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{-# LANGUAGE Safe #-}

--------------------------------------------------------------------------------

module Data.UTF8
  ( fromSingleBytes
  , toSingleBytes
  ) where

--------------------------------------------------------------------------------

import           Data.Bits
  ( (.&.)
  , (.|.)
  , shiftL
  , shiftR
  )
import           Data.Word
  ( Word8
  )

--------------------------------------------------------------------------------

fromSingleBytes
  :: [ Word8 ]
  -> Either String [ Char ]

toSingleBytes
  :: [ Char ]
  -> Either String [ Word8 ]

--------------------------------------------------------------------------------

l2s
  :: (Ord a, Num a)
  => [a]
  -> Bool

l3s
  :: (Ord a, Num a)
  => [a]
  -> Bool
  
l4s
  :: (Ord a, Num a)
  => [a]
  -> Bool

fsb
  :: [ Word8 ]
  -> Either String [ Char ]

u2a
  :: Char
  -> Either String [ Word8 ]

tsb
  :: [ Char ]
  -> Either String [ Word8 ]

msg
  :: String
  -> String

--------------------------------------------------------------------------------

fromSingleBytes =
  fsb

toSingleBytes =
  tsb

--------------------------------------------------------------------------------

{-

* Table 3.1. UTF-8 Bit Distribution

+----------------------------+----------+----------+----------+----------+
| Scalar                     | 1st Byte | 2nd Byte | 3rd Byte | 4th Byte |
+----------------------------+----------+----------+----------+----------+
| 00000000 0xxxxxxx          | 0xxxxxxx |          |          |          |
| 00000yyy yyxxxxxx          | 110yyyyy | 10xxxxxx |          |          |
| zzzzyyyy yyxxxxxx          | 1110zzzz | 10yyyyyy | 10xxxxxx |          |
| 000uuuuu zzzzyyyy yyxxxxxx | 11110uuu | 10uuzzzz | 10yyyyyy | 10xxxxxx |
+----------------------------+----------+----------+----------+----------+


* Table 3.1B. Legal UTF-8 Byte Sequences

+----------------------+----------+----------+----------+----------+
| Code Points          | 1st Byte | 2nd Byte | 3rd Byte | 4th Byte |
+----------------------+----------+----------+----------+----------+
| U+000000 .. U+00007F | 00 .. 7F |          |          |          |
| U+000080 .. U+0007FF | C2 .. DF | 80 .. BF |          |          |
| U+000800 .. U+000FFF | E0       | A0 .. BF | 80 .. BF |          |
| U+001000 .. U+00FFFF | E1 .. EF | 80 .. BF | 80 .. BF |          |
| U+010000 .. U+03FFFF | F0       | 90 .. BF | 80 .. BF | 80 .. BF |
| U+040000 .. U+0FFFFF | F1 .. F3 | 80 .. BF | 80 .. BF | 80 .. BF |
| U+100000 .. U+10FFFF | F4       | 80 .. 8F | 80 .. BF | 80 .. BF |
+----------------------+----------+----------+----------+----------+

Source: https://unicode.org/versions/corrigendum1.html

-}

l2s (b1:b2:[]) =
  -- U+000080 .. U+0007FF | C2 .. DF | 80 .. BF
  b1 > 0xC1 && b1 < 0xE0 &&
  b2 > 0x7F && b2 < 0xC0
l2s _ = False

l3s (b1:b2:b3:[]) =
  -- U+000800 .. U+000FFF | E0       | A0 .. BF | 80 .. BF
  -- U+001000 .. U+00FFFF | E1 .. EF | 80 .. BF | 80 .. BF
  (b1        ==      0xE0 &&
   b2 > 0x9F && b2 < 0xC0 &&
   b3 > 0x7F && b3 < 0xC0)
  ||
  (b1 > 0xE0 && b1 < 0xF0 &&
   b2 > 0x7F && b2 < 0xC0 &&
   b3 > 0x7F && b3 < 0xC0)  
l3s _ = False

l4s (b1:b2:b3:b4:[]) =
  -- U+010000 .. U+03FFFF | F0       | 90 .. BF | 80 .. BF | 80 .. BF
  -- U+040000 .. U+0FFFFF | F1 .. F3 | 80 .. BF | 80 .. BF | 80 .. BF
  -- U+100000 .. U+10FFFF | F4       | 80 .. 8F | 80 .. BF | 80 .. BF
  (b1        ==      0xF0 &&
   b2 > 0x8F && b2 < 0xC0 &&
   b3 > 0x7F && b3 < 0xC0 &&
   b4 > 0x7F && b4 < 0xC0)
  ||
  (b1 > 0xF0 && b1 < 0xF4 &&
   b2 > 0x7F && b2 < 0xC0 &&
   b3 > 0x7F && b3 < 0xC0 &&
   b4 > 0x7F && b4 < 0xC0)
  ||
  (b1        ==      0xF4 &&
   b2 > 0x7F && b2 < 0x90 &&
   b3 > 0x7F && b3 < 0xC0 &&
   b4 > 0x7F && b4 < 0xC0)
l4s _ = False

