module Exercise04 where

import Data.List

{-WETT-}
xmlLight :: String -> Bool
xmlLight s = fst $ xmlParse False s

xmlParse :: Bool -> String -> (Bool,String)
xmlParse recCall "" = (True,"")
xmlParse recCall ('<':'/':s) = (recCall,s)
xmlParse recCall (a:s)
  | a == '>'  = (False,s)
  | a == '<'  = (openTag /= ""
                 && intersect "/ <>" openTag == ""
                 && innerSuccess
                 && openTag == closeTag
                 && take 1 restSclosed == ">"
                 && nextSuccess,
                returnS)
  | otherwise = xmlParse recCall s
    where
        openTag = takeID s
        (innerSuccess,restS) = xmlParse True $ skipID s
        closeTag = takeID restS
        restSclosed = dropWhile (/= '>') restS
        (nextSuccess,returnS) = xmlParse recCall $ skipID restSclosed

skipID :: String -> String
skipID = drop 1 . dropWhile (/= '>')

takeID :: String -> String
takeID = reverse . dropWhile (== ' ') . reverse . takeWhile (/= '>')

{-TTEW-}