{-# LANGUAGE BangPatterns, MagicHash, UnboxedTuples #-}
{-# OPTIONS_GHC -O #-}
-- We always optimise this, otherwise performance of a non-optimised
-- compiler is severely affected

-- -----------------------------------------------------------------------------
--
-- (c) The University of Glasgow, 1997-2006
--
-- Character encodings
--
-- -----------------------------------------------------------------------------

module Encoding (
        -- * UTF-8
        utf8DecodeChar#,
        utf8PrevChar,
        utf8CharStart,
        utf8DecodeChar,
        utf8DecodeString,
        utf8EncodeChar,
        utf8EncodeString,
        utf8EncodedLength,
        countUTF8Chars,

        -- * Z-encoding
        zEncodeString,
        zDecodeString,

        -- * Base62-encoding
        toBase62,
        toBase62Padded
  ) where

import Foreign
import Data.Char
import qualified Data.Char as Char
import Numeric
import GHC.Exts

-- -----------------------------------------------------------------------------
-- UTF-8

-- We can't write the decoder as efficiently as we'd like without
-- resorting to unboxed extensions, unfortunately.  I tried to write
-- an IO version of this function, but GHC can't eliminate boxed
-- results from an IO-returning function.
--
-- We assume we can ignore overflow when parsing a multibyte character here.
-- To make this safe, we add extra sentinel bytes to unparsed UTF-8 sequences
-- before decoding them (see StringBuffer.hs).

{-# INLINE utf8DecodeChar# #-}
utf8DecodeChar# :: Addr# -> (# Char#, Int# #)
utf8DecodeChar# a# =
  let !ch0 = word2Int# (indexWord8OffAddr# a# 0#) in
  case () of
    _ | isTrue# (ch0 <=# 0x7F#) -> (# chr# ch0, 1# #)

      | isTrue# ((ch0 >=# 0xC0#) `andI#` (ch0 <=# 0xDF#)) ->
        let !ch1 = word2Int# (indexWord8OffAddr# a# 1#) in
        if isTrue# ((ch1 <# 0x80#) `orI#` (ch1 >=# 0xC0#)) then fail 1# else
        (# chr# (((ch0 -# 0xC0#) `uncheckedIShiftL#` 6#) +#
                  (ch1 -# 0x80#)),
           2# #)

      | isTrue# ((ch0 >=# 0xE0#) `andI#` (ch0 <=# 0xEF#)) ->
        let !ch1 = word2Int# (indexWord8OffAddr# a# 1#) in
        if isTrue# ((ch1 <# 0x80#) `orI#` (ch1 >=# 0xC0#)) then fail 1# else
        let !ch2 = word2Int# (indexWord8OffAddr# a# 2#) in
        if isTrue# ((ch2 <# 0x80#) `orI#` (ch2 >=# 0xC0#)) then fail 2# else
        (# chr# (((ch0 -# 0xE0#) `uncheckedIShiftL#` 12#) +#
                 ((ch1 -# 0x80#) `uncheckedIShiftL#` 6#)  +#
                  (ch2 -# 0x80#)),
           3# #)

     | isTrue# ((ch0 >=# 0xF0#) `andI#` (ch0 <=# 0xF8#)) ->
        let !ch1 = word2Int# (indexWord8OffAddr# a# 1#) in
        if isTrue# ((ch1 <# 0x80#) `orI#` (ch1 >=# 0xC0#)) then fail 1# else
        let !ch2 = word2Int# (indexWord8OffAddr# a# 2#) in
        if isTrue# ((ch2 <# 0x80#) `orI#` (ch2 >=# 0xC0#)) then fail 2# else
        let !ch3 = word2Int# (indexWord8OffAddr# a# 3#) in
        if isTrue# ((ch3 <# 0x80#) `orI#` (ch3 >=# 0xC0#)) then fail 3# else
        (# chr# (((ch0 -# 0xF0#) `uncheckedIShiftL#` 18#) +#
                 ((ch1 -# 0x80#) `uncheckedIShiftL#` 12#) +#
                 ((ch2 -# 0x80#) `uncheckedIShiftL#` 6#)  +#
                  (ch3 -# 0x80#)),
           4# #)

      | otherwise -> fail 1#
  where
        -- all invalid sequences end up here:
        fail :: Int# -> (# Char#, Int# #)
        fail nBytes# = (# '\0'#, nBytes# #)
        -- '\xFFFD' would be the usual replacement character, but
        -- that's a valid symbol in Haskell, so will result in a
        -- confusing parse error later on.  Instead we use '\0' which
        -- will signal a lexer error immediately.

