{-
Copyright (C) 2007-2010 John MacFarlane <jgm@berkeley.edu>

This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
-}

{- |
   Module      : Text.Pandoc.Readers.TeXMath
   Copyright   : Copyright (C) 2007-2010 John MacFarlane
   License     : GNU GPL, version 2 or above 

   Maintainer  : John MacFarlane <jgm@berkeley.edu>
   Stability   : alpha
   Portability : portable

Conversion of TeX math to a list of 'Pandoc' inline elements.
-}
module Text.Pandoc.Readers.TeXMath ( 
                                     readTeXMath
                                   ) where

import Text.ParserCombinators.Parsec
import Text.Pandoc.Definition
import Text.TeXMath.Parser

-- | Converts a raw TeX math formula to a list of 'Pandoc' inlines.
-- Defaults to raw formula between @$@ characters if entire formula
-- can't be converted.
readTeXMath :: String    -- ^ String to parse (assumes @'\n'@ line endings)
            -> [Inline]
readTeXMath inp = case readTeXMath' inp of
                        Nothing  -> [Str ("$" ++ inp ++ "$")]
                        Just res -> res

-- | Like 'readTeXMath', but without the default.
readTeXMath' :: String    -- ^ String to parse (assumes @'\n'@ line endings)
            -> Maybe [Inline]
readTeXMath' inp = case parse formula "formula" inp of
   Left _     -> Just [Str inp]
   Right exps -> expsToInlines exps

expsToInlines :: [Exp] -> Maybe [Inline]
expsToInlines xs = do
  res <- mapM expToInlines xs
  return (concat res)

expToInlines :: Exp -> Maybe [Inline]
expToInlines (ENumber s) = Just [Str s]
expToInlines (EIdentifier s) = Just [Emph [Str s]]
expToInlines (EMathOperator s) = Just [Str s]
expToInlines (ESymbol t s) = Just $ addSpace t (Str s)
  where addSpace Op x = [x, thinspace]
        addSpace Bin x = [medspace, x, medspace]
        addSpace Rel x = [widespace, x, widespace]
        addSpace Pun x = [x, thinspace]
        addSpace _ x = [x]
        thinspace = Str "\x2006"
        medspace  = Str "\x2005"
        widespace = Str "\x2004"
expToInlines (EStretchy x) = expToInlines x
expToInlines (EGrouped xs) = expsToInlines xs
expToInlines (ESpace _) = Just [Str " "]  -- variable widths not supported
expToInlines (EBinary _ _ _) = Nothing
expToInlines (ESub x y) = do
  x' <- expToInlines x
  y' <- expToInlines y
  return $ x' ++ [Subscript y']
expToInlines (ESuper x y) = do
  x' <- expToInlines x
  y' <- expToInlines y
  return $ x' ++ [Superscript y']
expToInlines (ESubsup x y z) = do
  x' <- expToInlines x
  y' <- expToInlines y
  z' <- expToInlines z
  return $ x' ++ [Subscript y'] ++ [Superscript z']
expToInlines (EDown x y) = expToInlines (ESub x y)
expToInlines (EUp x y) = expToInlines (ESuper x y)
expToInlines (EDownup x y z) = expToInlines (ESubsup x y z)
expToInlines (EText _ x) = Just [Emph [Str x]]
expToInlines _ = Nothing