-- |
-- utility functions
--
-- Version : $Id: Util.hs,v 1.1 2004/09/02 19:11:57 hxml Exp $

module Text.XML.HXT.DOM.Util
    ( stringTrim
    , stringToUpper

    , stringEscapeXml
    , attrEscapeXml

    , stringToInt
    , stringToHexString
    , charToHexString
    , intToHexString
    , hexStringToInt
    , decimalStringToInt

    , doubles
    , singles
    , noDoubles
    )
where

import Data.Char

-- |
-- remove leading and trailing whitespace with standard Haskell predicate isSpace

stringTrim	:: String -> String
stringTrim
    = reverse . dropWhile isSpace . reverse . dropWhile isSpace

-- |
-- convert string to upercase with standard Haskell toUpper function

stringToUpper	:: String -> String
stringToUpper
    = map toUpper

escapeXml	:: String -> String -> String
escapeXml escSet
    = concatMap esc
      where
      esc c
	  | c `elem` escSet
	      = "&#" ++ show (fromEnum c) ++ ";"
	  | otherwise
	      = [c]

-- |
-- escape XML chars <, >, ",  and ampercent by transforming them into character references
--
-- see also : 'attrEscapeXml'

stringEscapeXml	:: String -> String
stringEscapeXml	= escapeXml "<>\"\'&"

-- |
-- escape XML chars in attribute values, same as stringEscapeXml, but none blank whitespace
-- is also escaped
--
-- see also : 'stringEscapeXml'

attrEscapeXml	:: String -> String
attrEscapeXml	= escapeXml "<>\"\'&\n\r\t"

stringToInt	:: Int -> String -> Int
stringToInt base digits
    = sign * (foldl acc 0 $ concatMap digToInt digits1)
      where
      splitSign ('-' : ds) = ((-1), ds)
      splitSign ('+' : ds) = ( 1  , ds)
      splitSign ds         = ( 1  , ds)
      (sign, digits1)      = splitSign digits
      digToInt c
	  | c >= '0' && c <= '9'
	    = [ord c - ord '0']
	  | c >= 'A' && c <= 'Z'
	      =  [ord c - ord 'A' + 10]
	  | c >= 'a' && c <= 'z'
	      =  [ord c - ord 'a' + 10]
	  | otherwise
	      = []
      acc i1 i0
	  = i1 * base + i0


-- |
-- convert a string of hexadecimal digits into an Int

hexStringToInt		:: String -> Int
hexStringToInt		= stringToInt 16

-- |
-- convert a string of digits into an Int

decimalStringToInt	:: String -> Int
decimalStringToInt	= stringToInt 10

-- |
-- convert a string into a hexadecimal string applying charToHexString
--
-- see also : 'charToHexString'

stringToHexString	:: String -> String
stringToHexString	= concatMap charToHexString

-- |
-- convert a char (byte) into a 2-digit hexadecimal string
--
-- see also : 'stringToHexString', 'intToHexString'

charToHexString		:: Char -> String
charToHexString c
    = [ fourBitsToChar (c' `div` 16)
      , fourBitsToChar (c' `mod` 16)
      ]
    where
    c' = fromEnum c

-- |
-- convert a none negative Int into a hexadecimal string
--
-- see also : 'charToHexString'

intToHexString		:: Int -> String
intToHexString i
    | i == 0
	= "0"
    | i > 0
	= intToStr i
    | otherwise
	= error ("intToHexString: negative argument " ++ show i)
    where
    intToStr 0	= ""
    intToStr i'	= intToStr (i' `div` 16) ++ [fourBitsToChar (i' `mod` 16)]

fourBitsToChar		:: Int -> Char
fourBitsToChar i	= "0123456789ABCDEF" !! i

-- ------------------------------------------------------------

-- |
-- take all elements of a list which occur more than once. The result does not contain doubles.
-- (doubles . doubles == doubles)

doubles	:: Eq a => [a] -> [a]
doubles
    = doubles' []
      where
      doubles' acc []
	  = acc
      doubles' acc (e : s)
	  | e `elem` s
	    &&
	    e `notElem` acc
	      = doubles' (e:acc) s
	  | otherwise
	      = doubles' acc s

-- |
-- drop all elements from a list which occur more than once.

singles	:: Eq a => [a] -> [a]
singles
    = singles' []
      where
      singles' acc []
	  = acc
      singles' acc (e : s)
	  | e `elem` s
	    ||
	    e `elem` acc
	      = singles' acc s
	  | otherwise
	      = singles' (e : acc) s

-- |
-- remove duplicates from list

noDoubles :: Eq a => [a] -> [a]
noDoubles []
    = []
noDoubles (e : s)
    | e `elem` s = noDoubles s
    | otherwise  = e : noDoubles s

-- ------------------------------------------------------------