Pandoc filter for moving image caption [CC0]

move-image-caption.lua

-- If the image caption is a separate paragraph below the
-- image, then this script will move it into the curly braces in
-- Markdown and make sure it is not redundantly present.
-- For example:
--
--   ![](image1.png)
--                      ==>    ![Abb. 1: title](image1.png)
--   Abb. 1: title
--
-- You can configure which "prefixes" (like "Abb.") identify a caption paragraph
-- by setting the value of the metadata field "caption_labels" to a list of strings.

-- Changes by BPJ:
--
-- -  Make the list of caption label prefixes configurable
--    Either in the metadata or by editing the list below.
--    (This involves replacing a seq of or expressions with
--    a list lookup.)
--
-- -  I *think* this could fairly easily be extended to
--    cover tables as well, but given the uncertainty WRT
--    tables ATM I didn't implement it yet.

local caption_labels = pandoc.List:new{
  'Figure', 'Fig.',     -- en 
  'Abbildung', 'Abb.',  -- de
  'Bild',               -- sv
  'Mynd',               -- is
}

-- a "safe" stringify
local stringify
do
  local _stringify = pandoc.utils.stringify
  stringify = function (s)
    if 'table' == type(s) and s.t then
      return _stringify(s)
    else -- hope for the best!
      return tostring(s)
    end
  end
end

local function get_labels (meta)
  labels = meta.caption_labels
  if not labels then return nil end
  l = pandoc.List:new()
  if 'table' == type(labels) and 'MetaList' == labels.t then
    for _,v in ipairs(labels) do
      l[#l+1] = stringify(v)
    end
  else -- a single "string"?
    l[#l+1] = stringify(labels)
  end
  caption_labels = l
  return nil
end

local elementstoremove = {}

local function do_blocks (blocks)
  for i = 1, #blocks-1, 1 do
    -- go through all blocks and look at the current block and the one ahead
    if (blocks[i].t == "Para"
        and #blocks[i].c == 1
        and blocks[i].c[1].t == "Image"
        and blocks[i+1].t == "Para"
        and #blocks[i+1].c >= 1
        and blocks[i+1].c[1].t == "Str") then
      local img = blocks[i].c[1]
      local caption = blocks[i+1].c
      -- if caption is as expected
      if caption_labels:includes(caption[1].c) then
        if (#img.caption > 0) then
          -- old caption is saved in a special attribute
          img.attributes.oldcaption = stringify(img.caption)
        end
        img.caption = caption
        table.insert(elementstoremove, i+1)
      -- if caption is not as expected but redundant
      elseif (pandoc.utils.equals(caption, img.caption)) then
        table.insert(elementstoremove, i+1)
      end
    end
  end
  -- Remove the redundant elements after the previous loop
  -- because otherwise this might interfer with the loop.
  -- Important we go backwards through this list
  for j = #elementstoremove, 1, -1 do
    blocks:remove(elementstoremove[j])
  end
  return blocks
end

return {
  { Meta = get_labels },
  { Blocks = do_blocks },
}