{-# LANGUAGE OverloadedStrings #-}
{- |
   Module      : Text.Pandoc.Writers.BibTeX
   Copyright   : Copyright (C) 2021 John MacFarlane
   License     : GNU GPL, version 2 or above

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

Writes a BibTeX or BibLaTeX bibliographies based on the
'references' metadata in a Pandoc document.
-}
module Text.Pandoc.Writers.BibTeX
  ( writeBibTeX
  , writeBibLaTeX
  )
where

import Text.Pandoc.Options
import Text.Pandoc.Definition
import Data.Text (Text)
import Data.Maybe (mapMaybe)
import Citeproc (parseLang)
import Text.Pandoc.Class (PandocMonad)
import Text.Pandoc.Citeproc.BibTeX as BibTeX
import Text.Pandoc.Citeproc.MetaValue (metaValueToReference)
import Text.Pandoc.Writers.Shared (lookupMetaString)

-- | Write BibTeX based on the references metadata from a Pandoc document.
writeBibTeX :: PandocMonad m => WriterOptions -> Pandoc -> m Text
writeBibTeX = writeBibTeX' BibTeX.Bibtex

-- | Write BibLaTeX based on the references metadata from a Pandoc document.
writeBibLaTeX :: PandocMonad m => WriterOptions -> Pandoc -> m Text
writeBibLaTeX = writeBibTeX' BibTeX.Biblatex

writeBibTeX' :: PandocMonad m => Variant -> WriterOptions -> Pandoc -> m Text
writeBibTeX' variant opts (Pandoc meta _) = do
  let mblang = case lookupMetaString "lang" meta of
                 "" -> Nothing
                 t  -> Just $ parseLang t
  let refs = case lookupMeta "references" meta of
               Just (MetaList xs) -> mapMaybe metaValueToReference xs
               _ -> []
  return $ mconcat $
    map (BibTeX.writeBibtexString opts variant mblang) refs