{-

Copyright (C) 2012-2017 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.Slides

   Copyright   : Copyright (C) 2012-2017 John MacFarlane

   License     : GNU GPL, version 2 or above

   Maintainer  : John MacFarlane <jgm@berkeley.edu>

   Stability   : alpha

   Portability : portable

Utility functions for splitting documents into slides for slide

show formats (dzslides, revealjs, s5, slidy, slideous, beamer).

-}

module Text.Pandoc.Slides ( getSlideLevel, prepSlides ) where

import Text.Pandoc.Definition

-- | Find level of header that starts slides (defined as the least header

-- level that occurs before a non-header/non-hrule in the blocks).

getSlideLevel :: [Block] -> Int

getSlideLevel = go 6

  where go least (Header n _ _ : x : xs)

                 | n < least && nonHOrHR x = go n xs

                 | otherwise               = go least (x:xs)

        go least (_ : xs) = go least xs

        go least [] = least

        nonHOrHR Header{}       = False

        nonHOrHR HorizontalRule = False

        nonHOrHR _              = True

-- | Prepare a block list to be passed to hierarchicalize.

prepSlides :: Int -> [Block] -> [Block]

prepSlides slideLevel = ensureStartWithH . splitHrule . extractRefsHeader

  where splitHrule (HorizontalRule : Header n attr xs : ys)

                       | n == slideLevel = Header slideLevel attr xs : splitHrule ys

        splitHrule (HorizontalRule : xs) = Header slideLevel nullAttr [Str "\0"] :

                                           splitHrule xs

        splitHrule (x : xs)              = x : splitHrule xs

        splitHrule []                    = []

        extractRefsHeader bs             =

          case reverse bs of

               (Div ("",["references"],[]) (Header n attrs xs : ys) : zs)

                 -> reverse zs ++ (Header n attrs xs : [Div ("",["references"],[]) ys])

               _ -> bs

        ensureStartWithH bs@(Header n _ _:_)

                       | n <= slideLevel = bs

        ensureStartWithH bs              = Header slideLevel nullAttr [Str "\0"] : bs