module GF.Text.Transliterations (transliterate,transliteration,characterTable) where

import GF.Text.UTF8

import Data.Char
import qualified Data.Map as Map

-- transliterations between ASCII and a Unicode character set

-- current transliterations: devanagari, thai

-- to add a new one: define the Unicode range and the corresponding ASCII strings,
-- which may be one or two characters long

-- conventions to be followed: 
--   each character is either [letter] or [letter+nonletter]
--   when using a sparse range of unicodes, mark missing codes as "-" in transliterations
--   characters can be invisible: ignored in translation to unicode

transliterate :: String -> Maybe (String -> String)
transliterate s = case s of
  'f':'r':'o':'m':'_':t -> fmap appTransFromUnicode $ transliteration t
  't':'o':'_':t -> fmap appTransToUnicode $ transliteration t
  _ -> Nothing

transliteration :: String -> Maybe Transliteration
transliteration s = case s of
  "devanagari" -> Just transDevanagari
  "thai" -> Just transThai
  _ -> Nothing

characterTable :: Transliteration -> String
characterTable = unlines . map prOne . Map.assocs . trans_from_unicode where
  prOne (i,s) = unwords ["|", show i, "|", encodeUTF8 [toEnum i], "|", s, "|"]

data Transliteration = Trans {
  trans_to_unicode   :: Map.Map String Int,
  trans_from_unicode :: Map.Map Int String,
  invisible_chars    :: [String]
  }

appTransToUnicode :: Transliteration -> String -> String
appTransToUnicode trans = 
  concat .
  map (\c -> maybe c (return . toEnum) $
             Map.lookup c (trans_to_unicode trans)
      ) . 
  filter (flip notElem (invisible_chars trans)) . 
  unchar

appTransFromUnicode :: Transliteration -> String -> String
appTransFromUnicode trans = 
  concat .
  map (maybe "?" id . 
       flip Map.lookup (trans_from_unicode trans)
      ) . 
  map fromEnum


mkTransliteration :: [String] -> [Int] -> Transliteration
mkTransliteration ts us = Trans (Map.fromList (tzip ts us)) (Map.fromList (uzip us ts)) []
  where
    tzip ts us = [(t,u) | (t,u) <- zip ts us, t /= "-"]
    uzip us ts = [(u,t) | (u,t) <- zip us ts, t /= "-"]


unchar :: String -> [String]
unchar s = case s of
  c:d:cs 
   | isAlpha d -> [c]    : unchar (d:cs)
   | isSpace d -> [c]:[d]: unchar cs
   | otherwise -> [c,d]  : unchar cs
  [_]          -> [s]
  _            -> []

transThai :: Transliteration
transThai = mkTransliteration allTrans allCodes where
  allTrans = words $
    "-  k  k1 -  k2 -  k3 g  c  c1 c2 s' c3 y' d' t' " ++
    "t1 t2 t3 n' d  t  t4 t5 t6 n  b  p  p1 f  p2 f' " ++
    "p3 m  y  r  -  l  -  w  s- s. s  h  l' O  h' -  " ++
    "a. a  a: a+ i  i: v  v: u  u: -  -  -  -  -  -  " ++
    "e  e' o: a% a& L  R  S  T1 T2 T3 T4 K  -  -  -  " ++
    "N0 N1 N2 N3 N4 N5 N6 N7 N8 N9 -  -  -  -  -  -  "
  allCodes = [0x0e00 .. 0x0e7f]

transDevanagari :: Transliteration
transDevanagari = (mkTransliteration allTrans allCodes){invisible_chars = ["a"]} where
  allTrans = words $
    "M  N  -  - " ++
    "a- A- i- I- u- U- R- -  -  -  e- E- -  -  o- O- " ++
    "k  K  g  G  N: c  C  j  J  n: t. T. d. D. n. t  " ++
    "T  d  D  n  -  p  P  b  B  m  y  r  -  l  -  -  v  " ++
    "S  s. s  h  -  -  r. -  A  i  I  u  U  R  -  -  " ++
    "-  e  E  o  O "
  allCodes = [0x0901 .. 0x094c]