    {-
    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