module Data.Format
    ( Productish(..)
    , Summish(..)
    , parseReader
    , Format(..)
    , formatShow
    , formatParseM
    , isoMap
    , mapMFormat
    , filterFormat
    , clipFormat
    , enumMap
    , literalFormat
    , specialCaseShowFormat
    , specialCaseFormat
    , optionalFormat
    , casesFormat
    , optionalSignFormat
    , mandatorySignFormat
    , SignOption(..)
    , integerFormat
    , decimalFormat
    ) where

#if MIN_VERSION_base(4,9,0)
import Control.Monad.Fail
import Prelude hiding (fail)
#endif
#if MIN_VERSION_base(4,8,0)
import Data.Void
#endif
import Data.Char
import Text.ParserCombinators.ReadP


#if MIN_VERSION_base(4,8,0)
#else
data Void
absurd :: Void -> a
absurd v = seq v $ error "absurd"
#endif

class IsoVariant f where
    isoMap :: (a -> b) -> (b -> a) -> f a -> f b

enumMap :: (IsoVariant f,Enum a) => f Int -> f a
enumMap = isoMap toEnum fromEnum

infixr 3 <**>, **>, <**
class IsoVariant f => Productish f where
    pUnit :: f ()
    (<**>) :: f a -> f b -> f (a,b)
    (**>) ::  f () -> f a -> f a
    fu **> fa = isoMap (\((),a) -> a) (\a -> ((),a)) $ fu <**> fa
    (<**) ::  f a -> f () -> f a
    fa <** fu = isoMap (\(a,()) -> a) (\a -> (a,())) $ fa <**> fu

infixr 2 <++>
class IsoVariant f => Summish f where
    pVoid :: f Void
    (<++>) :: f a -> f b -> f (Either a b)


parseReader :: (
#if MIN_VERSION_base(4,9,0)
    MonadFail m
#else
    Monad m
#endif
    ) => ReadP t -> String -> m t
parseReader readp s = case [ t | (t,"") <- readP_to_S readp s] of
    [t] -> return t
    []  -> fail $ "no parse of " ++ show s
    _   -> fail $ "multiple parses of " ++ show s

-- | A text format for a type
data Format t = MkFormat
    { formatShowM :: t -> Maybe String
        -- ^ Show a value in the format, if representable
    , formatReadP :: ReadP t
        -- ^ Read a value in the format
    }

-- | Show a value in the format, or error if unrepresentable
formatShow :: Format t -> t -> String
formatShow fmt t = case formatShowM fmt t of
    Just str -> str
    Nothing -> error "formatShow: bad value"

-- | Parse a value in the format
formatParseM :: (
#if MIN_VERSION_base(4,9,0)
    MonadFail m
#else
    Monad m
#endif
    ) => Format t -> String -> m t
formatParseM format = parseReader $ formatReadP format

instance IsoVariant Format where
    isoMap ab ba (MkFormat sa ra) = MkFormat (\b -> sa $ ba b) (fmap ab ra)

mapMFormat :: (a -> Maybe b) -> (b -> Maybe a) -> Format a -> Format b
mapMFormat amb bma (MkFormat sa ra) = MkFormat (\b -> bma b >>= sa) $ do
    a <- ra
    case amb a of
        Just b -> return b
        Nothing -> pfail

filterFormat :: (a -> Bool) -> Format a -> Format a
filterFormat test = mapMFormat (\a -> if test a then Just a else Nothing) (\a -> if test a then Just a else Nothing)

-- | Limits are inclusive
clipFormat :: Ord a => (a,a) -> Format a -> Format a
clipFormat (lo,hi) = filterFormat (\a -> a >= lo && a <= hi)

instance Productish Format where
    pUnit = MkFormat {formatShowM = \_ -> Just "", formatReadP = return ()}
    (<**>) (MkFormat sa ra) (MkFormat sb rb) = let
        sab (a, b) = do
            astr <- sa a
            bstr <- sb b
            return $ astr ++ bstr
        rab = do
            a <- ra
            b <- rb
            return (a, b)
        in MkFormat sab rab
    (MkFormat sa ra) **> (MkFormat sb rb) = let
        s b = do
            astr <- sa ()
            bstr <- sb b
            return $ astr ++ bstr
        r = do
            ra
            rb
        in MkFormat s r
    (MkFormat sa ra) <** (MkFormat sb rb) = let
        s a = do
            astr <- sa a
            bstr <- sb ()
            return $ astr ++ bstr
        r = do
            a <- ra
            rb
            return a
        in MkFormat s r

