local label_map = {}               -- label has to be unique!

local function collect_labels(div) -- only collect labels in div
    if div.identifier and div.identifier ~= "" then
        label_map[div.identifier] = div:clone()
    end
    return nil
end

local function words(s)
    local res = {}
    for part in s:gmatch("[^,]+") do                -- split by commas
        local trimmed = part:match("^%s*(.-)%s*$")  -- remove leading/trailing spaces
        if trimmed ~= "" then
            table.insert(res, trimmed)
        end
    end
    return res
end

local function replace(e)
    local include = e.attributes["include"]
    if include then
        local blocks = {}
        -- Replace the Div contents
        for _, l in ipairs(words(include)) do
            if label_map[l] then
                table.insert(blocks, label_map[l]:clone())
                io.stderr:write("insert [" .. label_map[l].identifier .. ']\n')
            else
                io.stderr:write("Cannot find AST node with label " .. l)
            end
        end
        return pandoc.Div(blocks, e.attr)
    end
    return e -- no change
end

return {
    -- traverse = 'topdown',
    Pandoc = function(doc)
        -- collect labels
        for _, blk in ipairs(doc.blocks) do
            collect_labels(blk)
        end

        -- replace
        for i, blk in ipairs(doc.blocks) do
            doc.blocks[i] = replace(blk)
        end
        return doc
    end
}