    {-# LANGUAGE NoImplicitPrelude #-}
    {-
    Copyright (C) 2014-2018 Jesse Rosenthal <jrosenthal@jhu.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.Readers.Docx.Fields
       Copyright   : Copyright (C) 2014-2018 Jesse Rosenthal
       License     : GNU GPL, version 2 or above

       Maintainer  : Jesse Rosenthal <jrosenthal@jhu.edu>
       Stability   : alpha
       Portability : portable

    For parsing Field definitions in instText tags, as described in
    ECMA-376-1:2016, §17.16.5 -}

    module Text.Pandoc.Readers.Docx.Fields ( FieldInfo(..)
                                           , parseFieldInfo
                                           ) where

    import Prelude
    import Text.Parsec
    import Text.Parsec.String (Parser)

    type URL = String

    data FieldInfo = HyperlinkField URL
                   | UnknownField
                   deriving (Show)

    parseFieldInfo :: String -> Either ParseError FieldInfo
    parseFieldInfo = parse fieldInfo ""

    fieldInfo :: Parser FieldInfo
    fieldInfo =
      try (HyperlinkField <$> hyperlink)
      <|>
      return UnknownField

    escapedQuote :: Parser String
    escapedQuote = string "\\\""

    inQuotes :: Parser String
    inQuotes =
      (try escapedQuote) <|> (anyChar >>= (\c -> return [c]))

    quotedString :: Parser String
    quotedString = do
      char '"'
      concat <$> manyTill inQuotes (try (char '"'))

    unquotedString :: Parser String
    unquotedString = manyTill anyChar (try $ lookAhead space *> return () <|> eof)

    fieldArgument :: Parser String
    fieldArgument = quotedString <|> unquotedString

    -- there are other switches, but this is the only one I've seen in the wild so far, so it's the first one I'll implement. See §17.16.5.25
    hyperlinkSwitch :: Parser (String, String)
    hyperlinkSwitch = do
      sw <- string "\\l"
      spaces
      farg <- fieldArgument
      return (sw, farg)

    hyperlink :: Parser URL
    hyperlink = do
      many space
      string "HYPERLINK"
      spaces
      farg <- fieldArgument
      switches <- spaces *> many hyperlinkSwitch
      let url = case switches of
                  ("\\l", s) : _ -> farg ++ ('#': s)
                  _              -> farg
      return url