    module Data.Csv.Conversion.Internal
        ( decimal
        , realFloat
        ) where

    import Blaze.ByteString.Builder
    import Blaze.ByteString.Builder.Char8
    import Data.Array.Base (unsafeAt)
    import Data.Array.IArray
    import qualified Data.ByteString as B
    import Data.Char (ord)
    import Data.Int
    import Data.Monoid
    import Data.Word

    ------------------------------------------------------------------------
    -- Integers

    decimal :: Integral a => a -> B.ByteString
    decimal = toByteString . formatDecimal
    {-# INLINE decimal #-}

    -- TODO: Add an optimized version for Integer.

    formatDecimal :: Integral a => a -> Builder
    {-# RULES "formatDecimal/Int" formatDecimal = formatBoundedSigned
        :: Int -> Builder #-}
    {-# RULES "formatDecimal/Int8" formatDecimal = formatBoundedSigned
        :: Int8 -> Builder #-}
    {-# RULES "formatDecimal/Int16" formatDecimal = formatBoundedSigned
        :: Int16 -> Builder #-}
    {-# RULES "formatDecimal/Int32" formatDecimal = formatBoundedSigned
        :: Int32 -> Builder #-}
    {-# RULES "formatDecimal/Int64" formatDecimal = formatBoundedSigned
        :: Int64 -> Builder #-}
    {-# RULES "formatDecimal/Word" formatDecimal = formatPositive
        :: Word -> Builder #-}
    {-# RULES "formatDecimal/Word8" formatDecimal = formatPositive
        :: Word8 -> Builder #-}
    {-# RULES "formatDecimal/Word16" formatDecimal = formatPositive
        :: Word16 -> Builder #-}
    {-# RULES "formatDecimal/Word32" formatDecimal = formatPositive
        :: Word32 -> Builder #-}
    {-# RULES "formatDecimal/Word64" formatDecimal = formatPositive
        :: Word64 -> Builder #-}
    {-# NOINLINE formatDecimal #-}
    formatDecimal i
        | i < 0     = minus <>
                      if i <= -128
                      then formatPositive (-(i `quot` 10)) <> digit (-(i `rem` 10))
                      else formatPositive (-i)
        | otherwise = formatPositive i

    formatBoundedSigned :: (Integral a, Bounded a) => a -> Builder
    {-# SPECIALIZE formatBoundedSigned :: Int -> Builder #-}
    {-# SPECIALIZE formatBoundedSigned :: Int8 -> Builder #-}
    {-# SPECIALIZE formatBoundedSigned :: Int16 -> Builder #-}
    {-# SPECIALIZE formatBoundedSigned :: Int32 -> Builder #-}
    {-# SPECIALIZE formatBoundedSigned :: Int64 -> Builder #-}
    formatBoundedSigned i
        | i < 0     = minus <>
                      if i == minBound
                      then formatPositive (-(i `quot` 10)) <> digit (-(i `rem` 10))
                      else formatPositive (-i)
        | otherwise = formatPositive i

    formatPositive :: Integral a => a -> Builder
    {-# SPECIALIZE formatPositive :: Int -> Builder #-}
    {-# SPECIALIZE formatPositive :: Int8 -> Builder #-}
    {-# SPECIALIZE formatPositive :: Int16 -> Builder #-}
    {-# SPECIALIZE formatPositive :: Int32 -> Builder #-}
    {-# SPECIALIZE formatPositive :: Int64 -> Builder #-}
    {-# SPECIALIZE formatPositive :: Word -> Builder #-}
    {-# SPECIALIZE formatPositive :: Word8 -> Builder #-}
    {-# SPECIALIZE formatPositive :: Word16 -> Builder #-}
    {-# SPECIALIZE formatPositive :: Word32 -> Builder #-}
    {-# SPECIALIZE formatPositive :: Word64 -> Builder #-}
    formatPositive = go
      where go n | n < 10    = digit n
                 | otherwise = go (n `quot` 10) <> digit (n `rem` 10)

    minus :: Builder
    minus = fromWord8 45

    zero :: Word8
    zero = 48

    digit :: Integral a => a -> Builder
    digit n = fromWord8 $! i2w (fromIntegral n)
    {-# INLINE digit #-}

    i2w :: Int -> Word8
    i2w i = zero + fromIntegral i
    {-# INLINE i2w #-}

    ------------------------------------------------------------------------
    -- Floating point numbers

    realFloat :: RealFloat a => a -> B.ByteString
    {-# SPECIALIZE realFloat :: Float -> B.ByteString #-}
    {-# SPECIALIZE realFloat :: Double -> B.ByteString #-}
    realFloat = toByteString . formatRealFloat Generic