fsb [        ] =
  Right []
fsb bs @ (w:_)
  -- "w" can't be less than 0 or greater than 0xFF (HS Word8 constraints)
  | w < 0x80  = bs01 bs
  | w < 0xC2  = Left $ msg $ "Byte: " ++ show w
  | w < 0xE0  = bs02 bs
  | w < 0xF0  = bs03 bs
  | w < 0xF5  = bs04 bs
  | otherwise = Left $ msg $ "Byte: " ++ show w
  where
    (.<.) x y = x `shiftL` y
    char = toEnum . fromIntegral
    bs01 (b1:xs) =
      fsb xs >>= \ys ->
      Right $ char b1 : ys
    bs01 _______ =
      Left $ "Exhaustive pattern match."
    bs02 (b1:b2:xs)
      | l2s (b1:b2:[]) =
        let
          a = (fromIntegral $ b1 .&. 0x1F :: Int) .<. 0006
          b =  fromIntegral $ b2 .&. 0x3F :: Int
        in
          fsb xs >>= \ys ->
          Right
          $ toEnum (a .|. b) : ys
      | otherwise =
        Left $ msg $ "Two bytes: " ++ (show $ b1:b2:[])
    bs02 _________ =
      Left $ "Exhaustive pattern match."
    bs03 (b1:b2:b3:xs)
      | l3s $ b1:b2:b3:[] =
        let
          a = (fromIntegral $ b1 .&. 0x0F :: Int) .<. 0012
          b = (fromIntegral $ b2 .&. 0x3F :: Int) .<. 0006
          c =  fromIntegral $ b3 .&. 0x3F :: Int
        in
          fsb xs >>= \ys ->
          Right
          $ toEnum (a .|. b .|. c) : ys
      | otherwise =
        Left $ msg $ "Three bytes: " ++ (show $ b1:b2:b3:[])
    bs03 _____________ =
      Left $ "Exhaustive pattern match."
    bs04 (b1:b2:b3:b4:xs)
      | l4s $ b1:b2:b3:b4:[] =
        let
          a = (fromIntegral $ b1 .&. 0x07 :: Int) .<. 0018
          b = (fromIntegral $ b2 .&. 0x3F :: Int) .<. 0012
          c = (fromIntegral $ b3 .&. 0x3F :: Int) .<. 0006
          d =  fromIntegral $ b4 .&. 0x3F :: Int
        in
          fsb xs >>= \ys ->
          Right
          $ toEnum (a .|. b .|. c .|. d) : ys
      | otherwise =
        Left $ msg $ "Four bytes: " ++ (show $ b1:b2:b3:b4:[])
    bs04 ________________ =
      Left $ "Exhaustive pattern match."

u2a c
  -- "word" can't be less than 0 or greater than 0x10FFFF (HS Char constraints)
  | word < 0x000080 = bs01
  | word < 0x000800 = bs02
  | word < 0x010000 = bs03
  | otherwise       = bs04
  where
    (.>.) x y = x `shiftR` y
    word = fromEnum c
    bs01 =
      Right
      [ fromIntegral $ word
      ]
    bs02 =
      Right
      [ fromIntegral $ word .>. 0006          .|. 0xC0
      , fromIntegral $ word          .&. 0x3F .|. 0x80
      ]
      >>= valid l2s "Two bytes: "
    bs03 =
      Right
      [ fromIntegral $ word .>. 0012          .|. 0xE0
      , fromIntegral $ word .>. 0006 .&. 0x3F .|. 0x80
      , fromIntegral $ word          .&. 0x3F .|. 0x80
      ]
      >>= valid l3s "Three bytes: "
    bs04 =
      Right
      [ fromIntegral $ word .>. 0018          .|. 0xF0
      , fromIntegral $ word .>. 0012 .&. 0x3F .|. 0x80
      , fromIntegral $ word .>. 0006 .&. 0x3F .|. 0x80
      , fromIntegral $ word          .&. 0x3F .|. 0x80
      ]
      >>= valid l4s "Four bytes: "
    valid lfn txt bs =
      if
        lfn $ bs
      then
        Right bs
      else
        Left $ msg $ txt ++ (show $ bs)

tsb [    ] =
  Right []
tsb (x:xs) =
  u2a x  >>= \ws ->
  tsb xs >>= \ys ->
  Right $ ws ++ ys

msg x =
  x
  ++ " is/are not a Legal UTF-8 Byte Sequence, see Table 3.1B at:\n"
  ++ " -- http://unicode.org/versions/corrigendum1.html"

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{-# LANGUAGE Safe #-}

--------------------------------------------------------------------------------

module Main where

import qualified Data.UTF8 as UTF8

--------------------------------------------------------------------------------

main
  :: IO ()

--------------------------------------------------------------------------------

class Monad m => InteractM m where
  interact'
    :: (String -> String) -> m ()

--------------------------------------------------------------------------------

instance InteractM IO where
  interact'
    = interact

--------------------------------------------------------------------------------

main =
  interact'
  $
  \xs ->
    case UTF8.fromSingleBytes $ map (fromIntegral . fromEnum) xs of
      Left msg ->
        msg
      Right ys ->
        ys

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{-# LANGUAGE Safe #-}

--------------------------------------------------------------------------------

module Main where

import qualified Data.UTF8 as UTF8

--------------------------------------------------------------------------------

main
  :: IO ()

--------------------------------------------------------------------------------

class Monad m => InteractM m where
  interact'
    :: (String -> String) -> m ()

--------------------------------------------------------------------------------

instance InteractM IO where
  interact'
    = interact

--------------------------------------------------------------------------------

main =
  interact'
  $
  \xs ->
    case UTF8.toSingleBytes xs of
      Left msg ->
        msg
      Right ys ->
        map (toEnum . fromIntegral) ys

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#!/bin/bash

clear

# tsb
ghc -Wall -Werror -O3 --make TSB.hs -o tsb

# fsb
ghc -Wall -Werror -O3 --make FSB.hs -o fsb

# clean
find . -name '*.hi' -delete
find . -name '*.o'  -delete

user@personal:~/.../src$ echo "Haskell in Japanese (ハスケル) and Chinese (哈斯克爾)" \
    | ./tsb \
    | ./fsb 
Haskell in Japanese (ハスケル) and Chinese (哈斯克爾)
user@personal:~/.../src$