{-# LANGUAGE CPP, MagicHash, BangPatterns #-}

-- |
-- Module      : Data.Text.Internal.Encoding.Utf8
-- Copyright   : (c) 2008, 2009 Tom Harper,
--               (c) 2009, 2010 Bryan O'Sullivan,
--               (c) 2009 Duncan Coutts
--
-- License     : BSD-style
-- Maintainer  : bos@serpentine.com
-- Stability   : experimental
-- Portability : GHC
--
-- /Warning/: this is an internal module, and does not have a stable
-- API or name. Functions in this module may not check or enforce
-- preconditions expected by public modules. Use at your own risk!
--
-- Basic UTF-8 validation and character manipulation.
module Data.Text.Internal.Encoding.Utf8
    (
    -- Decomposition
      ord2
    , ord3
    , ord4
    -- Construction
    , chr2
    , chr3
    , chr4
    -- * Validation
    , validate1
    , validate2
    , validate3
    , validate4
    ) where

import Data.Bits ((.&.))
import Data.Text.Internal.Unsafe.Char (ord)
import Data.Text.Internal.Unsafe.Shift (shiftR)
import GHC.Exts
import GHC.Word (Word8(..))

#if !MIN_VERSION_base(4,16,0)
-- harmless to import, except for warnings that it is unused.
import Data.Text.Internal.PrimCompat (word8ToWord#)
#endif

default(Int)

between :: Word8                -- ^ byte to check
        -> Word8                -- ^ lower bound
        -> Word8                -- ^ upper bound
        -> Bool
between x y z = x >= y && x <= z
{-# INLINE between #-}

ord2 :: Char -> (Word8,Word8)
ord2 c =
    -- ord2 is used only in test suite to construct a deliberately invalid ByteString,
    -- actually violating the assertion, so it is commented out
    -- assert (n >= 0x80 && n <= 0x07ff)
    (x1,x2)
    where
      n  = ord c
      x1 = fromIntegral $ (n `shiftR` 6) + 0xC0
      x2 = fromIntegral $ (n .&. 0x3F)   + 0x80

ord3 :: Char -> (Word8,Word8,Word8)
ord3 c =
    -- ord3 is used only in test suite to construct a deliberately invalid ByteString,
    -- actually violating the assertion, so it is commented out
    -- assert (n >= 0x0800 && n <= 0xffff)
    (x1,x2,x3)
    where
      n  = ord c
      x1 = fromIntegral $ (n `shiftR` 12) + 0xE0
      x2 = fromIntegral $ ((n `shiftR` 6) .&. 0x3F) + 0x80
      x3 = fromIntegral $ (n .&. 0x3F) + 0x80

ord4 :: Char -> (Word8,Word8,Word8,Word8)
ord4 c =
    -- ord4 is used only in test suite to construct a deliberately invalid ByteString,
    -- actually violating the assertion, so it is commented out
    -- assert (n >= 0x10000)
    (x1,x2,x3,x4)
    where
      n  = ord c
      x1 = fromIntegral $ (n `shiftR` 18) + 0xF0
      x2 = fromIntegral $ ((n `shiftR` 12) .&. 0x3F) + 0x80
      x3 = fromIntegral $ ((n `shiftR` 6) .&. 0x3F) + 0x80
      x4 = fromIntegral $ (n .&. 0x3F) + 0x80

chr2 :: Word8 -> Word8 -> Char
chr2 (W8# x1#) (W8# x2#) = C# (chr# (z1# +# z2#))
    where
      !y1# = word2Int# (word8ToWord# x1#)
      !y2# = word2Int# (word8ToWord# x2#)
      !z1# = uncheckedIShiftL# (y1# -# 0xC0#) 6#
      !z2# = y2# -# 0x80#
{-# INLINE chr2 #-}

chr3 :: Word8 -> Word8 -> Word8 -> Char
chr3 (W8# x1#) (W8# x2#) (W8# x3#) = C# (chr# (z1# +# z2# +# z3#))
    where
      !y1# = word2Int# (word8ToWord# x1#)
      !y2# = word2Int# (word8ToWord# x2#)
      !y3# = word2Int# (word8ToWord# x3#)
      !z1# = uncheckedIShiftL# (y1# -# 0xE0#) 12#
      !z2# = uncheckedIShiftL# (y2# -# 0x80#) 6#
      !z3# = y3# -# 0x80#
{-# INLINE chr3 #-}

chr4             :: Word8 -> Word8 -> Word8 -> Word8 -> Char
chr4 (W8# x1#) (W8# x2#) (W8# x3#) (W8# x4#) =
    C# (chr# (z1# +# z2# +# z3# +# z4#))
    where
      !y1# = word2Int# (word8ToWord# x1#)
      !y2# = word2Int# (word8ToWord# x2#)
      !y3# = word2Int# (word8ToWord# x3#)
      !y4# = word2Int# (word8ToWord# x4#)
      !z1# = uncheckedIShiftL# (y1# -# 0xF0#) 18#
      !z2# = uncheckedIShiftL# (y2# -# 0x80#) 12#
      !z3# = uncheckedIShiftL# (y3# -# 0x80#) 6#
      !z4# = y4# -# 0x80#
{-# INLINE chr4 #-}

validate1 :: Word8 -> Bool
validate1 x1 = x1 <= 0x7F
{-# INLINE validate1 #-}

validate2 :: Word8 -> Word8 -> Bool
validate2 x1 x2 = between x1 0xC2 0xDF && between x2 0x80 0xBF
{-# INLINE validate2 #-}

validate3 :: Word8 -> Word8 -> Word8 -> Bool
{-# INLINE validate3 #-}
validate3 x1 x2 x3 = validate3_1 || validate3_2 || validate3_3 || validate3_4
  where
    validate3_1 = (x1 == 0xE0) &&
                  between x2 0xA0 0xBF &&
                  between x3 0x80 0xBF
    validate3_2 = between x1 0xE1 0xEC &&
                  between x2 0x80 0xBF &&
                  between x3 0x80 0xBF
    validate3_3 = x1 == 0xED &&
                  between x2 0x80 0x9F &&
                  between x3 0x80 0xBF
    validate3_4 = between x1 0xEE 0xEF &&
                  between x2 0x80 0xBF &&
                  between x3 0x80 0xBF

validate4 :: Word8 -> Word8 -> Word8 -> Word8 -> Bool
{-# INLINE validate4 #-}
validate4 x1 x2 x3 x4 = validate4_1 || validate4_2 || validate4_3
  where
    validate4_1 = x1 == 0xF0 &&
                  between x2 0x90 0xBF &&
                  between x3 0x80 0xBF &&
                  between x4 0x80 0xBF
    validate4_2 = between x1 0xF1 0xF3 &&
                  between x2 0x80 0xBF &&
                  between x3 0x80 0xBF &&
                  between x4 0x80 0xBF
    validate4_3 = x1 == 0xF4 &&
                  between x2 0x80 0x8F &&
                  between x3 0x80 0xBF &&
                  between x4 0x80 0xBF