utf8DecodeChar :: Ptr Word8 -> (Char, Int)
utf8DecodeChar (Ptr a#) =
  case utf8DecodeChar# a# of (# c#, nBytes# #) -> ( C# c#, I# nBytes# )

-- UTF-8 is cleverly designed so that we can always figure out where
-- the start of the current character is, given any position in a
-- stream.  This function finds the start of the previous character,
-- assuming there *is* a previous character.
utf8PrevChar :: Ptr Word8 -> IO (Ptr Word8)
utf8PrevChar p = utf8CharStart (p `plusPtr` (-1))

utf8CharStart :: Ptr Word8 -> IO (Ptr Word8)
utf8CharStart p = go p
 where go p = do w <- peek p
                 if w >= 0x80 && w < 0xC0
                        then go (p `plusPtr` (-1))
                        else return p

utf8DecodeString :: Ptr Word8 -> Int -> IO [Char]
utf8DecodeString ptr len
  = unpack ptr
  where
    !end = ptr `plusPtr` len

    unpack p
        | p >= end = return []
        | otherwise  =
        case utf8DecodeChar# (unPtr p) of
           (# c#, nBytes# #) -> do
                chs <- unpack (p `plusPtr#` nBytes#)
                return (C# c# : chs)

countUTF8Chars :: Ptr Word8 -> Int -> IO Int
countUTF8Chars ptr len = go ptr 0
  where
        !end = ptr `plusPtr` len

        go p !n
           | p >= end = return n
           | otherwise  = do
                case utf8DecodeChar# (unPtr p) of
                  (# _, nBytes# #) -> go (p `plusPtr#` nBytes#) (n+1)

unPtr :: Ptr a -> Addr#
unPtr (Ptr a) = a

plusPtr# :: Ptr a -> Int# -> Ptr a
plusPtr# ptr nBytes# = ptr `plusPtr` (I# nBytes#)

utf8EncodeChar :: Char -> Ptr Word8 -> IO (Ptr Word8)
utf8EncodeChar c ptr =
  let x = ord c in
  case () of
    _ | x > 0 && x <= 0x007f -> do
          poke ptr (fromIntegral x)
          return (ptr `plusPtr` 1)
        -- NB. '\0' is encoded as '\xC0\x80', not '\0'.  This is so that we
        -- can have 0-terminated UTF-8 strings (see GHC.Base.unpackCStringUtf8).
      | x <= 0x07ff -> do
          poke ptr (fromIntegral (0xC0 .|. ((x `shiftR` 6) .&. 0x1F)))
          pokeElemOff ptr 1 (fromIntegral (0x80 .|. (x .&. 0x3F)))
          return (ptr `plusPtr` 2)
      | x <= 0xffff -> do
          poke ptr (fromIntegral (0xE0 .|. (x `shiftR` 12) .&. 0x0F))
          pokeElemOff ptr 1 (fromIntegral (0x80 .|. (x `shiftR` 6) .&. 0x3F))
          pokeElemOff ptr 2 (fromIntegral (0x80 .|. (x .&. 0x3F)))
          return (ptr `plusPtr` 3)
      | otherwise -> do
          poke ptr (fromIntegral (0xF0 .|. (x `shiftR` 18)))
          pokeElemOff ptr 1 (fromIntegral (0x80 .|. ((x `shiftR` 12) .&. 0x3F)))
          pokeElemOff ptr 2 (fromIntegral (0x80 .|. ((x `shiftR` 6) .&. 0x3F)))
          pokeElemOff ptr 3 (fromIntegral (0x80 .|. (x .&. 0x3F)))
          return (ptr `plusPtr` 4)

utf8EncodeString :: Ptr Word8 -> String -> IO ()
utf8EncodeString ptr str = go ptr str
  where go !_   []     = return ()
        go ptr (c:cs) = do
          ptr' <- utf8EncodeChar c ptr
          go ptr' cs

utf8EncodedLength :: String -> Int
utf8EncodedLength str = go 0 str
  where go !n [] = n
        go n (c:cs)
          | ord c > 0 && ord c <= 0x007f = go (n+1) cs
          | ord c <= 0x07ff = go (n+2) cs
          | ord c <= 0xffff = go (n+3) cs
          | otherwise       = go (n+4) cs

-- -----------------------------------------------------------------------------
-- The Z-encoding

{-
This is the main name-encoding and decoding function.  It encodes any
string into a string that is acceptable as a C name.  This is done
right before we emit a symbol name into the compiled C or asm code.
Z-encoding of strings is cached in the FastString interface, so we
never encode the same string more than once.

