module Exercise04 where

import Data.Char

{-WETT-}

xmlLight :: String -> Bool
xmlLight xml = null $ validsub (xml ++ "</>") ""

validsub :: String -> String -> String
validsub ('<' : '/' : xml) tag = removeTag (tag == parseTag xml) xml
validsub (x : xml) tag =
  case x of
    '<' -> removeTag (parseTag xml /= ">") xml `validsub` parseTag xml `validsub` tag
    '>' -> ">"
    _ -> validsub xml tag
validsub _ _ = ">"

removeTag :: Bool -> String -> String
removeTag cond xml = if cond then tail $ dropWhile (/= '>') xml else ">"

parseTag :: String -> String
parseTag (x : xml) =
  case x of
    '/' -> ">"
    '<' -> ">"
    ' ' -> if head (dropWhile isSpace xml ++ "<") == '>' then "" else ">"
    '>' -> ""
    _ -> if parseTag xml /= ">" then x : parseTag xml else ">"
parseTag _ = ">"

{-TTEW-}