) && head xml == '/' = not (null tags) && isJust endTag && head tags == fst (fromJust endTag) && snd (fromJust endTag) `helper` tail tags
--   | f == '<' = isJust openTag && snd (fromJust openTag) `helper` (fst (fromJust openTag) : tags)
  | f == '>' = False
  | otherwise = helper xml tags
  where 
    openTag = tagParser xml
    endTag = tagParser $ tail xml

tagParser :: String -> Maybe (String,String)
tagParser [] = Nothing
tagParser (f : xml)
  | null xml = if f /= '>' then Nothing else Just ("", xml)
  | f == ' ' = case head xml of
                ' ' -> next
                '>' -> next
                _   -> Nothing
  | f == '<' = Nothing
  | f == '>' = Just ("", xml)
  | otherwise = if isJust next then Just $ first (f : ) (fromJust next) else Nothing
  where next = tagParser xml

{-TTEW-}