-- Render content below header in three columns

local multicol_begin = pandoc.RawBlock('latex', [[
\begin{multicols}{3}\raggedcolumns
]])
local multicol_end = pandoc.RawBlock('latex', [[
\end{multicols}
]])

-- TODO: detect pre-quarto-filter pattern too
local function is_newpage_command(elem)
  return elem.t == "RawBlock" and elem.text == "\\newpage{}"
end

-- TODO: include header level 2 and author paragraph above multicolumn
function is_author(elem)
    return elem.t == Para and elem.content[1].text == "Forfatter:"
end

function Pandoc(doc)
  if FORMAT:match 'latex' then

    -- locate topmost-only elements where multicol state should change
    local multicol_now = false
    local multicol_places = {}
    for i, elem in ipairs(doc.blocks) do
      if elem.t == "Header" and elem.level == 1 then
        multicol_places[i] = multicol_now and "renew" or "begin"
        multicol_now = true
      elseif is_newpage_command(elem) then
        if multicol_now then
          multicol_places[i] = "end"
          multicol_now = false
        end
      elseif elem.t == "HorizontalRule" then
        if multicol_now then
          multicol_places[i] = "end"
          multicol_now = false
        end
      end
    end
    if multicol_now then
      multicol_places[#doc.blocks] = "end"
    end

    -- apply multicol, in reverse order since it shifts later indices
    for i = #doc.blocks, 1, -1 do
      local state = multicol_places[i]
      if state ~= nil then
        if state == "begin" then
          doc.blocks:insert(i + 1, multicol_begin)
        elseif state == "renew" then
          doc.blocks:insert(i + 1, multicol_begin)
          doc.blocks:insert(i, multicol_end)
        elseif state == "end" then
          doc.blocks:insert(i, multicol_end)
        end
      end
    end

    if #multicol_places >= 1 then
      return doc
    end
  end
end