Pandoc Lua filter which converts docx with poetry as found in the wild to one line block per verse

pandoc-poetry-line-blocks.lua

--[[

Pandoc Lua filter which converts docx with poetry as found in the wild
where each line is a paragraph and each verse is separated by an empty
paragraph into one Pandoc line block per verse, if run like this:

    pandoc -r docx+empty_paragraphs --lua-filter pandoc-poetry-line-blocks.lua poetry.docx -so poetry.md

Note the `+empty_paragraphs` extension! It is necessary for this filter to
do its work correctly!

| This software is Copyright (c) 2018 by Benct Philip Jonsson.
| 
| This is free software, licensed under:
| 
|   The MIT (X11) License
| 
| The MIT License
| 
| Permission is hereby granted, free of charge, to any person
| obtaining a copy of this software and associated
| documentation files (the "Software"), to deal in the Software
| without restriction, including without limitation the rights to
| use, copy, modify, merge, publish, distribute, sublicense,
| and/or sell copies of the Software, and to permit persons to
| whom the Software is furnished to do so, subject to the
| following conditions:
| 
| The above copyright notice and this permission notice shall
| be included in all copies or substantial portions of the
| Software.
| 
| THE SOFTWARE IS PROVIDED "AS IS", WITHOUT
| WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
| INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
| MERCHANTABILITY, FITNESS FOR A PARTICULAR
| PURPOSE AND NONINFRINGEMENT. IN NO EVENT
| SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
| LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
| LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
| TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
| CONNECTION WITH THE SOFTWARE OR THE USE OR
| OTHER DEALINGS IN THE SOFTWARE.

]]

function Pandoc (doc)
    local old = doc.blocks
    local blocks = {{}}
    for _,elem in ipairs(old) do
        if 'Para' == elem.tag then
            local content = elem.content
            if #content > 0 then
                local block = blocks[#blocks]
                block[#block+1] = content
            else
                blocks[#blocks+1] = {}
            end
        else
            blocks[#blocks+1] = elem
            blocks[#blocks+1] = {}
        end
    end
    local new = {}
    for _,block in ipairs(blocks) do
        if block.t then
            new[#new+1] = block
        elseif #block > 1 then
            new[#new+1] = pandoc.LineBlock(block)
        else
            new[#new+1] = pandoc.Para(block[1] or {})
        end
    end
    return pandoc.Pandoc(new, doc.meta)
end