The basic encoding scheme is this.

* Tuples (,,,) are coded as Z3T

* Alphabetic characters (upper and lower) and digits
        all translate to themselves;
        except 'Z', which translates to 'ZZ'
        and    'z', which translates to 'zz'
  We need both so that we can preserve the variable/tycon distinction

* Most other printable characters translate to 'zx' or 'Zx' for some
        alphabetic character x

* The others translate as 'znnnU' where 'nnn' is the decimal number
        of the character

        Before          After
        --------------------------
        Trak            Trak
        foo_wib         foozuwib
        >               zg
        >1              zg1
        foo#            foozh
        foo##           foozhzh
        foo##1          foozhzh1
        fooZ            fooZZ
        :+              ZCzp
        ()              Z0T     0-tuple
        (,,,,)          Z5T     5-tuple
        (# #)           Z1H     unboxed 1-tuple (note the space)
        (#,,,,#)        Z5H     unboxed 5-tuple
                (NB: There is no Z1T nor Z0H.)
-}

type UserString = String        -- As the user typed it
type EncodedString = String     -- Encoded form


zEncodeString :: UserString -> EncodedString
zEncodeString cs = case maybe_tuple cs of
                Just n  -> n            -- Tuples go to Z2T etc
                Nothing -> go cs
          where
                go []     = []
                go (c:cs) = encode_digit_ch c ++ go' cs
                go' []     = []
                go' (c:cs) = encode_ch c ++ go' cs

unencodedChar :: Char -> Bool   -- True for chars that don't need encoding
unencodedChar 'Z' = False
unencodedChar 'z' = False
unencodedChar c   =  c >= 'a' && c <= 'z'
                  || c >= 'A' && c <= 'Z'
                  || c >= '0' && c <= '9'

-- If a digit is at the start of a symbol then we need to encode it.
-- Otherwise package names like 9pH-0.1 give linker errors.
encode_digit_ch :: Char -> EncodedString
encode_digit_ch c | c >= '0' && c <= '9' = encode_as_unicode_char c
encode_digit_ch c | otherwise            = encode_ch c

encode_ch :: Char -> EncodedString
encode_ch c | unencodedChar c = [c]     -- Common case first

-- Constructors
encode_ch '('  = "ZL"   -- Needed for things like (,), and (->)
encode_ch ')'  = "ZR"   -- For symmetry with (
encode_ch '['  = "ZM"
encode_ch ']'  = "ZN"
encode_ch ':'  = "ZC"
encode_ch 'Z'  = "ZZ"

-- Variables
encode_ch 'z'  = "zz"
encode_ch '&'  = "za"
encode_ch '|'  = "zb"
encode_ch '^'  = "zc"
encode_ch '$'  = "zd"
encode_ch '='  = "ze"
encode_ch '>'  = "zg"
encode_ch '#'  = "zh"
encode_ch '.'  = "zi"
encode_ch '<'  = "zl"
encode_ch '-'  = "zm"
encode_ch '!'  = "zn"
encode_ch '+'  = "zp"
encode_ch '\'' = "zq"
encode_ch '\\' = "zr"
encode_ch '/'  = "zs"
encode_ch '*'  = "zt"
encode_ch '_'  = "zu"
encode_ch '%'  = "zv"
encode_ch c    = encode_as_unicode_char c

encode_as_unicode_char :: Char -> EncodedString
encode_as_unicode_char c = 'z' : if isDigit (head hex_str) then hex_str
                                                           else '0':hex_str
  where hex_str = showHex (ord c) "U"
  -- ToDo: we could improve the encoding here in various ways.
  -- eg. strings of unicode characters come out as 'z1234Uz5678U', we
  -- could remove the 'U' in the middle (the 'z' works as a separator).

zDecodeString :: EncodedString -> UserString
zDecodeString [] = []
zDecodeString ('Z' : d : rest)
  | isDigit d = decode_tuple   d rest
  | otherwise = decode_upper   d : zDecodeString rest
zDecodeString ('z' : d : rest)
  | isDigit d = decode_num_esc d rest
  | otherwise = decode_lower   d : zDecodeString rest
zDecodeString (c   : rest) = c : zDecodeString rest

decode_upper, decode_lower :: Char -> Char

decode_upper 'L' = '('
decode_upper 'R' = ')'
decode_upper 'M' = '['
decode_upper 'N' = ']'
decode_upper 'C' = ':'
decode_upper 'Z' = 'Z'
decode_upper ch  = {-pprTrace "decode_upper" (char ch)-} ch

