module URLdecode(Query,decodeQuery,decode,
                 -- ** Helper functions
                 fromhex4,fromhex2,fromhex) where
import Utils2(aboth,chopList,breakAt)
import Data.Char(chr,ord,toUpper)
import URLQuery

-- | The function 'decodeQuery' undoes the effect of 'URLencode.encodeQuery'.
decodeQuery :: String -> Query
decodeQuery = map (aboth decode . breakAt '=') . chopList (breakAt '&')

-- | The function 'decode' undoes the effect of 'URLencode.encode'.
decode :: String->String
decode [] = []
decode ('%':'u':d1:d2:d3:d4:cs) = chr(fromhex4 d1 d2 d3 d4):decode cs
decode ('%':d1:d2:cs) = chr(fromhex2 d1 d2):decode cs
decode ('+':cs) = ' ':decode cs
decode (c:cs) = c:decode cs

-- ** Helper functions

fromhex4 d1 d2 d3 d4 = 256*fromhex2 d1 d2+fromhex2 d3 d4
fromhex2 d1 d2 = 16*fromhex d1+fromhex d2

fromhex c =
  if '0'<=c && c<='9'
  then ord c - ord '0'
  else ord (toUpper c)-(ord 'A'-10)