{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE OverloadedStrings #-}

module Text.Pandoc.SideNote (usingSideNotes) where

import           Data.List           (intercalate)
import           Data.Text           (Text, append, pack)

import           Control.Monad.State

import           Text.Pandoc.JSON
import           Text.Pandoc.Walk    (walk, walkM)

getFirstStr :: [Inline] -> Maybe Text
getFirstStr []                 = Nothing
getFirstStr (Str text:_      ) = Just text
getFirstStr (_       :inlines) = getFirstStr inlines

newline :: [Inline]
newline = [LineBreak, LineBreak]

-- This could be implemented more concisely, but I think this is more clear.
getThenIncr :: State Int Int
getThenIncr = do
  i <- get
  put (i + 1)
  return i

-- Extract inlines from blocks
coerceToInline :: [Block] -> [Inline]
coerceToInline = concatMap deBlock . walk deNote
 where
  deBlock :: Block -> [Inline]
  deBlock (Plain     ls    ) = ls
  -- Simulate paragraphs with double LineBreak
  deBlock (Para      ls    ) = ls ++ newline
  -- See extension: line_blocks
  deBlock (LineBlock lss   ) = intercalate [LineBreak] lss ++ newline
  -- Pretend RawBlock is RawInline (might not work!)
  -- Consider: raw <div> now inside RawInline... what happens?
  deBlock (RawBlock fmt str) = [RawInline fmt str]
  -- lists, blockquotes, headers, hrs, and tables are all omitted
  -- Think they shouldn't be? I'm open to sensible PR's.
  deBlock _                  = []

  deNote (Note _) = Str ""
  deNote x        = x

filterInline :: Inline -> State Int Inline
filterInline (Note blocks) = do
  -- Generate a unique number for the 'for=' attribute
  i <- getThenIncr

  -- Note has a [Block], but Span needs [Inline]
  let content  = coerceToInline blocks

  -- The '{-}' symbol differentiates between margin note and side note
  let nonu     = getFirstStr content == Just "{-}"
  let content' = if nonu then tail content else content

  let labelCls = "margin-toggle" `append`
                 (if nonu then "" else " sidenote-number")
  let labelSym = if nonu then "&#8853;" else ""
  let labelHTML = mconcat
         [ "<label for=\"sn-"
         , pack (show i)
         , "\" class=\""
         , labelCls
         , "\">"
         , labelSym
         , "</label>"
         ]
  let label = RawInline (Format "html") labelHTML

  let inputHTML = mconcat
        [ "<input type=\"checkbox\" id=\"sn-"
        , pack (show i)
        , "\" "
        , "class=\"margin-toggle\"/>"
        ]
  let input             = RawInline (Format "html") inputHTML

  let (ident, _, attrs) = nullAttr
  let noteTypeCls       = if nonu then "marginnote" else "sidenote"
  let note              = Span (ident, [noteTypeCls], attrs) content'

  return $ Span ("", ["sidenote-wrapper"], []) [label, input, note]

filterInline inline = return inline

usingSideNotes :: Pandoc -> Pandoc
usingSideNotes (Pandoc meta blocks) =
  Pandoc meta (evalState (walkM filterInline blocks) 0)