    {-# LANGUAGE OverloadedStrings #-}
    {-
    Copyright (C) 2009-2018 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.Templates
       Copyright   : Copyright (C) 2009-2018 John MacFarlane
       License     : GNU GPL, version 2 or above

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

    A simple templating system with variable substitution and conditionals.

    -}

    module Text.Pandoc.Templates ( module Text.DocTemplates
                                 , renderTemplate'
                                 , getDefaultTemplate
                                 ) where

    import Prelude
    import Control.Monad.Except (throwError)
    import Data.Aeson (ToJSON (..))
    import qualified Data.Text as T
    import System.FilePath ((<.>), (</>))
    import Text.DocTemplates (Template, TemplateTarget, applyTemplate,
                              compileTemplate, renderTemplate, varListToJSON)
    import Text.Pandoc.Class (PandocMonad, readDataFile)
    import Text.Pandoc.Error
    import qualified Text.Pandoc.UTF8 as UTF8

    -- | Get default template for the specified writer.
    getDefaultTemplate :: PandocMonad m
                       => String           -- ^ Name of writer
                       -> m String
    getDefaultTemplate writer = do
      let format = takeWhile (`notElem` ("+-" :: String)) writer  -- strip off extensions
      case format of
           "native"  -> return ""
           "json"    -> return ""
           "docx"    -> return ""
           "fb2"     -> return ""
           "pptx"    -> return ""
           "odt"     -> getDefaultTemplate "opendocument"
           "html"    -> getDefaultTemplate "html5"
           "docbook" -> getDefaultTemplate "docbook5"
           "epub"    -> getDefaultTemplate "epub3"
           "beamer"  -> getDefaultTemplate "latex"
           "markdown_strict"   -> getDefaultTemplate "markdown"
           "multimarkdown"     -> getDefaultTemplate "markdown"
           "markdown_github"   -> getDefaultTemplate "markdown"
           "markdown_mmd"      -> getDefaultTemplate "markdown"
           "markdown_phpextra" -> getDefaultTemplate "markdown"
           "gfm"               -> getDefaultTemplate "commonmark"
           _        -> let fname = "templates" </> "default" <.> format
                       in  UTF8.toString <$> readDataFile fname

    -- | Like 'applyTemplate', but runs in PandocMonad and
    -- raises an error if compilation fails.
    renderTemplate' :: (PandocMonad m, ToJSON a, TemplateTarget b)
                    => String -> a -> m b
    renderTemplate' template context =
      case applyTemplate (T.pack template) context of
           Left e  -> throwError (PandocTemplateError e)
           Right r -> return r