    -- | Control the rendering of floating point numbers.
    data FPFormat = Exponent
                  -- ^ Scientific notation (e.g. @2.3e123@).
                  | Fixed
                  -- ^ Standard decimal notation.
                  | Generic
                  -- ^ Use decimal notation for values between @0.1@ and
                  -- @9,999,999@, and scientific notation otherwise.
                    deriving (Enum, Read, Show)

    formatRealFloat :: RealFloat a => FPFormat -> a -> Builder
    {-# SPECIALIZE formatRealFloat :: FPFormat -> Float -> Builder #-}
    {-# SPECIALIZE formatRealFloat :: FPFormat -> Double -> Builder #-}
    formatRealFloat fmt x
       | isNaN x                   = fromString "NaN"
       | isInfinite x              = if x < 0
                                     then fromString "-Infinity"
                                     else fromString "Infinity"
       | x < 0 || isNegativeZero x = minus <> doFmt fmt (floatToDigits (-x))
       | otherwise                 = doFmt fmt (floatToDigits x)
     where
      doFmt format (is, e) =
        let ds = map i2d is in
        case format of
         Generic ->
          doFmt (if e < 0 || e > 7 then Exponent else Fixed)
                (is,e)
         Exponent ->
            let show_e' = formatDecimal (e-1) in
            case ds of
              [48]    -> fromString "0.0e0"
              [d]     -> fromWord8 d <> fromString ".0e" <> show_e'
              (d:ds') -> fromWord8 d <> fromChar '.' <> fromWord8s ds' <>
                         fromChar 'e' <> show_e'
              []      -> error "formatRealFloat/doFmt/Exponent: []"
         Fixed
              | e <= 0    -> fromString "0." <>
                             fromByteString (B.replicate (-e) zero) <>
                             fromWord8s ds
              | otherwise ->
                 let
                    f 0 s    rs  = mk0 (reverse s) <> fromChar '.' <> mk0 rs
                    f n s    []  = f (n-1) (zero:s) []
                    f n s (r:rs) = f (n-1) (r:s) rs
                 in
                    f e [] ds
           where mk0 ls = case ls of { [] -> fromWord8 zero ; _ -> fromWord8s ls}

    -- Based on "Printing Floating-Point Numbers Quickly and Accurately"
    -- by R.G. Burger and R.K. Dybvig in PLDI 96.
    -- This version uses a much slower logarithm estimator. It should be improved.

    -- | 'floatToDigits' takes a base and a non-negative 'RealFloat' number,
    -- and returns a list of digits and an exponent.
    -- In particular, if @x>=0@, and
    --
    -- > floatToDigits base x = ([d1,d2,...,dn], e)
    --
    -- then
    --
    --      (1) @n >= 1@
    --
    --      (2) @x = 0.d1d2...dn * (base**e)@
    --
    --      (3) @0 <= di <= base-1@

