module Exercise04 where

import Data.Char ( isSpace )

{-WETT-}
xmlLight :: String -> Bool
xmlLight xs = mainParse xs []

mainParse :: String -> [String] -> Bool
-- Closing Tags
mainParse ('<' : '/' : xs) (ts: tss) = let (rs, ts') = tagId xs in (ts' == ts) && mainParse rs tss
mainParse ('<' : '/' : _) [] = False

mainParse ('>' : _) _ = False

-- Opening Tag
mainParse ('<' : xs) tss = let (rs, ts) = tagId xs in mainParse rs (ts : tss) 

-- Plain Text
mainParse (_ : xss) tss = mainParse xss tss

-- End of String 
mainParse [] tss = null tss

-- Input -> (remaining String, TagID)
tagId :: String -> (String, String)
tagId ('>' : xs) = (xs, [])
tagId ('<' : _) = (">", [])
tagId (x : xs)
    | isSpace x && null ts = res
    | isSpace x = (">", [])
    | otherwise = (rs, x : ts)
    where res@(rs , ts) = tagId xs
tagId [] = (">", []) --return ">" character that will always evaluate to false

{-TTEW-}