{-# LANGUAGE GeneralizedNewtypeDeriving #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE OverloadedStrings #-}
{- |
   Module      : Text.Pandoc.Templates
   Copyright   : Copyright (C) 2009-2020 John MacFarlane
   License     : GNU GPL, version 2 or above

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

Utility functions for working with pandoc templates.
-}

module Text.Pandoc.Templates ( Template
                             , WithDefaultPartials(..)
                             , WithPartials(..)
                             , compileTemplate
                             , renderTemplate
                             , getTemplate
                             , getDefaultTemplate
                             , compileDefaultTemplate
                             ) where

import System.FilePath ((<.>), (</>), takeFileName)
import Text.DocTemplates (Template, TemplateMonad(..), compileTemplate, renderTemplate)
import Text.Pandoc.Class.CommonState (CommonState(..))
import Text.Pandoc.Class.PandocMonad (PandocMonad, readDataFile, fetchItem,
                                      getCommonState, modifyCommonState)
import qualified Text.Pandoc.UTF8 as UTF8
import Control.Monad.Except (catchError, throwError)
import Data.Text (Text)
import qualified Data.Text as T
import Text.Pandoc.Error

-- | Wrap a Monad in this if you want partials to
-- be taken only from the default data files.
newtype WithDefaultPartials m a = WithDefaultPartials { runWithDefaultPartials :: m a }
 deriving (Functor, Applicative, Monad)

-- | Wrap a Monad in this if you want partials to
-- be looked for locally (or, when the main template
-- is at a URL, via HTTP), falling back to default data files.
newtype WithPartials m a = WithPartials { runWithPartials :: m a }
 deriving (Functor, Applicative, Monad)

instance PandocMonad m => TemplateMonad (WithDefaultPartials m) where
  getPartial fp = WithDefaultPartials $
    UTF8.toText <$> readDataFile ("templates" </> takeFileName fp)

instance PandocMonad m => TemplateMonad (WithPartials m) where
  getPartial fp = WithPartials $ getTemplate fp

-- | Retrieve text for a template.
getTemplate :: PandocMonad m => FilePath -> m Text
getTemplate tp = UTF8.toText <$>
  ((do surl <- stSourceURL <$> getCommonState
       -- we don't want to look for templates remotely
       -- unless the full URL is specified:
       modifyCommonState $ \st -> st{
         stSourceURL = Nothing }
       (bs, _) <- fetchItem $ T.pack tp
       modifyCommonState $ \st -> st{
         stSourceURL = surl }
       return bs)
   `catchError`
   (\e -> case e of
             PandocResourceNotFound _ ->
                -- see #5987 on reason for takeFileName
                readDataFile ("templates" </> takeFileName tp)
             _ -> throwError e))

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

-- | Get and compile default template for the specified writer.
-- Raise an error on compilation failure.
compileDefaultTemplate :: PandocMonad m
                       => Text
                       -> m (Template Text)
compileDefaultTemplate writer = do
  res <- getDefaultTemplate writer >>=
          runWithDefaultPartials .
           compileTemplate ("templates/default." <> T.unpack writer)
  case res of
    Left e   -> throwError $ PandocTemplateError (T.pack e)
    Right t  -> return t