    floatToDigits :: (RealFloat a) => a -> ([Int], Int)
    {-# SPECIALIZE floatToDigits :: Float -> ([Int], Int) #-}
    {-# SPECIALIZE floatToDigits :: Double -> ([Int], Int) #-}
    floatToDigits 0 = ([0], 0)
    floatToDigits x =
     let
      (f0, e0) = decodeFloat x
      (minExp0, _) = floatRange x
      p = floatDigits x
      b = floatRadix x
      minExp = minExp0 - p -- the real minimum exponent
      -- Haskell requires that f be adjusted so denormalized numbers
      -- will have an impossibly low exponent.  Adjust for this.
      (f, e) =
       let n = minExp - e0 in
       if n > 0 then (f0 `quot` (expt b n), e0+n) else (f0, e0)
      (r, s, mUp, mDn) =
       if e >= 0 then
        let be = expt b e in
        if f == expt b (p-1) then
          (f*be*b*2, 2*b, be*b, be)     -- according to Burger and Dybvig
        else
          (f*be*2, 2, be, be)
       else
        if e > minExp && f == expt b (p-1) then
          (f*b*2, expt b (-e+1)*2, b, 1)
        else
          (f*2, expt b (-e)*2, 1, 1)
      k :: Int
      k =
       let
        k0 :: Int
        k0 =
         if b == 2 then
            -- logBase 10 2 is very slightly larger than 8651/28738
            -- (about 5.3558e-10), so if log x >= 0, the approximation
            -- k1 is too small, hence we add one and need one fixup step less.
            -- If log x < 0, the approximation errs rather on the high side.
            -- That is usually more than compensated for by ignoring the
            -- fractional part of logBase 2 x, but when x is a power of 1/2
            -- or slightly larger and the exponent is a multiple of the
            -- denominator of the rational approximation to logBase 10 2,
            -- k1 is larger than logBase 10 x. If k1 > 1 + logBase 10 x,
            -- we get a leading zero-digit we don't want.
            -- With the approximation 3/10, this happened for
            -- 0.5^1030, 0.5^1040, ..., 0.5^1070 and values close above.
            -- The approximation 8651/28738 guarantees k1 < 1 + logBase 10 x
            -- for IEEE-ish floating point types with exponent fields
            -- <= 17 bits and mantissae of several thousand bits, earlier
            -- convergents to logBase 10 2 would fail for long double.
            -- Using quot instead of div is a little faster and requires
            -- fewer fixup steps for negative lx.
            let lx = p - 1 + e0
                k1 = (lx * 8651) `quot` 28738
            in if lx >= 0 then k1 + 1 else k1
         else
            -- f :: Integer, log :: Float -> Float,
            --               ceiling :: Float -> Int
            ceiling ((log (fromInteger (f+1) :: Float) +
                     fromIntegral e * log (fromInteger b)) /
                       log 10)
    --WAS:            fromInt e * log (fromInteger b))

        fixup n =
          if n >= 0 then
            if r + mUp <= expt 10 n * s then n else fixup (n+1)
          else
            if expt 10 (-n) * (r + mUp) <= s then n else fixup (n+1)
       in
       fixup k0

      gen ds rn sN mUpN mDnN =
       let
        (dn, rn') = (rn * 10) `quotRem` sN
        mUpN' = mUpN * 10
        mDnN' = mDnN * 10
       in
       case (rn' < mDnN', rn' + mUpN' > sN) of
        (True,  False) -> dn : ds
        (False, True)  -> dn+1 : ds
        (True,  True)  -> if rn' * 2 < sN then dn : ds else dn+1 : ds
        (False, False) -> gen (dn:ds) rn' sN mUpN' mDnN'

      rds =
       if k >= 0 then
          gen [] r (s * expt 10 k) mUp mDn
       else
         let bk = expt 10 (-k) in
         gen [] (r * bk) s (mUp * bk) (mDn * bk)
     in
     (map fromIntegral (reverse rds), k)

    -- Exponentiation with a cache for the most common numbers.
    minExpt, maxExpt :: Int
    minExpt = 0
    maxExpt = 1100

    expt :: Integer -> Int -> Integer
    expt base n
        | base == 2 && n >= minExpt && n <= maxExpt = expts `unsafeAt` n
        | base == 10 && n <= maxExpt10              = expts10 `unsafeAt` n
        | otherwise                                 = base^n

    expts :: Array Int Integer
    expts = array (minExpt,maxExpt) [(n,2^n) | n <- [minExpt .. maxExpt]]

    maxExpt10 :: Int
    maxExpt10 = 324

    expts10 :: Array Int Integer
    expts10 = array (minExpt,maxExpt10) [(n,10^n) | n <- [minExpt .. maxExpt10]]

    -- | Unsafe conversion for decimal digits.
    {-# INLINE i2d #-}
    i2d :: Int -> Word8
    i2d i = fromIntegral (ord '0' + i)