-- | Module used for CSS compression. The compression is currently in a simple
--   state, but would typically reduce the number of bytes by about 25%.
module Text.Hakyll.Internal.CompressCss
    ( compressCss
    ) where

import Data.List (isPrefixOf)

import Text.Hakyll.Regex (substituteRegex)

-- | Compress CSS to speed up your site.
compressCss :: String -> String
compressCss = compressSeparators
            . stripComments
            . compressWhitespace

-- | Compresses certain forms of separators.
compressSeparators :: String -> String
compressSeparators = substituteRegex "; *}" "}" 
                   . substituteRegex " *([{};:]) *" "\\1"
                   . substituteRegex ";;*" ";"

-- | Compresses all whitespace.
compressWhitespace :: String -> String
compressWhitespace = substituteRegex "[ \t\n][ \t\n]*" " "

-- | Function that strips CSS comments away.
stripComments :: String -> String
stripComments [] = []
stripComments str
    | isPrefixOf "/*" str = stripComments $ eatComments $ drop 2 str
    | otherwise = head str : stripComments (tail str)
  where
    eatComments str' | null str' = []
                     | isPrefixOf "*/" str' = drop 2 str'
                     | otherwise = eatComments $ tail str'