abstract-section.lua

--[[
abstract-section – move an "abstract" section into document metadata

Copyright: © 2017–2023 Albert Krewinkel
License:   MIT – see LICENSE file for details
]] local stringify = (require 'pandoc.utils').stringify
local section_identifiers = {abstract = true}
local collected = {}
--- The level of the highest heading that was seen so far. Abstracts
--- must be at or above this level to prevent nested sections from being
--- treated as metadata. Only top-level sections should become metadata.
local toplevel = 6

--- Extract abstract from a list of blocks.
local function abstract_from_blocklist(blocks)
    local body_blocks = {}
    local looking_at_section = false

    for _, block in ipairs(blocks) do
        if block.t == 'Header' and block.level <= toplevel then
            toplevel = block.level
            if section_identifiers[block.identifier] then
                looking_at_section = block.identifier
                collected[looking_at_section] = {}
            else
                looking_at_section = false
                body_blocks[#body_blocks + 1] = block
            end
        elseif looking_at_section then
            if block.t == 'HorizontalRule' then
                looking_at_section = false
            else
                local collect = collected[looking_at_section]
                collect[#collect + 1] = block
            end
        else
            body_blocks[#body_blocks + 1] = block
        end
    end

    return body_blocks
end

Pandoc = function(doc)
    local meta = doc.meta

    -- configure
    section_identifiers_list =
        (doc.meta['abstract-section'] or {})['section-identifiers']
    if section_identifiers_list and #section_identifiers_list > 0 then
        section_identifiers = {}
        for i, ident in ipairs(section_identifiers_list) do
            section_identifiers[stringify(ident)] = true
        end
    end
    -- unset config in meta
    doc.meta['abstract-section'] = nil

    local blocks = {}
    if PANDOC_VERSION >= {2, 17} then
        -- Walk all block lists by default
        blocks = doc.blocks:walk{Blocks = abstract_from_blocklist}
    elseif PANDOC_VERSION >= {2, 9, 2} then
        -- Do the same with pandoc versions that don't have walk methods but the
        -- `walk_block` function.
        blocks = pandoc.utils.walk_block(pandoc.Div(doc.blocks),
                                         {Blocks = abstract_from_blocklist})
                     .content
    else
        -- otherwise, just check the top-level block-list
        blocks = abstract_from_blocklist(doc.blocks)
    end
    for metakey in pairs(section_identifiers) do
        metakey = stringify(metakey)
        local abstract = collected[metakey]
        if not meta[metakey] and abstract and #abstract > 0 then
            meta[metakey] = pandoc.MetaBlocks(abstract)
        end
    end
    return pandoc.Pandoc(blocks, meta)
end