module ImgTex (plugin) where
{-

This plugin provides a clear math LaTeX output.
(* latex and dvipng executable must be in the path.)

like this:

~~~ {.dvipng}
\nabla \times \bm{V}
=
\frac{1}{h_1 h_2 h_3}
  \begin{vmatrix}
    h_1 e_1 & h_2 e_2 & h_3 e_3 \\
    \frac{\partial}{\partial q_{1}} &
    \frac{\partial}{\partial q_{2}} &
    \frac{\partial}{\partial q_{3}} \\
    h_1 V_1 & h_2 V_2 & h_3 V_3
  \end{vmatrix}
~~~

License: GPL
written by Kohei OZAKI <i@smly.org>
modified by John MacFarlane to use withTempDir

-}

import Network.Gitit.Interface
import System.Process (system)
import System.Directory
import Data.ByteString.Lazy.UTF8 (fromString)
import Data.Digest.Pure.SHA
import System.FilePath
import Control.Monad.Trans (liftIO)

plugin :: Plugin
plugin = mkPageTransformM transformBlock

templateHeader, templateFooter :: String
templateHeader = concat
    [ "\\documentclass[12pt]{article}\n"
      , "\\usepackage{amsmath,amssymb,bm}\n"
      , "\\begin{document}\n"
      , "\\thispagestyle{empty}\n"
      , "\\[\n"]

templateFooter =
      "\n"
      ++ "\\]\n"
      ++ "\\end{document}\n"

transformBlock :: Block -> PluginM Block
transformBlock (CodeBlock (_, classes, namevals) contents)
    | "dvipng" `elem` classes = do
  cfg <- askConfig
  let (name, outfile) =  case lookup "name" namevals of
                                Just fn   -> ([Str fn], fn ++ ".png")
                                Nothing   -> ([], uniqueName contents ++ ".png")
  curr <- liftIO getCurrentDirectory
  liftIO $ withTempDir "gitit-imgtex" $ \tmpdir -> do
    setCurrentDirectory tmpdir
    writeFile (outfile ++ ".tex") (templateHeader ++ contents ++ templateFooter)
    system $ "latex " ++ outfile ++ ".tex > /dev/null"
    setCurrentDirectory curr
    system $ "dvipng -T tight -bd 1000 -freetype0 -Q 5 --gamma 1.3 " ++
              (tmpdir </> outfile <.> "dvi") ++ " -o " ++ (staticDir cfg </> "img" </> outfile)
    return $ Para [Image name ("/img" </> outfile, "")]
transformBlock x = return x

uniqueName :: String -> String
uniqueName = showDigest . sha1 . fromString