    {-# LANGUAGE CPP #-}
    {-
    Copyright (C) 2013-2015 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.Writers.OPML
       Copyright   : Copyright (C) 2013-2015 John MacFarlane
       License     : GNU GPL, version 2 or above

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

    Conversion of 'Pandoc' documents to OPML XML.
    -}
    module Text.Pandoc.Writers.OPML ( writeOPML) where
    import Text.Pandoc.Definition
    import Text.Pandoc.XML
    import Text.Pandoc.Writers.Shared
    import Text.Pandoc.Shared
    import Text.Pandoc.Options
    import Text.Pandoc.Templates (renderTemplate')
    import Text.Pandoc.Writers.HTML (writeHtmlString)
    import Text.Pandoc.Writers.Markdown (writeMarkdown)
    import Text.Pandoc.Pretty
    import Text.Pandoc.Compat.Time
    import qualified Text.Pandoc.Builder as B

    -- | Convert Pandoc document to string in OPML format.
    writeOPML :: WriterOptions -> Pandoc -> String
    writeOPML opts (Pandoc meta blocks) =
      let elements = hierarchicalize blocks
          colwidth = if writerWrapText opts == WrapAuto
                        then Just $ writerColumns opts
                        else Nothing
          meta' = B.setMeta "date" (B.str $ convertDate $ docDate meta) meta
          Just metadata = metaToJSON opts
                          (Just . writeMarkdown def . Pandoc nullMeta)
                          (Just . trimr . writeMarkdown def . Pandoc nullMeta .
                             (\ils -> [Plain ils]))
                          meta'
          main     = render colwidth $ vcat (map (elementToOPML opts) elements)
          context = defField "body" main metadata
      in  if writerStandalone opts
             then renderTemplate' (writerTemplate opts) context
             else main

    writeHtmlInlines :: [Inline] -> String
    writeHtmlInlines ils = trim $ writeHtmlString def
                                $ Pandoc nullMeta [Plain ils]

    -- date format: RFC 822: Thu, 14 Jul 2005 23:41:05 GMT
    showDateTimeRFC822 :: UTCTime -> String
    showDateTimeRFC822 = formatTime defaultTimeLocale "%a, %d %b %Y %X %Z"

    convertDate :: [Inline] -> String
    convertDate ils = maybe "" showDateTimeRFC822 $
    #if MIN_VERSION_time(1,5,0)
      parseTimeM True
    #else
      parseTime
    #endif
      defaultTimeLocale "%F" =<< (normalizeDate $ stringify ils)

    -- | Convert an Element to OPML.
    elementToOPML :: WriterOptions -> Element -> Doc
    elementToOPML _ (Blk _) = empty
    elementToOPML opts (Sec _ _num _ title elements) =
      let isBlk (Blk _) = True
          isBlk _     = False
          fromBlk (Blk x) = x
          fromBlk _ = error "fromBlk called on non-block"
          (blocks, rest) = span isBlk elements
          attrs = [("text", writeHtmlInlines title)] ++
                  [("_note", writeMarkdown def (Pandoc nullMeta
                                  (map fromBlk blocks)))
                    | not (null blocks)]
      in  inTags True "outline" attrs $
          vcat (map (elementToOPML opts) rest)