yeganesh-2.0: Version.hs

-- boilerplate {{{
module Version (CurrentFormat, parseCurrentFormat) where
import Data.Map (Map, elems, empty)
import Data.Time (UTCTime, getCurrentTime)

type CurrentFormat = FormatV2

parseCurrentFormat :: String -> IO CurrentFormat
parseCurrentFormat = parseFormatV2
-- }}}
-- v2 {{{
type FormatV2 = (UTCTime, FormatV1)

parseFormatV2 :: String -> IO FormatV2
parseFormatV2 = parse parseFormatV1 upgradeFormatV1
-- }}}
-- v1 {{{
type FormatV1 = Map String Double

upgradeFormatV1 :: FormatV1 -> IO FormatV2
upgradeFormatV1 v1 = fmap (flip (,) popularities) getCurrentTime where
    maximal = case (elems v1, maximum (elems v1)) of
        ([], _) -> 1
        (_ , 0) -> 1
        (_ , m) -> m
    popularities = fmap (/maximal) v1

parseFormatV1 :: String -> IO FormatV1
parseFormatV1 = parse (const (return empty)) return
-- }}}
-- utilities {{{
parse :: Read new => (String -> IO old) -> (old -> IO new) -> (String -> IO new)
parse old upgrade s = maybe (old s >>= upgrade) return (readMaybe s)

readMaybe :: Read a => String -> Maybe a
readMaybe s = case reads s of
    [(x, "")] -> Just x
    _         -> Nothing
-- }}}