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--------------------------------------------------------------------------------
-- | 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 Hakyll.Web.CompressCss
( compressCssCompiler
, compressCss
) where
--------------------------------------------------------------------------------
import Data.Char (isSpace)
import Data.List (isPrefixOf)
--------------------------------------------------------------------------------
import Hakyll.Core.Compiler
import Hakyll.Core.Item
import Hakyll.Core.Util.String
--------------------------------------------------------------------------------
-- | Compiler form of 'compressCss'
compressCssCompiler :: Compiler (Item String)
compressCssCompiler = fmap compressCss <$> getResourceString
--------------------------------------------------------------------------------
-- | Compress CSS to speed up your site.
compressCss :: String -> String
compressCss = compressSeparators . stripComments . compressWhitespace
--------------------------------------------------------------------------------
-- | Compresses certain forms of separators.
compressSeparators :: String -> String
compressSeparators [] = []
compressSeparators str
| isPrefixOf "\"" str = head str : retainConstants compressSeparators "\"" (drop 1 str)
| isPrefixOf "'" str = head str : retainConstants compressSeparators "'" (drop 1 str)
| stripFirst = compressSeparators (drop 1 str)
| stripSecond = compressSeparators (head str : (drop 2 str))
| isPrefixOf ";}" str = '}' : compressSeparators (drop 2 str)
| otherwise = head str : compressSeparators (drop 1 str)
where
prefix p = isPrefixOf p str
stripFirst = or $ map prefix [" ", " {", " }", ";;"]
stripSecond = or $ map prefix ["{ ", "} ", "; "]
--------------------------------------------------------------------------------
-- | Compresses all whitespace.
compressWhitespace :: String -> String
compressWhitespace [] = []
compressWhitespace str
| isPrefixOf "\"" str = head str : retainConstants compressWhitespace "\"" (drop 1 str)
| isPrefixOf "'" str = head str : retainConstants compressWhitespace "'" (drop 1 str)
| otherwise = replaceAll "[ \t\n\r]+" (const " ") str
--------------------------------------------------------------------------------
-- | Function that strips CSS comments away.
stripComments :: String -> String
stripComments [] = []
stripComments str
| isPrefixOf "/*" str = stripComments $ eatComments $ drop 2 str
| otherwise = head str : stripComments (drop 1 str)
where
eatComments str'
| null str' = []
| isPrefixOf "*/" str' = drop 2 str'
| otherwise = eatComments $ drop 1 str'
--------------------------------------------------------------------------------
-- | Helper function to handle string constants correctly.
retainConstants :: (String -> String) -> String -> String -> String
retainConstants f delim str
| null str = []
| isPrefixOf delim str = head str : f (drop 1 str)
| otherwise = head str : retainConstants f delim (drop 1 str)
|
