module Text.Pandoc.CSS ( foldOrElse

                       , pickStyleAttrProps

                       , pickStylesToKVs

                       )

where

import Text.Pandoc.Shared (trim)

import Text.Parsec

import Text.Parsec.String

ruleParser :: Parser (String, String)

ruleParser = do

    p <- many1 (noneOf ":")  <* char ':'

    v <- many1 (noneOf ":;") <* optional (char ';') <* spaces

    return (trim p, trim v)

styleAttrParser :: Parser [(String, String)]

styleAttrParser = many1 ruleParser

orElse :: Eq a => a -> a -> a -> a

orElse v x y = if v == x then y else x

foldOrElse :: Eq a => a -> [a] -> a

foldOrElse v xs = foldr (orElse v) v xs

eitherToMaybe :: Either a b -> Maybe b

eitherToMaybe (Right x) = Just x

eitherToMaybe _         = Nothing

-- | takes a list of keys/properties and a CSS string and

-- returns the corresponding key-value-pairs.

pickStylesToKVs :: [String] -> String -> [(String, String)]

pickStylesToKVs props styleAttr =

  case parse styleAttrParser "" styleAttr of

    Left _       -> []

    Right styles -> filter (\s -> fst s `elem` props) styles

-- | takes a list of key/property synonyms and a CSS string and maybe

-- returns the value of the first match (in order of the supplied list)

pickStyleAttrProps :: [String] -> String -> Maybe String

pickStyleAttrProps lookupProps styleAttr = do

    styles <- eitherToMaybe $ parse styleAttrParser "" styleAttr

    foldOrElse Nothing $ map (`lookup` styles) lookupProps