decode_lower 'z' = 'z'
decode_lower 'a' = '&'
decode_lower 'b' = '|'
decode_lower 'c' = '^'
decode_lower 'd' = '$'
decode_lower 'e' = '='
decode_lower 'g' = '>'
decode_lower 'h' = '#'
decode_lower 'i' = '.'
decode_lower 'l' = '<'
decode_lower 'm' = '-'
decode_lower 'n' = '!'
decode_lower 'p' = '+'
decode_lower 'q' = '\''
decode_lower 'r' = '\\'
decode_lower 's' = '/'
decode_lower 't' = '*'
decode_lower 'u' = '_'
decode_lower 'v' = '%'
decode_lower ch  = {-pprTrace "decode_lower" (char ch)-} ch

-- Characters not having a specific code are coded as z224U (in hex)
decode_num_esc :: Char -> EncodedString -> UserString
decode_num_esc d rest
  = go (digitToInt d) rest
  where
    go n (c : rest) | isHexDigit c = go (16*n + digitToInt c) rest
    go n ('U' : rest)           = chr n : zDecodeString rest
    go n other = error ("decode_num_esc: " ++ show n ++  ' ':other)

decode_tuple :: Char -> EncodedString -> UserString
decode_tuple d rest
  = go (digitToInt d) rest
  where
        -- NB. recurse back to zDecodeString after decoding the tuple, because
        -- the tuple might be embedded in a longer name.
    go n (c : rest) | isDigit c = go (10*n + digitToInt c) rest
    go 0 ('T':rest)     = "()" ++ zDecodeString rest
    go n ('T':rest)     = '(' : replicate (n-1) ',' ++ ")" ++ zDecodeString rest
    go 1 ('H':rest)     = "(# #)" ++ zDecodeString rest
    go n ('H':rest)     = '(' : '#' : replicate (n-1) ',' ++ "#)" ++ zDecodeString rest
    go n other = error ("decode_tuple: " ++ show n ++ ' ':other)

{-
Tuples are encoded as
        Z3T or Z3H
for 3-tuples or unboxed 3-tuples respectively.  No other encoding starts
        Z<digit>

* "(# #)" is the tycon for an unboxed 1-tuple (not 0-tuple)
  There are no unboxed 0-tuples.

* "()" is the tycon for a boxed 0-tuple.
  There are no boxed 1-tuples.
-}

maybe_tuple :: UserString -> Maybe EncodedString

maybe_tuple "(# #)" = Just("Z1H")
maybe_tuple ('(' : '#' : cs) = case count_commas (0::Int) cs of
                                 (n, '#' : ')' : _) -> Just ('Z' : shows (n+1) "H")
                                 _                  -> Nothing
maybe_tuple "()" = Just("Z0T")
maybe_tuple ('(' : cs)       = case count_commas (0::Int) cs of
                                 (n, ')' : _) -> Just ('Z' : shows (n+1) "T")
                                 _            -> Nothing
maybe_tuple _                = Nothing

count_commas :: Int -> String -> (Int, String)
count_commas n (',' : cs) = count_commas (n+1) cs
count_commas n cs         = (n,cs)


{-
************************************************************************
*                                                                      *
                        Base 62
*                                                                      *
************************************************************************

Note [Base 62 encoding 128-bit integers]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Instead of base-62 encoding a single 128-bit integer
(ceil(21.49) characters), we'll base-62 a pair of 64-bit integers
(2 * ceil(10.75) characters).  Luckily for us, it's the same number of
characters!
-}

--------------------------------------------------------------------------
-- Base 62

-- The base-62 code is based off of 'locators'
-- ((c) Operational Dynamics Consulting, BSD3 licensed)

-- | Size of a 64-bit word when written as a base-62 string
word64Base62Len :: Int
word64Base62Len = 11

-- | Converts a 64-bit word into a base-62 string
toBase62Padded :: Word64 -> String
toBase62Padded w = pad ++ str
  where
    pad = replicate len '0'
    len = word64Base62Len - length str -- 11 == ceil(64 / lg 62)
    str = toBase62 w

toBase62 :: Word64 -> String
toBase62 w = showIntAtBase 62 represent w ""
  where
    represent :: Int -> Char
    represent x
        | x < 10 = Char.chr (48 + x)
        | x < 36 = Char.chr (65 + x - 10)
        | x < 62 = Char.chr (97 + x - 36)
        | otherwise = error "represent (base 62): impossible!"