instance Summish Format where
    pVoid = MkFormat absurd pfail
    (MkFormat sa ra) <++> (MkFormat sb rb) = let
        sab (Left a) = sa a
        sab (Right b) = sb b
        rab = (fmap Left ra) +++ (fmap Right rb)
        in MkFormat sab rab

literalFormat :: String -> Format ()
literalFormat s = MkFormat {formatShowM = \_ -> Just s, formatReadP = string s >> return ()}

specialCaseShowFormat :: Eq a => (a,String) -> Format a -> Format a
specialCaseShowFormat (val,str) (MkFormat s r) = let
    s' t | t == val = Just str
    s' t = s t
    in MkFormat s' r

specialCaseFormat :: Eq a => (a,String) -> Format a -> Format a
specialCaseFormat (val,str) (MkFormat s r) = let
    s' t | t == val = Just str
    s' t = s t
    r' = (string str >> return val) +++ r
    in MkFormat s' r'

optionalFormat :: Eq a => a -> Format a -> Format a
optionalFormat val = specialCaseFormat (val,"")

casesFormat :: Eq a => [(a,String)] -> Format a
casesFormat pairs = let
    s t = lookup t pairs
    r [] = pfail
    r ((v,str):pp) = (string str >> return v) <++ r pp
    in MkFormat s $ r pairs

optionalSignFormat :: (Eq t,Num t) => Format t
optionalSignFormat = casesFormat
    [
        (1,""),
        (1,"+"),
        (0,""),
        (-1,"-")
    ]

mandatorySignFormat :: (Eq t,Num t) => Format t
mandatorySignFormat = casesFormat
    [
        (1,"+"),
        (0,"+"),
        (-1,"-")
    ]

data SignOption
    = NoSign
    | NegSign
    | PosNegSign

readSign :: Num t => SignOption -> ReadP (t -> t)
readSign NoSign = return id
readSign NegSign = option id $ char '-' >> return negate
readSign PosNegSign = (char '+' >> return id) +++ (char '-' >> return negate)

readNumber :: (Num t, Read t) => SignOption -> Maybe Int -> Bool -> ReadP t
readNumber signOpt mdigitcount allowDecimal = do
    sign <- readSign signOpt
    digits <-
        case mdigitcount of
            Just digitcount -> count digitcount $ satisfy isDigit
            Nothing -> many1 $ satisfy isDigit
    moredigits <-
        case allowDecimal of
            False -> return ""
            True ->
                option "" $ do
                    _ <- char '.' +++ char ','
                    dd <- many1 (satisfy isDigit)
                    return $ '.' : dd
    return $ sign $ read $ digits ++ moredigits

zeroPad :: Maybe Int -> String -> String
zeroPad Nothing s = s
zeroPad (Just i) s = replicate (i - length s) '0' ++ s

trimTrailing :: String -> String
trimTrailing "" = ""
trimTrailing "." = ""
trimTrailing s | last s == '0' = trimTrailing $ init s
trimTrailing s = s

showNumber :: Show t => SignOption -> Maybe Int -> t -> Maybe String
showNumber signOpt mdigitcount t = let
    showIt str = let
        (intPart, decPart) = break ((==) '.') str
        in (zeroPad mdigitcount intPart) ++ trimTrailing decPart
    in case show t of
           ('-':str) ->
               case signOpt of
                   NoSign -> Nothing
                   _ -> Just $ '-' : showIt str
           str ->
               Just $ case signOpt of
                   PosNegSign -> '+' : showIt str
                   _ -> showIt str

integerFormat :: (Show t,Read t,Num t) => SignOption -> Maybe Int -> Format t
integerFormat signOpt mdigitcount = MkFormat (showNumber signOpt mdigitcount) (readNumber signOpt mdigitcount False)

decimalFormat :: (Show t,Read t,Num t) => SignOption -> Maybe Int -> Format t
decimalFormat signOpt mdigitcount = MkFormat (showNumber signOpt mdigitcount) (readNumber signOpt mdigitcount True)
