module Exercise04 where

import Data.List
import Data.Maybe

{-WETT-}

xmlLight' :: String -> [String] -> Bool
xmlLight' [] stack = null stack
xmlLight' (s : ss) stack 
    | s == '>' = False
    | s == '<' = let 
                        close = head ss == '/'
                        newStr = if close then tail ss else ss
                        closingTagIdx = elemIndex '>' newStr
                        r = splitAt (fromMaybe 0 closingTagIdx) newStr
                        tagContent = words $ fst r
                        tagId = head tagContent
                        restStr = tail $ snd r
        in 
            not (null ss) && isJust closingTagIdx && length tagContent == 1 && head (fst r) /= ' ' && notElem '/' tagId && notElem '<' tagId &&
            if close 
            then 
                not (null stack) && head stack == tagId && xmlLight' restStr (tail stack) 
            else 
                xmlLight' restStr (tagId : stack)
    | otherwise = xmlLight' ss stack

xmlLight :: String -> Bool
xmlLight s = xmlLight' s []
{-TTEW-}