    {-
    Copyright (C) 2013 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 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 Data.Time
    import System.Locale (defaultTimeLocale)
    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
                        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
      $ parseTime 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)