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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.List (isPrefixOf)
--------------------------------------------------------------------------------
import Hakyll.Core.Compiler
import Hakyll.Core.Item
--------------------------------------------------------------------------------
-- | 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
| isConstant = head str : retainConstants compressSeparators (head str) (drop 1 str)
| stripFirst = compressSeparators (drop 1 str)
| stripSecond = compressSeparators (head str : (drop 2 str))
| otherwise = head str : compressSeparators (drop 1 str)
where
isConstant = or $ map (isOfPrefix str) ["\"", "'"]
stripFirst = or $ map (isOfPrefix str) $ [";;", ";}"] ++ (map (\c -> " " ++ c) separators)
stripSecond = or $ map (isOfPrefix str) $ map (\c -> c ++ " ") separators
separators = [" ", "{", "}", ":", ";", ",", ">", "+", "!"]
--------------------------------------------------------------------------------
-- | Compresses all whitespace.
compressWhitespace :: String -> String
compressWhitespace [] = []
compressWhitespace str
| isConstant = head str : retainConstants compressWhitespace (head str) (drop 1 str)
| replaceOne = compressWhitespace (' ' : (drop 1 str))
| replaceTwo = compressWhitespace (' ' : (drop 2 str))
| otherwise = head str : compressWhitespace (drop 1 str)
where
isConstant = or $ map (isOfPrefix str) ["\"", "'"]
replaceOne = or $ map (isOfPrefix str) ["\t", "\n", "\r"]
replaceTwo = or $ map (isOfPrefix str) [" \t", " \n", " \r", " "]
--------------------------------------------------------------------------------
-- | Function that strips CSS comments away.
stripComments :: String -> String
stripComments [] = []
stripComments str
| isConstant = head str : retainConstants stripComments (head str) (drop 1 str)
| isPrefixOf "/*" str = stripComments $ eatComments $ drop 2 str
| otherwise = head str : stripComments (drop 1 str)
where
isConstant = or $ map (isOfPrefix str) ["\"", "'"]
eatComments str'
| null str' = []
| isPrefixOf "*/" str' = drop 2 str'
| otherwise = eatComments $ drop 1 str'
--------------------------------------------------------------------------------
-- | Helper function to handle string constants correctly.
retainConstants :: (String -> String) -> Char -> 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)
--------------------------------------------------------------------------------
-- | Helper function to determine whether a string is a substring.
isOfPrefix :: String -> String -> Bool
isOfPrefix = flip isPrefixOf
|
