{-# LANGUAGE OverloadedStrings #-}

module Data.SCargot.Language.HaskLike
  ( -- $info
    HaskLikeAtom(..)
  , haskLikeParser
  , haskLikePrinter
  ) where

import           Control.Applicative ((<$>), (<*>), (<$))
import           Data.Maybe (catMaybes)
import           Data.String (IsString(..))
import           Data.Text (Text, pack)
import           Text.Parsec
import           Text.Parsec.Text (Parser)

import           Prelude hiding (concatMap)

import Data.SCargot.Common
import Data.SCargot.Repr.Basic (SExpr)
import Data.SCargot (SExprParser, SExprPrinter, mkParser, flatPrint)

{- $info

This module is intended for simple, ad-hoc configuration or data formats
that might not need their on rich structure but might benefit from a few
various kinds of literals. The 'haskLikeParser' understands identifiers as
defined by R5RS, as well as string, integer, and floating-point literals
as defined by the Haskell spec. It does __not__ natively understand other
data types, such as booleans, vectors, bitstrings.

-}


-- | An atom type that understands Haskell-like values as well as
--   Scheme-like identifiers.
data HaskLikeAtom
  = HSIdent  Text  -- ^ An identifier, parsed according to the R5RS Scheme
                   --   standard
  | HSString Text  -- ^ A string, parsed according to the syntax for string
                   --   literals in the Haskell report
  | HSInt Integer  -- ^ An arbitrary-sized integer value, parsed according to
                   --   the syntax for integer literals in the Haskell report
  | HSFloat Double -- ^ A double-precision floating-point value, parsed
                   --   according to the syntax for floats in the Haskell
                   --   report
    deriving (Eq, Show)

instance IsString HaskLikeAtom where
  fromString = HSIdent . fromString

pString :: Parser Text
pString = pack . catMaybes <$> between (char '"') (char '"') (many (val <|> esc))
  where val = Just <$> satisfy (\ c -> c /= '"' && c /= '\\' && c > '\026')
        esc = do char '\\'
                 Nothing <$ (gap <|> char '&') <|>
                   Just <$> code
        gap  = many1 space >> char '\\'
        code = eEsc <|> eNum <|> eCtrl <|> eAscii
        eCtrl  = char '^' >> unCtrl <$> upper
        eNum   = (toEnum . fromInteger) <$>
                   (decNumber <|> (char 'o' >> octNumber)
                              <|> (char 'x' >> hexNumber))
        eEsc   = choice [ char a >> return b | (a, b) <- escMap ]
        eAscii = choice [ try (string a >> return b)
                        | (a, b) <- asciiMap ]
        unCtrl c = toEnum (fromEnum c - fromEnum 'A' + 1)

escMap :: [(Char,  Char)]
escMap = zip "abfntv\\\"\'" "\a\b\f\n\r\t\v\\\"\'"

asciiMap :: [(String, Char)]
asciiMap = zip
  ["BS","HT","LF","VT","FF","CR","SO","SI","EM"
  ,"FS","GS","RS","US","SP","NUL","SOH","STX","ETX"
  ,"EOT","ENQ","ACK","BEL","DLE","DC1","DC2","DC3"
  ,"DC4","NAK","SYN","ETB","CAN","SUB","ESC","DEL"]
  ("\BS\HT\LF\VT\FF\CR\SO\SI\EM\FS\GS\RS\US\SP\NUL\SOH" ++
   "\STX\ETX\EOT\ENQ\ACK\BEL\DLE\DC1\DC2\DC3\DC4\NAK" ++
   "\SYN\ETB\CAN\SUB\ESC\DEL")

pFloat :: Parser Double
pFloat = do
  n <- decNumber
  withDot n <|> noDot n
  where withDot n = do
          char '.'
          m <- decNumber
          e <- option 1.0 exponent
          return ((fromIntegral n + asDec m 0) * e)
        noDot n = do
          e <- exponent
          return (fromIntegral n * e)
        exponent = do
          oneOf "eE"
          s <- power
          x <- decNumber
          return (10 ** s (fromIntegral x))
        asDec 0 k = k
        asDec n k =
          asDec (n `div` 10) ((fromIntegral (n `rem` 10) + k) * 0.1)

power :: Num a => Parser (a -> a)
power = negate <$ char '-' <|> id <$ char '+' <|> return id

pInt :: Parser Integer
pInt = do
  s <- power
  n <- pZeroNum <|> decNumber
  return (fromIntegral (s n))

pZeroNum :: Parser Integer
pZeroNum = char '0' >>
  (  (oneOf "xX" >> hexNumber)
 <|> (oneOf "oO" >> octNumber)
 <|> decNumber
 <|> return 0
  )

pHaskLikeAtom :: Parser HaskLikeAtom
pHaskLikeAtom
   =  HSFloat   <$> (try pFloat     <?> "float")
  <|> HSInt     <$> (try pInt       <?> "integer")
  <|> HSString  <$> (pString        <?> "string literal")
  <|> HSIdent   <$> (parseR5RSIdent <?> "token")

sHaskLikeAtom :: HaskLikeAtom -> Text
sHaskLikeAtom (HSIdent t)  = t
sHaskLikeAtom (HSString s) = pack (show s)
sHaskLikeAtom (HSInt i)    = pack (show i)
sHaskLikeAtom (HSFloat f)  = pack (show f)

-- | This `SExprParser` understands s-expressions that contain
--   Scheme-like tokens, as well as string literals, integer
--   literals, and floating-point literals. Each of these values
--   is parsed according to the lexical rules in the Haskell
--   report, so the same set of string escapes, numeric bases,
--   and floating-point options are available. This spec does
--   not parse comments and does not understand any reader
--   macros.
--
-- >>> decode haskLikeParser "(0x01 \"\\x65lephant\")"
-- Right [SCons (SAtom (HSInt 1)) (SCons (SAtom (HSString "elephant")) SNil)]
haskLikeParser :: SExprParser HaskLikeAtom (SExpr HaskLikeAtom)
haskLikeParser = mkParser pHaskLikeAtom

-- | This 'SExprPrinter' emits s-expressions that contain Scheme-like
--   tokens as well as string literals, integer literals, and floating-point
--   literals, which will be emitted as the literals produced by Haskell's
--   'show' function. This printer will produce a flat s-expression with
--   no indentation of any kind.
--
-- >>> encode haskLikePrinter [L [A (HSInt 1), A (HSString "elephant")]]
-- "(1 \"elephant\")"
haskLikePrinter :: SExprPrinter HaskLikeAtom (SExpr HaskLikeAtom)
haskLikePrinter = flatPrint sHaskLikeAtom